Deep Hole Drilling
- Thread starter Chavez
- Start date
I do have vague idea of how it is done but not enought to answer the question well, I'll leave that to someone better qualifed.
you need what's commonly referred to as a "gun drill"..at least that's what we called the one I used to run years ago. This was a machine built by the "Dadson" company. It was a high pressure cutting oil type system. We were't making gun barrels but we drilled from .250" to 2.0" holes up to 48" deep. The .250" to about .50" holes were not fun, you had to get your spindle speed up to about 5000 rpm for the material we were drilling and you had to keep a real close eye on your whip guides. Anyone who's ever run one of these will know what the whip guides are and why you have to pay close attention to them and make sure they follow the spindle and you don't get a large enough un-supported area which will start to "balloon" or "whip"..if unchecked very nasty things can happen...and did..once. I wasn't there but apparently it wasn't pretty.
A gun drill's cutting edge looks like this.
Large relitively blunt and cuts on only one surface, it needs high pressuure coolant oil (called gun drill oil) pumped to the tip to clear the chips other wise they will build up and seize the drill or break the end. the chips travel up the groove (flute) to the chip box. The large often carbide tip is perfectly the size of the hole and allows the drill to follow a straight path to great depths.
here you can see the through oil lines on this broken drill
Definately not possible without a modified lathe or gundrilling machine unless you just peck the hole and clear the chips from it constantly.
Large relitively blunt and cuts on only one surface, it needs high pressuure coolant oil (called gun drill oil) pumped to the tip to clear the chips other wise they will build up and seize the drill or break the end. the chips travel up the groove (flute) to the chip box. The large often carbide tip is perfectly the size of the hole and allows the drill to follow a straight path to great depths.
here you can see the through oil lines on this broken drill
Definately not possible without a modified lathe or gundrilling machine unless you just peck the hole and clear the chips from it constantly.
skeetgunner
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With the barrel mounted through the headstock, and a boreing bar mounted in the tailstock, you might be able to drill a straight hole over a short distance. You'd probably have to weld drill rod onto the end of the boring bar.
I've never tried this, but sugguest it as a home shop improv. Really, I'm a network nerd, not a machinist.
I've never tried this, but sugguest it as a home shop improv. Really, I'm a network nerd, not a machinist.
The boring bar would deflect more and more as it gets longer, thus giving you an uncontrolled tapered hole. The only way around this is to make skid plates for the back of the bar so it can't go anywhere.
This would require a lot of toying around to make sure it's the correct size but could potentially work. You would probably not want to mount it in the tailstock as you wouldn't have a power feed thus your surface finish could be iffy if you're not very consistant in advancing the tailstock.
This would require a lot of toying around to make sure it's the correct size but could potentially work. You would probably not want to mount it in the tailstock as you wouldn't have a power feed thus your surface finish could be iffy if you're not very consistant in advancing the tailstock.
Skid plates are usually areas (the dark in the picture) that are made of either non ferrous material like brass or copper, or some type of plastic poylmer that rides on the finished bore after the cutter to center it down the part.
I just finished a day making parts which included gundrilling a 5.7mm hole 122 mm deep in 4140 material. I have used 8.7mm gundrills @ 400 mm deep. The carbide length of the gun drill is considerably longer than the diameter of the drill and centers itself. Chip size is more like eraser crumbs when they come out. We don't get a good finish but we don't need to. They're for lubricating cross holes. You'd pretty well have to hone for a good finish after gun drilling but the hole is dead nuts center to where you want it to be. You usually don't hear them break because they twist right off the stem. The head will almost always fall out of the hole with gravity. I've been gundrilling a fair bit with the lathe I run at work. They're mounted in the live tooling @ 2000 - 3000rpm.
At home, I'd gundrill from both ends and then button rifle. That should suit your purposes.
Hobbyists can buy them but they are expensive. The little ones are worth $200 and change when bought in bulk. We can usually get 8 m. of drilling before resharpening.
I just finished a day making parts which included gundrilling a 5.7mm hole 122 mm deep in 4140 material. I have used 8.7mm gundrills @ 400 mm deep. The carbide length of the gun drill is considerably longer than the diameter of the drill and centers itself. Chip size is more like eraser crumbs when they come out. We don't get a good finish but we don't need to. They're for lubricating cross holes. You'd pretty well have to hone for a good finish after gun drilling but the hole is dead nuts center to where you want it to be. You usually don't hear them break because they twist right off the stem. The head will almost always fall out of the hole with gravity. I've been gundrilling a fair bit with the lathe I run at work. They're mounted in the live tooling @ 2000 - 3000rpm.
At home, I'd gundrill from both ends and then button rifle. That should suit your purposes.
Hobbyists can buy them but they are expensive. The little ones are worth $200 and change when bought in bulk. We can usually get 8 m. of drilling before resharpening.
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