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- Aug 7, 2013
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Deep Hole Drilling
- Thread starter LJP
- Start date
- Joined
- May 5, 2013
- Messages
- 310
Wermie, George, thanks for the answers! This is the way I am going to approach the project. I will take pictures of the set up when it happens.
Dan, this will be a barrel of a scratch built pistol. I will copy a S&W 3rd Model Perfected target .22. Brownells sells a "rifled liner" for less than $40. Standard practice is to bore out an old .22 to 5/16" with a piloted bit and epoxy in a new liner to give an old mistreated barrel a new life. The difference is that I dont have an old barrel to use, and new barrels are all about 1.25" diameter. The barrel I will make was machined, about 1910 ± on a mill and is rectangular, it was not turned on a lathe, finished dimensions of the breech are .59" x 1.75", and the bore is not centered in the 1.75" dimension. I will drill the hole on the lathe to get as true a hole as possible, and then mill to get the hole centered on the finished barrel. My biggest concern at this point is to get as straight a hole as possible.
Dan, this will be a barrel of a scratch built pistol. I will copy a S&W 3rd Model Perfected target .22. Brownells sells a "rifled liner" for less than $40. Standard practice is to bore out an old .22 to 5/16" with a piloted bit and epoxy in a new liner to give an old mistreated barrel a new life. The difference is that I dont have an old barrel to use, and new barrels are all about 1.25" diameter. The barrel I will make was machined, about 1910 ± on a mill and is rectangular, it was not turned on a lathe, finished dimensions of the breech are .59" x 1.75", and the bore is not centered in the 1.75" dimension. I will drill the hole on the lathe to get as true a hole as possible, and then mill to get the hole centered on the finished barrel. My biggest concern at this point is to get as straight a hole as possible.
- Joined
- Jul 26, 2011
- Messages
- 4,142
I suggest you drill out a way too thick billet of steel. Then,you can mill the billet down to get the bore on center. You hopefully will not drill a CURVED hole. I would not use a parabolic bit. They are too easily deflected. If you use a D bit carefully and gently,you should be able to drill a straight hole that is pretty close to centered. Since your drill will be long and more flexible,you need to be extra careful to not flex it while applying pressure to make it drill.
Keep your D bit sharp. There needs to be a slight angle on the front end,as Wermie's sketch tried to show. The cutting edge needs to be foremost. Of course,there needs to be a clearance angle as well. I suggest after grinding,stone the cutting edge with a fine India stone.
A tricky part in making a D bit is to not have the half diameter part warp while hardening and quenching. Just heat up the tip where it cuts. Dip that into the quench just at the cutting end,then lower the drill slowly. Or,you can harden the bit in the round and grind it to half diameter + a few thou. That might be the best way to proceed. A belt grinder,if you have one,will make less heat with a new,coarse blue belt. Switch to a finer one when you get near 1/2 diameter. The cutting edges of your drill need to be smooth on both surfaces where the surfaces come together. DIP your D bit every 2 seconds of grinding with a SHARP belt. You don't want the 01 steel to turn blue. I dip,leaving water on the tool. When the water sizzles,I dip instantly. Have the can of water very close to your grinding.
If you make the D bit's 1/2 diameter part about 1" long,you will have to withdraw the bit about every 3/32" of drilling,or less,to clear the chips,which you must not allow to overload. Keeping patience is essential.
P.S.: A more standard practice these days is to use permanent Loctite,a 600 series. I can't recall the exact number,but they even stick double barrel shotgun barrels together with it. It seems like a miracle,but it will hold together with the shock of firing. My friend Jon,a trained gunsmith,uses it.
Keep your D bit sharp. There needs to be a slight angle on the front end,as Wermie's sketch tried to show. The cutting edge needs to be foremost. Of course,there needs to be a clearance angle as well. I suggest after grinding,stone the cutting edge with a fine India stone.
A tricky part in making a D bit is to not have the half diameter part warp while hardening and quenching. Just heat up the tip where it cuts. Dip that into the quench just at the cutting end,then lower the drill slowly. Or,you can harden the bit in the round and grind it to half diameter + a few thou. That might be the best way to proceed. A belt grinder,if you have one,will make less heat with a new,coarse blue belt. Switch to a finer one when you get near 1/2 diameter. The cutting edges of your drill need to be smooth on both surfaces where the surfaces come together. DIP your D bit every 2 seconds of grinding with a SHARP belt. You don't want the 01 steel to turn blue. I dip,leaving water on the tool. When the water sizzles,I dip instantly. Have the can of water very close to your grinding.
If you make the D bit's 1/2 diameter part about 1" long,you will have to withdraw the bit about every 3/32" of drilling,or less,to clear the chips,which you must not allow to overload. Keeping patience is essential.
