Lapping Brass?

Evening all,

I want to improve the form of some brass gear teeth.
They are involute profile, so I think running them against a rack form with some sort of cutting compound would do this.

However I very much do not want the compound to embed in the gears, or when they are in service they will lap the mating pinions, probably leading to premature wear / failure.

Any idea on what to make the lap from, what cutting compound to use or other tips?

Dave

Without knowing the sizes, current finish and purpose it's difficult to make a worthy suggestion, however, this is not a very good idea for several reasons and clock makers like me try to get good dimensions and finish straight from the cutting process such that brass wheels come into the world as near to perfect for purpose as possible.

That said, you could try by making a small hardboard wheel and mounting this on an arbour in the lathe...then charge this wheel with 'T-Cut' car body cutting compound which is easily obtained, gentle in abrasive action and easily cleaned form the workpiece. Work the cut teeth evenly and gently frequently using an eye glass to check both process and missed teeth etc. On clock teeth there is every risk of changing the tooth shape and size so be very careful and work carefully.

Good luck!

Hi,
Use Timesaver yellow label abrasive for brass
https://www.heritagesteamsupplies.co.uk/lapping-compound-yellow-very-fine-3oz.html

Other grades available medium , fine and this one very fine.

John

These are involute not cycloidal profile, 32dp IIRC. Largest tooth count is 144.
They were cut using the Sunderland method, so inevitably have a small number of facets on each tooth.

Being involute the rack is straight sided, so I was thinking of “just” making a length a bit longer than the max number of teeth and running them one way on it - using the rack a bit like a file if that makes sense.

Is timesaver one of the “none embedding” compounds? Would you run it brass on brass?

Dave