drilling deep holes

well moderately deep anyway. In this case, 8mm dia and 65mm deep.
This is a hole in the end of a bit of BMS bar, so the bar is in the lathe
and the drill in a chuck in the tailstock. First 25-30mm goes fine and then
the deeper it gets the more the swarf doesn't clear from the drill bit
flutes, and in the end I have to wind the drill back out to clear it.
Using cutting fluid seems to make it slightly better although it still
happens.
Initially, the drill makes nice long curly bits of swarf, but they get
shorter the deeper it gets, till it only makes little bits which don't find
their way out.
any ideas?
Reply to
Austin Shackles
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Gun drills.
E.g.
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or
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and
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would be reasonably expensive I guess, or just use a small boring bar? Might take a while.
Is there another way to make the part? like, the 65mm deep hole being a through hole so you can work at it from both sides?
Zed
Aust> well moderately deep anyway. In this case, 8mm dia and 65mm deep. >
Reply to
zedbert
That's normal. You are supposed to 'peck drill ' in that you retract to clear swarf. Rule of thumb is 2 x D to start and 1 x D as you get deeper -- Regards,
John Stevenson Nottingham, England.
Visit the new Model Engineering adverts page at:-
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Reply to
John Stevenson
As John says you got to peck at a hole that deep.
This is where a lever operated tailstock comes into it's own.
Also a normal jobber drill is not really designed for this kind of job, but can be made to perform within fairly well. A drill with Parabolic flutes works a lot better.
Wayne...
Reply to
Wayne Weedon
Of course you do. That's normal. Drills never clear swarf entirely in deep holes. I'm surprised you even get that far in without having to wind out and clear the flutes. You'll also find, unless your drills and machine centres are spot on, that the hole will wander off to one side if it's that deep. That's the exact dimension of a Ford CVH bronze valve guide but I can't make one from scratch that's properly concentric without drilling first and then turning the o/d between centres to clean up the drilling error. Maybe it's just me or my lathe. -- Dave Baker Puma Race Engines
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Camp USA engineer minces about for high performance specialist (4,4,7)
Reply to
Dave Baker
For deep holes I talk to a nice man with a fast hole EDM and a wire eroder that owes me favours. Certainly made my life easier when I needed a new countershaft clutch spindle for the ML7 and I didn't fancy trying to hold a 3/8" bore concentric over 11" in a 3/4" dia. bit of silver steel.
I was just too chicken to attempt this.
Peter
Reply to
Peter Neill
I'm sure it isn't the proper way but when I needed to do drill a deep 8mm hole (10 inches or so deep) to make a lathe drawbar I took a bit of 8mm silver steel filed 1inch down to half diameter (accurately) backed the end off so it would cut and then hardended and tempered it.
I then drilled and bored a hole 1in deep 8mm dia (to counter drill run out) and then used the above tool -- withdrawing frequently to clear swarf and it seemed to work well.
Alan
Reply to
Alan Bain
On or around 22 Nov 2006 11:29:16 -0800, snipped-for-privacy@gmail.com enlightened us thusly:
it *is* worked from both sides. the thing's 124mm long.
Reply to
Austin Shackles
On or around Wed, 22 Nov 2006 21:32:42 -0000, "Dave Baker" enlightened us thusly:
I dare say it does wander, but in this case it's not a major issue. It's the thing I might yet get around to making a pair of taper tools for - at the moment, it's drilled through 8mm, then drilled to ever-shallower depths with 9, 10, 11, 12, 13, 14, 15 and 16. Ideally, the finished article would have a smooth taper from 16 down to 8 on each end, one at about 10° and one at about 3°, although in practical terms the stepped hole is doubtless as good. It's a bit about intensive, mind, they take about half an hour each to make.
I did try upping the speed to 696 (nominal) which made things go better, but the larger sizes of drill don't sound very happy at that speed so I end up slowing it down part way through.
I did actually get the lathe working at 1200 today - cuts very nicely with a carbide tipped tool as well. Not sure how well the HSS stuff would fare. Also had an impressive failure to part a bit of the 20mm bar off - not sure how, it started cutting fine and then stopped cutting and then dug in sufficiently hard as to stall the machine - amazingly, without breaking the parting-off blade.
Reply to
Austin Shackles
As John said, pecking is required.
Just for the sake of completeness:-
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I have a 8.1x265mm gun drill that I picked up off of fleabay when I was thinking about making an ML7 clutch. I got it to show me how they were made. I haven't yet got round to making a holder and coolant pump for it... one day it'll prove useful.
Mark Rand RTFM
Reply to
Mark Rand
Hmm, I'm contemplating exactly that job; I've already made a replacement bronze bush which only slightly reduced the rattling from the clutch, the shaft is visibly worn and needs replacing. Bulk buy anyone? Martin
Reply to
Martin Whybrow
I'm just curious to know whether you just prop the drilled hole between centres, or do you centre-drill the ends of the drilled hole to make 60 degree chamfers for the centres ?
Reply to
Boo
The former because that's the only way to be sure you're holding concentric with the hole you've just drilled. If you put a centre drilling in each end and the drilled hole wanders off centre then you're stuffed because the piece will rotate about the centre drillings not the hole once you mount it between centres. You then need a mandrel of some sort to resolve the problem.
I do a huge amount of turning using only tailstock pressure and friction to hold the piece I'm working on. Valve guides, valve seat inserts, pistons. It's a very overlooked way of achieving concentricity because the books don't mention it and most engineers won't think of it at all or if they do they'll say it's not a 'proper' way of holding something. In fact it's surprising how large a cut you can take with sharp tooling.
I'm not just talking about holding between centres here either. Let's say you have a plain disc and you want to turn the o/d down a bit. You can't easily use a chuck because that will obscure the o/d you're trying to machine. Solution - chuck a bit of scrap and face it true to act as a pad for one end. Centre drill another bit of scrap. Press the disc between the two, dial gauge on the o/d and tap until it runs true, tighten tailstock, machine o/d, job done. -- Dave Baker Puma Race Engines
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Camp USA engineer minces about for high performance specialist (4,4,7)
Reply to
Dave Baker
lots of good sound stuff, as usual, but what he didn't tell us - and *somebody* has to ask - is the answer to that bloody crossword clue at the end of his signature block and which has been nagging me for weeks!
I thereby offer a prize of £20 for the solution I consider the most appropriate or funny which I receive by e-mail in the next couple of weeks or so! Rather than constipate the newsgroup with *too* much OT stuff, send entries to me by e-mail, address above, and I'll subsequently publish a summary in the newsgroup when I announce the winner. Contestants named Dave Baker need not apply! However, I hope that Dave might at least tell me privately what his answer is so that I can let you all know in due course.
My decision is final!! --
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"
Reply to
Chris Edwards

