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Thursday, December 31, 2020

A Thrifty Guide to Buying Tools

I have learned a lot about buying tools over the past 20 years, from working with my dad, involvement in many student clubs, my own hobbies, engineering research projects, and building up my garage shop. The goal of this guide is to organize my mental notes on thrifty tool-buying with the hope that it will help some people. If you have $1000's and want to buy a whole shop worth of tools in one go, this is not the guide for you. If you want to, or are in the process of, buying tools as you need them and are on a budget, this is the guide for you.

I've organized this post by general descriptions first, then a buyers guide at the end. 


First, you need shop space in order to store your tools and use them. This might also be the most expensive tool/shop related thing you buy: land/square footage is expensive! If you're buying a house, make sure you have garage or basement that you can use for your shop, and that it is easy to access (some tools are large and heavy). When I was young, this was our basement. Now I have a garage, and since it's Florida, I only need to put a car in it if there's a hurricane. If you're in an apartment, you'll need a temporary multi-use space solutions, like a tool-closet, fold-down work bench, plastic sheeting for dust containment, etc. If you simply don't have room, you can rent storage units/garages with electricity and use those as a shop. If you're a school organization, get your own space from the school and fiercely protect it. More space is ALWAYS better. You can have the most efficient storage solutions in the world, and someone with more space will be able to organize their stuff better than you. I have a large-ish two car garage with 7.5ft ceilings, and I wish I had a four car garage with 14ft ceilings (though if I had that, I'd probably want even more space, haha). 

The environment of your space is also important. Ideally, it should be climate controlled and a place that can get messy. AC is especially important in hot+humid environments. If it's too hot in your garage, you won't want to work in it. Humidity will cause iron and steel to rust, and since most tools have steel in them, most tools will rust in a humid shop. 

Safety Gear

Normally, safety is first, but since there's no point owning safety gear without a space for it, I talk about it second. My #2 safety rule: When you buy a tool, but the proper safety gear for it at the same time. My #1 safety rule: Wear proper PPE! PPE=Personal Protection Equipment, a.k.a. safety gear. At a minimum, you'll likely need safety glasses or goggles for eye protection, leather/work and latex/nitrile gloves for hand protection, dust masks for lung protection, and ear muffs or plugs for ear protection. Luckily, these are all pretty inexpensive. Other gear you might need: long pants, long sleeve shirt, long leather gloves, steel toe boots, hard hat, cut proof gloves, respirator with appropriate cartridges (dust masks don't catch VOCs!). There are many tool-specific PPE, such as welding helmets, sand blasting hoods, etc. Most tool manuals list the required PPE, so they're a good place to look to see what PPE you need to buy: consider it part of the tool cost.  

There's also non-personal safety gear. Some examples: A flammables cabinet is a good idea if you have a lot of flammables, e.g. acetone, gasoline, etc. Welding curtains are used to protect other peoples' eyes from welding arcs. Table saws should always be used with a riving knife or splitter installed to help prevent kick-back. Correct wavelength spec'd laser goggles are a must when operating a laser cutter. If a tool comes with a safety device, never remove it. 

You must also consider what you shouldn't wear when operating tools. For example, long hair should always be pulled back/put up when drilling (rip hair out), using a lathe (pulls your head into the lathe = death), welding (hair is flammable), etc. Jewelry should pretty much always be taken off. Don't wear leather gloves when operating drill presses, lathes, or mills (it's better to rip your skin than suck your hand in). 

When learning to use a power tool, it's a good idea to read/watch videos about common mistakes when using it. It's easier to not start a bad habit than to break one. This info will usually contain information about proper tool safety.

Proper tool maintenance is also very important for safety. Don't try to use partially broken tools. 

Hand Tools

Finally, getting to the tools part of the tool guide. Hand tools are powered by hand and are an essential part of any shop. Examples of often used hand tools: flat, philips, torx, hex screw drivers, sockets + socket wrenches, crescent wrenches/spanners, adjustable wrenches, pliers (100's of types), hex/allen keys, hammers, saws, chisels, knives, stapler, caulk gun, clamps, tape measure, level, shears, etc. The exact ones you'll need are dependent on what you're doing of course, but if you're starting out, the general rule is that you'll never have the exact tool you need at the moment you need it. Another general rule is that, if you find something is very difficult to do, there is probably a better tool for the job and you should borrow/buy it (this goes for power tools, too). 

While you can wait to buy hand tools until you need them, they're usually cheap enough to buy in sets. For example, if you need a 1/2" socket, buy a whole socket set. If you need a philips screw driver, buy a whole set of screw drivers. This will save you money in the long run, and save time (trips to the hardware store). That being said, you don't need three socket sets or 20+ philips screw drivers because you'll never use them all. That's my current situation...merged household hand tool sets, I have them all organized now, but I need to purge some. 

