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View Full Version : I get mixed opinions on lathe drilling tailstock taper protection



Cannonmn
08-12-2016, 08:36 PM
1950's texts I used said you had to use a drill holder (hammer-shaped thing) when doing large-diameter drilling or the torque of the bit's taper might tear up the tailstock taper. The Leblond lathe manual ca. 1980's says just put a lathe dog on the bit to transfer excess torque to the compound. A video on large-diameter drilling put out by U of Wisconsin College of Engineering doesn't show any tailstock protection but recommends peck drilling, which I guess minimizes chance of grabbing.

What's the best method? Also, when using a dog, is it good enough to tighten the clamp screw on the round shank or does it have to catch in the flutes? Here's a current job showing the dog's screw in the drill flutes. Yes that's a poor man's excuse for a 4-jaw Chuck.

https://springfieldarsenal.files.wordpress.com/2016/08/image3.jpeg

firbikrhd1
08-12-2016, 08:48 PM
I certainly don't claim to be an expert, but what I do has always worked.
I use a lathe dog clamped to the drill bit where the drill flutes end. That way if any damage is to be done by the grub screw it won't be where the size of the bit is listed. I let the load be carried by resting the lathe dog on the compound but am careful to not let it apply pressure on the unsupported part of the "T" slot.
I have been looking to some time for a straight tail lathe dog with a capacity of about an inch or so, which I think may be more useful for this operation.

Spin Doctor
08-12-2016, 08:57 PM
well 1-1/32nd isn't very big to start with. I'm assuming the tailstock is a #3 taper. Yes peck drilling is a good idea if for no other reason than to break the chips into more manageable lengths. Myself I've always put the set screw on the section of the screw that has the size on it. Where you have that in the picture is an accident waiting to happen IMO. If excessive torque was transfered to the drill and it started to spin that area is quite hard and could break or shatter. Plus it is a really good idea to use core drills if you can get you hands on them. For deep holes if you are bracing against the compound it is best to have the compound at a right angle to the ways. Also of course it helps to keep the taper clean as we all know. One good idea is to either use a cut off taper drill (or some other piece of tapered tooling) as a plug to keep the crap out. Large two flute drills seem to grab more readily than core drills. I think its because the twist angle is higher and there is a greater tendency to self feed which will cause the taper to come disengaged. If the lathe has enough grunt it will twist the tang right off. Plus certain materials are worse than others. Copper alloys (bronze, brass, Ampco) need a negative rake on the cutting edge of the drill of course plus they pick up heat so fast they not only will expand on the OD but also on the ID grabbing the drill. Plastics will do the same thing. Worst IMO is UMHW.

JoeLee
08-12-2016, 09:56 PM
I can also see the dog transferring some of the force sideways which could help push the drill off center depending on how the dog contacts the surface it's resting on. I would also be concerned about shearing the key in the TS's quill.
A simple solution is to work you way up to the finish hole size.
If I have to drill a 1" hole in something I always pilot and work my way up by at least 1/4" increments.

JL...............

Cannonmn
08-12-2016, 10:01 PM
Thanks, appreciate the info, the Leblond 2E lathe has a #4 taper tailstock.

Lew Hartswick
08-12-2016, 10:40 PM
Our lathes have a #3 Morse tail stock ram and I have only up 1-1/32 bit and all of them have a tang that goes in the slot in the ram so never worried about
the torque. I hardly ever go directly to that large a bit from a center drill, do it a couple of steps.
...lew...

fixerup
08-12-2016, 11:05 PM
My Standard modern lathe tailstock has a MT2 with no tang retainer inside, it would not take too much torque to get the shank spinning in the taper. I used a reamer to try to repair the taper but didn't have much luck, when ever a drill grabbed really hard it would spin in the shank again. I though of using a lathe dog but never did, maybe because I don't have one :) after reading the previous posts, i will make and used a lathe dog next time the opportunity arises it will definitely prevent further damage to my tailstock taper.
One concern I had, is the friction of the lathe dog dragging on the top slide, so I will put a slippery plastic in between the two.
Cheers!
Phil

J Tiers
08-12-2016, 11:15 PM
No matter what anyone says, it is a very good idea to use a dog, or other device to prevent rotation.

The setscrew can go on the round part, because the round area is generally not hard, and the setscrew will hold better. On a hardened section, it is likely not to hold, and then let the drill spin as he dog is spun up the flutes like a nut. I have never had the setscrew be inadequate.

As for the tang, that's a "maybe".

In the first place, the tang can break off, I have a drill with a half tang, broken and twisted-off. Then also, what is holding the tailstock ram? There is some form of key, but in many machines, what looks to be a substantial key is actually held in place by one little "stem", the key is not sunk into the tailstock housing itself, other than just the one little stem.

Possibly if there is a full length key, grooved into both the ram and the housing, that might be able to handle the torque of a heavy chuck plus workpiece, plus drivetrain, as the drill gets stuck and attempts to stop all that in a fraction of a turn. You could figure out the peak foot-lbs, and I bet it is significant.

rohart
08-12-2016, 11:30 PM
I generally go up in steps, but I agree with JTiers' worries that a key holding the tailstock ram may be less substantial that I imagine.

Well, I kill two birds with one stone. If I use a standard MT3 taper arbor in my tailstock, bottomed out I lose a good inch of workpiece length. That is important on the occasion I want a long workpiece, but also increases the hangout, which reduces the travel of the tailstock screw.

