Need to drill a long hole..

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jgarrett

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I need to drill a 1/8" hole in the center of a piece of 1" x 8" aluminum. It has to be centered within a few thou.
How do I keep it from wandering or not drill true after I get it started???
I will be using my Emco V10P lathe. I have a 1/8" x 12" "aircraft" drill bit.
I may need to drill one 24" for another project so any advice on drilling looong holes??
Thanks,
Julian
 

toolznthings

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Hi,

You need to send it out for gun drilling, especially the longer part. Also, if the hole needs to be on center line end for end you would be wise to have the stock O.D. a little over size and machine to the hole after drilling.
 

jgarrett

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Thanks,
I guess I will invest in a couple of gun drills...
Julian
 

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Simon
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Would a D-bit not do the same thing? I've used one for deep drilling, admittedly not as deep as in this instance, but I got good results.
 

NitroExpress

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I think your best chance of success here will be to drill the hole first in oversize material, then machine the outside to the size you require, to drill a hole this long with any accuracy will hinge on luck rather than judgment, especially with home workshop machines.
 

Wizard69

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Thanks,
I guess I will invest in a couple of gun drills...
Julian

It isn't that simple, gun drilling is usually done on specialized machines. These machines feed high pressure fluid down a hollow drill bit to flush out the chips. On top of that you usually need a fixture at the end of the part that aligns and starts the cutting end of the gun drill.

Even with all of these features it is very hard to get a absolutely straight hole. Actual gun barrels are often straightened after drilling operations.
 

Swifty

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I would be using a long spiral flute drill, they are shown next to the gun drills in the link. I have found the best way to drill with them, seeing that you won't have 8" of travel in your tailstock, is to set up the saddle as a stop for the tailstock, drill a bit, then move the whole tailstock and drill back to clear the chips. Then move the tailstock back to the stop (saddle) and continue to drill. When you run out of travel on the tailstock, just wind it back, adjust your saddle stop, and continue drilling.

Paul.
 

Woodster

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Even with all of these features it is very hard to get a absolutely straight hole. Actual gun barrels are often straightened after drilling operations.
I work for a gun drilling company and although possible to drill the hole, it would be unlikely to run perfectly true. We would normally use massively oversize stock, drill and hone the stock then true up between centres on the lathes before final machining.

http://www.subcondrilling.co.uk/
 

Wizard69

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I work for a gun drilling company and although possible to drill the hole, it would be unlikely to run perfectly true. We would normally use massively oversize stock, drill and hone the stock then true up between centres on the lathes before final machining.



http://www.subcondrilling.co.uk/

I've only worked on one gun drilling machine in my life and that was repair work, so I know the principles. I just see this as a massive challenge to do on a conventional lathe. He might have success with a D type bit with a lot of full length pecking and plenty of cutting fluid. It would be an extremely tedious operation though on a manual lathe. This might be more viable if the drill bit is captured in the saddle in some manner instead of the tail stock as you could rack in and out quickly. At best you would get a few thousands at a time of new depth so that is a lot of the old in and out.

Using more conventional tooling I've done some rather deep holes and not done to bad but no where near as many diameters deep as this task. This hole is so deep though that I can't see anything I've done even applying here. He's asking for 64 diameters depth and frankly that is out of the range of conventional drilling.
 

tornitore45

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I work for a gun drilling company
And gun caliber is much bigger that 1/8".

Did everyone miss the 1/8" size? 12" x 1/8" diameter is just a a bit larger than spaghetti, I do not know about industrial settings, but on a HSM is impossible.
The oversize stock method will produce a a cylinder with two centered entrance and a curved hole in between, because the reason the bit came out off center is that it follower a curved path due to microscopic tool asymmetry.
 

jgarrett

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Well, I guess I will just tuck my tail and get back on the porch!!!!

Just one of those things that HSM stuff won't or can't do.
Thanks for the inputs..
Julian
 

MCRIPPPer

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could you build it from two halves? mill down each side with 1/8 ball end mill and bolt together?
 

kquiggle

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I was thinking along the same lines. There is more than one way to skin a cat - perhaps if you told us in more detail what you are trying to do, we could offer suggestions for accomplishing the same result in a different way.


