Drilling problem – the sequel.

[Robin GrahamParticipant @robingraham42208]

Hello. I picked up a set of Dormer drills (to replace the cheapo Screwfix set I had been using)  and a Rohm chuck and arbour (to replace those supplied with my Axminster drill press) at the Midlands ME exhibition last weekend.  Good Lord, what a difference! Apart from the fact that the drills cut so much faster and with far less effort than the old ones, I’m now getting parallel bores.  However…whilst drilling aluminium and steel is fine, if I try a smallish (4mm) hole in brass, after getting in about 1mm the bit decides it can do without my help and pulls in to the work for another 2-3mm on its own (noisily and at alarming speed!). Things then go normally for perhaps 0.5mm, then the same happens again and so on. At larger diameters (>6mm) the chuck actually pulls out of the spindle taper. Any ideas as to cause / remedy?
Regards, Robin.

[Robin GrahamParticipant @robingraham42208]

[Rob ManleyParticipant @robmanley79788]

Thats what happens with brass and nice sharp tools that are cork-screw shaped sadly.  I tend to lower the drilling speed as much as possible and lightly clamp the quill to prevent this, making sure that the job is firmly held in a fixed drill press vice (ok not all the time).   I have my drill press (a 60+ years old and reasonably tyred machine) on the slowest speed it can go – being a modern machine i suspect yours will go way too fast for me anyway – I hardly change from bottom speed unless im drilling 1/8 or under and dont seem to have too many problems.   Oh, this is also very useful when opening up holes in brass because it will most certainly snatch!

Edited By Rob Manley on 22/10/2009 19:24:21

[chris stephensParticipant @chrisstephens63393]

Hi Robin,

Welcome to the quality tooling appreciation society. There is no substitute for good quality sharp drills, and that is your problem with drilling brass. 

Brass does not like sharp drills, in the normal sense, it like zero or near zero rake, that’s provided by  the twisty flute on a normal drill. Brass drills are often straight fluted, but who of us can afford to buy a set of those? The alternative is to use your cheapo drills but to modify the flute at the cutting edge, with a slip stone or Diamond plate, and make the lip in line  with the axis of the drill, only needs a few strokes, makes all the difference. I know the above might not make sense, but I am sure some one will explain it better or point you to a web page somewhere with pictures. If you know what a “D” bit looks, like think in those terms but in miniature, for each flute.

chris stephens

[MichaelRParticipant @michaelr]

Give the drill point a little flat by rubbing on a oil stone, in other words blunt the drill, doing this can help, it also works when drilling  Perspex..

[Robin GrahamParticipant @robingraham42208]

Thanks Rob – that’s reassuring. I shall try clamping the quill somewhat as you suggest.  I was going at about 800 rpm – the lowest speed the machine offers is 500rpm.  Would that  still be fast by your standards?

Regards, Robin

[Robin GrahamParticipant @robingraham42208]

Hi Chris, thanks for your welcome to QTAS. ‘Tis too true.  I had a similar experience with taps/dies – having blown most of my start-up budget on the lathe, I went for a cheap (about 30 quid) set of dies and taper taps.  I then needed a bottoming tap for some reason and bought one-off from a ‘proper’ engineering supplies merchant (about a fiver for one tap). And then worried that I’d cut the core too big ’cause it slid through so easily…

 I’m attracted by your idea of modifying the cheapo drills, though I confess I don’t quite understand your instructions, but shall think on’t.

Regards, Robin.

[mgjParticipant @mgj]

I think you’ll find that if you go to zero rake, you’ll be able to drill at a good speed, without having to lock quills and other bodgery.

if Robin, you don’t quite follow, just blunt the cutting edges with fine stone. So the cutting face is a little wall. Don’t go mad, just take the edge off the drill with a couple of wipes of a stone.

[John Somers 2Participant @johnsomers2]

The ‘grabbing’ of metals during milling operations in the lathe, particularly brass and phosphor bronze, can result in the rotation of the drill chuck and its taper in the tailstock. This tendency can be prevented with a simple modification to the tailstock ram. It requires a morse taper with a tang and the fitting of a grub screw in the correct position in the tailstock ram.

I can provide further details and step by step pictures should anyone be interested.

JohnS

[mgjParticipant @mgj]

Yes, or in model engineering sizes you can use a 3MT- the leverage of the larger diameter…. but all that is curing the symptom not the disease IMO.

 

Best have it not grab and cut straight an not oversize etc because  you are still getting the tip flexing and the like which are causing the forces which cause the grab.  Its going to show somewhere – like the drill spin in the chuck and score the shank. There being no such thing as a free lunch.

 

Another “fix” is to cure the backlash in the tailstock quill- because thats whats allowing the thing to jump forwards. I think we have heard of this just recently…….. Its still symptom not disease, but it does help. As will INCREASING the feed rate of course.

[Rob ManleyParticipant @robmanley79788]

Surely blunting tools is a step backwards and not solving the problem (especially expensive new ones and blunting your old set will just produce tapered bores again).  The problem being that the machine isn’t really good enough for the operation (none are really) – im not suggesting locking the quill tight but preventing the drill bit from snatching can be done with the very least amount of resistance on the quill.  When in industry it always made me laugh to see apprentices tickling the end of the job with the drill bit then see their faces when i took over and would wind the drill bit in at a more suitable speed BUT the machine must be strong enough to take it – normal myfords and drill presses wont take it. 

