Help drilling bronze

Hello all,

In the process of making a water pump ( side tracked from building the minnie ) need to drill a 33/64 hole into the existing one shown in the picture below but really worried about the drill snatching, can anyone offer any advice to reduce the risk.

Thanks.

Edited By Brian Abbott on 09/07/2015 00:10:28

Edited By Brian Abbott on 09/07/2015 00:09:31

I have just drilles 1 mm hole 7/8 inch through a 5 mm diameter spigot..I think its a spigot! Then put a thread on the outside..No problems at all..Its colphos 90 ..

Last week I turned a piece of pb for a canon and it was very ' chewy' I ended up using emery cloth to get a nearly smooth finish..

An elderly friend at work who spent a few years at an engineering firm said he used 1/2 water1/2 milk to lubricate pb..I havent tried it but he s not daft!

i now decided to use colphos 90 all the time!

Jonathon

Brian - Have you ground flats on the cutting lips of the drill, parallel to the drill axis? (to remove the helix lead angle in the lips)

Look up "grinding drills for brass" on Google if you are not sure what I mean.

This will reduce or eliminate snatching during drilling in brasses and bronze (except in thin sheets) . Drop of good cutting oil doesn't hurt either.

In thin sheets, a stepped "Christmas tree" type drill works well.

Good luck, JD

I've never been one to modify drill bits and not had too many grab. As its a bit over 1/2" I would open it up with the boring head.

J

Brian,

This appears to be already set-up on a mill ...

My preference would be to use a milling cutter, or a single point boring tool: either of these would be lower risk than using a drill.

MichaelG.

I would not go anywhere near the grinder to modify a drill for brass or bronze. All you need to do is generate a flat parallel to the axis of the drill on each cutting lip/flute of the drill with a small emery stone. You only need a few thou to give you zero rake and eliminate any grabbing. I suspect that's what Jeff meant when he said 'grind'.

regards Martin

I am building up a set of brass drills by taking the cutting edge of the lips by dressing off with a diamond hone... it only removes a couple of thou' but it's enough to stop the 'grab' if through drilling, or pulling effect in a blind hole.

George.

I've just recently drilled a couple of 12mm holes in some PB rod.

I was opening out the second hole to final dimensions when the drill badly jammed in the hole. The drill bit was nearly new too (pretty sure I'd only used it on brass a few times previously). When I went to take it out of the collet - the work and drill were still quite warm - suggesting a good deal of rubbing/friction had been going on. I finally got the drill out (maybe the bad language helped) but the outside of the work was scored in the process.

So in future with PB, I will move over to a boring tool as soon as practical...

Regards,

IanT

I have seen accidents with drills grabbing bronze,grind flats on the drill lips on a grinding wheel ,you require a visible flat not a bit of honing on a half inch drill,and on the casting in the photo I would use two clamps,better than wrecking a casting, the correct method would be to use a straight fluted drill or straight fluted milling cutter.For one offs a boring tool in the mill is possibly the safest option.For cutting fluid I would use ordinary soluble oil,cooling the tool is more important than lubrication,When drilling drawn phosphor bronze,possibly the worst material for "snatching" start off with minimum depth of centre drill and then drill to required size with one drill,grind the drill so that one cutting edge is slightly longer than the other one so that the drill make a slightly oversize hole as drills not only snatch in bronze they also tend to bind in the hole if the depth is greater than 2x dia.

Don't suppose you have a picture of the required modification to a drill bit by any chance Martin?

There is a picture here

**LINK**

Martin

Fair comment from Nigel. I do tend to put bigger flats on larger size drills and it is possible to do it on a grinder but for a first go hand work with a stone is more controllable.

Martin

There is a world of difference between drilling a hole in bronze and drilling a hole in a hole in bronze.

:0)

Martin

My point Jason was that when drilling into solid without breaking through as you would on a lathe making bushes from bar stock the chisel point of the drill controls the grab and you can get away with it.

regards Martin

Puting it in the lathe with a four jaw and a small boring bar would work, as I just done that yesterday when I had to make a phosphor bronze cylinder with a 8mm bore.

Thank you Martin, that makes it very clear.

Thanks all for taking the time to reply, not sure which way to jump but will post a picture of the results.