V2 Gearbox Shells

[Pewpewpetie]

Hi all currently building a dmr and when I split the specna gearbox I noticed none of the bearings sit flush with the shell. I have tried standard bushings(shs and modify) and all sit to high so can't shim. Is the best option to buy a new shell or drill the bushing hole slightly deeper

[SheriffHD]

Not all do. and tbh them not sitting flush is a good thing otherwise gears would rub on the shell. so test a fit first then see how it goes.

[Iceni]

I wouldn't drill it as it looks like you only have to remove a small amount of material. Drilling when there's only a small cut pretty much always causes the holes to go off centre.

It also looks like the flanges haven't fully seated down.

The method I would use is a little unconventional. You take a dremel and a straight shanked tool, If you haven't got a flat (smooth shanked) tool then you might be able to mount a diamond bit in the wrong way round.

You then grab some tape and fine wet and dry. Cut an even width strip of wet and dry the same width as the tape. wrap the tape onto the shaft of the tool and once you have a few wraps stick the end of the tape to the wet and dry, Then keep wrapping till all the wet and dry is spooled. If you spooled it in the correct direction the spin of the dremel will keep everything in place. you then just drop that in the hole and run it for a few seconds, Test and repeat.

This page show a similar setup done on a much larger scale with a drill bit.... You are not trying to fill the hole with wet and dry, and it shouldn't be anywhere near a tight fit, It wants to be nice and loose in the hole, and just let the action of the dremel throw the wet and dry out, rather than putting any pressure on any metal part.

If your in doubt test it on something else first like the inside of a 8mm nut.

https://www.mybusyretiredlife.com/diy-simple-honing-tool/


 

If you need to make the rebate deeper then you get into all sorts of issues. By far the easiest and dirtiest solution is to remove flange material off a solid bushing using a sharpening stone/diamond hone. You need to be as accurate as possible to get a flat finish on the bushings. A drill press and wooden dowel can make this significantly easier.

Making the rebates deeper on the shells is far more involved, and requires a well setup drill press/mill that is running as true as possible, and a suitably sized end mill cutter held with a collet. Doing it any other way could lead to damaged gearbox shells.



All of this is of course assuming one thing. You didn't lay the gearbox on a flat hard surface when you tried to put the bearings in..... As this will pretty much always prevent the bearings seating as they poke out of the gearbox. Drill a hole in a bit of wood and put the hole under the bearing this way the bearing can go past the outer wall of the shell  when you push them in.

Edited March 21, 2021 by Iceni