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Trautmann hook [3D printed steel parts, assembly, first use]

Cite this article:
Wolf Schweitzer: Technical Below Elbow Amputee Issues - Trautmann hook [3D printed steel parts, assembly, first use]; published December 28, 2016, 17:53; URL: https://www.swisswuff.ch/tech/?p=7037.

BibTeX: @MISC{schweitzer_wolf_1571595753, author = {Wolf Schweitzer}, title = {{Technical Below Elbow Amputee Issues - Trautmann hook [3D printed steel parts, assembly, first use]}}, month = {December},year = {2016}, url = {https://www.swisswuff.ch/tech/?p=7037}}


First, I had performed a feasibility test using a PLA model that I had printed myself to see whether I really wanted a Trautman hook. After that, I had decided that I wanted one.

I ordered one set of right hand version related Trautman STL files (Thingiverse link, Shapeways link) to be manufactured as steel parts.

Parts mailed

The packaging was good and parts were sufficiently padded. I would definitely order from Shapeways again.

Overall appreciation and assembly of parts

The models were both bent, and not precise, so significant manual post processing was in order. For a total of around 155 USD, I was not bothered.

The hook parts did not fit together. Apparently, the dark add-on to the metal added to the dimensions. So, serious post processing.

Also the threading was layered with the dark stuff, and it did not fit into the regular UNC 1/2-20 thread normally used for US-American prosthetic arm attachments. Not a problem of the STLs though - the PLA model had had a perfect threading, so 3D printing plastics may be a lot more precise than 3D printing metal using the process that Shapeways uses for that. Maybe avoiding the dark coating will help a next time.

So I made a fit-on adapter for my <16mm sized wrist adapters by first implementing an aluminum UNC 1/2-20 to 15,5mm tube (below left, below right) but to allow the oversized Trautmann adapter threading to fit, I sawed the aluminum tube open lengthwise (right) and distended it a little. Then it came on easy as a feather.

With that, I could fit it over the oversized Trautmann threading and squeeze it into fixed submission into my wrist adapter as seen here; the sawed split is at 11 o'clock in the below picture. Ultimately a perfectly snug fit resulted, no wiggle.

The hook sides were bent and not precisely manufactured; particularly the lower part (below image: the lengthy part on the right of the image) shows a "slight" but mechanically relevant curve. So I carefully filed these surfaces straight.

After that, I found the screw holes to be too large for a snug fit and mount.

So I 3D printed screw hole adapters for small M2 screws.

Screw hole adapter in place as can be seen below. Now, M2 screws fit well.

The assembled Trautmann hook.

First use - Trautmann hook - EC microworks

I obviously had to test it. Immediately. See here.

The grip performance particularly for the low item size range is absolutely insane. Also, when using a broom or floor cleaner, it back locks. What a convenient and light weight little gripper really.

Spring

Small rubber

Smallest rubber

First extended testing results

It did pay to get a metal version for extended testing. The PLA would not have survived an hour. And the metal hook is really useful, as such.

For the next revision, a few aspects became relevant in my view:

  • This Trautman hook freebases rubbers like no other. The "fixed finger" part is far too edgy, and rips through any set of rubbers in no time. That means that their profile must be rounded to a far greater degree than currently is the case.
  • Secondly, I will have a very close look at just how well these parts are designed, in 3D, to fit. The degree of fit is a real issue here.
  • Thirdly, the overall size, in my opinion, is too small. This needs to be bigger.
  • And last but not the least I will want the screw holes to be tightly precise to my metric screws that I plan to put in. All screw hole diameter adapters are sweet and all, but let us not underestimate the power of tight precision for this item here.

 

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