Fixing Power Tools With Robots (How to Use a RepRap)





Introduction: Fixing Power Tools With Robots (How to Use a RepRap)

About: Currently pursuing a degree in Mechanical Engineering. contact: jamesrpatrick(at)
Here's an example of the how a RepRap 3D printer can be used as a regular household utility, with the ability to fix many consumer products.

In this case, the plastic tensioning bracket of a Craftsman 10in band saw had shattered due to excessive pressure. I was able to design and print out a replacement in under one hour.

The printer used in this article is the RepRap eMAKER Huxley #307, which I built in about three days. You can read more about it on my blog. To learn about open-source desktop 3D printers, visit


Step 1: Tools/Materials

-3D Printer(RepRap, Makerbot, Ultimaker, Printrbot)
-ABS plastic
-calipers/precision steel rule
-3D design software(123D, Sketchup, Blender, Inventor)

ABS plastic is chosen over other types for its strength and degradation resistance. It is also very easy to machine or finish. PLA is not chosen because it is biodegradable(made from corn). PLA is useful for prototyping wherein multiple iterations yield a large number of obsolete parts, which can simply be composted. This becomes a problem for a functional part,  however, if the part is exposed to water for an extended period of time, or if the part comes into contact with any strong chemicals. ABS is a fairly standard plastic that many consumer products already incorporate. 

Ideally, one would print every iteration in PLA, switching to ABS only for the "final draft." Or better yet, if the service is available, print only in ABS and recycle any obsolete parts. 

Step 2: Design a New Part is like a public library of 3D design files. Search for your part there first. If it's a common problem, someone may have already designed a solution. You can download this part from Thingiverse. 


Use calipers to precisely measure all of the part's dimensions. Then translate these dimensions into your design. 

There are three objectives to consider when designing a new part:
1. Retain all critical features of the original.
-keep holes the same diameter, depth, and position
-retain the placement of supplemental parts(screws, bolts, etc.)

2. Resolve any design flaws of the original.
-determine what made the original part fail
-reinforce any weak points

3. Make it printable.
-support any overhangs
-consider the use of breakaway support material
-use polygons instead of circles to minimize the vertex count

With my bracket, I kept the length and width of the original. The inner diameters of the holes were left unchanged, as was their proximity(they breach at one point). The original cracked when the bolt cylinder was compressed along its axis. I fixed this in the new design by making the cylinder's wall much thicker. I also changed the shape from a cylinder to a hexagonal extrusion to make that section easier to print. Before I started drawing, I chose to orient the part so that I could print it without support material. 

Step 3: Print the New Part

When printing parts that serve a functional purpose, strength is the key factor. Due to the thermal expansion of ABS plastic, it is difficult to print a solid plastic part without warping. For this reason, most home 3D printers actually print in a kind of structural foam. By printing a thick shell and filling it with a porous lattice structure, it is possible to create a part with nearly 100% of  the strength of a solid, but without warping and with much less material. For functional parts, you should print at the maximum density that your printer will allow, with at least two shells. 

I printed this part at 50% solidity with three shells. 

Step 4: Assemble

This should be the easiest step. If you made close enough measurements, and the printer is calibrated sufficiently, the new printed part should be a drop-in replacement for the old one. If it doesn't fit, or if something's not quite right, just go back to the design file and  modify accordingly. 

My new bracket was designed with large tolerances in mind and only required one iteration. 



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    What if a part on the 3D printer breaks? How do you fix that one?

    2 replies

    Many RepRap owners print out a spare set of parts just to be safe. The parts can be made with regular shop tools and wood. Designs are open source. You could also ask someone to print you a replacement.

    I had almost the exact same break on a Sears saw too.

    A little super glue to the bolt tube than a tight spiral twist of non streching twine, followed by a good epoxy coat and 48 hour cure.

    I figured out the twine probably made the part around 6 times stronger. Since the side to side forces were the problem in the first place, the twine takes the forces instead of the plastic part.

    The saw has been working now for about 4 years.

    Much cheaper then ~$1300 for the Rep-rap and very strong too.

    5 replies

    I believe the point was to show how the RepRap could be used for common repairs among the myriad other things that can be done with it. Yes there are probably relatively simple fixes that *could* be employed and the "$1300 Rep-Rap" was not purchased for the sole purpose of repairing that part.

    Not to mention that not every repair method is successful, Superglue does not hold up under shear forces and sometimes one cannot add "bulk" to the part with reinforcements.

