Deep hole drilling on the manual lathe

Cole2534 · Jan 8, 2019

I've the need to drill a 1-1/8" diameter 19" deep hole on a 30" C/C lathe, and the material won't fit through the head stock. It also has a blind end.

My plan is to fasten the piece to the carriage and hold the drill in the headstock, but where do I get a 20" long drill? Can I grind the unfluted portion from a reduced shank drill and attach it to an extension? Will this provide enough chip evacuation? The thought process there is that I could feed the drill in to my travel limits, then reset carriage position and bring the drill further out of the headstock. To ensure it starts straight I'm going to bore the first few inches.

The hole is for clearance only, so as long as it's not sticking out the side, we're good to go.

Am I missing any obviously flaws, besides the need for a longer lathe?

Greatbasin · Jan 8, 2019

I would look at tubing and bore to size. Or drill from both ends and bore to size. Good luck. John

Cole2534 · Jan 8, 2019

Greatbasin said:
I would look at tubing and bore to size. Or drill from both ends and bore to size. Good luck. John

It has a blind end. I make this now as a weldment, I'd like to make it from a solid.

It's a super deep socket is all, nothing wild about it.

Dumpster_diving · Jan 8, 2019

My thought is that the 19" isn't the problem, given the way you plan to set it up. A 1.125" S&D bit brazed to a 20" rod extension should work fine if you take it in stages as you describe. Chip evacuation should be fine if you retract now and then (and perhaps even fine just so long as the rod is smaller diameter than your bit).

But I think the real problem is going to be keeping the one thou tolerance. I don't think you're going to keep to 1.125" over 19" regardless of how you do it. Particularly the positional accuracy. Even if you drill undersize and ream to 1.125"...I think there's a fair chance the hole wanders from your starting position if you do it from only the one open end and don't bore.

My $0.02.

Cole2534 · Jan 8, 2019

Sorry if I wasn't clear on the tolerances, I have .075" to work with. Of the 19" hole, the first 3" will get bored to 1.200", the rest is just clearance.

I'll order up a drill.

Rob F. · Jan 8, 2019

I think he is saying that since you put 3 decimals that implies tight tolerance, you should have said drilling 1 1/8" hole.
For example:
1 1/2" ,1.5", 1.50" ,1.500" all would use the same bit but have tighter tolerances as you add zeros.
(smaller drill and bore to size on tighter holes)

Dumpster_diving · Jan 8, 2019

Cole2534-

That makes sense and 0.075 seems like a decent margin for error. If it becomes a concerned, you could maximize the extension diameter. Maybe a tube extension just a bit shy of the 1.125" (enough to evacuate chips rather than a rod. And advance the extension out of the headstock in small increments so there's less flex on the extension. Perhaps even a ring or rings around the extension to support the bar and eliminate flexing inside the hole. But I suspect that's all overkill...

Best.

Cole2534 · Jan 8, 2019

Rob F. said:
I think he is saying that since you put 3 decimals that implies tight tolerance, you should have said drilling 1 1/8" hole.
For example:
1 1/2" ,1.5", 1.50" ,1.500" all would use the same bit but have tighter tolerances as you add zeros.
(smaller drill and bore to size on tighter holes)

Yup, my bad.

Now to figure out how to add an extension without brazing equip.

Dumpster_diving · Jan 8, 2019

Flat ground on the bit shank. Extension bored to diameter of the shank. Set screws in the extension bearing on the flat.

Or silver braze with a maap torch.

Cole2534 · Jan 8, 2019

Dumpster_diving said:
Flat ground on the bit shank. Extension bored to diameter of the shank. Set screws in the extension bearing on the flat.

Or silver braze with a maap torch.

That's what I'm thinkin.

Dumpster_diving · Jan 8, 2019

1.125" is quite a bit of torque. Try and keep the wall thickness of the tube generous, maybe use multiple set screws, perhaps even thru-pins (depending on the diameter of the bit shank).

