Introduction: Using 3D Printing to Make a Custom Work Stool
As an engineering student, I always enjoy projects that merge technology with common things. For a while my workbench has been missing a good work stool to sit on while making projects, so I went to find inspiration for a work stool that I could build with few tools. Eventually I found a stool created by Julian Goulding. I really enjoyed the design that they created, which can be found here: https://www.behance.net/gallery/9102919/3D-printed... However, I did have a few reservations about the design and possible complexities that could arise from it, such as the pegs that are printed for the seat requiring precise drilling, which is something I could not replicate with my few tools. It is at this point that I realized that the best way to be able to use this design and be able to create it with the tools I had was to design it myself. The CAD design for the parts I created was done in a student version of Autodesk Inventor and using skills learned in a design class, I adjusted the printed parts for the tolerances of the parts being used and used 100% infill while printing to ensure strength with the PLA plastic based parts.
The work stool was made from these materials and their respective sources. However, pieces such as the work stool legs can be substituted for other materials, such as rectangular steel tubing. In total this project cost me about $40, however the cost could have been reduced by avoiding online ordering or by already having some of the pieces already. The cost of bolts could be greatly reduced by finding them in person and buying only as many as you need. Buying the nuts and bolts in person instead of ordering them online from Amazon will reduce the cost of the project to ~$27. I would highly recommend this if you have the time or the means to go to the store and purchase them.
Work Stool Legs:(3 pieces) 36"x2"x1" Aspen Board, which can be found at places such as Home Depot or Menards, for about $3.00 a piece.
Seat: (1 piece) Edge Glued Round Panel, which can also be found at Home Depot or Menards. In this I used a 18" diameter, but your design may vary.
Wood Screws: (6 pieces) #8 x 1" General Wood Screws, can be found at any hardware store, this design uses at least 6 screws. These can often be purchased in boxes of varying unit counts or sometimes even as a singular unit. These links demonstrate both options, and how costs varies between them.
Nuts/Bolts: (12 pieces of each) 3/8" x 1.5" Bolts, these were ordered online but could most likely be found at a hardware store or places such as Fastenal.
Printed Parts: (4 pieces total) Parts for this design will be available for free download from www.thingiverse.com for free.
The Inventor files for the parts can be found attached to this step.
Link to STL Files - http://www.thingiverse.com/thing:2247917
A 3D Printer with a minimum 6"x6"x6" print bed
Filament for the 3D Printer
A power drill capable of accepting a 3/8" Drill bit or larger
Drill bit set including a 3/8" drill
9/16" wrenches or adjustable wrenches to tighten 3/8" bolts
A screwdriver with matching drive for the wood screws you choose
A handsaw or other tool capable of cutting through Aspen board
For straighter cuts: Substitute a miter saw for the handsaw
For easier sanding of the plastic parts: Substitute a Dremel with a sanding tool for the sandpaper
For perfectly perpendicular holes: Substitute a drill press for the power drill
Step 1: Design Basics
When designing, especially for 3D printing, it is important to take into account the tolerances of the system you are building. In this case the design should account for the dimensional errors produced by 3D printing and the dimensional error in the wood. Holes in the design were enlarged to account for the undersized holes produced by the expansion of plastic during 3D printing, and were enlarged further to account for the error in the Aspen boards. If you do not account for tolerance, you could spend a great deal of extra time sanding off the excess or going back to the design phase to account for the holes being too large. You also want to account for things like the fit of screws and bolts. Under-sizing holes for wood screws, can cause wood to split, and in the case of this design, plastic to crack. Think carefully about how things are assembled, and where tolerance should be accounted for. The files used to make the pieces for the work stool still required a small bit of sanding as the 3D printer shifted layers once or twice throughout the print. I have attached the Inventor part files and STL files so that you can adjust the tolerances of the parts to your liking and to match the accuracy of your 3D printer. However, I would recommend that you keep in mind that too loose of a tolerance could allow the legs to bow from having too much room in the slot that holds each leg. As far as tolerances go, I would add enough clearance between the leg and the slot to achieve what is called a "slip fit", that is a fit that in this case would allow the leg to slip through the slots but not wiggle/move around in the slot. Due to the varying thickness of wood and possibly the plastic, I added between 10 and 20 thousandths of an inch in clearance in the slots. This applies to the caps on the legs as well.