Power Tools

Power tools are powered, usually by electricity. Commonly used power tools are: cordless drill and driver (yes, those are different, and you should have both), corded drill, circular saw, jig saw, table saw, miter saw, shop vacuum, palm/orbital sander, belt sander, disk sander, angle grinder (useful for far more than grinding angles), welders, etc.  

Some power tools are pneumatic. The air supply is compressed with a compressor, which is electric powered, but the actual work done by the tools is done by the air. Some pneumatic tools are lighter/better than their electric counterparts. Common pneumatic tools: nailers, staplers, grinders, buffers, impact drivers/wrenches, socket wrenches, drills, hammers, paint sprayers, etc. 

I suggest waiting to buy a power tool until you know you'll need it.

Machine Shop Tools

Metal/machine shops often have much larger, more expensive tools. These include mills, lathes, metal brakes, drill presses, large band saws, etc. 

Unless you're opening a machine shop business (in which case, this guide isn't for you anyways), you should wait to buy these until you need them, or if you stumble across a super good deal and think you might use one in the future. See below. 

Electronics Tools

Tools for working on electronic components include: multimeters (volt/ammeter), wire strippers, soldering iron, heat shrink heat gun, helping hands, fume extractor, power supplies, oscilloscopes, etc. Even if you aren't working on electronics, wire strippers and a multimeter are a great thing to have for general household troubleshooting.


An often overlooked, but necessary item, is the workbench. Unless you plan on doing everything on a floor, you'll need a workbench. They come in all shapes, sizes, and budgets. There are whole businesses, blogs, and even a subreddit devoted to them. The one you buy (or make!) is entirely dependent on what you plan to do with it. 

Basic workbenches are rectangular, consist of a solid top, and four legs. To make one on the cheap, you could buy a used wood table, a (folding) plastic table, or a solid core door and screw it to a couple of saw horses. You can make nicer ones, often with shelves or tool storage features, out of lumber, e.g. 2x4's, using the many free online plans. Or you can design your own to fit your needs. I'll be doing this soon. I'm going to make one with features to hold my table saw, router, miter saw, and band saw, and flat blanking plates to go in their places when I take the tools out to store them on the shelf underneath so I can have a large flat topped workbench when I don't need the tools. They can be rolling (with casters) or stationary. You can even buy leg kits, both metal or reinforced plastic, just supply the plywood for the top and possibly a shelf. I strongly suggest looking at pictures of what other people have done

Woodworking workbenches are usually made from wood, and usually by the woodworker planning to use it as a right-of-passage. They have many features, such as vises and bench dogs, specific to working with wood. There are many free online plans for these. You can also buy them for $100's to $10,000's.

Welding working workbenches are made of steel because the bench needs to be conductive. Again, making your welding workbench is usually a right-of-passage for beginner welders.

Electronics work benches can be metal or wood, but they always have an ESD (electrostatic discharge) safe top surface. They usually have lots of outlets for convenient positioning of electronics equipment, and sometimes built in DC power supplies. 

Tool Storage and Organization

Another often overlooked thing is how you're going to store and organize your tools. Piling them on top of each other on a shelf or in a bucket is not a good solution: it'll be hard to find a tool when you need it, and it's easier to break tools that way. Each tool should have a specific place. Workbenches often have cabinets/drawers for small power tools and hand tools. Free standing cabinets are good for larger power tools. Some people like displaying their tools with peg boards or French-cleat systems. Large, heavy tools should generally have a designated stationary place in your shop. 

Like a workbench, you should try to get your storage and organization solution sorted before getting in too deep with tools. 

Buying Guide

So you've figured out what tool(s) you need and researched them. There are many good places to buy tools, and many bad ones, and it's usually dependent on what tool you're buying. 

You can buy pretty much anything online, and it's often listed cheaper, but tools are usually heavy, and shipping on larger tools can be very expensive. You can also get scammed pretty easily, since you can't actually inspect the tool you're buying...buying from reputable people/websites is a must. Even if you get your money back from a scam, it's always a pain and a waste of time. Amazon often has decent deals, but you have to watch for knock-offs and where the tool is shipping from (overseas shipping can take months). You can get ok deals on new and used tools on eBay, but make sure to check the seller's location and feedback rating. Major hardware stores have online shops, and there are also many specialized tool websites. 

Local places (USA) to buy tools include major hardware stores like Home Depot and Lowes. Don't forget ACE hardware: they may be smaller, but there are usually more of them, and they often carry many small/hard-to-find tools/items that the big hardware stores don't. These are great places to buy pretty much every hand tool you'll need, and most power tools. 

