#3 mt - #2 mt & r8

SonofaMachinist · Feb 7, 2020

Hello Everyone,

My first post, so be gentle.

I have 2" drill bit with a #3 MT and want to use it in both my 16" South Bend lathe that has a #2 MT tail stock and also in my Bridgeport with the R8 spindle.

The job I am doing only requires through drilling about 1 1/2" depth. Same part for both the lathe and mill. The difference being whether the part is pre-welded in an assembly or not. Probably do this a couple of times per month, in pairs.

Here are the options as I see them:
Buy adapters for both tapers. (expensive for what I'm doing)
Turn the drill taper down to #2 MT and buy an adapter for the mill. (Saves some $)
Turn the drill to 5/8" straight shank to use in drill chuck (lathe) and collet (mill). (Is 5/8" sufficient to hold the torque of a 2" drill?)

The adapters to make this happen add length that I don't really need. The drill is 8" long plus the MT. So, I'm tempted to shorten the drill itself. This was a freebie and I don't anticipate using it for anything else. But, I would hate for whoever winds up with my junk, after my demise, to need it longer.

Thoughts or opinions?

Thanx,

Bruce

eKretz · Feb 7, 2020

I would absolutely not turn it to a small straight shank - spin city... In such a situation I think I'd go with the #3 adapter. If that is too long to fit, turn the taper down to #2 Morse and be very cautious. Step drill for sure. This is assuming that you're capable of turning an accurately fitting taper...if not you'll have a snapped off tang for sure.

If you need to shorten the drill go ahead. Whoever acquires it after you won't mind, they'll most likely never know it was longer unless they're attentive and notice the thicker than normal web..

metalmagpie · Feb 7, 2020

A 2MT taper doesn't have enough surface area to withstand the cutting forces of a 2" drill into steel. Sorry.

metalmagpie

DDoug · Feb 7, 2020

SonofaMachinist said:
Hello Everyone,

My first post, so be gentle.

I have 2" drill bit with a #3 MT and want to use it in both my 16" South Bend lathe that has a #2 MT tail stock and also in my Bridgeport with the R8 spindle.

The job I am doing only requires through drilling about 1 1/2" depth. Same part for both the lathe and mill. The difference being whether the part is pre-welded in an assembly or not. Probably do this a couple of times per month, in pairs.
Here are the options as I see them:
Buy adapters for both tapers. (expensive for what I'm doing)
Turn the drill taper down to #2 MT and buy an adapter for the mill. (Saves some $)
Turn the drill to 5/8" straight shank to use in drill chuck (lathe) and collet (mill). (Is 5/8" sufficient to hold the torque of a 2" drill?)

The adapters to make this happen add length that I don't really need. The drill is 8" long plus the MT. So, I'm tempted to shorten the drill itself. This was a freebie and I don't anticipate using it for anything else. But, I would hate for whoever winds up with my junk, after my demise, to need it longer.

Thoughts or opinions?

Thanx,

Bruce

Uhm...buy a couple more drills to fit each machine ?

johnoder · Feb 7, 2020

As to BP - sounds like the perfect way to shear the little round spindle key possessed by BPs

SBLatheman · Feb 7, 2020

The taper in your 16” South Bend tailstock spindle is a #3MT (if it is original equipment)
Tef

Gordon Heaton · Feb 7, 2020

An adapter for this: https://www.mscdirect.com/product/details/66161886

is much easier to make than a precise taper, and the cutting force (torque) is much lower than a twist drill. I use them often. (It will fit directly into a 3/4 collet on your mill).

dana gear · Feb 7, 2020

johnoder said:
as to bp - sounds like the perfect way to shear the little round spindle key possessed by bps

yup...……………………...

thermite · Feb 7, 2020

metalmagpie said:
A 2MT taper doesn't have enough surface area to withstand the cutting forces of a 2" drill into steel. Sorry.

metalmagpie

Neither does an R8! But at least on the SB one can use a torque-reaction device.

Nor does either machine cited have the balls to make effective USE of a 2" helical twist drill at more than snail-velocity, even if properly gripped.

Put it into perspective. My 2" range MT drills have the motive power of a PIV-belted and geared-head 7 HP Alzmetall AB5/S, 5 MT back of their ass. Even Heavy Hams Hans @ 4,400 lbs avoir is only rated for 2 1/2" holes in mild steel, 3" in Cast Iron.

