Sad or what?

[DMQuinn]

Then switch on the power feed and drink a cup of tea, whilst watching the lathe bore out the wood for me.

If you do it right, you won't have time for a cup of tea.

I would strongly advise against relying on feed via the leadscrew. Bill's recommendation to hold the shank and feed up by hand is a good one on several levels, not the least of which is that this obliges you to be there and to pay attention to what's going on.

If you've got enough bed length to do it, I'd suggest rigging some way of holding the gun drill in the tailstock (which has been discussed here already, I think) just for the sake of alignment, and feeding the tailstock up by hand.

[uillmann]

Some lathes have fine feed tumblers which allow for a feed rate of .002"/rev. Is this too fast? I run the lathe spindle at around 400rpm. It has always left an amazing hole, even with the less than optimal "R2" and "R4" Eldorado tips. This arrangement has never strayed more than 1/8' or so from the center at the exit, but usually comes out damn near dead center. When the drill exits at the end of the bore, the loud shhhh of air inside the chuck tells you to put down your tea cup, but I have always kept myself in front of the machine in case of any trouble. Sometimes, especially 18'' bores, I will dampen the shaft of the gundrill near the steady with my fingers to minimize any vibration, being sure not to upset the true approach of the drill.

[DMQuinn]

... Is this too fast?
... When the drill exits at the end of the bore, the loud shhhh of air inside the chuck tells you to put down your tea cup, but I have always kept myself in front of the machine in case of any trouble. Sometimes, especially 18'' bores, I will dampen the shaft of the gundrill near the steady with my fingers to minimize any vibration, being sure not to upset the true approach of the drill.

I think the most important thing is that you're there. Your results speak for themselves. All I'm saying is that I don't think it's a good idea to get into the habit of taking your attention away from the process. Suppose you were to slip into a tea-induced reverie and missed the whoosh. What would give way first? The steady rest or the leadscrew chain? I have no doubt that Mark Uillmann is there when he needs to be. Anyone who is contemplating using gun drills and automatic feed needs to remember to "Be here now."

[billh]

Sane advice.

FWIW, the feed rate of 400RPMx.002"/rev, i.e. 0.8"/minute is about the same as what I use at twice the rotation speed; much faster and things just 'feel' a bit forced to me, with the small drills. If you could get the rate down to 0.001" per thou my guess is it would be about right, but I, too, like to steady the end of the drill a bit to reduce buckling and dampen the vibrations.

[Jumper]

Suppose you were to slip into a tea-induced reverie and missed the whoosh. What would give way first? The steady rest or the leadscrew chain?

South Bend lathes have a clutch on the longitudinal feed (which is separate from the half nuts used for screw-cutting), so a carriage stop on the ways will prevent such a collision (and allow unlimited reverie!). Not so on the Atlas or Myfords?

Not that I would encourage anyone to shift their focus away from the task at hand when working with whirling machinery, of course.

David, you have previously alluded to your preference for step-drilling tapered bore pilot holes from large to small. I understand some of the reasons for this; large-diameter drills are stiffer and thus bore a straighter hole than the small ones, and the smallest, most flexible bits are only required to make short cuts, rather than full-length ones.

But since gundrills are not self-centering, how do you maintain concentricity when drilling each smaller step? Without some sort of guidance near the cutting edge, the smaller bit has a tendency to follow the tangential edge of the larger hole, not the center.

[marcpipes]

I badly want one of these, but would I be wasting my money since I only have a midi lathe? I mean, if I can hand feed a D-bit through the tailstock, I should be able to do the same with a gun drill. Yes or No?
Marc

[billh]

Suppose you were to slip into a tea-induced reverie and missed the whoosh. What would give way first? The steady rest or the leadscrew chain?

South Bend lathes have a clutch on the longitudinal feed (which is separate from the half nuts used for screw-cutting), so a carriage stop on the ways will prevent such a collision (and allow unlimited reverie!). Not so on the Atlas or Myfords?

Not that I would encourage anyone to shift their focus away from the task at hand when working with whirling machinery, of course.