So I cut the tang and an inch or so off all my drill arbours. The chuck bottoms out much closer to the tailstock body, giving me back the full travel, and it also allows the arbour to spin in the tailstock if the drill snags.

If the drill snags, it is because it is suddenly pulled into the workpiece, so when it and the arbour spins in the tailstock the taper has already left its seat, so there is no danger of any damage being done to the surface of the taper. I just wind back, unwind drill and chuck from the workpiece and slap the arbour back into the tailstock a little harder.

justanengineer
08-13-2016, 01:40 AM
Unless youre drilling above 2" I wouldnt worry about it. Even if you are, you can help prevent the drill grabbing by feeding it fast/hard and making big jumps between drill sizes.

Cannonmn
08-13-2016, 03:23 AM
Thanks, interesting. This has got me wondering about the exact original purpose of the hammer-shaped drill holders, which btw I can't seem to find being sold anywhere today. They consist of a Morse taper socket with a center hole in the end opposite the socket ("head" of hammer shape.). The heavy steel "handle" part is at right angle to the head and is maybe 10" long. Socket has a drill tang slot at the end. These would be most useful when you need to drill using a bit with a taper shank larger than your tailstock taper, because nothing goes in tailstock but a dead center. You manually hold the drill holder with its center hole on the dead center, start the drill on the pilot drill hole, and let the handle lie on the compound for support. I've used them like this before and it sounds clumsy but works well.

J Tiers
08-13-2016, 08:45 AM
Unless youre drilling above 2" I wouldnt worry about it. Even if you are, you can help prevent the drill grabbing by feeding it fast/hard and making big jumps between drill sizes.

THAT sure is a generalization....one size fits all..... NOT...... Fine advice for a 20 inch Monarch. Not so good for a 10" Southbend.

My tailstock taper is good. Yet, I have had the drill yanked out and spun even after setting it ẃith a copper hammer, and that with 5/16 drill in the MT2 taper and a clean taper on the drill.

It happens. Using a dog when the drill is bigger than the small end of the taper shank is a good plan.

2" forsooth.....

JCHannum
08-13-2016, 10:46 AM
The drill holders were manufactured by companies such as Williams and Armstrong. I have one I acquired at some point, but have never used. I doubt they were a big seller for a couple of reasons, they take up a lot of the bed length, the idea of hanging on to a two foot long bar powered by a multiple horsepower driver is a recipe for disaster.

The lathe dog on the compound is simpler, cheaper and safer. If you have concerns about wear to the compound, it is easy to follow the progress of the dog with the hand feed.

Edwin Dirnbeck
08-13-2016, 06:49 PM
I have been driving lathes since 1954. The only time I ever used a dog was when the drill tangs were completely torn off . In your picture ,it appears as if the dog is about 45 degrees from horizontal.I allways tried to rest the dog tail on a toolholder so that it was in a more horizontal position. Edwin Dirnbeck

GEP
08-13-2016, 07:09 PM
Never clamp a dog in the flutes always on the part of the drill

J Tiers
08-13-2016, 07:44 PM
Edwin D:

Most of the smaller lathes (Atlas, Southbend, some Sheldon, Logan, etc) have no slot for the tang, and even if they did, they often have a very small key, possibly only a rod of perhaps 3/16", to prevent rotation of the quill.

boslab
08-13-2016, 08:10 PM
A clean socket really helps
https://www.cromwell.co.uk/shop/spindle-nose-and-workholding/taper-socket-cleaners/no-1-morse-taper-socket-cleaner/p/KEN4068010K
Mark

RWO
08-14-2016, 01:24 PM
Years ago I milled a 1/4"wide x 1/2" deep slot in the face of the tailstock ram. I then installed a short .230" dia. pin in the drill chuck arbor to enter the slot when the arbor is fully seated in the #2M taper. Never had a problem since. Of course, the drill torque is now carried by the ram's anti-rotation key, but on my 1988 Jet there has been no apparent damage. However, I always step drill when going over 1/2" in steel.

RWO

BCRider
08-14-2016, 03:25 PM
Edwin D:

Most of the smaller lathes (Atlas, Southbend, some Sheldon, Logan, etc) have no slot for the tang, and even if they did, they often have a very small key, possibly only a rod of perhaps 3/16", to prevent rotation of the quill.

Yep, that can make working with big cuts from large drills rather desctructive.

When I've done my own larger size drilling up to 1 1/4 (I don't have anything larger) I've always gone with the idea of using 3 or even 4 intermediary steps in size. This has occasionally resulted in the bigger sizes pulling into the work and coming loose but when set again with a lead hunk instead of just by hand they always stuck. I'm thinking now that I've mostly been lucky that they stuck from reading some of the stories in this thread.

And FWIW my 12 x 36 Chinese made lathe doesn't have a slot for the tang either. At that size I'm thinking that some may and some might not have a slot.

And now that you make me think about the load on that small key for the ram I'm thinking I might just use a dog on the bigger sizes in the future. And a packing bar so the dog is more or less level. GEP is more than right about the lift that would occur with as strongly angled a dog as shown in that picture. That force along might be enough to add to the other forces and cause the drill to fail.