    The name of the Instructable explained it's purpose quite adequately... perhaps you can write an instructable about using *your* method...

    We had superglue in "battle damage" repair kits for Phantom aircraft in the 70's. Superglue is excellent in shear, if the glue joint is correctly designed, and the material is both suitable and suitably prepared. I know in a repair situation, it's not always possible to design a glued repair, I just take issue with the "superglue not holding up in shear" statement. Effective glued joints used in tension, or in shear, usually have huge glued areas, not always achievable in repairs.

    Why yes, that is true... and did you not also have a "filler"? According to Mil-A-46050 Rev C Cyanoacrylates had very specific properties and uses. They were NOT to be used in structural applications and had specific activators and fillers for certain uses which I shall not detail here. According to the manufacturers specifications (Loctite, Eastman and Permabond), Cyanoacrylates have a relatively low shear and peel strength and certain preparations must be performed to increase adhesion in these applications.

    If even the manufacturers make this statement, who are you to say otherwise? You may take "issue" all you want but facts are facts.

    I realize the point of the article.   My point is "Old School" still works and is usually cheap to do.

    The super glue was never intended to deal with any forces.   It only held the part together till the swine and epoxy were set.

    Since the end to end forces on the tube want to split the tube radially, the radial twisted twine provides re-enforcing wall around the tube and the epoxy just keeps it all together.   In this way, even the epoxy offers very little actual strength, it is all in the twine.

    As a reference, look at how a fishing pole is made.   The joints that take the load are wrapped in twine and sealed giving them far more strength than the pole itself.

    Remember, this has been working for over 4 years without failure.

    $1300 for a RepRap! Holy cow! You should never pay that much for any standard kit. Maybe a Makerbot, but those are almost cheating. Printrbot is the latest, most affordable campaign, and kits are getting cheaper every month. Unlike epoxy, 3D printers are good for more than one use, capable of creating a permanent, near-professional result.

    Having owned several old vehicles, my thought was: "A 3-D printer would be AWESOME for making lenses and other unavailable parts for classic cars!"

    Does kinko's offer 3d printing services anywhere yet? I am curious where the closest printer is to me. This is a great idea. (Although I would hope for a 3d copy machine so that a taped or glued back together broken piece could be copied to a solid single piece.)

    1 reply

    Haha no Kinko's doesn''s not that mainstream at this point. But you can send your files to a company such as Shapeways to have them print it and ship it to you(at a much higher cost than a RepRap print). Your best bet is to get a RepRap operator in your area to make parts for you. Try this map to see if there is a 3D printing group near you. Other hackerspaces also probably have members with printers. Most operators will have no problem printing you a part or two for free(this one was <$0.25 in materials).

    I would have tried that first(if I had all of the pieces). But since I had the ability, and it was someone else's broken part, I figured a proper, permanent fix was in order.

    It seems from your instruct-able that you had all the pieces. Am I wrong?

    I have had much success using superglue, assuming that you have all the pieces, and they still fit flush. Often, any recurring breaks happen somewhere else than the place of repair.

    Not to be negative or anything. Just trying to point out a simpler approach. Very professional job however. The end result looks nice.

    Super glue doesn't really work on parts that have a lot of tension like this put on them. Also if the original part wasn't structurally sound enough to hold under that tension, it would be even weaker using super glue to fix it. I tried using super glue to fix a part for my recliner that connected the button release to the cable going to the release latch. I let everything dry and waited a day to put it back on, but it broke again as soon as I used it.

    I would have used this same method to fix it if I had a setup like that.

    The section that broke was shattered into multiple pieces, most of which got eaten when the inside was vacuumed out.

    Hi! did you use the 1062 and if so how did you setup the program? Are you using I have all the parts to make a reprap 3d printer and I have a phidgets 1062 motion control board but didn't know it would work. I figured the reprap was arduino!

    Any help will be good, I will really look over what you posted later. I will be posting any findings along with the finished result on my website when finished. Currently I have a three axis Mill I build from scratch on the website, just a picture more detail soon.

    1 reply

    I used a Sanguinololu, an open source board designed specifically for RepRaps. It has extra outputs for the heatbed and hotend. It also uses Arduino firmware(I think) it's caled Sprinter.

    For a part like this, would there be any benefit to drilling holes after the part is printed instead of printing the holes in? Easier-to-print, perhaps?

    Would it be possible to print in a "center mark" for holes drilled after-the-fact?

    I don't yet have experience with 3D printing, but will soon have access to a RepRap at work. :)