Drilling Brass

[Richard T]

I've never had a problem drilling brass before, not that I've done a lot of it, as I have only drilled small holes for the likes of woodscrews.

Now I come to drilling holes to tap for lever cap screws it's a different animal. I am a great fan of pilot holes and can drill these without incident but when I came to drill out with a 3/8" bit ... it wouldn't get in to its full diameter before digging in on both sides. I clamped everything tight to the pillar drill table - the belt slipped. Fortunately I have the bits of scrap to practise on so have not ruined any lever caps - yet.

So I did some asking round and some reading and find that I have two options; 1: to buy boring tools - not even sure what I would be looking for there and 2: to put a vertical edge on the drill on either cutting edge with a slip stone so that instead of the edge falling away into the curve of the twist of the drill, it has a small, vertical flat that does the cutting. Much less fierce.

I think I will go for the second option but thought I would ask if anyone else is familiar with this trick before I set upon the relevant drill bits with me oil stone and ruin them for steel. Does it work ??

Many vanks in adthance

 

[Oryxdesign]

Yes number 2, you are effectively cutting out the rake on the cutting edge. Set the correct speed (Zeus?) and you should be fine, however, it may not be a straight forward brass and some are very hard to drill.

You can resharpen them after, there's plenty of videos on you tube showing how to do it. Some people keep a separate set of drills for brass, my father (watchmaker) kept a different set of saws, drills and files for brass.

 

[CHJ]

You may find it easier to just take out the curve of the cutting edge on the corner of the grinding wheel so that it presents similar to a tipped masonry drill

 

[Tinbasher]

What cutting lube are you using?

 

[jasonB]

A lot of people say stone the edge of the drill to give zero or negative rake, never bothered myself though if you have the option to drill with the lathe or mill that will avoid the quill being drawn down if the drill grabs. Drilled several holes this weekend into both brass and bronze 1/4" pilot, then 7/16 or 1/2" finish and no snatches.

Don't need any cutting lube for brass

 

[Richard T]

Thanks for all the replies folks.

I use suds. Don't know what sort - probably ex Rover. :-" But as Jason says I thought that I had heard that brass doesn't need it.

I haven't tried it in the lathe Jason as haven't got a vertical slide yet but I think I will try the drill modification first.

I found that the drill size for 7/16" acme tap is 3/8". Now all I need to do is work out the drill size for 1/2" and 5/8" acme taps and go ahead and find the drills that need modifying. At least they are all the same at 10 tpi.

 

[CHJ]

Take care with 'ACME' definition.

ACME (USA)
Stub ACME (USA)

If all your thread stock is 10 TPI across all diameters then you should be able to work out your tapping size from here

 

[jasonB]

Can you not clamp the cap to your faceplate to drill It in the lathe. That would Also allow you to use a small boring bar or slot drill to cut the hole to final size if you don't have the right size drill bits.

 

[AES]

@Richard T:

The brass you're trying to drill must be "hard" rather than the usual "half hard". As per Tubal Cain's "Model Engineer's Handbook" you can stone (or grind) off the top angle of the drill. I've done this (rarely, I seldom find it necessary) and if you can use an off hand grinder (and if the drill is a reasonable/seeable dia) then it's quite easy to put the proper angle back again afterwards. I've heard that people who use brass regularly keep a set of drills prepared especially for that purpose.

But whatever you do do NOT try the new (ish) "4 facet" drills as these "grab" and pull the drill into the work with unpleasant consequences.

Don't want to teach granny to suck eggs but don't forget that when doing any sort of machining on any sort of brass it's quite normal for tiny chips to come off the work very fast, and they go all over the place, including you. Being non magnetic it would be a very painful experience to get such a chip out of you eye (my wife got VERY fed up with me because without realising it I got a few chips down my shirt front when maching some brass - I sit at my lathe - and lo and behold, when I went to bed that night they ending up sharing the bed with us! She was NOT very impressed ;-) ).

Also, everyone says that you don't need lubricant when machining brass and that's true, you don't, but I have found that brushing either a drop of paraffin or WD 40 on the job does help to at least reduce that awfual "squealing" noise that brass often makes.

Hope that helps.

Krgds
AES

 

[CHJ]

......But whatever you do do NOT try the new (ish) "4 facet" drills as these "grab" and pull the drill into the work with unpleasant consequences.
.....but I have found that brushing either a drop of paraffin or WD 40 on the job does help to at least reduce that awfual "squealing" noise that brass often makes.
....

You don't need a 'grabby' drill to frighten the daylights out of you, my first lesson in the perils of brass drilling was when a very large (250 X 150 X 250mm) block of brass in the form of an S Band Waveguide Choke climbed up a drill and spun round before flying a good 2mtrs (all in old money in those days of course) when the drill snapped. That was the day that I learnt that the niece sample of brass that had machined far easier than the other half dozen had its own perverse ways of causing agro.
And another one for a splash of paraffin to calm and cool things down.

 

[Richard T]

Thanks for the heads up Chas - though I think they will be right, all coming from this supplier:

http://www.rdgtools.co.uk/acatalog/ACME ... HAND_.html

No idea of the country of origin of course, and the price is a bit of a worry. (Very cheap)

Jason - I have thought about turning (boring) the hole and about cutting the female thread in it. I could cut a square thread this way. I think that Norris must have made them like that; I can't think of any other way.
But not having had much use of the lathe I have no idea what I am doing. Balancing it for a start - ??? Not even sure if we have a face plate come to think of it.
In the future I hope to learn all about it. (I have the relevant books). I want to make adjusters eventually and make them well but for drilling and tapping these first two lever caps I will do the best I can with drills and hand taps. Then the big adventure will be turning and threading the screws: don't mind so much if I scrap a few of those.

AES - Not sure about the hardness of the brass; it cuts very well with an 18 tpi hack saw and a curved dreadnought file but hardly anything else. Whatever cuts it needs to be spiky/bristly. Normal files are only good for smoothing it rather than removing any significant amount of material.
So I think that the drills dig in because it is soft rather than hard.
It doesn't make a squealing noise - if only. The only noise thus far has been that of the belt that drives the pillar drill merrily slipping round.

 

[jasonB]

At those diameters it should not be too hard to screw cut square threads, I've done it on smaller 1/4" x 16tpi but you really need to make a tap at the same time as making the make thread so you can chase the profile into the roughed out female part.

As for balancing work on teh faceplate just bolt on a few spare change wheels

Funny enough most of my drilling is with the Dormer A002/A012 split point drills which are 4 facet.

You want good sharp files for brass otherwise they will just skid over the surface. Also try a new hacksaw blade put in the wrong way round next time you come to saw some brass, works well.

Some of the weekends brass/bronze bashing at the start of this album

 

[Richard T]

Blimey Jason :shock:

Lots to think about. "make a tap" ...

 

[AES]

@JasonB:

Personally I have problems with 4 facet/split point drills "grabbing" in any material, but "Your mileage may vary" as they say! Nothing against them, on the contrary, but they really do grab if you aren't careful (for me any way). BTW, mine are a set I got with a DeWalt drill, very posh with that golden TIN plating, and they cut well, but for me real care is needed when about to break out.

AES

 

[Gary Morris]

when i was at school, a longtime ago, we annealed brass plates due to work hardening, could this be a cause and would annealing be good to do, admitedly we didn't have to have the same shape piece at the end as at the start.

Gary

 

[CHJ]

Annealing Brass will more than likely increase the risk of a sharp drill grabbing as the brass will be softer and the drill may attempt to penetrate like a wood screw if there is no restriction on quill movement.