Changing The Files:
If you need to change the tolerances you can adjust the size of the slots and holes inside of Autodesk Inventor. The picture in the middle of the bottom row of pictures shows the dimensions that can be changed in order to widen/narrow the slots for the legs in the Center Leg Holder. The picture on the furthest right of the bottom row of the pictures shows the dimensions to change to increase the size of the slot in the Leg Cap. The files can be changed in various ways, however do keep in mind that excessively loose tolerances may cause the assembly to weaken and excessively tight tolerances will prevent assembly all together (unless you intend to greatly sand the finished parts)
Step 2: Printing the Parts
The 3D printed parts for this project are already scaled properly, however they may needed to be re-oriented in the slicing software you use. For those without access to 3D printing, services like "3DHubs" (https://www.3dhubs.com/) may be able to help get these parts made for you, however this may increase the cost of the project. Unfortunately the price seems to be more than double the cost of the other parts combined if using a service like 3D hubs, so try and find someone you know who might have a 3D printer, a makerspace should have one as well. For those printing these parts yourselves, I would recommend a good balance between layer thickness and the amount of time you are willing to wait for the part to print. Finer layers will produce better holes on the printed parts however this could add hours to the final print time depending on how detailed you would like the part to be, so it best to find compromise. Depending on your print speeds and layer thickness these parts can vary in print time significantly, however my prints using 0.3mm layer thickness and 100mm/s speeds throughout every print took about 6 hours total. All parts should be printed at 100% infill for maximum strength and parts should be not be used if there are defects, such as missing infill or cracks.
Once the parts have finished printing, the larger holes should be drilled out to 3/8" in case the printer did not exactly meet this diameter. The smaller holes should be drilled to 1/8" inch, as these holes will be used to correctly space the wood screws at a later time, and 1/8" is the correct pilot hole diameter for the #8 wood screws. Once the holes have been drilled, carefully "de-burr" them using sandpaper or very carefully using a hobby knife to get rid of any small surface imperfections that could cause the legs to bind up while be inserted through the slots. After this superficial sanding has been completed, you can attempt to slide the legs through each slot.
Step 3: Leg Positioning and Initial Test Fit of Legs
Depending on the tolerances you used for the Center Leg Holder piece printed earlier, one or more of your legs may have bound up while being inserted into this piece. Now it is important to check every orientation of the legs, as one combination of legs and slots may actually work perfectly with the varying tolerances of the pieces. If you have found a combination of legs and slots that allows each leg to slip freely through each slot you can stop reading here and begin the next step. Otherwise continue on to the next paragraph
One or more of the legs does not fit into the slots:
So you have three options at this point, 1: Sand the inside of each slot to clean up any burrs that still may be binding up the leg while it is being inserted or 2: Sand the leg itself to make it fit into the possibly undersized slot or 3: Re-print the Center Leg Holder using adjusted tolerances. While working on this portion I used a mix of both options, the first option being more effective but more difficult to do as it requires you fit sandpaper inside of the narrow slots which during sanding can cause your fingers to catch the plastic and possibly cut your finger. This led to me try the second option intermittently. However, in hindsight, It probably would have been smarter to re-print the piece using better tolerances instead of putting in the immense effort of sanding all the parts until they eventually fit together. If possible, go with option 3 and save yourself the trouble. If option 3 is not an option for you, please take care when sanding the pieces to avoid your fingers getting cut up like mine were.