I'd be leery of using the screw in the flute as well. IN fact I don't really like the idea of the V on the other side bearing down on the edges of the other flute either. If we don't want to screw it down at the reduced collar with the size label I'm thinking that grinding a small flat for the set screw between the information collar and the beginnings of the fluting is a better way to go. So no damage to the size collar info and a better grip for the dog to work with as well as the dog isn't putting any pressure on the somewhat brittle flutes at all.

Lots of good information to consider from this thread. Good topic!

Rosco-P
08-14-2016, 04:15 PM
Edwin D:

Most of the smaller lathes (Atlas, Southbend, some Sheldon, Logan, etc) have no slot for the tang, and even if they did, they often have a very small key, possibly only a rod of perhaps 3/16", to prevent rotation of the quill.

The tang on a taper shank drill isn't there to drive the drill, it's there to eject the drill from the machine. The interference fit between the tapers drives the drill. At least that's what I was taught in the machine shop classes I've taken.

https://en.wikipedia.org/wiki/Drill_bit_shank
http://www.vikingdrill.com/Regular-Taper-Shank.php

BCRider
08-14-2016, 04:46 PM
In a drill press I've never seen a quill that did not have a slot to take the tang. If it was not there to act as a rotational stop if the taper slipped then it would be a deeper hole instead of the narrow through slot. And the blade like tang would be simply a round knob that the wedge could bear against. So it may be one of those cases where theory in texts and classes is one thing but somewhat worn machines that need to keep on running is a different issue.

Why a lot of lathes do not mimic that same method is a mystery to me. Perhaps because the ram on the tail stock IS only keyed with a small pin it's a safety factor. Better to let the item spin than to shear off and gall to destruction the ram, pin and likely the tail stock casting.

becksmachine
08-14-2016, 05:19 PM
Mixed opinions? Well yes, this opinion will mix them some more I am sure!

I am not sure exactly where I would draw the line as to using/not using a pilot drill, but I do know I have a much different perception than many on this forum. I am sure it is affected somewhat by the weight/size of machines that I use daily, but I believe the same principles apply.

I cringe whenever I read of someone recommending using steps of 1/4" when drilling a 1" - 2" hole in an attempt to be "easy on the machine", and sometimes in the same post worrying about scarring the taper of whatever is holding the drill in the machine (chuck, taper shank drill etc.) when the shank spins in the tapered hole of the quill.

The ability of any tapered shank to resist torque is in direct proportion to the thrust pushing the shank into the hole. Yes, it is possible to give the tapers an initial "set" by whacking the point of the tool with a brass/lead/wood hammer but this will not equal the "seating forces" of continuous axial pressures that are applied when the tool is vibrating and being pushed sideways by forcing it into a virgin workpiece.

When using a standard HSS twist drill, these axial forces are in large part required to force the chisel edge of drill into the workpiece. These relatively heavy forces also tend to limit the penetration of the lips of the drill into the workpiece thus keeping the ratio of torque to thrust relatively "low".

However when drilling into a pilot hole, this ratio of torque to thrust is turned on it's head. Not only is there less axial pressure forcing the two tapers together, but since it takes less thrust to make the lips penetrate the workpiece, many (most?) operators will take advantage of this to twist the wheel faster and thus increase the torque required to twist the drill because of the greater penetration of the lips of the drill.

As for the tang of the drill resisting the tendency of the shank to spin in the socket, this is also a matter of the wildest conjecture. The tang on a 1/4" drill with a #1 or #2 taper has a pretty fair chance of resisting the torque required to break the drill even with no help from the taper. The tang on a 3" drill with a #5 taper, well, not so much. And this is, I think, a most reliable indicator of the separate functions of tangs and tapers, as I routinely use this 3" drill to drill from the solid and have no trouble at all twisting tangs off the shank, and this is where you might reasonably expect this to be a problem, given the relation of shank size to drill size.

The only truly reliable method that I have ever seen to prevent a (probably ill fitting) taper shank from spinning in it's (probably ill fitting) socket was called a "use them up" modification to the shank and corresponding socket. This involved milling or grinding a full length flat on the exterior taper that then required a correspondingly modified socket for the shank to fit into. As you might imagine, this did nothing to accentuate the concentricity of said shank in said socket, but it sure as hell guaranteed that the shank would twist off the tool before it spun in the socket!

This leaves out entirely the stress placed on any means of preventing quills or spindles from undesired rotation. Or driving quills and spindles to achieve desired rotation. Or stress required to achieve the forces needed to force the drill into a virgin workpiece.

YMMV, Dave

J Tiers
08-14-2016, 05:46 PM
The tang on a taper shank drill isn't there to drive the drill, it's there to eject the drill from the machine. The interference fit between the tapers drives the drill. At least that's what I was taught in a the machine shop classes I've taken.
...

Which is exactly what I also say..... have said many times, and have gotten thoroughly jumped on for it..........

HOWEVER.....

If you DO manage to loosen the drill in the socket (and I TOTALLY agree with "Becksmachine" on step drilling), the tang will likely stop it spinning, assuming the forces do not break off the tang.

What Dave (becksmachine) says is 100% right on.

If you step drill in small increments (and I see people recommend as small as 1/16" size increments) you are doing no favors.

1) You wear and try to break the edges off the drills, as the drill "snags" in a way similar to what happens as you break through on somewhat ductile material.

2) The drills rarely start well, and may run off-center after a bad start if the drill does "snag" and get forced to one side of center

3) You are keeping the highest torque part of the drilling, so much for being "easy o the drill or machine".

