taper shank drill question

metalmagpie · Sep 7, 2020

I noticed years ago that you can't find no. 2 Morse taper shank drills larger than a certain size (7/8"?). I surmised that there are limits to the holding power of a taper shank which would be exceeded if a drill larger than that were used.

Now I'm working on restoring an antique drill press with a 3MT spindle and I wonder how large a 3MT drill is commonly found. 1-1/2"? What is the upper practical limit on 4MT?

Info? Insights?

metalmagpie

ChipSplitter · Sep 7, 2020

Nothing comprehensive, but this is about as good a reference as you'll get. McMaster-Carr

You can get reverse adapters like these.......McMaster-Carr ....designed to help Darwinism.

BSCustoms · Sep 8, 2020

We have definitely seen the issue of larger size drills not being available in a 2MT so frequently have to modify the shanks for use in portable mag base drills. We have used up to 2" successfully. I have not seen any sort of info on "limits" of the holding taper, though it has to be out there somewhere.

Garwood · Sep 8, 2020

I don't see how it has anything to do with the drill bit itself.

A machine made with a 2MT taper is going to be very small. Stands to reason anyone with a real small machine is not going to buy larger sized twist drills so why make them?

I have bought a few large Jacobs super chucks used with 1/2" straight shanks on them. Never made any sense to me.

eKretz · Sep 8, 2020

You can use a pretty darn large drill with a small taper if you do it right. Don't try to punch it through in one go, step it out. Obviously this won't fly in a shop looking to optimize speed. In that case, move to a larger machine. For a home shop or field expedient type situation just go easy on the drill so it's not loaded across the entire lip of the drill and it will be fine. And yeah, it's gonna be a pretty low demand item, so you probably won't find many very large drills on small tapers.

Phil in Montana · Sep 8, 2020

I twisted many undersized shanks off in the hbm but with all the tork in the world it is hard to judge hp...Phil

Garwood · Sep 8, 2020

I have a 3.5" 40" long twist drill with an MT6 taper.

I should turn an MT2 shank on it and put it on ebay. Somebody can use it on their sherline right?

Ohio Mike · Sep 8, 2020

I think the largest drill you typically see in 4MT is a 2 inch.

jspivey · Sep 9, 2020

Largest I have in mt3 is a 1.25 and I definitely step it out quite a bit. I would guess that on most lathes, the strength of the taper and tang are not the issue. More likely to shear the key with a big drill in a little 2mt tailstock.

metalmagpie · Sep 10, 2020

Since I started this thread I have found a 3MT drill in size 1.5" but I have no idea if it would work in tough steel. I don't know if I've ever seen a 1" 2MT taper shank drill, but close.

So, roughly, 2MT up to 1", 3MT up to 1.5", 4MT up to 2" is what I'm hearing.

metalmagpie

crossthread · Sep 10, 2020

Sometimes when I am drilling tough material, I put a lathe dog on the shank to keep the drill from spinning in the taper.

Garwood · Sep 10, 2020

I've drilled a lot of holes in 1045 and 4140PH with larger twist drills and never had a problem spinning one. I've gotten a few twist drills with the tangs twisted off. I either weld a new tang on or just turn the shank round and mill a flat. That way it works in a CNC turret or a big Jacobs chuck.

In the lathe, radial drill or HBM I might drill a pilot hole the thickness of the drill bit's web. In CNC use I never drill a pilot hole. They can push a lot harder than the manual machines can and don't care pilot hole or not. many, many times I will save boring time by sharpening a twist drill off center so it cuts a bigger hole. Works like a champ.

Most of my twist drills are MT4. I think I have a 2.5" in MT4. I have spade holders that hold whatever in MT4. So there's no real size limit to what you can do.

MT4 sure seems like the most used, most popular size MT shank size to me.

jariou · Sep 10, 2020

crossthread said:
Sometimes when I am drilling tough material, I put a lathe dog on the shank to keep the drill from spinning in the taper.

How a propos! I got the following in an email yesterday from the Home Shop Machinist magazine.

Dog the Drill by Aaron Kohler

Jacques

Phil in Montana · Sep 10, 2020

That was the old way to drill holes, they made a taper socket with a center and you use a dog to take the tork and the center in the tail stock for the push...Phil

Bill D · Sep 10, 2020

South bend lathe used a mt2 in the tailstock. under one horsepower. My 13x40 lathe with 3hp has a mt3 in the tailstock.
I think the little sears lathe used a mt1 tailstock for around 1/2 hp
Bill D

EPAIII · Sep 11, 2020

I suspect that the matter of limits of the sizes of taper shank drill bits was more or less determined by the users and buyers of those bits. If larger sizes were made and they just sat on the shelves of the suppliers, those suppliers would not order any more and the factories would not make any more.

This is just the "demand" side of "supply and demand" at work. And it functions well.

So for better or worse, correctly or incorrectly, it was determined by your fellow machinists, probably past tense, fellow machinists.

boslab · Sep 13, 2020

Guy from cleave and drills I think said the max bit size was the big end of the taper roughly as the bar gets more economically used, made sense, might have been osbourne tools on thinking,
Mark

PackardV8 · Sep 13, 2020

Most standard drills fall in the range:

#1MT - 3/16" to 1/2"
#2 MT - 31/64" to 25/32"
#3 MT - 51/64" to 1-1/8"
#4 MT - 1-1/6" to 2"

There are a few overlaps, but most outside these ranges are custom.

jack vines

MattiJ · Sep 13, 2020

eKretz said:
You can use a pretty darn large drill with a small taper if you do it right. Don't try to punch it through in one go, step it out. Obviously this won't fly in a shop looking to optimize speed. In that case, move to a larger machine. For a home shop or field expedient type situation just go easy on the drill so it's not loaded across the entire lip of the drill and it will be fine. And yeah, it's gonna be a pretty low demand item, so you probably won't find many very large drills on small tapers.

And with step drilling its much easier to spin the taper if mating surfaces are not immaculate. Lot less axial thrust to keep the taper from spinning.

MattiJ · Sep 13, 2020

Quite moderate shank is enough as long as drilling goes nicely: 1" twist drill needs around 30Nm in mild steel, 8mm or 5/16" mild steel shaft would be enough to drive 1" drill. UNTIL something binds or snags.

If someone is enough interested you can calculate the maximum torque for machine tool tapers:
Principles of Engineering Manufacture - V. Chiles, S. Black, A. Lissaman, S. Martin - Google-kirjat

I'm getting about 30Nm maximum torque from the equation for MT2 taper assuming 4000N thrust. Seem to match pretty well what is available in MT2

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