Step 4: Achieving a Level Sitting Surface
At this point, the legs of the stool should slide freely through the slots of the Center Leg Holder and now you can level the seat. This is done by putting the Leg Caps on one end of the legs and putting the legs through the slots of the Center Leg Holder. Now you can place the seat loosely on top of the capped ends of the legs and place a level of some kind on top of the stool, this can be done with a small level like one used for hanging pictures, a smartphone with leveling app, or even by sight. Because the stool has three legs, the stool won't rock back and forth if you don't achieve perfect level, but the seat will be tilted towards one leg or another. After leveling my stool by eyesight, I found the small tilt I noticed to be negligible when actually sitting on the stool. To check level accurately you want to place the level in line with with each leg as you check, if the bubble in your level remains in the "level" zone across all three of these planes, your seat should be perfectly level. You might want to tape the legs so they don't move as you go around the stool so the positions you found do not change. If the seat is not level, raise and lower the legs one leg/plane at a time until each leg/ plane is level.
As you can tell from the pictures just because it appears level in one plane does not mean it is level in the rest, I didn't mind the tilt too much as the stool was just a proof of concept for me, however the tilt may be uncomfortable after extended use, so take your time and do it right.
Step 5: Drilling the Legs
At this time, the legs should be inserted through the Center Leg Holder and the legs should be held in the position you left them in once you were done leveling. At this time you have a few options depending on the tools you have on hand. For those of you with just a power drill and some drill bits, you have two techniques of drilling through the legs.
Technique #1: Line up the drill perpendicular to the surface of the leg by eyesight and go through the existing holes on the Center Leg Holder using a 3/8" drill bit. You can drill a pilot hole using a smaller drill bit if you would like, but I find this process to be easier if you jump straight to 3/8" drill bit because the hole on the Center Leg Holder will act as a guide if you do so.
Technique #2: Get a 1-2" thick piece of material with a 3/8" hole placed accurately through it. This can be used a guide for the holes on the legs as this prevents the drill bit from walking off center. So if you can carefully place a very straight hole through this one piece, you won't have to focus to hard on keeping the remainder of your holes on center as it will be basically a guarantee with the guide.
For those using a drill press, you will want to mark the holes and remove them from the Center Leg Holder. Line up these marked holes under your drill press and use a 3/8" drill bit to make the holes. You can also drill the holes that will go through the Leg Caps.
At a minimum: You should drill all the holes that marked by the Center Leg Holder as the Leg Caps don't necessarily need bolts placed through them for any structural purpose. Placing the bolts through the Leg Caps serves only a decorative purpose, so you if you do not like how it looks, do not go through the effort of placing the holes, because you cannot un-drill them.
Step 6: Cutting the Legs
At this point: The legs should be inserted into the Center Leg Holder and holes drilled through the Center Leg Holder and the legs. If you have not done these things, please refer to an early step to make sure you have not missed anything.
Now, if the legs are currently in the Center Leg Holder, carefully mark each leg in an inconspicuous spot which slot each leg was in, this will ensure that when the legs are re-inserted later everything will line up perfectly. After you have marked each leg, remove them from the Center Leg Holder and take note of where the holes you drilled for the Center Leg Holder are. If the Leg Caps are still attached, remove them. If you have drilled holes for the Leg Caps, you will be cutting the legs on the other end of the board. If you have not drilled holes for the Leg Caps, you will cut the board on the end that is the furthest away from your Leg Center Holder holes.
Cutting the legs - Preparation
The amount of material you remove from each leg will determine how high the stool sits. The more material you remove, the lower it sits. My stool sits almost even with my workbench after remove 9-12" from each leg. It is Absolutely Important that you cut off the same amount from each board or the level you determined for your seat will no longer be correct. The best way to ensure this is to line up each board next to each other and align all of them across the end closest to your Center Leg Holes or your Leg Cap holes (if you have them). Then draw a straight line across all three boards whatever length you would like your legs to be, away from the aligned edge. That is: If you want your legs to be 30" tall (Unusually tall, as in Bar Stool height tall) you will place your cut line 30" away from the end where all the boards are aligned.
Cutting the legs - Showtime
Once you have marked the line on which you are going to cut, you have two ways of cutting the legs. Option #1: For those of you with only a handsaw, you place the end you are going to cut off over an edge (like your front porch if it elevated or clamped over the edge of workbench), then you can carefully cut across the cut line you marked earlier being careful not to chip the ends as this may decrease it's overall appearance.