P.S.: A more standard practice these days is to use permanent Loctite,a 600 series. I can't recall the exact number,but they even stick double barrel shotgun barrels together with it. It seems like a miracle,but it will hold together with the shock of firing. My friend Jon,a trained gunsmith,uses it.
- Joined
- Apr 9, 2013
- Messages
- 92
D bits are like guided drills - an accurately bored starting hole gets the D bit going in the right direction. An inch or two of full diameter on the D bit after the cutting edge is the guide that prevents direction from deviating. The remainder of the tool length is just for driving the cutting edge + guide section so this can be smaller, possibly mild steel silver soldered on to allow reaching the desired depth.
A drawback in use is that D bits don't pull swarf out of the hole as twist drills (usually) do so there's a lot of time spent clearing swarf. For deep holes it may be helpful to make a twist drill extension bit by silver soldering a smaller drill into the end of an extension, also providing a (brass) bearing surface near the drill to approximately center the drill. Drill an inch or so with this bit to remove most of the material, then use the D bit to accurately extend the full size hole. Repeat.
A 1/8" extension bit using 1/4" steel extension with a 1/2" wide brass collar (just under 5/16" OD) fit near the drill end of the extension should be easy to make and would produce a centered hole in the flat bottom left by a D bit. A long 1/4" twist drill could be used to remove most of the material and would follow the 1/8" pilot so it would remain centered for this inch increment. Clear swarf, then follow with the D bit; while relatively little material is left to remove it will still require care to avoid filling the small cavity of the D bit. When the D bit completes the inch or so increment, repeat as needed.
A drawback in use is that D bits don't pull swarf out of the hole as twist drills (usually) do so there's a lot of time spent clearing swarf. For deep holes it may be helpful to make a twist drill extension bit by silver soldering a smaller drill into the end of an extension, also providing a (brass) bearing surface near the drill to approximately center the drill. Drill an inch or so with this bit to remove most of the material, then use the D bit to accurately extend the full size hole. Repeat.
A 1/8" extension bit using 1/4" steel extension with a 1/2" wide brass collar (just under 5/16" OD) fit near the drill end of the extension should be easy to make and would produce a centered hole in the flat bottom left by a D bit. A long 1/4" twist drill could be used to remove most of the material and would follow the 1/8" pilot so it would remain centered for this inch increment. Clear swarf, then follow with the D bit; while relatively little material is left to remove it will still require care to avoid filling the small cavity of the D bit. When the D bit completes the inch or so increment, repeat as needed.
- Joined
- Jul 26, 2011
- Messages
- 4,142
I used a 1 3/8" diameter twist drill with an extension welded onto its#3 Morse taper shank to drill a fairly large cannon I was making from 5" diameter bronze rod some time ago. The hole was over 2 feet deep.
Someone else had welded the extension on,and I must say,they did a good,if not quite perfect job of getting the drill concentric with the extension. The bore of the cannon was not critical,so I took a light grind down the side of the drill with a tool post grinder to get the drill absolutely concentric. It bored a hole so smooth it looked like an automobile cylinder!
However,my whole point here is, I still could bore only about 1/8" deep each time in,and had to withdraw the drill many times to clear the chips even with the twist drill. It took 2 days to bore the hole. This was in very tough manganese bronze that seemed about as tough to turn as some kind of stainless steel.
Someone else had welded the extension on,and I must say,they did a good,if not quite perfect job of getting the drill concentric with the extension. The bore of the cannon was not critical,so I took a light grind down the side of the drill with a tool post grinder to get the drill absolutely concentric. It bored a hole so smooth it looked like an automobile cylinder!
However,my whole point here is, I still could bore only about 1/8" deep each time in,and had to withdraw the drill many times to clear the chips even with the twist drill. It took 2 days to bore the hole. This was in very tough manganese bronze that seemed about as tough to turn as some kind of stainless steel.
- Joined
- Jan 16, 2020
- Messages
- 8
One little trick that does help with removing chips when using a D-bit in the lathe: Keep the flat of the D-bit facing up. The chips land on the flat and most of them stay there as the bit is withdrawn from the work. Once the bit is clear of the work, brush it off, apply a bit of oil, and start drilling again. If the flat is left in any other position, the chips all stay in the bore when the drill is withdrawn.
This will not remove all of the chips with each withdrawal, but it will get most of them.
This will not remove all of the chips with each withdrawal, but it will get most of them.
- Joined
- Jul 26, 2011
- Messages
- 4,142
Yes,definitely keep the flat uppermost,or you will have to remove the workpiece and dump out the chips every time you need to clear the chips!!