What Gordon said. Look at a 2" slug-depth capable annular cutter? Lower force required to "trepan" as you are only turning a small cylindrical tube area into air and chip from the solid metal.

I bought sets. 1" and 2" depth both. Hougen and Milwaukee.

They are waaaay nicer on thin stock than helical twist-drill "breakout" as well. Try your 2 MT 2" drill in 1/8" plate - or even 3/4" inch, and you'll "get it in one".

You'd need but the one unit. Plus driver shank(s) as appropriate to lathe & mill.

Then - if need be - even on the light-duty machines you have, go the next size under and the raw hole can be reamed. Or finish bored to as tight a figure as your machines can hold.

gbent · Feb 8, 2020

You are seriously overloading either machine with your 2" twist drill. I believe sooner, rather than later, it will end poorly. The 2" rotabroach may work, I've never tried one that large.

Another choice is an APT Multi-Tool. Before annular cutters it was, hands down, the best way to put big holes in with a bridgeport. I now have big hole machines, so have never made a comparison between the annular cutter and a Multi-Tool. The Multi-Tool doesn't have the depth limitation of a annular cutter.

The Multi-Tool is a PILOTED flat bottom spade drill. The pilot makes all the difference in the world.

projectnut · Feb 8, 2020

I would use a boring bar on the lathe or a boring head in the mill for the finished hole size. I wouldn't go past a 1" drill on the Bridgeport or a lathe with a MT#2 tailstock. In either case I would step up to the 1" diameter with a couple smaller size drills.

thermite · Feb 8, 2020

gbent said:
You are seriously overloading either machine with your 2" twist drill. I believe sooner, rather than later, it will end poorly. The 2" rotabroach may work, I've never tried one that large.

Another choice is an APT Multi-Tool. Before annular cutters it was, hands down, the best way to put big holes in with a bridgeport. I now have big hole machines, so have never made a comparison between the annular cutter and a Multi-Tool. The Multi-Tool doesn't have the depth limitation of a annular cutter.

The Multi-Tool is a PILOTED flat bottom spade drill. The pilot makes all the difference in the world.

APT sets are still "out there". Google 'em. Losts of distributors stock them.

They still work, same as ever. Make a hole. Spot face. Counterbore. Front side or back. Hence the "multi" moniker.

And yah forgot to mention the neatest part of all...

Ability to easily craft CUSTOM HOLE SIZES!

Cheaply, even! See "resizing fixture".

Rudd · Feb 8, 2020

APT is great. I bought a 'starter" on Ebay, E size, then filled it out with new stuff where needed. 2 1/2" dia. hole in 4" thick CI on a 1 horse lathe, no problem.

thermite · Feb 8, 2020

Rudd said:
APT is great. I bought a 'starter" on Ebay, E size, then filled it out with new stuff where needed. 2 1/2" dia. hole in 4" thick CI on a 1 horse lathe, no problem.

Full set on my RTWL (Round-Tuit Wish List) as well. Allied's own guru sez the biggest "high power" spade drill I can push, even with good high-pressure coolant, on my 7 HP Alzmettal is still only 1 1/4". I ain't ever in that much of a HURRY, my age! And can do without the rude mess HP coolant makes as well.

That said, it is the APT system's ability to create custom SIZES that lights my fire - either tribe of spade drills.

Small s**t, half-inch and under, my go-to since teen years has been turned and torch-hardened "D" drills and reamers- any size the need dictated, and on-size, not OVER size, thanks.

Large holes, that's just too b***dy tedious.

May as well mount one of the Chandler-Duplex boring and facing heads and pound sand on the side for "a while".

Enter APT. No support for the pilot? That ain't hard to provide, is it?

SonofaMachinist · Feb 9, 2020

Thanx everyone for your input.

Just looking at the size of the taper on the drill was what prompted me to ask. All things considered, I think I will just continue to bore the holes.

The part comes with about a 1" hole. I bore a 2.865" bearing pocket to .900". The 2" was just to get most of the excess material out of the way.

Again, thank you! Glad I asked.

Mohawk Dave · Feb 13, 2020

I vote for annular cutter as well.

Note: I am not a skilled machinist, but do fab and work with heavy metal a lot. I love my annular cutters. I have adapters for just about every which way.

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