Nut cavity in extruder gear too large

So I printed my extruder before I had my hobbed bolt, and now that I have both, the nut cavity in the extruder gear is a bit too large for the bolt head. There's just a bit more wobble than I'd like, especially since I'm using retraction. Actually, in any event, it would seem to be to be best with no wobble whatsoever.

So I had thought to put some epoxy (specifically JB Weld) into the cavity before assembly, and let it harden around the nut head, but I don't like the idea of using epoxy like this. To me it's too irreversible, and since the gear won't last forever, I wanted to make sure I could easily extract the bolt at some future date.

I could always print another gear with a smaller cavity, but it would be a shame not to use this one, especially because it turned out to be of excellent quality.

Could anybody offer an alternative to the epoxy?

Thanks

Edited 1 time(s). Last edit at 07/25/2013 12:29AM by jbernardis.

I can't offer an alternative that is as effective. Due to wear I had to epoxy my bolt head into the gear today, but I did consider silicone.

I should point out that generic clear 5 minute epoxy comes off easily with a bit of heat. It becomes soft like wax over 100° celsius or so. JB Weld withstands more heat(250°C?) than that, so it might be harder to take off.

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Yvan

Singularity Machine

Thanks for the info. Based on that, I don't feel too bad about using epoxy - I see you recommend the 5 minute clear, for a good reason. I just like the results I get from JB Weld - it's a quality product..

jbernardis,

I had exactly the same problem, and I temporarily solved it by making my hex head bigger with electrical tape. I say temporarily because the tape will eventually slip out, but it gives you plenty of time to print a new gear with exactly the head size you need. If you need an appropriate stl or scad file, I can help.

The other approach I've seen people use is for the nut to sit in the hex hole on the gear. In fact, I think this might be what was intended, though from an aesthetic perspective, I don't like it.

if you go with the epoxy solution then you can always wrap the bolt head in kitchen cling film first. that way the epoxy on sticks to the gear and not the bolt

good luck

I ended up just using the JB Weld epoxy. I figured that if worse came to worse, I could destroy the gear to extract the bolt. Then the bolt head itself could probably be cleaned off with a stiff wire brush in my dremel.

I have occasionally solved a problem like this by manually extruding plastic into the void. I just run the extruder manually from pronterface, extruding about 10mm of filament at a time while I hold the piece under the hotend.

I've fixed this a couple of times by building up an appropriate number of aluminum foil squares with a hole punched through them to allow the bolt to pass through, then draw the aluminum foil into the nut cavity/recess with the bolt to tightly shim the space between the cavity and the nut/bolt head. Adjust number of foil layers if necessary to get the fit right, then trim off excess foil.

This has provided a reliable interface between the bolt and extruder gear on my RRP mini extruders after the bolt head initially worked its way loose in the recess in the big gear that it should have stayed in.