For those of you with a miter saw, you can clamp all the boards and cut across the cut line being careful to avoid chipping of the cut edge. If you want the feet of your stool to be flush with the ground, you can determine the angle in many ways, this could be done by quickly placing the legs back in position before you cut them and marking a line parallel to the ground and measuring the angle of this line with a protractor. You can find this angle in many ways by measuring different pieces of the stool and determining the angle but most of them require re-assembling the stool anyway, so drawing a line parallel to the ground should take as much time as the other possibilities anyway.
It is almost guaranteed that your first cut will leave the legs too tall. This is perfectly fine, however you want to repeat the line drawing process exactly how it was done in "Cutting the legs - Preparation" otherwise you may not be able to reassemble the stool or use the stool, as the holes for the Center Leg Holder will now be much closer to the top of the stool and will leave a lot more of the seat hanging over air.
Step 7: Assembly and Attaching the Seat to the Legs
At this point: Your legs should be cut to length and drilled. If not, refer to earlier steps
Assembly should be fairly straightforward, where ever you have a 3/8" hole, place a a 3/8" bolt through it. If you want to match the style of the stool featured in the pictures, put them through the holes so the head of the bolt faces outward so that it is angled toward the sky. If you have drilled holes for the Leg Caps, do the opposite for these such that the head of the bolt faces toward the ground. All that should be remaining is the seat and the wood screws.
Attaching the seat to the legs:
You can line up the holes for the wood screws in two ways. Option #1: Line it up by eyesight and save a lot of time as it will be close enough to on center that 99% of people won't even notice. Mark the points you will drill into the seat through the Leg Caps. Option #2: Find the exact center of the triangle at the center of the Center Leg Holder and match it to the exact center of the seat.
You can drill the seat off the assembly, or you can just stack books or something with good weight to it so that if you push up to drill the underside of the seat, the seat won't move. If you are drilling the seat from underneath, Wear Safety Glasses/Goggles! You're either going to be getting sawdust in your eyes or not looking where you are drilling, neither of those are good at all. The drilling should be done with a 1/8" drill bit to a depth of: (Length of screw - thickness of region in Leg Cap). Next, you want to remove the seat if you have not already and drill straight through the smaller holes in the Leg Caps with a 5/32" drill bit to provide clearance for the screw that will pass through this area.
If you have drilled holes for bolts to be placed through your Leg Caps, insert these bolts now and fasten them with the matching nuts. Now that the holes in the seat have been drilled, you can place the seat back over the Leg Caps and screw into the seat through the Leg Caps with the #8 wood screws with a screwdriver matching the drive of your wood screws. (I prefer Phillips head, but i'm sure Robertson will be just as good). Make sure all wood screws are firmly screwed into the seat through the Leg Caps.
Step 8: Congrats! You Should Now Have a New Work Stool
The completed work stool should look similar to the one picture with these instructions. The stool is quickly disassembled and reassembled making it easy to store if you need extra space in the workshop or need to move the stool elsewhere easily.
This project was made with new makers in mind, as it requires very few tools and ones that a good portion of people already have. For me as a maker, the most fun part of the process is finding a way to bring my vision to life with only the tools I have which only include a few small hand tools and the ones presented in this Instructable, I also find this to be better in the end overall because it forces you to think more creatively about how things are put together and ways to avoid anything that is at all unnecessary. I would also strongly encourage those who see this project to take this project in a new/fresh direction and make it unique. Add lighting, or change the angles of the legs, or make it a table, or even add upholstery. The sky is the limit.
The only strength testing that was done can only confirm that: "With 150lbs/(68Kg) of weight on the stool, the legs did not bow". This is in no way a guarantee of it's strength as this is determined by many factors in the build process. Beyond that, I have no other data indicating the limits of the design or how negatively its limits can be effected by the build process. Sit at your own risk.
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Please be positive and constructive.