There are also "cheap" tool stores, like Harbor Freight ("Harbor Fraud") and Northern Tool. These places sell lower quality tools for A LOT cheaper than other hardware stores, and often cheaper than you can buy online. All of the tools they sell cut corners in manufacturing and quality control. This can lead to huge safety problems (google "harbor freight car jack stands"), but usually just leads to wasted money. Their website ratings are also inflated: if you see a rating less than 4 stars, assume the tool is worthless. Things I would/will never again buy from Harbor Freight: air tools (other than a paint sprayer), things holding a lot of weight (car jack stands, engine cranes), electronic test equipment, needle nose pliers (had a set that I could bend with my hands). Some things that are good to buy from harbor freight: super glue, sockets, wrenches, screw drivers, drill bits, sand blasting media, angle grinder disks, tarps, furniture dollys, paint brushes, etc. If it's a very simple item, chances are better that they didn't screw up making it. This is only true if you aren't using these tools anywhere near their limits. For example, I have broken harbor freight crescent wrenches and sockets before, but only in high torque applications. Don't expect their drill bits to be able to drill through hardened steel. I've been too scared to buy many of their power tools, so I can't speak to those, but reviews seem to be mixed: some power tools are good, some aren't. Generally, you can find online reviews (text or videos) by googling "harbor freight" + the tool name. Be warned though, these "cheap" tool places aren't always cheap. I've found better deals at home depot and walmart before. Examples: T-squares were cheaper and better quality at home depot, and lithium grease tubes were cheaper at walmart. I strongly suggest checking prices and reviews before buying anything from stores like these.

Speaking of walmart, stores like Target and Walmart can be good places to find basic tools, and they're usually reasonably priced. 

Don't buy tools at flea markets. The new ones are almost always cruddy imported junk. The used ones are usually worn out, and if not, are usually priced higher than than they would be on craigslist. Garage sales can be ok, if you can find the tools hidden by all the other junk, but can also be a huge waste of time.   

My favorite place to buy tools is local classified ads, like craigslist/facebook marketplace. If you're patient and in a decently populated area, almost every tool imaginable will eventually pop up, and you can get some incredible deals. Workbenches, storage solutions, and safety gear, too. The item is local, which means no shipping, and you can inspect it before buying. However, you need to already know what your looking for and the information about the tool when you go to buy it (but you should know that stuff anyways since you're planning to buy it). Inspecting it is important...there are a lot of scammers. The pictures will usually you show you what kind of condition it is in, but inspect it carefully when you go to buy it. If the person sounds sketchy when messaging them, don't bother. If you're handy, you can get amazing deals on broken tools (even get them for free) and fix them yourself. I did this with my air compressor: I bought three partially working, similar craftsman air compressors. Fixed one, sold it, used another for parts, and got the third fully working. Ended up costing me about $0, not including my time. But if you're patient enough, and quick about messaging the seller, you can get amazing deals on fully working (sometimes new) tools, too: I've scored a big, fully working table saw for $25, and a mini metal lathe for $100. I've also bought a tool I know I'll need, then end up reselling it for the same price (or more) because I found a better one or better deal later. As long as you only buy good deals and don't wreck the tool after you buy it, you won't lose money this way (only time driving around), because the used tool price has already bottomed out. Craigslist/FB marketplace are also great places to buy collections of tools if you're starting out, like toolboxes full of hand tools: you get your storage solution, screw drivers, sockets, wrenches, etc all in one go for much much less than you could buy them new. And new tools from "cheap" tool stores (see above) are often worse quality than used, good-quality/brand tools, so don't always assume new is better.  

Final Thoughts

I hope this guide was useful to you. Good luck and have fun buying tools!

Refurbishing an Antique Metal Workbench

 This is one of those projects that I massively underestimated...

I won an antique metal work bench in an auction for $50 (along with the tooling cabinet I showed in a previous post).  

With drawers removed

Pretty sure it was a Craftsman because of the dark gray paint + red drawers, along with the fastener type. It was stuffed with metal chips, rusty, a drawer was jammed, bent up, and the MDF top was soaked in machining coolant. Also had a bunch of bolts/nuts in it, as well as an almost complete Crescent-brand wrench set, which was a nice bonus.

I removed the top and threw it away. I made a new one by cutting two 3/4" plywood rectangles with a circular saw, then bonding them together with wood glue, using temporary short screws and clamps to apply pressure. I then evened-out and rounded the edges with a palm sander. 


I had the plywood and glue already, and the screws were cheap. This part took about 3 hours. I'm planning to do a white or grey epoxy coat on top. I really like epoxy tops for work benches; it's durable and easy to repair: fill holes with putty, sand, re-pour epoxy. 

I then disassembled it. Took lots of pics so I would be able to put it back together. 

Next step was pressure washing all the gunk off, which took about an hour. This also stripped off some of the paint. It's not like I could make it much rustier, so I just let the parts air dry.  

Then I took a two month break from working on it. The next step was sandblasting and grinding all of the rust and loose paint off. I started with sandblasting with soda with my little hand held gravity fed sand blaster, but it's not really powerful enough to get scale off, even with glass beads instead of soda. I ended up switching to a wire brush on an angle grinder for everything except hard-to-reach places. This strategy worked well on the heavily rusted air tank, and it worked well for this, too. I didn't take any pics of this step, but I set up a large plastic tarp on some saw horses to kind of form a bowl to contain the blasting soda and paint/rust flakes. Super messy. Essential safety gear: arm-length leather gloves, face mask, goggles, face shield/hood, long sleeve shirt, jeans. Total time for this step was about 6 hours. I wore out a wire brush and used about 10lbs of soda, so total cost was around $15. 

