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

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

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 reprap.org.

 

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

Thingiverse.com 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. 

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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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21 Comments

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

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.

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!"