[SOLVED] Auto Hub Assembly is stiff / hard to rotate

[johncclayton]

Hi

I'm building the E7SE and I'm up to the main gear / auto hub assembly.  Parts fit is great, I'm enjoying the build.  I would like to know if the auto hub should be difficult to turn by hand, or should it feel like a ball bearing (super easy) to turn.

When I had the entire main gear assembled, I needed both thumbs to be able to turn the auto hub with the assembly bolted in the main frames.  The main shaft drops through the three bearings without pushing, so I know that its aligned nicely - the main gear also rotates easily, it's just the auto hub that is relatively stiff.

Because I was concerned that maybe I hadn't seated a bronze bush properly I removed the bushings by putting the auto hub minus all other parts into the oven at 230 deg. centigrade for 20 minutes (loctite 648 does its job!)

Now when I inserted just the auto hub sleeve and then turn the assembly - I feel still "significant" resistance.  Is this normal?

[curmudgeon]

I believe the problem is the 610-151 Delrin Shims.  You may have to reduce the thickness of these two shims with fine grit sandpaper.

[johncclayton]

Hi

Thanks for the reply.  I was meaning that when I turn the sleeve within the hub bearing without having the shims installed, that its hard to rotate the sleeve within the hub.  I feel theres a lot of friction.  It's not notchy as it would be if perhaps there was a nicked bearing/race within the hub.

I was trying to think of a world wide universal way to describe the amount of friction required to turn the hub within the sleeve... to turn the hub I need more force than is required to drag a eraser over paper.  Hmmm, difficult to think of examples that make sense yet don't require exact measurement!

In any case, I can imagine experiencing a blade stop *extremely* quickly with the hub like this.

Re: the delrin shims, can I replace them with some metal ones that are thinner?

[Chris Sexton]

Yeah I completely missed that you had already double checked the bushings. 

What Rob said next

[Rob Cherry]

Hey John -  If you have some fine grit sand paper, 1000 or better, roll some into a cylinder shape and lightly sand the inside of the brass bushings. Use oil as a lubricant. You can also lightly sand the outside of the sleeve as well, but use nothing less than 1000 grit, and always use oil while doing it.

And no, you shouldn't replace the delrin with metal shims, you'll have metal to metal contact in a location that's not designed for that.

[Danny Dugger]

   Are you saying that the insert feels too tight in the one-way with no bushings and no auto gear installed? The one-way will not feel free like a radial bearing, there will be some resistance but should not feel like you have to force it. Do you have a feathering shaft wrench that uses a 10mm one-way? Spinning the main shaft in that should feel similar to spinning the main shaft (bolted to insert) in the auto hub.
   With the entire main and auto gear assembly put together on the main shaft you should be able to hold the shaft in one hand and spin the main gear easily. It should free spin for about a second or so if you give it a good flick.

[johncclayton]

Fixed - here's what I did:

1. sanded the inside of the brass bearings
2. sanded ONE of the delrim shims to that instead of being 0.75mm it's 0.5mm - so I removed 0.25mm

The hub is now very very smooth, and my autos will hopefully be smooth too :-)

Thanks for the hints - esp oil and not using metal shims - great to know what not to do, it's just as important as the correct stuff to do.

[Rob Cherry]

Awesome John!