I didn't strip off paint that looked well-adhered, but I kind of wish I had. After stripping, I used a hammer and vise-grips to straighten, flatten, rebend, etc. all of the parts. I then wiped everything down with a damp cloth, and then with denatured alcohol to get the grime off. The alcohol would dissolve some of the paint I didn't strip off and make leave streaks, which was annoying. I should have spent the extra ~hour to grind off all of the paint I could reach. I then taped off the drawer handles, door hinges, and lock. These steps took about 2 hours. I went through a lot of shop rags. Results: 

Prepping for paint

Table saw and old shop-vac make an appearance

This was my first time using a paint spray gun. I bought a harbor freight air powered purple HVLP gun for $10 (on sale, normally $16). It comes with a gravity feed 20 oz cup and 1.4mm nozzle. I used it to anti-rust primer everything, as well as paint everything gloss black (except the drawers and drawer slides). The drawer slides I left primer-ed, and tried not to get primer in the tracks, which will be greased anyways, so shouldn't rust. I sanded all of the primer with 220 grit sandpaper. This was very necessary, the primer ended up being pretty rough. I decided to spray paint the drawers "regal red' (pretty close to craftsman red) with a rattle can, ended up using 3 cans. With the sprayer, I used one whole 32 oz can of primer and [will end up using] one whole 32 oz can of gloss black.

My thoughts on spraying vs rattle cans: Paint spray guns are nice. You can get a very consistent spray, and you can spray a lot more paint, faster than with a rattle can. The paint is also cheaper than rattle cans. One 32oz can of paint will cover about 5x the area that a rattle can can. Rattle cans are about 12oz, but about half of that is propellant. A 32oz can of paint is $9-10, while a rattle can is about $4-6, so the spray gun paint is about 2-3x cheaper, more so if bought by the gallon. However, spray guns have some major downsides: You have to buy the spray gun. You also need a large volume compressor (mine's 63 gal, 6HP, and it could just barely keep up with continuous spraying), a hose, and regulator to run it. The spray guns also clog fairly easily, but I luckily haven't had a clog yet, probably because I filtered my paint and cleaned mine regularly. Paint filtering is a pain, especially primer, which tends to clog the filters. The paint filters are cheap luckily, as was the stand to hold the gun and filter (actually more than the gun, which was also cheap) during paint filtering. I started with 120 mesh, but it was way too slow, so switched to 60 mesh, which might let particles large enough to clog the gun through, but it is what it is. You also might need to thin the paint, depending on what it is. I thinned the oil-based paint a little with acetone. Latex paint has to be thinned a lot, with water, to use in a spray gun. Cleaning them is a pain, takes about 10 minutes, and requires a lot of acetone, gloves, and shop rags. You have to wipe out the cup with acetone soaked rags, and if you don't get all of the old paint out, it will dry and cause clogs, or mix with your new paint causing your color to be wrong. You also have to clean the cup's threads, the internal filter, the spray gun nozzle, needle, and spray gun body. You're supposed to disassemble the whole gun to clean the insides, but I haven't done that because harbor freight stopped including (and never sold) the super thin 19mm wrench required to take the nozzle off/needle out. Instead, I just spray a few ounces of acetone through it into a box after cleaning it. The result of all of this is a bag of trash after every use. I wiped the nozzle on mine and left it sitting with paint in the cup for about 4 hours once, and it didn't clog, but I don't think I would let it sit for longer than that without emptying the paint cup and running acetone through it. Did that and left it over night a couple times, no problem. I suggest a full clean if it'll sit longer than 12 hours. Because spray guns use compressed air to atomize the paint, they move a lot of air, which means that any dust within about 5 ft of what your painting will end up in the paint. Also Florida bugs love paint, ugh. Rattle cans don't move as much air, so dust is less of a problem, and since they are disposable, you don't have to worry about cleaning them, except maybe flipping them over for a few short bursts of propellant to clean the nozzle. Final conclusions: 

  1. If you already have a spray gun, stand, filters, cleaning supplies, large compressor, regulator, and hose, then it's worth the effort to use the sprayer if your project will use greater than about 5 rattle cans worth of paint. For example, I plan on re-staining/sealing my wood fence and deck eventually - that will be a good project to use the sprayer on due to the large volume of sealer needed and long-duration sprays. 
  2. If you already have the large compressor, but not the spray gun, stand, filters, cleaning supplies, and don't plan on doing many large paint projects, I suggest buying cases of rattle cans up to about 12 cans...over that, probably worth getting the spray gun.
  3. If you don't have the large compressor or any of the spraying equipment, use rattle cans up to about 12 cans. If you're doing a large paint project, you can buy a decent airless sprayer for about $100. They have the same clogging and cleaning downsides, but they're cheaper than a full compressor set up (unless you're in to repairing old tools like me). 