and one afterthought, please put the word 'Crossword' in the subject line of e-mails - otherwise you might get spam-filtered to the place 'where the birds don't sing and the sun don't shine'! --
Chris Edwards (in deepest Dorset) "....there *must* be an easier way!"
Reply to
Chris Edwards
is that : 'one day' as a technical term, being defined as :- "The day on which you realise that something which you threw away yesterday is essential for starting tomorrow's project"
Dave
Reply to
dave sanderson
I would be starting with the biggest drill first and working down. Mark
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Reply to
mark

I'm afraid the answer may be as dull as "Puma Race Engines" as this clearly fits the 4-4-7 spec - however, his clue doesn't follow the normal rules of anagram clues in that case...tsk tsk
Regards, Tony
Reply to
Tony Jeffree
It most certainly does ! -- Dave Baker Puma Race Engines
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Camp USA engineer minces about for high performance specialist (4,4,7)
Reply to
Dave Baker
That's a very interesting description but it leaves me with an obvious question :
How do they make the coolant hole down the length of a gun drill ? Maybe with another smaller diameter gun drill of the same length ? But does that imply that you regress until the required hole size is smaller than the inter-atomic spacing of the atoms of the material ? I suppose at that point the problem goes away but you must have to use some very special kind of coolant ?
Cheers,
Reply to
Boo

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