Develop a protocol for unit testing of rods and plastic pieces

[tareko]

The large variation of available materials and production printers means that it is difficult to know what pieces are fit for use.

For each piece, there seem to be a few common characteristics to test:

Rods

• Are they straight enough? What is straight enough?
• Are they the correct thickness?
• Do they have evidence of rust?

Printed parts

• Are the holes the right sizes and tolerances?
• Is the entry of the rods and pins smooth?
• Is the entry of the bolt smooth?
• Do the parts clamp onto the parts properly when bolted?

Nuts and bolts

• Are they rusted?
• Do they couple correctly?

[apopanda]

For the holes being the right engineering fit, you could use "go - nogo" gauge.

https://www.qualitymag.com/ext/resources/Issues/January2015/DEPT101/QM0115-DEPT-101-p1SL.webp

It's easy to manufacture with an access to a lathe, at least for the tolerances that we need. Simple to use, so anyone can check it. Repeatable and quick to check too

[jenwilsonglia]

For Rods

• to test the quality of stainless steel, a magnet is used, and if there is low magnetism, then the quality of stainless steel is adequate (316 or 304)
• straightness can be tested against a set square
• thickness can be tested with calipers
• any rust observed on stainless steel means that the layer of chromium oxide on the surface has been effected by mechanical wear, chemical corrosion, and/or contamination by iron particles, and therefore the rod is not suitable to use

Nuts and Bolts

• only Regular Nuts should be used
• if rusted, do not use
• run the regular nut down the threads of the bolt to make sure that the threads are good and smooth

Printed Parts

• to check if holes are the proper sizes and tolerances, insert rod into the rod clamp hole, the pin into the pin clamp hole, and the bolt into the bolt hole
• if the entry of the rods and pins are too tight, a drill with a rod or pin used as the bit can be used to drill into the hole to widen it to the appropriate tolerance (test again after drilling)
• to check if the rods and pins are too loose in their respective holes, tighten parts together with a nut and bolt (rod clamp with rod and pin clamp with pin), and if the rod or pin still moves then the printed parts are not to be used
• if the entry of the bolt is not smooth, it can be screwed in using a wrench
• if the rod clamp and pin clamp do not hold onto the parts properly when bolted, they should not be used

Pinch Test

• this was used for parts printed in ABS and may not be useful for Petg

Tightening Test

• this test must be done to determine if all the parts work together to be tightened so that they don't move (still need to determine the exact amount of tightening that is adequate for surgery)
• every nut and bolt used for this test must be tested on their own before and after each test with parts to make sure that the threads are smooth
• overuse of the nut and bolt will result in deformation of the threads and an inability to undue the nut and bolt
• overtightening of the nut and bolt will result in deformation of the threads and an inability to undue the nut and bolt

[apopanda]

I'd test the rods by shining a light under them on a flat smooth surface, like a print bed. If it's uneven, the light will shine through the bottom. I'd also specify what "regular nuts" means - DIN 934 A2 M8 1.25mm pitch (i.e. regular pitch, not fine or coarse). The nut that is used for testing the kits should be the one that is going with that specific screw, we shouldn't have someone sit with the same nut testing a box of screws. The "printed parts" section feels very vague to me - being asked to tighten the device, when do I stop? Do I go full torque? We might want to specify based on the gap in the front for instance (i.e. tighten till the corners meet, tighten till the corners start moving) or just give torque numbers in Nm or something

[tareko]

Remind me, is there a PR with these tests written in? If so, do you mind typing out the number (e.g., PR #xx) so the issue and PR are linked

[jenwilsonglia]

I'm creating a PR right now with these tests. Will put the number here once done.

[jenwilsonglia]

I've made Pull Request #34 to align with this issue.