4) The drill is very likely to snag and then try to "screw into" the material, with it's flutes as the "thread". This will pull the drill out of the taper socket, usually. With just to outermost part cutting, there is nothing to moderate this "pull", as there is when the drill is also cutting near the center.


Taper drills, as Dave point out, are different. They NEED axial force to seat, and to prevent the drill being yanked right out of the socket.

And, even of you use a chuck in the tailstock, IT seats in a taper, so you still have the same deal as a taper shank drill. It can be yanked out, spun, etc. So step drilling in tiny steps is just a bad idea all around.

If you want to do step drilling, drill a pilot the size of the chisel point on the final drill. This will reduce the force needed, by eliminating the need for the final size drill to have it's chisel point driven into the material. But it leaves plenty of material left for good seating force, to control self-feeding and prevent the drill from spinning in the socket. Then put in the final size drill and drill the hole.

BCRider
08-14-2016, 06:45 PM
I cringe whenever I read of someone recommending using steps of 1/4" when drilling a 1" - 2" hole in an attempt to be "easy on the machine", and sometimes in the same post worrying about scarring the taper of whatever is holding the drill in the machine (chuck, taper shank drill etc.) when the shank spins in the tapered hole of the quill.

Dave, I do agree with you in principle. But the reality is that a lot of us hobby types don't have a machine that can hog out that much material and that will not flex like a wet noodle at that sort of pressure on the quill.

When I've done my own big size drilling in my fairly modest 3 inch column machine if I tried to run a 1/4 or 3/8 pilot and then drill a 1 inch hole directly I get a lot of visible flexing from the pressure needed to keep the 1 inch drill biting well. To avoid that I had to run a 1/4 pilot then a 5/8 and finally the 1 inch. That resulted in no visible flex and a hole that didn't rub the drill heavily due to spring back when being withdrawn.

But as you mentioned if I tried to run it up in 1/4 size increments then I did in fact have issues. I tried it in an effort to avoid the flexing in the machine but as you note it pulls the drill loose. Not DURING the cut but when I try to disengage to clear the chips and add some lube in a deeper hole I was doing that's when it let go. I switched to the 1/4, 5/8 and final 1 inch and didn't have any more issue and the downfeed pressure was tolerable to the modest amount of meat in my drill press. The tang on the 1" took a good whack on the wedge to break it loose too.

Paul Alciatore
08-14-2016, 07:37 PM
There is much food for thought here. For perspective, I have a SB9; not the most powerful or sturdy lathe in the world. But a good machine. After reading the comments here, I do intend to take the tail stock apart and see just what is in there to prevent the spindle from rotating. I will do that, but not today.

Becksmachine makes a lot of sense. I tried drilling in small steps and quickly gave up on that. As he says, it is an invitation for the drill to dig in and grab. At the most, I would drill a small pilot hole and then step up to full size. In the future I will keep that pilot hole smaller than the web thickness of the full size drill, perhaps half of it.

OK, I agree with Becksmachine. But then BCRider also has a point in post #21. I have thought about this previously. If a tang is not to prevent rotation, then why is it shaped the way it is? I had a taper adapter that did not have a tang. I put it on a drill chuck and mounted it in my SB tail stock and drilled some holes. Then I tried to remove it. The fact that it did not have a tang meant that backing up the feed screw did no good: there was nothing there for the center tit to push against. I eventually did get it out, but I immediately modified it so that I would not have that problem again. Did I create a tang shaped piece to add to it? NO, I did not. It was completely obvious that all that was needed was a central, ROUND pin. I turned one, drilled a hole in the adapter, and used Loc-Tite to hold it in. And it worked perfectly.

In a drill press spindle the tang shape is also not needed for a tapered key to be used to eject the taper. If you just make the taper itself a bit longer, the tapered key will work just fine for ejection. This will be easier to make, stronger, and cheaper than a tang.

So, WHY go to all the trouble of designing and machining a flat tang on the end of a taper? And of creating a matching pocket in the spindle of, at least some, drill presses? WHY? I ask those of you who do machining for a living to give me a rough estimate of the increased cost of making these features on the tapers and in the spindles of the DPs. I bet it will not be cheap. So, WHAT purpose does all this extra effort and expense serve? The only possible answer to that question that I can see is that the tang IS there to prevent rotation. I defy any of you to come up with another purpose for it in light of the additional expense required.

My conclusion is that the tang is there to prevent the drill from spinning in the taper. It works just fine for small diameter drills. A 1/16", a 1/8", a 1/4" and probably even a 1/2" twist drill will break long before the tang on even a #1 Morse taper would. But then the drills got bigger and bigger. The drill presses also got bigger and more powerful to allow the use of those bigger drills. And the bosses/bean counters got more demanding in the amount of work expected in an hour. So the machinists pressed the DPs and drills to the limits and beyond and some tangs broke. When that happened those machinists concluded that the tangs were not adequate for preventing slipping. And they were right, at least for those bigger drills and more powerful DPs. I am sure that broken tangs on 1/8" drills were almost non existent. The machines and drills had just outgrown the original design. But that does not change the original purpose of the tang: to prevent slippage.

I am sure that all this took time. Some of the machinists who experienced tang breakage became instructors and they rightly or wrongly warned their students about the problem. The original intent of the tang was lost in the process.

