"Deep hole" drilling

[OregonBill]

Trying to envision this. If I had a 12-inch piece of , say, 1.25" diameter round 12L14 bar stock and wanted to drill a half-inch hole 8 inches deep, how big would the lathe need to be and would it require any special tooling? Or could this be accomplished by going slow, using plenty of cutting fluid and backing out the bit to clear chips ever diameter or two?

 

[chrsbrbnk]

well, center drill for the start then I ussally drill as far as possible with a regular length drill. then shift to a long drill. back the drill out for chips as you said. I do this often by sliding the tail stock back and forth, faster than cranking all the way in and out. for a 1/2 drill I'd shoot for say 250 to 300 rpm if you lathe is big enough you can increase the centering accuracy of the hole by first drilling in an inch or two with say a .05 under size drill then bore the hole to exactly .500 then drill with the regular 1/5 drill to its max depth.

 

[robcas631]

I observed a training video made for British students. The video indicated NOT to lubricate a drill bit as it could drift off center. Is this true?

 

[Tin Falcon]

you will likely need at least a 24" center to center lathe equipped with a steady rest. and a couple of Morse taper drill bits. That fit your tail stock.

you will need a long drill bit.
http://www.victornet.com/subdepartments/HS-Taper-Shank-Drills-Long-and-mm/1214.html
if you need a finished hole add a Morse taper reamer to the list.

center drill first then drill say a 1/4 inch hole then open up to 1/2 or if using a reamer open up to 31/64 then run the reamer run the reamer at half the speed of the drill.

Most hobby size lathes only have a 3/4 inch bore though the spindle . if you have a larger swing lathe you may be able to put the material through the head stock and get by with out a steady rest.
what size lathe do you have access to ? make model?
tin

 

[steamin]

My approach is to center drill first; then use a short stubby drill for the first inch or so to establish a good concentric hole with the centerline of the lathe. Then use a regular length drill and then a longer drill to reach the finished depth. The key to deep drilling is to make sure the point of the drill is on the center line of the shank and both cutting sides are at the same angle with the proper relief for the material you are drilling. What causes the drill to drift is applying to much pressure on the drill to make it cut or to be in to big of a hurry to get the job done. Patience and by all means use cutting fluid and keep the chips cleared from the web of the drill. If they are allowed to build up, the drill will drift. Do not hesitate to take the drill out and re-sharpen if excessive pressure is needed to drill the hole. To help with the cutting pressure, I like to thin the web of the drill bit at the point. Typically the point is not doing a whole of cutting, it is just keeping the drill on track.
Anyway, my two cents worth and a whole lot of hole drilling over the past 50 years.
Till later, Larry

 

[kvom]

A 1/2" drill bit with am 8" drill depth costs $27 at McMaster Carr.

I don't know what use your part is but an alternate approach would be to find a piece of .5" ID steel tube and weld onto one end, or alternatively a 8" piece of solid bar that could be drilled from either end.

 

[chrsbrbnk]

sometimes you can get away with silver soldering a reg length bit on to an extension rod,( slightly undersized so it doesn't rub) might want to keep the chip load down using this method

 

[jixxerbill]

Not to get into your business to much but could you use a piece of DOM tubing ? It comes in a variety of od and id sizes.. You said you had a 12 inch piece and wanted a 8 inch hole, You would have to get a solid piece of cold rolled to weld to the end of the 8 inch piece of DOM if you needed it to be 12 inches long.. Its not recomended to weld 12L it has to high lead and sulpher content..Bill

 

[lemelman]

sometimes you can get away with silver soldering a reg length bit on to an extension rod,( slightly undersized so it doesn't rub) might want to keep the chip load down using this method

The chuck ends of drill bits are not hardened. I've extended several bits by drilling and tapping the end, and tapping an extension rod to fit, which should, of course, be thinner than the drill.
This way there is no possibility in overheating the cutting end, and you can easily remove the extension afterwards.

 

[OregonBill]

Lots of great replies here fellas, and thank you. I asked the question to help guide my choice of which lathe to buy. Still thinking hard about the Grizzly 10 X 22.
Here is what I would like to be able to make, in addition to small steam engine parts:

http://www.handgonne.com/gonne_4a.html

The 14th century Swede who made this really had an eye for subtle lines, eh?

 

[Mainer]

I'd clear chips far more often than "every diameter or two." It gets pretty tedious to drill a deep hole, but it's certainly do-able. One way to get a true starting hole is to drill, say, 31/64" for an inch or so then chuck a 1/2" single-end end mill and skim out that hole to 1/2".

 

[Tin Falcon]

why not just buy a piece of bronze that is already bred through then thread and plug the end .
Tin