I found out about the dust and bugs problems the hard way...first coats of black on the frame ended up covered in dust and bugs:


I painted the sides I wouldn't see first in case something went wrong, but it still sucks. I'm taking a break from the project at this point...really stopped being fun. Eventually, I'll sand all the parts down after the paint hardens and try again, maybe with the parts standing up and only doing the top halves, then flipping them over, so I'm not painting near the ground. I finished the drawers (rattle cans), though, and they came out nice.

I have about 4 hours invested so far in the painting, about $35 of paint, and about $50 in supplies, including the spray gun. It'll probably take another 5 hours or so to finish painting, will update this post when I work on it again.

Estimated total cost and time: ~$150 and 25 hours. Working min wage, I could have afforded ~2x new work benches for the time and money I've put into this one. That's not really the point, though, it's all about the love of the craft...yeah....sure... Note to self: Don't do a project like this again.

At least I learned a lot, and I will have a really nice work bench by the end of it. 

To do:

  • Sand paint, finish painting black
  • Re-assemble
  • Epoxy top
  • 3D print TPU rubber feet to prevent steel bottoms from scraping/rusting. 

Monday, December 21, 2020

Homelab/Cluster update

The cluster is no more. I sold off the compute nodes and the sound proof cabinet for an embarrassingly low sum, but the guy was local, so I didn't have to figure out how to ship any of it. I kept the FDR infiniband system and the headnode, the former because I plan to build a new cluster eventually, the latter because it makes a decent desktop. 

CentOS 7 is now ancient to the point where I'm having trouble installing new software on it, so I updated the desktop's OS CentOS 8 Stream. There's a lot of controversy surrounding RedHat's decision to go to "stream" (continuously updating) rather than long term support, which was one of the key features of CentOS in the past. I like CentOS, so I figured I'd try the stream version out. 

First thing I did was create a tar.gz of /etc, /home, and all the configuration files I could think of. I moved that to the RAID1 drives. 

I created the DVD installer USB by following the instructions on the CentOS website. Like previous versions, the only way I could get it to not fail the media test upon boot was to dd the iso to the USB drive twice. The installer also didn't like my hardware RAID drives...caused it to crash, so I had to unplug those (probably a good idea to do anyways). Then it installed fine. 

I like the new GUI. CentOS still has problems with wifi adapters, though. The 300N one I have is recognized but refuses to connect to any network, so I had to go back to the old penguin 150 N . That one sometimes causes CentOS to crash if I pull it out, and sometimes I lose wifi if I plug in another USB device. *shrug . At least it mostly works. 

There's a new software I want to try that requires CUDA, so I installed that following this guide. I copied over the samples directory to a directory in my home folder and chown'd it. I was able to make and run many of the samples, but I wanted to try some of the simulation samples, which require cuFFT and OpenGL. OpenGL is part of the NVIDIA driver. I followed NVIDIA's guide for installing cuFFT; my original GTX Titan GPU just barely meets the minimum requirement for that. I also had to follow the directions under "Install Third-party Libraries" because I didn't have all of those. Once I had all of that, the simulation samples built. Very cool. 

When I went to plug the HDD's from the RAID1 data array back in, the LSI raid controller thought it was degraded. I could still mount one of the drives in centos and see the files. The full LSI software raid utility interface isn't available in the version of the BIOS I have...not sure why, but doing ctrl + M like the motherboard manual says to do doesn't do anything and the only LSI interface I have is a very limited one inside the BIOS. It's missing many of the commands that the manual says it should have. One of the missing ones is rebuilding an array. What I ended up doing was deleting the virtual drive configuration and recreating an identical one with both drives, and then NOT initializing the array. I saved and exited the BIOS, then booted into CentOS. I was then able to mount the array as before and see the data. So I'm not sure what happened there, but this method will allow me to "rebuild" a RAID1 array. I hate this utility; definitely need to buy hardware RAID controllers for future server work. 


Friday, September 25, 2020

Quick, easy, cheap sprinkler guards

The new house has a sprinkler system. Ended up having to replace 3 heads because they'd been chewed up by edgers/mowers, so I decided to do something about that. I don't like the concrete rings...they're bulky, wide, hard to cut into partial rings, you can't adjust their depth (they sit on the ground) so if the sprinkler head is taller than them, then they don't work, etc. 

I ended up buying a 10ft piece of 4" PVC "gravity sewer pipe" and using a miter saw to cut it into ~5-6" long pieces. It's schedule 10, so pretty thin, which makes it easier to hammer into the ground to the depth needed for each sprinkler. I did this with a piece of wood on top of them and a 4lb sledge hammer. I even cut some into partial rings for places where a full ring wouldn't fit, like when a sprinkler head was up against something concrete, e.g. driveway. Bonus: the pipe is green, so it doesn't look bad in the yard.