My suggestion is to know your equipment and it's limitations. If you have a tail stock where the spindle is restrained from spinning by a small pin, then please do use some additional device to prevent the drill from spinning in the taper. On the other hand, if you are drilling a 1/16" or a 1mm hole, you don't have to sweat it. That would be OK even on my Unimat which is about a 2" x 6" lathe. The tail stock uses a threaded chuck, but the spindle is sturdy enough for fairly large hole drilling. Heck, I have drilled 1/2" holes using the tail stock on the Unimat and that is roughly equivalent to over 2" diameter on the 9" SB.

Another suggestion I would make is to use drills where the rake angle has been reduced. This would be a gun style drill or a standard twist drill with the rake angle reduced by grinding the cutting edges like you would do for drilling brass. Then you can use a smaller feed rate with no danger of the drill grabbing. A smaller feed rate means lower cutting force, less torque, and therefore less chance of breaking anything. A final suggestion is to use a cutting fluid with good lubrication properties and use plenty of it. Back the drill out often to allow it to lubricate the cutting edge: in other words, peck drill.

JCHannum
08-14-2016, 08:06 PM
The tang is called a driving tang by Morse, the originator of the Morse Taper. The reason for that can be twofold.

I do not know the full history behind the original use of the MT system, but suspect it was first used in drilling machines, then added to lathes. In a drill, with a solid spindle there is no means to get behind the MT to eject it, thus the slot in the drill press spindle to permit the use of the drift to eject. There is no need for this feature in a tailstock spindle as the feedscrew can be employed to jack it out. The drift will work equally well with or without the tang, so I question the need for it if not for added resistance to rotation. Smaller lathes typically lack the flats, larger machines often do.

The choice of means of restraining the MT tooling from rotation is up to the user, with the caution that many smaller lathes do have a very small key to prevent spindle rotation and might not be up to handling the torque of a large drill bit.

J Tiers
08-14-2016, 08:27 PM
"Driving tang" can easily be "driving-out tang"... not necessarily meaning the tang drives rotation.

That said, I am sure it does on occasion take some torque. Why wouldn't it? It does not "know" it isn't supposed to need to.....

Why the tang shape?

I think that is actually quite simple.

1) It only requires a smallish slot in a solid part of the drilling machine spindle. The slot does not damage the strength much, and it is quite easy to make, just an end mill operation. It is fairly non-critical as to size of tang, also, the wedge accepts a wide variety of tang sizes, even broken-off ones.

2) The slot aligns the wedge, and allows a simple flat wedge to do the job. Easy to make the wedge with just a saw and a file. or forge it if you are a blacksmith, which is who had lots of drill presses at the time.

3) If a drill is not seated well, the tang will allow it to avoid spinning until pressure of cutting seats it and takes the torque by friction.

TN Pat
08-14-2016, 08:45 PM
Well... here's how I look at it. The tang is there to keep the tool from spinning. You shouldn't step-drill in 1/4" increments. If your machine is that weak - and I understand totally, my home lathe is a little 6" Craftsman - you'd be better off opening the hole with a boring bar and not worrying about all this stuff.

On that same note, though, as I said, I have a 6" Craftsman lathe. Of the Atlas variety. It has an MT1 tailstock - and I use up to 1/2" drills, using a drill chuck with no tang on the arbor - this lathe has no tang socket.

It is due to a lack of power that I pilot drill. If I'm using a 1/2" drill, I do pilot with a 1/4". I would not use any larger drill on this little lathe, mainly as it wouldn't have the power or rigidity to take it. If I need a bigger hole, I break out a boring tool.

Professionally, I've used lathes with MT4 and MT5 tailstocks. If I drill a hole larger than 3/4", I'll pilot, mainly due to not having the power to crank the handle for a larger drill! But I'll go from a 3/4", to a 1-1/2", to 2-1/8", in 30 Rc 4140... hard enough you need a wrench on the handle nut to get any torque!

I wouldn't put a lathe dog on a drill myself. If I was that worried about it, I would - as I said - start boring. I feel that if you have the HP to entertain using a 2" drill, you'd do just as well to peel out .100 at a time with a big bar. Ah, granted, that may not be possible with a deep hole, but - I digest.

JCHannum
08-14-2016, 09:24 PM
The design and shape of the slot and drift for MT ejection is clear enough. As I point out, however, the tang itself is not needed for ejection. Its presence adds several steps to the machining of the shank as well as increasing the cost of the tooling. If its main purpose was ejection, an extended, reduced diameter nub on the shank would suffice. It is absent on much MT tooling, but present on all drills. MT is the only taper used for drills.

Rosco-P
08-14-2016, 10:01 PM
FWIW, this doesn't cloud nor clairfy the issue: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3779551/

J Tiers
08-14-2016, 11:01 PM
The design and shape of the slot and drift for MT ejection is clear enough. As I point out, however, the tang itself is not needed for ejection. Its presence adds several steps to the machining of the shank as well as increasing the cost of the tooling. If its main purpose was ejection, an extended, reduced diameter nub on the shank would suffice. It is absent on much MT tooling, but present on all drills. MT is the only taper used for drills.

The tang is absent on ANY tooling that uses a drawbar, for reasons that should be obvious with a few seconds of consideration. Since the drawbar simply acts to ensure the taper is solidly held, it should be pretty obvious that the forces are expected to be handled by friction. All that is needed is for the taper to stay in place.