David, you have previously alluded to your preference for step-drilling tapered bore pilot holes from large to small. I understand some of the reasons for this; large-diameter drills are stiffer and thus bore a straighter hole than the small ones, and the smallest, most flexible bits are only required to make short cuts, rather than full-length ones.

But since gundrills are not self-centering, how do you maintain concentricity when drilling each smaller step? Without some sort of guidance near the cutting edge, the smaller bit has a tendency to follow the tangential edge of the larger hole, not the center.

I'll let David have the last word here - but I do know that he ensures that his bores _start_ concentric by using pilot bits, at each stage he uses a bit whose outer diam is the same as the previously-bored step, with a concentric pilot bit the same as the 'next smallest' drill in the series. After experimenting with different methods, this one ended up working best for me too (no surprise). Gun drills are liable to start eccentrically otherwise. Since they tend to be self-centering after that, there seems to be no problem with wandering once you start them concentrically.

Bill

[billh]

I badly want one of these, but would I be wasting my money since I only have a midi lathe? I mean, if I can hand feed a D-bit through the tailstock, I should be able to do the same with a gun drill. Yes or No?
Marc

Yes; but of course you do need the compressor. If you're buying one, don't skimp on the tank capacity, otherwise you'll forever be annoyed waiting for it to refill, since gun drills (especially the bigger ones) take more air than many air tools.

Bill

p.s. I use this compressor:


http://www.axminster.co.uk/product.asp? ... 33&recno=2

[Brian Lee]

I'm gonna start using lasers to blast away the bore! I should probably patent it though....what to call it. Hmmm....the Light Saber technique? Naaa...probably have all the Lucas cronies on me quicker than flies on, well....you know.

[David Lim]

I'll let David have the last word here - but I do know that he ensures that his bores _start_ concentric by using pilot bits, at each stage he uses a bit whose outer diam is the same as the previously-bored step, with a concentric pilot bit the same as the 'next smallest' drill in the series. After experimenting with different methods, this one ended up working best for me too (no surprise). Gun drills are liable to start eccentrically otherwise. Since they tend to be self-centering after that, there seems to be no problem with wandering once you start them concentrically.

Bill

Its unlikely I will have a large selection of gun drills available to me for this method of step drilling.

For a wide bored D chanter is it unreasonable to bore out the whole thing with a 3/16" gun drill, then step drill with engineer's type drills along the pilot hole?

David (not the one Bill is referring to above)

[billh]

step drilling along a pilot is probably fine, no worries about the quality of finish on the holes since you'll be reaming them away anyhow.

But engineer's drills in such long lengths are likely to give trouble, not sure how well they will follow the pilot (assuming you can get them in the first place). Perhaps you'd be better off with D bits? Or perhaps you could machine 'pilot following' tips on the twist drills... not sure about that.

Bill

[djm]

I thought about a laser to create the initial centre bore. Even priced out second hand units ($20K used and up). Consider that you have to flush and fill the chamber with nitrogen to prevent your target going up in flames and you start to see that the heat is too excessive to safely bore a dense wood like ebony. The wood oils, combined with the plasma from the burning, would create a tarry substance that would have to be cleared from the bore, as well. Ebony tends to split and check when exposed to high heat. I imagine the other dense woods used for musical instruments would probably be as difficult.

djm

[Brian Lee]

Yeah but.........it's a LASER man!

The coolness factor alone makes it worth it I would think! Yeah BABY!

[BigDavy]

Hi DJM

What type of laser were you thinking about using? Would a high power pulsed laser be more effective, as the material would not be subjected to continuous heat.

David

[djm]

Davy, any laser produces heat. It burns at such a temperature that stuff is vapourized to plasma before it gets a chance to ignite. All the commercial laser units I found were designed for burning thin metal or plastic templates. Even if you only shot one pulse per several minutes, you are still burning, not cutting, and you'd have to do that the entire length of the chanter. I can't see you getting away with that on heavy exotic woods like ebony that can't even tolerate the heat of hand machining on a lathe. Also, it would take forever, eliminating any time savings.

djm