Method of gluing a shaft into a ball bearing

[Darren Freeman]

Hi all,

Abstract: A method of gluing an undersized shaft into a ball bearing,
such that it is nicely centred.

Here's the problem that I've solved:

On a Wade extruder, you have two 608 roller-skate bearings with an M8
hobbed bolt going through them. My bolt is unfortunately quite a bit
narrower than the inner sleeve of the bearing, so it is very loose. Even
with the stepper motor locked into position, the filament has a lot of
play in it, due to the bolt sliding up and down as you push on it. This
gives terrible results, with blobs of plastic where the extruder was
supposed to have retracted to stop from dribbling.

I had previously used Teflon plumbing tape to pack the gap, which worked
for a while, but the tape fell apart and it was back to square one.

So here's my "permanent" solution:

Position the extruder on it's side, with the hobbed bolt vertical and
the printed gear hanging below. (Glued onto the bolt and triple checked
to be at right angles to it.) Use a couple of nuts on the other end of
the bolt to adjust it to hang exactly where you want it. You don't need
washers etc. to permanently set the position of the bolt, as the glue
will do that. Back off the stepper motor so as not to apply sideways
force to the large gear. It's allowed to be fairly loose, as long as it
will still drive the gear.

Now dribble some 5-min epoxy into the gap between the shaft and the
sleeve in the lower bearing only. (The upper one shouldn't be disturbed,
as it temporarily sets the height of the bolt.)

Set the extruder to run the bolt at a few RPM for the next 20 minutes.
Clean up the excess epoxy while it's still runny. (Yes, it does go
everywhere!) Your bearing needs to have an insert that covers up the
balls, or you will surely stuff it. Just clean up what you can. The
motion keeps the spilled glue from locking the bearing as it cures.

What happens next is a little bit like magic. At first, the bearing
doesn't turn, only the bolt does. As the glue becomes more viscous, it
will start to drag the inner sleeve of the bearing, but it will not turn
as fast as the bolt. So the glue is still going around inside the gap
like a lubricant. (It seems to be sucked down into the gap, too.) The
magical part is that it begins to self-centre in the process!

By the time the bearing is going around at the same speed as the bolt,
it really is amazingly well centred. The epoxy has, in effect, acted
like a fluid bearing, forcing it to centre.

After the 20 min is up, you can remove the nuts and do the same thing to
the upper bearing.

I'm really happy with the results. I can't see any wobble by eye, with
it spinning at 60 RPM.

Note that I had to cut away part of the plastic of the extruder in order
to better access the lower bearing, i.e. the one closest to the gear. I
didn't want to try putting glue down a narrow gap between the bolt and
the plastic, and the plastic that I removed wasn't doing anything
besides hiding the bearing.

I hope this tip comes in handy for someone else :)

Have fun,
Darren

[Rob B]

Depending how loose the shaft is , I have used brass shim to centre a shaft in bearings, if you don’t have thin shim you may find cutting up a Coke can with scissors does the job. You can add glue to ensure it all stays in place or loctite.

Regards Rob Brittain

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