...or belt and suspenders and screw and braze

Cole2534 · Jan 8, 2019

I'm currently more concerned with the drill thrust, after some quick searching it looks like I could see north of 500lbs. That may be enough to lift the carriage, and sink my plan.

FWIW, material is 1144SP.

Rob F. · Jan 8, 2019

Heat shrink it on. You could even machine a slight taper on bit shank and matching hole in bar heat bar and press it on?

michiganbuck · Jan 8, 2019

We used to silver solder an extension shank with having a tight fit deep and a .006 or so lose fit for the silver solder to flow in..

You could possible pin this drill to a 1" shank and make pecker feeds through..you could use a 1 1/8 center-cut end mill with extension and peckkering through. Might even grind a hex and drive it with a socket wrench and extension.

Good job for a manual lathe so the tail center would locate the out end...with the part on the saddle. but still a job to make the set-up.

1-1/8" Drill, 1/2" Shank Diam, 118deg 13418 - MSC

*If a repeat job I would dedicate a (heavy duty) drill press for just this job...

24" long drill bit.
https://www.amazon.com/HSS-1-1-Extra-Long-Drill/dp/B00ELK4A0G

Cole2534 · Jan 8, 2019

michiganbuck said:
Good job for a manual lathe so the tail center would locate the out end...with the part on the saddle. but still a job to make the set-up.

This is a prototype, if it fails I'll go back to weldments. For fixturing, I'm going to make a two-piece clamp with the part-line on the spindle's CL. It'll bolt in place of the toolpost, then get bored to size in situ. I figure that you can't really get more true than that and it will prove or disprove the idea.

Spinit · Jan 8, 2019

Rigidity is a big factor. Seeing you have the blind hole and must go so deep with a flat bottom is a pain.

Cole2534 · Jan 8, 2019

Spinit said:
Rigidity is a big factor. Seeing you have the blind hole and must go so deep with a flat bottom is a pain.

The lathe is a Monarch, it's up to the task if the carriage won't lift. Luckily not a flat bottomed hole, I added some unneeded length to allow for the drill point.

Dumpster_diving · Jan 8, 2019

Cole2534 said:
This is a prototype, if it fails I'll go back to weldments. For fixturing, I'm going to make a two-piece clamp with the part-line on the spindle's CL. It'll bolt in place of the toolpost, then get bored to size in situ. I figure that you can't really get more true than that and it will prove or disprove the idea.

Would a steady rest butted-up right next tot he carriage get you to roughly the same place (without the trouble of the two-piece clamp)?

MattiJ · Jan 8, 2019

Cole2534 said:
The lathe is a Monarch, it's up to the task if the carriage won't lift. Luckily not a flat bottomed hole, I added some unneeded length to allow for the drill point.

I have used similar method with 25mm drill on a 11x24 kerry and that is not half the lathe Monarch is. Drill drifting out of your stock would be my biggest concern. 0.015" per inch for twist drills was given somewhere as reasonable expectation, ie About 0,3" exit location tolerance for your 20" drill :willy_nilly:

Tig weld, braze or just order enough long drills. Just sit down before you ask the price..

Dormer has been my go-to for silly spaghetti drills..they have A952 series 28mm dia drills with 385mm flute lenght and 580mm total but that is not enough for your case.

yardbird · Jan 8, 2019

Just an idea I'll toss at you to consider or not? Lol..

I make long drill by threading the end of the drill bit then drill and tap a extension rod. I have access to some already hardened H13 or Viscount drill rod that's been ground so it's pretty straight.

I don't have the best luck keeping the pieces straight at the joint when I try to weld or solder the two. If I was given this job I wouldn't hesitate making a extension out of a piece of one inch rod as long as its fairly straight. I like to make the extension a tad bit smaller then the drill if possible? Good luck!

Brent

https://www.practicalmachinist.com/...length-drills-309685-post2628023/#post2628023

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