Also (not that this will solve your problem) you may be interested in getting hold of a copy of this:

Machinery Reference Series - No. 25 Deep Hole Drilling
 

NitroExpress

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While dragging cables through long holes for our cooker power supply, I have given this problem further thought, it seems that I am not the only one to come up with the idea of making this in two halves, given that it is in Aluminium, 1/8" Dia and 8" (or 24" ) long I can see this would be almost the only option, the only other way I can think of is to make a series of drillable length sections that screw into each other end to end, you could then pass your long drill through to clean up.
Good Luck!
 

Woodster

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And gun caliber is much bigger that 1/8".

Did everyone miss the 1/8" size? 12" x 1/8" diameter is just a a bit larger than spaghetti, I do not know about industrial settings, but on a HSM is impossible.
The oversize stock method will produce a a cylinder with two centered entrance and a curved hole in between, because the reason the bit came out off center is that it follower a curved path due to microscopic tool asymmetry.
Gun Drilling is the name of the process used for deep hole drilling, not solely for Gun barrels! It is the most common way of producing deep, accurately sized, straight holes. That's why the method was developed. Apparently we can drill a 1.2mm hole 100mm deep in Inconell 725 , according to Italian Frank at work, though i think he's being a bit optimistic!
Gun Drill geometry is very different to normal drill geometry. They are single flute, single point and bizarrely, the drill point is off centre. On Gun drilling machines, the workpiece and drill counter rotate.

It probably wouldn't cost Julian that much to get the holes done properly.
 

goldstar31

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Just think that Hexham Abbey in deepest Northumbria has a stone carving of bagpipes which were obviously in use in the 16th Century.
If my memory is holding out, the drones were a lot longer than 4"(125mm) and thinner whilst the chanter was near enough 12" and a dead parallel bore of an 1/8th. The choice then was either ivory or hardest wood and today's choice is African Blackwood or Kingswood.

It is still being bored today on very ordinary and somewhat ancient model engineers lathes.

How do I know? Well, I've done it. At 84 do you really expect me to get overly excited about much? Sausage, eggs and chips perhaps but boring a hole- well, no, not really!

Norman
 

tornitore45

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Does the hole needs to be 1/8" all the way trough?
Could the hole be larger and two bushing of suitable length at the ends?
 

MachineTom

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You can home shop a gun drill setup. First and most important you need a bed long enough for the length of dill 12 & 24 plus room for the carriage, If the work will fit down the spindle bore you can get away with a 30" bed and a 12" bit for 24 you will need 36+.If the work is larger then the spindle you need a bed length of that amount more than I stated. Second thing is a power feed carriage that has, or can be modified to have an advance of .0002-.0007 per rev. Which is not at all common. so you will need to change some gears to get a feed that slow.

You will need at least a 1hp air compressor, to provide enough air/coolant mist to lube the drill and remove chips, as a gun drill does to have flutes that carry away the chips. The process is not at all like drilling a hole.

The end of a gun drill is a piece of carbide with 1 or two grooves in it, and 1 or two cutting edges ground in it. The shank of the drill has a straight flute running the length, as well as a bored hole to get coolant to the tip.


To start a gun drill you first bore a hole, .001" larger than the bit, 1/2-3/4 deep, this starts the drill on center, for a drill that size you would need as fast a speed as your lathe has, 2000rpm +

the drill is mounted on a tombstone instead of the compound.

These Photos should explain.
The first shot is a .875 gun drill about 18" long, the mount end is 1.25, the tombstone is drilled at the rear for 1/4 npt, I stick an o-ring in the bore and push the drill tight against it to seal. The next shot is a boring bar holder in the 1" bore, that was used to thread a bore.
The last shot is a bit ckoser.

Not shown is the modification to slow the feed down, I removed the reversing feed, and made a plate and shafts with gears that cut all the feed speeds in half. This lathe has a 3/4 hp motor and will bog in chips stack up in the bore, when cutting with a Gun drill at 1500 rpm and .0005 feed that baby is loaded. The larger drill are sometimes easier as there is more chip clearance.y
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