[mgjParticipant @mgj]

Its not blunt – it has zero rake.  I don’t mean a mankey chipped old thing. Personally mine are razor sharp 4 facet sharpened drills – a lot sharper than they are when brand new.But they are properly configured for brass – and when finished, they are cleaned up on the lips to put them back into steel mode. I suppose I should have 2 sets, but its too expensive.

 

I agree about feed rate – the tendency is to feed as one would with steel. In fact to stop grabbing, as you suggest you increase the feed. Basically you push it faster than it can cut, so all the backlash is taken up, and kept taken up so it cannot pull forwards. So I lean on the thing pretty firmly and drive it pretty hard.

 

Yes you do have to resharpen because you are converting from one tip geometry to another.

 

However, everyone is trying to dance round the problem which is terribly terribly simple: a drill or lathe tool ground for the brasses and bronzes is not suitable for steel, and vice versa. The characteristics of the metals are different . Lathe tools with low rake angles will work. Drills, which have higher rake angles make the point for you – sometimes quite forcibly.

 

 

Tools for the job, and those who don’t know about rake angles and grabbing etc – learn or otherwise find out, (Ian Bradleys book for a start) because brass and gunmetal are our stocks in trade, and not knowing will cost castings, time and grief.

 

 Myfords not being up to it? 

 

Depends on diameter and I’m not up to industrial rates of course, but doing 1″ ID bearings for a traction engine in bronze –  lots of coolant to contol binding from expansion,  centre drill, 1/8 pilot, 4.5mm gun drill (needs initial stabilisation because of the length) all at top speed. , 3/4″ 2mt (biggest 2MT drill I have) at 1000rpm. Bore to -.005″ and ream to size. Nothing grabs, nothing jams. Why should it? I have my tips sorted.

 

With respect – the Myford takes it just fine. A 1/8 bit can grab in the 6″ lathe, which weighs God knows what and is as solid as the rock of Gibraltar. Is that not up to drilling a 1/8″ hole in bronze?

 

 

Edited By meyrick griffith-jones on 23/10/2009 14:22:36

[chris stephensParticipant @chrisstephens63393]

Hi Guys,

I do have a set of 1-13mm in 0.5 step drills from Screwfix, that I modify for brass and leave for brass only, before you ask, no, I did not buy them they were left to me, and had to think of some way to use them. Anyway they are fine enough quality for their new purpose, but I could not say the same about other materials I drill. Brass is so easy to drill compared to Stainless or worse still Titanium, for these I bit the bullet and bought a set of  German made Guhring cobalt drills, oh the joy. Thank you J&L, 60 quid well spent!

chris stephens

PS Meyrick, are you going to Sandown?

[mgjParticipant @mgj]

Yes- is that a pickup?

[Rob ManleyParticipant @robmanley79788]

Thats a fair point – im using a ML7 as a daily driver and i have the belts on the loose side so that if anything happens there isnt a hugh crash – so far i havnt needed that… Also i was thinking about much larger holes – if a myford cant drill an 1/8″ hole in bronze you have a serious problem. 

On a slightly different note- has anyone tried placing a piece of cloth between the job and countersink then re-cutting to clean up a chattered countersink?  A friend of mine here was talking about it and as im no where near my workshop (100+miles) i cant test the practice…

[chris stephensParticipant @chrisstephens63393]

Hi Meyrick,

If you play your cards right, dearie.

Sorry, I could not resist it.

I was due to be ‘demo-ing’ on the SMEE stand all three days, but “day job” threatens to get in the way, still hopeful though. If I can make it, i can show you a good time, no that’s wrong err, show you a Tangential tool., especially the Tangential thread cutting one. Might even make a convert of you!

chris stephens 

[stevieboyParticipant @stevieboy]

Hi Rob if ive ever got drill a large size hole and dont want it triangular shaped i always tear off a piece of used inch emery strip and place it over the hole before bringing the drill down and then drill straight through, hey presto a perfect hole. Once youve tried it you will be amazed. Think its got something to do with not letting the drill run round the edge of the hole. Regards Stevieboy

[AlasdairMParticipant @alasdairm]

Posted by chris stephens on 22/10/2009 19:23:38:

… but I am sure some one will … point you to a web page somewhere with pictures…

 

 

I would love it if someone could post a link to some pictures, as whilst I “think” I understand what to do with my drill bits and oilstone (to enable me to drill brass without grabbing), I would hate to get it wrong!!

 

 

Regards, A

 

[mgjParticipant @mgj]

Herewith.

 

One 4 facet sharpened drill with a little diamond lap about to “blunt” the cutting edge -AKA  zero rake. don’t go mad- a couple of strokes is plenty, one is usually fine.

 

Actually it needs resharpening, but since it still cuts better than a new drill it can wait!!!

 

 

Edited By meyrick griffith-jones on 30/10/2009 14:07:34

Edited By meyrick griffith-jones on 30/10/2009 14:08:48

[AlasdairMParticipant @alasdairm]

Meyrick – many thanks for the picture and explanation – I will now go ahead with confidence!!

 

Regards, A

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