Lathe tooling has been standardized without the tang. such that the ejection normally occurs (on SB, Atlas, etc) at about the point the ram is flush with the end of the T/S. A tang fouls that up, pushing the ejection point farther out, and limiting the ram travel.

Some MT drills DO NOT HAVE A TANG, contrary to the statement quoted. I have one or two that just have a narrow pin in that position, which is generally in the form of the tang profile, but is round, and can not in any way provide any torque enhancement whatsoever.

It seems pretty obvious that while the tang CAN provide torque, it is not included primarily for that purpose, the taper is intended to do that. It is a "self-holding" taper, and can seize the drill shank so tightly that it is difficult to get it out at all. I've had to bore out a center, and chip the case hardened shell out of the taper. I used to have a hollow piece I removed intact while getting a center out of the taper (no it was not rusted).

BCRider
08-15-2016, 02:35 AM
I'm thinking it's not as easy or obvious as it looks.

In the case of a drill press it would be simplicity itself to drop the tang altogether and just move the quill slot down so it exposes the narrow end of the MT shank. The shank being given a slightly reduced size button end to take the tapered drift so the taper doesn't bruise the edge of the taper. This would be both easier to produce at the same time as the rough shaping of the taper and drill and slightly cheaper overall since the material used for the longer tang could go into making another whole drill bit about every 20 to 30 drill bits worth of rod stock. But mostly it would avoid the need for any milling operations.

With a draw bar retained taper it's simplicity itself to generate a far more solid locking torque than we can achieve with a hand rammed taper such as found on a drill press. Something the taper fit only with a drill press cannot do. So this leads me to agree with the point JTiers makes when he posted;


3) If a drill is not seated well, the tang will allow it to avoid spinning until pressure of cutting seats it and takes the torque by friction.

In my reply I certainly did not intend to in any way suggest that the tang is intended to perform the driving function as a main and primary option. If I did then I'm sorry.

But with the design of the flat tangs and drill press quills being what they are it seems to me that SOME degree of driving is the intent of the drill and press makers even if it is only to limit the amount of slip that can occur until the pressure can re-lock the taper. I feel it's there to avoid the galling that would otherwise occur and which could ruin the quill of the drill press. A rather costly result if that were to occur.

In the case of the tail stock taper we are feeding the drill in with a screw run by a hand wheel. So the ram cannot jam forward in the same way that the quill in a drill press can. Or at least it would require a rather heavy handed operator to ignore a spinning drill and force the ram onto the loose and spinning taper.

So perhaps that's the difference. It's too easy to push the quill down onto a loosened taper and cause damage so we use the flat tang in the driving slot to limit the amount of spin until the taper can be re-locked. But on the lathe ram the drill bit will tend to break free and jump forward and away from the sort of pressure contact that would produce the galling damage. And the expectation is that the lathe operator would recognize this issue and retract the ram instead of advancing it into the taper to try to re-lock the drill or chuck taper.

RB211
08-15-2016, 09:46 AM
I'd sooner use a boring bar to enlarge a hole than a large drill bit

JCHannum
08-15-2016, 10:00 AM
I never mentioned drawbar tooling. Obviously MT collets and other drawbar tooling does not require, nor an use a tang. There is other quite common MT tooling that does not incorporate a tang. The most common examples being centers and any other tailstock tooling that does not require restraint from rotation lack the tang.

While I won't question their existence, I have never seen MT drills as you describe that were not a shop modification of a damaged tang. They must be few and far between for a reason.

It would be interesting to see in the original patent if any mention was made on the purpose of the tang. Absent that we will have to assume and presume and it is difficult not to believe that it has some function in preventing rotation. In the best interests of maintaining the bore of your tailstock spindle, it is not a bad idea to provide some supplemental means of restraining the drill from rotation. The dog, properly applied is as good as any.

RB211
08-15-2016, 10:22 AM
Tangs are for drift punches used to remove the mt tooling from spindles on drill presses. Thats what the slot in spindles are for. On lathes, retracting the tailstock pops them out. Certain spindle designs have slots that the tang slips into to prevent rotation.
I am not certain why this discussion is even heated? On a lathe, your supposed to use a boring bar for large holes, not stress out the tail stock.

J Tiers
08-15-2016, 10:27 AM
I never mentioned drawbar tooling. Obviously MT collets and other drawbar tooling does not require, nor an use a tang. ...

And why would that be? The collet might hold a fly cutter, or the taper might directly hold an R8 face mill, with a larger diameter, and more torque, than many drills. It would seem that there would be MORE need for secure holding against rotation, and the drawbar itself has next to no direct holding effect on the taper, it is threaded, and naturally turns without much resistance.

Presumably a drawbar is effective because it ensures the axial pressure that quite effectively holds the taper against the torque of whatever tool is involved, end mill, large diameter shell or face mill, fly cutter, drill, etc.


I'd sooner use a boring bar to enlarge a hole than a large drill bit

Drilling is about the most efficient metal removal method there is, on an energy per cubic inch basis. That seems to be a well-known fact that most any text states. So actually, if you can do it, drilling would be the best way to make a hole, small or large.

Not that is is appropriate in every case. It isn't not very precise, neither as to location, nor as to size. And there isn;t much to a hole beyond location and size.... depth is about all that is left. But to get rid of material, ready to finish up, drilling is pretty good. Or if your tolerances are not too narrow.