Partial ring

I think they look better than concrete rings. They're cheaper, too. Win-win-win


New house, new garage

Ugh, 4 months since the last update. Lots of stuff going on. We bought a new house, and I've finally started to put the garage together. I've been cleaning, painting the walls, purging junk, unpacking, setting up shelves, etc. 

These made it pretty much unscathed. Time to restart assembly of CubeXY!

Some of the rockets didn't make it...oops.

We had a lot of tools, but I purchased some more, mainly off of craigslist or fb marketplace. 

Mini hydraulic press, pressure washer

Wet tile saw

There's a table saw under there

Tooling cabinet I got from a machine shop auction.

Bins full of metal stock and tooling that was in the cabinet.
I'll be replacing these cabinets/workbench later.

Got a great deal on this Kennedy Toolbox

There's a craftsman bandsaw under there that I need
to reassemble. Bought new bolts for it.

32" radial drill press that I decided I don't really need and am trying to sell.

Nice floor standing drill press.

33 gal, 6HP compressor. New regulator, made the handle out of 
PVC+wooden dowel. The plastic cover came off another one. 

Lots of good stuff. The compressor didn't come with a handle, and the regulator was broken. It also didn't have the plastic pump cover, but I luckily found a very similar era one on FB marketplace for $30. Took the cover from that. I had already made the PVC handle, but I'll keep the metal handle. The $30 actually worked, despite being super rusty. Turns out that 9/10 of the parts are compatible, so I stripped them all of for spares: 

Spare compressor parts

That left the tank...eek. Very rusty. I really didn't want to make a bomb. Hydro-static testing is fairly safe because water is basically incompressible. As long as you get all of the air out, there won't be much stored energy in the tank. 

Lots of rust...the inside was worse.

Filling with garden hose after plugging the other two holes. 

Very full. Shook it around to get air bubbles out. 

Brass schrader valve in a 1/2 - 1/8 NPT adapter

$20 300 psi AAA brand tire inflator from amazon
Only air in the system was the compressor air hose.

I had to clamp the compressor in place to keep it from shaking around. There's a little USB snake camera held looking at the pressure gauge. I turned the compressor on, then got in my car and plugged it in while watching the camera feed on my phone. Unplugged it to turn it off. Let it get to 200 psi (1.6x 125 psi, which is operating pressure). Then held it there for 10 minutes. The schrader valve was leaking...could hear the hiss, it was about 5 psi/minute, so I had to repress a few times. But it passed! No water leaks. Total cost was about $35 for the compressor and fittings. You could probably figure out a way to do it without the $50 USB snake camera...maybe a gauge on an air hose T'd off of the schrader valve fitting. 

Not that those boards would do anything if it blew, 
but they made me feel better.

Used one of these to depressurize it. 

Sprayed water everywhere. 

Removed schrader valve and drain plug. 
30 gallons is a lot of water...

I'm letting it dry out now. Then I'll sandblast the outside, give it a coat of anti-rust primer, and paint the outside. Then the plan is to mount it on the wall as a second storage tank. The 33 gal compressor will normally be hooked up to it to provide air to my garage via a 50' retracting hose reel. When I need air elsewhere, I'll unhook the compressor, wheel it around, and leave this tank on the wall. 

My plan is to eventually turn the garage into a machine shop. I'll be insulating the ceiling and installing a window AC unit before next spring. Planning to save up for a CNC bed router, CNC mini-mill, and a CNC lathe. Possibly also a laser cutter. The garage is ~24'x24'x8', so it's not a lot of space, but I might be able to cram all of that in there. 

I also scored ~750ft of good quality Cat6 riser cable off craigslist for $25. I'm going to eventually wire the whole house with ethernet drops. 

We've done a ton of other projects...painting, new light fixtures, various minor repairs, etc. This was just what was in the garage this morning when I was taking pictures. I'll make some more posts later.  

Friday, May 8, 2020

CubeXY X-axis Re-redesign

One of the great things about hobbies is the lack of deadlines. Unlike in the real engineering-world, I can keep tweaking and perfecting designs as much as I want. This printer is turning out to be a great outlet for that.

I mentioned in an earlier post that the "12"mm SS rods that come with the CubeX are undersized. I finally measured them with a micrometer. They're 80um under, which for linear bearings, is WAY undersized. The THK linear bearing spec for 12mm LM shafts calls for -6 to -17 um. That probably contributed to the bad bearing wear I saw on the stock bearings. I purchased 4 new 12mm rods from PDTech on eBay: they actually listed a diameter tolerance spec, and they were case hardened, both of which are important for linear shafts (and neither are common for cheap chinese linear shafts). The only downside is that they're chrome plated steel, not stainless steel, but case hardened stainless steel shafts are very expensive, so I didn't buy those. I only purchased four since only four of them will have linear bearings on them. They ended up being about 11um undersized, which is right in the middle of the THK tolerance range. They result in noticeably smoother linear bearing movement and less (almost no) slop.

