Lapping your gear bushings

[Pseudotectonic]

I noticed on the SHS/Rocket bushings the factory surface finish is really inconsistent. Some are very rough but some are relatively smooth. This difference can be literally highlighted with some lapping.

What I am doing here is used a 7000 grit paper and then 3M 0.3 micron lapping film sitting on a piece of marbel for some basic lapping. I am not aiming for any super precision here but only aiming to knock down the high points on a reasonably flat surface. If I were to lap it all completely flat it will probably take away too much material.

You can actually feel the difference by running your fingernail on it in circular motion. In the first picture is the bushings in various stages of lapping process. The second picture is when they are done I am trying to grade and pair them up, which I am going to use the rough ones for sector gear and smoothest ones for bevel. Just because bevel spins the most.

It may not look much but judging by feel of fingernail, it is already massively improved over factory finish. In theory it should at least reduce a tiny little bit of friction and helps with the breaking-in.

View attachment 119229

View attachment 119230

 

[Sewdhull]

I can't help but do things like this. I can't imagine it makes any difference in the great scheme but I like to do it 

 

[Egon_247]

I'd start at 1500 grit and see how much it takes off. I do paint blemishes with 1500 and thats soft as poo. 

If you wanna get anal with it, put the wet n dry onto a small piece of flat glass. then sand it. glass=flat.

 

[Egon_247]

Although they'd hold grease in those grooves....?

 

[Pseudotectonic]

The reason I didn't lap it all the way flat was it will probably take down too much and weaken the flange that holds it in place in the gearbox, and also my shims are really just half the size of the bushing, so it is just the inner half of the circle it is resting on, and because there are not much axial load all it needs to do is keep the gear aligned and nudge it when it is off, and having the peaks removed will help the shim does its job and remove most of the point loads from the poor finish against the shim to prevent shim deformation, and there will be grease anyway so yeah, a bit of grooves are good for grease retention

I've also polished the gears with tiny amount of Peek (the metal polish) and a dremel buffing wheel on a drill, just to remove the factor sharp corners on the teeth generally

 

[Rogerborg]

If you wanna get anal with it

When you're lapping a bushing, you generally want to stay away from anal.

 

[Shamal]

When you're lapping a bushing, you generally want to stay away from anal.

Oo er matron ?

 

[Egon_247]

You lost me at flange....???

 

[Adolf Hamster]

glass=flat.

technically it isn't, especially when it's a large enough peice

put practically yes.

I can't help but do things like this. I can't imagine it makes any difference in the great scheme but I like to do it 

tbh it's one of those things that on it's own probably results in the square root of bugger all.

but ounces make pounds, and lots of little improvements can end up being meaningfull.

 

[Sewdhull]

Glass is pretty flat, good enough for our purposes. There's no friction reduction to be had since friction is independent of area, the high points produce no more friction than if the load was spread over the whole shim.

Our gearboxes are not precision machines, we can shim to 100 microns, were using plain bearings, with mediocre gears and unknown manufacturing tolerances for anything. Anything we do like this is because we like to fettle.

Breaking in a gearbox is not something I've ever done, only the bevel gear could wear and offer a chance to correct the wear and that only between the motor pinion and bevel gear. Gearboxes have slack right from the outset, gear backlash, bearing to shaft gap, gear end float etc. It's not put together tight like an ICE for example and run in. Maybe that's something to try, build it tight and run it at low load until its not tight any more...

Sure is fun to fettle tho.

 

[Egon_247]

Having recently rebuilt an EP6CDT engine and a cyma v7 gearbox I have to say that it's a close run thing on which I'd rather work!!!! ??

. It's not put together tight like an ICE for example and run in. Maybe that's something to try, build it tight and run it at low load until its not tight any more...

Sure is fun to fettle tho.