JoeLee
08-15-2016, 10:32 AM
Mixed opinions? Well yes, this opinion will mix them some more I am sure!

I am not sure exactly where I would draw the line as to using/not using a pilot drill, but I do know I have a much different perception than many on this forum. I am sure it is affected somewhat by the weight/size of machines that I use daily, but I believe the same principles apply.

I cringe whenever I read of someone recommending using steps of 1/4" when drilling a 1" - 2" hole in an attempt to be "easy on the machine", and sometimes in the same post worrying about scarring the taper of whatever is holding the drill in the machine (chuck, taper shank drill etc.) when the shank spins in the tapered hole of the quill.

The ability of any tapered shank to resist torque is in direct proportion to the thrust pushing the shank into the hole. Yes, it is possible to give the tapers an initial "set" by whacking the point of the tool with a brass/lead/wood hammer but this will not equal the "seating forces" of continuous axial pressures that are applied when the tool is vibrating and being pushed sideways by forcing it into a virgin workpiece.

When using a standard HSS twist drill, these axial forces are in large part required to force the chisel edge of drill into the workpiece. These relatively heavy forces also tend to limit the penetration of the lips of the drill into the workpiece thus keeping the ratio of torque to thrust relatively "low".

However when drilling into a pilot hole, this ratio of torque to thrust is turned on it's head. Not only is there less axial pressure forcing the two tapers together, but since it takes less thrust to make the lips penetrate the workpiece, many (most?) operators will take advantage of this to twist the wheel faster and thus increase the torque required to twist the drill because of the greater penetration of the lips of the drill.

As for the tang of the drill resisting the tendency of the shank to spin in the socket, this is also a matter of the wildest conjecture. The tang on a 1/4" drill with a #1 or #2 taper has a pretty fair chance of resisting the torque required to break the drill even with no help from the taper. The tang on a 3" drill with a #5 taper, well, not so much. And this is, I think, a most reliable indicator of the separate functions of tangs and tapers, as I routinely use this 3" drill to drill from the solid and have no trouble at all twisting tangs off the shank, and this is where you might reasonably expect this to be a problem, given the relation of shank size to drill size.

The only truly reliable method that I have ever seen to prevent a (probably ill fitting) taper shank from spinning in it's (probably ill fitting) socket was called a "use them up" modification to the shank and corresponding socket. This involved milling or grinding a full length flat on the exterior taper that then required a correspondingly modified socket for the shank to fit into. As you might imagine, this did nothing to accentuate the concentricity of said shank in said socket, but it sure as hell guaranteed that the shank would twist off the tool before it spun in the socket!

This leaves out entirely the stress placed on any means of preventing quills or spindles from undesired rotation. Or driving quills and spindles to achieve desired rotation. Or stress required to achieve the forces needed to force the drill into a virgin workpiece.

YMMV, Dave Your welcome to treat you machine any way you like!!!!

I cringe when I hear of some one trying to force a large dia. drill through a piece of work because they may think it takes too long to drill in steps.
Know your machine's capabilities.

JL................

JCHannum
08-15-2016, 11:35 AM
Well, duh...., drawbar tooling does not use a tang because the drawbar occupies the tang location.

MT & B&S collets are notoriously poor end mill holders as they do not exert enough pressure and are generally limited to around 1/2" shank tooling. That is why the R8 was developed. It is not the be all and end all, but offers an improvement. Non-collet MT & B&S drawbar tooling can be seated much more positively and with more pressure by the action of the drawbar as opposed to seating with the downfeed or a hammer smack. It would seem that the drawbar offers more secure retention than the tang in those cases that require it.

Carm
08-15-2016, 11:47 AM
I'd sooner use a boring bar to enlarge a hole than a large drill bit

On a pea shooter lathe, absolutely.
Or learn how to trepan and let power feed do the work.

Anyone using the tang on morse tools to drive them must have buggered sockets.
If it was supposed to drive w/tangs why bother with a taper.

BCRider
08-15-2016, 01:05 PM
.....MT & B&S collets are notoriously poor end mill holders as they do not exert enough pressure and are generally limited to around 1/2" shank tooling. ......

It's quite the opposite actually. The narrow angle can grab the tool shank like no one's business. The issue is in releasing the collet from the quill. The self locking angles used on the MT and B&S tapers become so tight when pulled in to hold the tooling that it's a bugger to beat or press them loose. As I understand this stuff and read the history of them the R8, ER and BT series tapers were introduced because they use non-locking angles in an attempt to produce "enough" hold on the tooling while ensuring centering and easing the issues of tooling swaps.

And too Weldon shank tooling was intended to be secured with a set screw in an appropriate holder. It seems to be a relatively recent thing that we rely on split collets to hold these items. Where the MT and B&S arbors work well is when we are not using split collets.

The old mill/drill I had used MT3 arbors and collets. A couple of times that I tried the collets instead of a set screw holder I found that the taper locked up in the quill so well by the time I could not turn the end mill that I feared for the health of the quill bearings. I tended to stick to my home made short overhang holders with set screws after that whenever I could.

J Tiers
08-15-2016, 02:36 PM
Well, duh...., drawbar tooling does not use a tang because the drawbar occupies the tang location.

....

Not quite.....