I purchased them long, partially because some of PDTech's non-standard lengths were actually cheaper than their standard lengths (455mm was cheaper than 450mm, not sure why), but mainly because I plan on making the printer taller. I mentioned this in passing in a previous post, but there is a lot of room between the top of the top aluminum cylinder shaft holders and the top of the acrylic shell. I can safely increase the length of the vertical shaft/rods by 40mm and still leave plenty of clearance between the hot end assembly and the lid. 40mm is convenient because the stock vertical shafts are 400mm long, and the stock X-axis shafts are 440mm long, so I can replace the 4x 400mm stock shafts with the two 440mm long old x-axis shafts (rear of printer) and two of the new tighter tolerance shafts (front of printer). I'll have to redrill 4 screw holes in the acrylic shell, and cut some acrylic out around the XY motors in the wire-mounting back plate, but that's pretty much it. Totally worth getting another 40mm of Z travel, for a total of about 325mm.

Taller CubeXY
While trying to find actual tension force measurements of belts in corexy printers (never found any), I stumbled across this interesting post on belt compliance. This person measured belt compliance at 10N preload (tension) + 10N. Basic 6mm GT2 fiberglass reinforced belt (like the kind I bought), has  modulus of 0.0067 %/N, while 6mm GT2 steel core belt has a modulus of 0.0024%/N. The given example is a 1kg carriage being accelerated at 3000 mm/s2 with a 1000mm belt. 1kg*3m/s2=3N. 0.0067%/N*3N = 0.02%. 0.0002*1000mm = 0.2mm, which is about half a nozzle width, which would probably result in very bad ringing. I had been planning to drive my corexy, which has approximately 2m long belts, at 6000+ mm/s2, with an approximately 1kg carriage. Doing this math for my printer yields 0.8mm of stretch, which is terrible. A steel core belt would be about 0.29mm of stretch. I bought some to try. The disadvantage of steel core belts is that they're heavier and stiffer, which means less power ends up in the motion of the carriage. Steel core belt minimum radius is also larger, mainly to prevent kinking and fatigue, so I may not be able to use them...we'll see. I'll probably start with fiberglass core belts. This post has a lot of details on belts.

X-axis Re-redesign

Due to the FEA results from the last post, I decided to completely redesign the X-axis to make it stiffer. 

The X-axis plate is flat now, and the pulley blocks also hold the linear bearings. The Hemera exttruder has been rotated 90 deg. The x-axis plate is 149g and made of aluminum. It's about 25% lighter than the previous steel design, and 45-75% stiffer, depending on the bending mode. It'll be machined out of scrap 1/4" ground plate. The pulley blocks will be machined from T6-6061 bar stock. The fan mount plate will be band sawed out of 1/8" aluminum plate, and I'm going to use flush press-in threaded inserts in it instead of threading it. The motor-carriage mount will be milled from 2x2" x 1/8" wall square aluminum tube, which holds the extruder motor on the inside almost perfectly. Unfortunately, almost all of the previous machining I did won't be used. Luckily, the nozzle ended up in very close to the same place, so the same bed plate can be used. I will have to print new bed mounts, though, because the bed has to be shifted in +Y 5mm. This system should result in  much stiffer X and Y axes. Here's a close up of the new extruder assembly:

This version is far less elegant than the previous one. The belt tensioner on the previous version was very simple and compact. This one uses the two stock X-axis belt tensioner cylinder things mounted inside of a 3D printed ratcheting assembly. I'll use a wrench on the printed hexes to tighten the belts, then tighten the button head screws down to hold the tensioner in position. Mounted off of that assembly is the inductive probe, which is conveniently closer to the nozzle now. The other side of the extruder has the fixed belt mount which takes each belt in and turns them 180 deg for plenty of belt engagement. Both the belt mount and radial fan are screwed to the 1/8" aluminum plate, which in turn is screwed to the side of the Hemera extruder motor. The fan location and duct are also less elegant. The previous duct completely encircled the nozzle. This one only has room to blow from one side. Because the belt heights are fixed by where the motors are mounted, and the requirement that belt segments be straight, the belt tensioner and fixed belt mount could only be located in the locations shown. Also, since Hemera was rotated so the length was along Y, the only place with room for the fan was on one of the X faces. Because the fan has its inlet on one side, that restricted the fan to the -X side. The fan also couldn't be located too far in +Y or it would impede the cooling flow from the hot end cooling fan. All of these things meant that the fan had to be mounted kind of high and in the location as shown. The LED light will be taped under the motor. I tried about every way I could think of to come up with a better way to configure the extruder assembly, but this was the best. While it's not as pretty or elegant, this should be a far stiffer and better performing design.

I've put in new material and screw orders. I should be able to finish machining the new X-axis plate next week. I'll start 3D printing the new plastic parts this weekend.

