Gun drill attachment (light duty)
Hi,
Here is the work of the day.
I'm still enhancing my process for musical instrument making, I'm talking here about wood wind instrument. And to make them, you need to drill a loooong and straight bore, and that's not the less tricky part of the job.
Until now, I used to use D bits for doing that , I think I have already showed this here :
Homemade Boring Bit
and it works fine.
The pros don't bother any longer with D bits nowadays, and they usually use industrial gun drills for doing that. It is said to be fast and accurate. The drawback is that it is a really expensive tool and very difficult to find here in Europe for the hobbyist.
I was happy with my D bits, until I recently found on eBay a really good offer for gun drills, the exact dimensions I needed.
So I decided to invest a little bit and give it a try.
http://www.labellenote.fr/file/homem..._holder_01.jpg
The usual use of such industrial tools is to drill deep holes in steel, possibly hard steel, and it uses a flow of oil or coolant sent under pressure through the little hole inside the shaft up to the tip in order to lubricate, cool the work, and send back the chip towards the exterior through the V flute.
Using these necessitate a particular setup, not to say a dedicated machine.
Usually the bit turns and the stock is fixed. So you need a special fixture in order to be able to insert the coolant while the drill is spinning.
All this is very complicated and expensive.
For using these bits on wood, even the hardest woods, it is much easier. Actually, most of the flute or pipe maker (I mean here "bagpipe :idea:) use them with the wood turning in the chuck, supported by a steady rest, and with the gun drill mounted on the tailstock. The coolant is also more simple, it's simply compressed air.
So I needed to make some kind of holder that would fit in the tailstock (both metal or wood lathe) and with the possibility to inject compressed air through the center hole.
I needed to save some length, especially for my metal lathe, because you need to have on the bed enough length for the wood blank, the drill, and the tail stock, so no room for a long setup using a drill chuck for instance.
So here is my solution :
http://www.labellenote.fr/file/homem..._holder_02.jpg
It is a mono-block piece of aluminum, with the head bored to exactly fit the shank of the drill bit (19mm, seems to be standard). Three pressure screws at 120 ° (thanks to the indexing plate ;) ) hold the drill.
A center hole is drilled a little deeper than the bore and a side hole allows to connect the air.
http://www.labellenote.fr/file/homem..._holder_03.jpg
A the other end, I turned a morse taper MT2 to fit directly the tailstock.
The air is driven through a piece of brass tube, epoxied in the aluminum, and the hose was heated soft to be fitted on the brass tube.
http://www.labellenote.fr/file/homem..._holder_04.jpg
Here we go, ready to drill.
Tomorrow, I will show an example, hope it will work fine !
