10" hole in delrin ?

Hi,
I need to drill a 9mm dia hole 10" long </mixed up units from a mixed up man> through delrin bar. I need a reasonable surface finish inside because sail
slides have to slide up it without sticking and it needs to be reasonably straight because the ends of the hole have to match up with holes in the thing in which it fits or again they will stick.
Obviously I need a long series drill, but what's the best for the job ?
Thanks,
Boo
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On 12/10/2011 15:30, Boo wrote:

Make yourself a spade bit. They work well in delrin.
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wrote:

The problem is with the insulating properties of the plastic and the trouble with expansion due to friction, the best way is to get a normal jobber drill and grind away the flutes behind the tip so it will not rub, drill the first bit then solder it to ever longer bits of 8mm rod until you get through, you can then ream the hole if you wish. The main thing is to avoid heating the plastic so take it steady.
Peter
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Drawfiler wrote:

A recipe for disaster. There's no way anyone can solder a drill to other bits of metal accurately enough to make a straight drill bit and even if you could it still wouldn't drill straight. And where do you think anyone can find a 10" long 9mm reamer?
--
Dave Baker



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The ends of drills that go in the chuck are not hardened. When I've required long drills I've just obtained a rod the same diameter as the drill, and drilled and tapped one end with a suitably sized tap. Then I've turned the end of the drill down and threaded it so it screws into the rod. Don't turn the assembly the wrong way else the drill will get unscrewed - but you can always Loctite it if needed.
--
Regards, Gary Wooding
(To reply by email, change gug to goog in my address)On 15/10/2011
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On Wed, 12 Oct 2011 15:30:55 +0100, Boo

Been there done that about 3 yrs ago, but it was a 10mm dia hole in a 10" length of Delrin, which had to have a finished OD of 22mm. These were for sliding rollers to ease the fit of a test collar over an oil pipleine.
Whatever you do it won't drill straight.
What I did was drill with a normal long series jobber - you can actually go quite fast with a bit of water for lube - until I'd finished the batch. Off-centre distance was between 0.5mm and 1.5mm on the batch.
I then turned up a little push-fit boss with a stub to locate in the drilled hole at one end with the other end of this piece centre drilled for a talistock centre, then turned another similar stub for the other end, but left this one in the chuck after turning.
The rollers were then mounted on the stub in the chuck, the tailstock stub was pushed in the other end and reasonably heavily pressured with the tailstock centre which created a little 'friction drive' and the rollers were turned to size in one cut from the 25mm stock Delrin rod using a CCGT sharp insert.
All done on a Myford ML7 and turned out spot on, and completed pretty quickly. If I can dig out a picture I'll post a link to it.
Peter
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A proper gun drill (very expensive) plus the very precisely centred machinery needed to use it. No normal twist fluted drill, long series or otherwise will drill a straight centred hole more than about 5D deep. With my somewhat imperfect tail stock chuck I can't drill a concentric 8mm hole through 50mm or so bronze when I'm making valve guides and I no longer try to obtain concentricity even over that short length. I turn the o/d of the bar last after drilling and reaming the hole by holding the part finished guide between centres. A fixed centre in the chuck and a running one in the tailstock and enough pressure to hold the bar just with friction. Light cuts so the bar doesn't slip and it's an easy final op.
Gun drills have a completely different geometry to normal drills with a single cutting edge and pads to hold the drill concentric.
Either start with oversize Delrin and turn the o/d after drilling to correct the runout or farm it out to a gun drilling specialist. You have no chance of doing it in a single drilling op with normal tooling.
--
Dave Baker



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On 10/12/11 14:30, Boo wrote:

One way to do that, depending on the external diameter, might be to fabricate from tube and several internal press fit or glued spacers at various points along the length of the tube...
Regards,
Chris
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On Wed, 12 Oct 2011 15:30:55 +0100, Boo

If its for a sail slide then won't you need a slot in the side?
If so you might need an entirely different sequence of operations, on different machine tools, and the part will probably go nowhere near a lathe.
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