Tuesday, April 21, 2020

CubeXY Fabrication Part 3 and X-axis redesign part 2

I re-machined the pulley blocks today. They required a relief cut in them for the longer 450mm rail. Speaking of which, here's the "new" (ugh, see below) X-axis design.

Right pulley block

The x-axis plate is contoured for mass savings, which I extended to the 3D printed pulley blocks for aesthetics. The M3 screws were also shifted around some.

I also pressed-in the linear bearings to the old aluminum x-axis plate and test assembled it on the printer.

The good news it that is slides well, and I think I got the linear bearing spacing correct. The bad news is that this let me see a bending mode I hadn't thought of until now. Previously, I analyzed what I thought was worst case: both motors being used to apply max force such that the x-axis was maximally accelerated in y. I applied this y acceleration to the FEA model with both ends of the x-axis restrained. This is not the worst case, though. For corexy, in order to move diagonally, one motor applies force while the other does not. This causes both the X and Y axes to translate, resulting in diagonal motion. Here's the basic corexy belt layout I discussed a few posts ago:

If you spin the bottom right motor clockwise, for example, that will pull the x axis carriage in -X and the whole x-axis in +Y, resulting in diagonal movement. All of the belts are still tensioned, but belts H and D are tensioned more, by exactly the force required to accelerate the axes' masses, and that force is applied by the motor torque to the pulley. Because H (and D,  M and J, but they don't matter for this discussion) has more tension, there is a net torque on the X axis assembly about Z, which has to be countered by the Y axis linear bearings. Remember how I said linear bearings don't handle torque loads well? Oops. But there's another problem. If the X-axis is not very stiff, then the net force in segment H will cause the X-axis to be bent. My design is essentially a beam supported by two rollers, or if you think of the system as static, a pin (pulley P1) and a roller (the linear bearing under P2). This is causes a different mode shape, one that results in more deflection than the previously analyzed case, despite using the force of only one motor instead of two.

I removed the Y axis acceleration (left gravity), left the radial roller supports in the linear bearing holes, left the fixed support in one of the shoulder bolt (pulley) holes, and applied half the previous force (one motor only) to the other shoulder bolt hole. This caused negligible Z deflection, but the Y deflection of one side relative to the other was about 1.8mm! Yikes.

This is the bending mode I was seeing with just the linear bearings and aluminum x-axis plate (no steel rail)...I was able to move them about 5-10mm relative to each other. If there's any play at all in the bearings or frame (impossible to remove all of it), and if the beam connecting them isn't perfectly rigid (never is), then the linear bearings can move axially relative to each other. In the FEA case above, no displacement in X of the linear bearing surface was allowed (bearing or frame slop), so it's likely that the real world deflection would be > 1.8mm.

The frame will be stiffer when the 12mm rods/shafts are locked in place (set screws) and the acrylic shell is on, but that won't eliminate bending in the rods and aluminum brackets holding them. There's also no way to the play between the undersized rods (talked about previously) and the linear bearings...I can add some pretension, but I don't think it'll be enough. Accelerating much slower (~factor of 10, ugh) also fixes this problem, but slow printing was something about this printer I was trying to fix. Ultimately, the right way to handle this problem is to make the X-axis stiff enough to not deflect significantly, which I'm not sure how to do at this point.

The weird thing is that other corexy's aren't immune to this, including ones with rail guides. Linear rails are designed to handle torque, but they still don't limit axial motion, which is where this bending mode comes from. This X-axis design is actually stiffer than Railcore II's unsupported MGN12 rail, at least according to my FEA, so how does that printer work so well? This lead me to re-examine my model inputs, specifically what I'm using for force and acceleration.

I first used just the motor torque and pulley radius to calculate a force. I then used an online calculator for stepper motors that accounts for rotor inertia, applies a factor for reducing the holding torque to a more realistic torque value in order to reduce positioning error, and applies another factor for microstepping torque reduction. I could have written my own simulation program, and have for (much larger) linear motion applications before, but meh...if a calculator exists, why not use it. This dropped the max per motor acceleration to 3 m/s2 from a previous 32 m/s2. I also checked forums for maximum real world accelerations for other high performance corexy printers. It seems that 6-20 m/s2 are about the maximum. 20 m/s2 results in 200mm/s in 1mm and 0.01s. I'll probably redo these analyses with that.

Update: I re-ran the final design with 20m/s2 and 6m/s2. 2*20m/s2 in case 1 (the bending mode shown previously) resulted in a Y deflection of 0.062mm, and 0.55mm at the nozzle and 1mm at the unconstrained y bearing block for case 2 (the bending mode shown above). 2*6m/s2 in case 1 resulted in a Y deflection of 0.017mm, and 0.16mm at the nozzle and 0.3mm at the unconstrained y bearing block for case 2. The Y deflection for 20m/s2 is still unacceptable, and I'll probably have bad ringing at 6000mm/s2 if the motion is somewhat diagonal. Not good.