Help required on drilling PB102 in the lathe

[greensands]

Can anyone offer any tips or advice on drilling PB102 phosphor bronze. I have always had problem drilling this material and typically the current job calls for a 5/32" diameter hole drilled to a length of 7/8". My technique is to use a succession of pilot drills at relatively low lathe speeds to avoid heating up of the stock and frequent withdraws to clear the swarf but always with the same effect - a binding drill and much frustration. I wonder if the use of carbide or perhaps tin coated drills would make any difference? Any hints and tips would be much appreciated - Reg

[springcrocus]

Extract from my diary a couple of posts back...

The bushes were just a straightforward bit of turning on the lathe although phosphor bronze is one of my most hated materials to work with. Drilling the hole is a pain because the stuff heats up and expands very quickly during cutting, then cools and contracts causing the drill to bind. A good tip is to grind the anvil of the drill slightly off-centre which causes the drill to cut on one side and, consequently, slightly oversize. This stops the binding, but you need to be able to regrind the drill to its correct form for normal use.

If you grind an offset on, say, a 3.8mm drill you may well get it to cut 5/32" diameter. Hope this helps, you could always have a practice run.

Steve

[Deleted]

I also have some bearings to make in the coming weeks, I have got the material ready....hearing about the heating issue would not copious amounts of cooling/cutting fluid help?

cheers

Pete

[Roger]

I'm surprised this causes so much difficulty, I think a lot of the time it's due to insufficient coolant and running too fast. Brushing coolant on isn't really very satisfactory, you need a pumped system of suds or oil else it's hard to get the heat away. I'd avoid using drills that have been sharpened with the four facet method, they tend to grab in my experience. A sharp drill is essential though. Just use plenty of cutting oil, slow RPM, and don't be afraid of it. Feed the drill firmly and smoothly, withdrawing every so often when you get in beyond say 1/4". Being too tentative is only going to make it rub and make it hot. Just one pilot drill ought to be enough.

[alanstepney]

A staight fluted drill is my answer to the job.
Not too easy to find these days but worth having.

[vulcanbomber]

you want all of about 95 RPM and a feed of about 3 or 4 thou a rev to give you some idea. and it needs to be very wet.... water would do fine.

[greensands]

Cannot sat that the idea of of grinding a drill, even a little off centre appeals as I have enough trouble with drills wandering off without actively encouraging them. To take note of Roger's point, I do not have the luxury of a flood or even piped/drip-can form of lubrication on my lathe, always having made do with a brush and a motor oil/paraffin mix which works well in most circumstances but this could well be the root of the problem. Reg

[chris vine]

Hi Reg,

Further to all the good advice above:
I do like you, a succession of pilot drills, so that say you want a 10 mm hole, start with 9 and go in a bit, then do an 8mm and go in a bit further (it isn't rubbing on the previous hole as it is smaller). work downwards in size as you go deeper.

Then when to depth, run the size you want all the way in, opening out to size.

There is a good hint from Vulcanbomber, but maybe it is a bit hidden in the numbers: you want to keep the drill cutting, so don't feed too gently or it will rub and then heat/harden and then you are done for!

All the time you really need to have coolant running over the job, flooding it. I run the lathe quite fast, but others may disagree with this...

As long has you have sharp drills, you will find it is a doddle!!...

Chris.

[oldnorton]

Reg

I too used to find that conventional twist drills would seize in PB102. But I found that the standard Dormer jobber drills from Greenwood Tools were much better www.greenwood-tools.co.uk/shopscr130.html; they are a multi-facet cutting face. I have bought a lot of the individual drills that I now use for starting every job in steel, brass and bronze. I then use the conventionally ground 0.1 mm increment drill sets to take holes to a desired size.

Norm.

[Jim]

As a dispenser of coolant I use a recycled 'squirt' bottle that originally held shower cleaner or similar. I find the nozzle can be adjusted to give a jet, ideal for drilling or a larger spray for turning or milling tasks. Works for well me.

Jim

[peteh]

My coolant method is similar to Jim, except I use a 9l garden sprayer, resting on the floor. Once pressurised it works for ages before pumping required again.

[jma1009]

hi Reg,

you need really sharp drills that havent been used on steel. back off the land of the tips like you would do for brass. Steve's suggestion is that recommended by George H Thomas.

if the drill doesnt rub it wont cause the PB to get hot. coolant wont help if the drill isnt really sharp on the tips and sides.

cheers,
julian

[ejparrott]

The previous owner of my Colchester lathe fitted a single phase motor because he didn't have 3-phase. As a consequence of that he also couldn't use the coolant pump. Rather than change that to single phase, he hung a bucket from the roof, which had an ordinary garden tap in the bottom of it to provide the flow of coolant.

[joanlluch]

Just in case someone is not aware: You can easily get a source of 3 phase current by using a (2 phase) frequency converter connected to your normal 2 phase mains. This also adds the benefit of getting infinitelly variable speed at the 3phase motor you connect to it (such as a lathe)

[abby]

Everything covered it seems but I will just point out that motor oil is useless as cutting lubricant or coolant , paraffin is just about acceptable for aluminium if you don't mind the smell.
It is true that an inverter will give 3 phase power in the home but not , as far as I am aware , for 440 volt 3 phase motors as fitted for industrial use.

[Roger]

Oct 6, 2015 16:56:01 GMT abby said:

Everything covered it seems but I will just point out that motor oil is useless as cutting lubricant or coolant , paraffin is just about acceptable for aluminium if you don't mind the smell.
It is true that an inverter will give 3 phase power in the home but not , as far as I am aware , for 440 volt 3 phase motors as fitted for industrial use.

You can get 440 Inverters but they are very expensive. I've got lucky with several 440V motors which turned out to be universal types that could have their internal connections swapped from Star to Delta so I could use them with a standard inverter

[andyhigham]

I find WD40 to be an excellent cutting lubricant for aluminium

[Roger]

I use neat Exol Excelcut 427 on absolutely everything except Cast Iron, I think it's excellent. I have it pumped on the lathe and I apply it with a brush on the mill.

[greensands]

As an aside, the reaaon why I use a paraffin based lubricant as a general cutting fluid is precisiely to avoid the unpleasant smells so often associated with proprietary fluids sold for the purpose. I would also dispute paraffin bieing "just about acceptable" for use with aluminium alloys, finding it to be an extremely effective cutting fluid, something I picked up many years ago from reading "The Amateur's Lathe" by L H Sparey, still in my opinion the best guide for the model engineer ever written and essential reading. Reg

[andyhigham]

When I was an apprentice an old engineer told me the best tapping fluid for aluminium was spit.