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A project log for Arcus-3D-C1 - Cable 3D printer

3D printable, Open Source Hardware, tripod kinematics, cable driven 3D printer

daren-schwenkeDaren Schwenke 09/22/2018 at 01:153 Comments

The bearing ID is 8.13mm.  The shaft OD is 7.89mm.  So I needed something to make up that difference.

I went through all the rolls of tape I had around, and found one where exactly one wrap of tape, not overlapping, would make up the difference.  Worked, until now.

The steppers running at the higher current get a little warm now, and I didn't hook up an enable pin on the drivers, so they are always on.

Over the course of the last couple days, I've run them in and out a lot, and eventually an axis got 'rough'.  The adhesive had softened and the tape squirted out so the shaft was flopping around.  Another axis showed signs of failing soon...

Tried in vain to make some heat shrink work.  It goes on, but it never compresses evenly and so the shaft is always wobbly.

Then I tried AL foil.  Perfect.

It takes about a 180mm long strip of foil, about 8 smooth and flat wraps, to make up the gap.  I end the wrap right where it started, so it's also perfectly centered.  I feel much better about 8 wraps versus the one I had before.

There was a learning curve as to how to keep it from un-spiraling when you pull the bearing off though.

Basically, leave some extra and peel from the middle out to the edge... and then compress it.  It mushrooms down onto the surface and keeps the whole coil in place.

Pics later.  It's a tedious process taking about 5-10 minutes per bearing to do it right, but it's the only way I'm using these shafts without runout.

<EDIT>

The foil has worked well, with the exception of one where it also squirted out the end.  One drop of superglue fixed that.  I went back and did all the rest.

</EDIT>

Discussions

ekaggrat singh kalsi wrote 10/10/2018 at 05:37 point

look for apec9 or apec 7 spec bearings by nbc or skr.. they are mostly tight on 8mm rods.. the cheap ones are apec 4 or apec 5

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ekaggrat singh kalsi wrote 10/08/2018 at 09:05 point

you can use drill rods 5/16 they fit 608 bearings tightly or use 608 bearings with grub screws built in . Thoes have tighter tolereances for 8mm rods. Also 608 bearings have vairations in inner diameters depending on the company that makes them . For my GUS simpson i needed a tight fit on 608 bearings. i ordered bearings from different companies and found ones which were tight fits. last option use a 8x6mm brass pipe and sand it down on a drill press to fit the 608 tightly

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Daren Schwenke wrote 10/10/2018 at 05:27 point

The 5/16th rod I had did not.  The bearings I used here (and everywhere else) I bought by the hundred as they were originally destined for prototyping something similar to what the MPCNC became.  That design needed a minimum of 12 bearings per axis to be stable.  I never got around to finishing that up so I have a ton of them finding their way into projects.  They were ridiculously cheap and still very good quality.   I was really happy with what I got for the money, but it seems on this one point, I got what I paid for.

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