My question to you (which I answered, if you had read a few more words) is why the drawbar and taper does not need any tang "to keep it from spinning", despite it being the stem on a 3" face mill (or similar item) that is far larger diameter than any credible drill, and yet is not being spun in the taper..... The taper does not "know" what it is connected to, it only "knows about" the torque it must transmit, so the general run of forces due to cutting is similar in the case of drills or face mills, except face mills tend to add some impact..

BCR has it right....

And, the 1/2" shank is generally due to the common MT2 not physically fitting a larger shank. MT3 collets go up to 3/4", again about the max that fits. They grab tightly. I had to make special drawbars that "eject" the collet as I turn the back of the drawbar with wrenches. Pops the collet loose without pounding with a hammer and swearing. Still takes a bit of force, but I hated the pounding.

BCRider
08-15-2016, 02:43 PM
Not quite.....

My question to you (which I answered, if you read a few more words) is why the drawbar and taper does not need any tang "to keep it from spinning", despite it being the stem on a 3" face mill (or similar item) that is far larger diameter than any credible drill, and yet is not being spun in the taper..... The taper does not "know" what it is connected to, it only "knows about" the torque it must transmit.

I gotta agree with that too. If drill presses used a drawbar there would be no need at all for the flat tang. It would be super easy to consistently produce the locking tension needed to easily hold the chucks.

JTiers, I'm thinking that you hit the nail on the head with your item 3 about the tang in the quill slot being more of a damage avoidance feature that holds the arbor until the taper can get locked again.

If drill presses suddenly came out with draw bar equipped quills it would be "good riddance" to the flat tangs and taper drift slots.

Tundra Twin Track
08-15-2016, 02:48 PM
Unless youre drilling above 2" I wouldnt worry about it. Even if you are, you can help prevent the drill grabbing by feeding it fast/hard and making big jumps between drill sizes.

X2 on that!

Paul Alciatore
08-15-2016, 02:52 PM
You argue that tapers that use drawbars do not have tangs and that means that only the taper itself is responsible for preventing rotation. I would say that a tang is impossible with a drawbar. Either a central hole is needed on the taper for female threads or the small end of the taper will have external threads (a rare situation) which would normally require the full circumference. So there is no place to put a tang. And in this case, the case of using a drawbar, the tang is necessarily absent and the ONLY THING LEFT for preventing rotation is the taper.

And in the case of a drawbar being used, the drawbar will hold the taper together a lot better than would be possible without it. So, that taper will have a much greater capacity to resist rotation. So, it works.

But you can not use this to argue that the lack of a tang with drawbar operated tapers is proof that the tang in not intended for resisting rotation.

You say that lathe tooling has been standardized without the tang. Perhaps it is that way on some machines, but not on others so I doubt that it is "standardized". As I stated above and contrary to what you say, my SB tailstock will not eject a taper that does not have a tang or some similar protrusion at the small end of the taper. I learned this the hard way. And I find it strange that many lathe makers would build their tail stocks in a manner where tapers with tangs could not be used as your suggested standard would require. Perhaps yours is that way, but I doubt that many others are. Perhaps yours was modified by a former user.

Others have suggested that the tang shape is due to the ease of using an end mill to cut the slot in a quill. That is part of it, but if the ONLY reason for the tang shape on the end of the male taper is for ejection with a taper key, then it still represents a lot of wasted effort. A round nub would work just as well with the identical geometry in the DP quill. Millions, tens of millions, probably hundreds of millions of Morse tapers have been manufactured with the flat shape for the tang. I suspect it was originally done with milling cutters. Later most of them were probably forged. But in either case, it represents a lot of extra work which would be for absolutely no reason if not for the idea of using it to drive the drill. In the multiple decades since the Morse taper was invented, someone would have said, "We can save money by eliminating that tang shape and just use a round nub there." Someone? Heck, many, many someones would have. It would have been a riot of someones. The tang would never have survived WWII if it had no purpose beyond ejection. The standard would have been changed at that point in the interest of efficiency for the war effort.




The tang is absent on ANY tooling that uses a drawbar, for reasons that should be obvious with a few seconds of consideration. Since the drawbar simply acts to ensure the taper is solidly held, it should be pretty obvious that the forces are expected to be handled by friction. All that is needed is for the taper to stay in place.

Lathe tooling has been standardized without the tang. such that the ejection normally occurs (on SB, Atlas, etc) at about the point the ram is flush with the end of the T/S. A tang fouls that up, pushing the ejection point farther out, and limiting the ram travel.

Some MT drills DO NOT HAVE A TANG, contrary to the statement quoted. I have one or two that just have a narrow pin in that position, which is generally in the form of the tang profile, but is round, and can not in any way provide any torque enhancement whatsoever.

It seems pretty obvious that while the tang CAN provide torque, it is not included primarily for that purpose, the taper is intended to do that. It is a "self-holding" taper, and can seize the drill shank so tightly that it is difficult to get it out at all. I've had to bore out a center, and chip the case hardened shell out of the taper. I used to have a hollow piece I removed intact while getting a center out of the taper (no it was not rusted).

Paul Alciatore
08-15-2016, 03:09 PM
I have one more thought on the broken tang phenomenon. I would suggest that one reason for a tang to break is when the taper starts to slip and there is some rotation before the tang hits the slot. This means that the taper was not assisted by the tang in resisting the forces of drilling. So the taper loses it's grip and only a short time later does the tang get into the position where it can try to take over this task. So, it too must resist those forces by itself. If the drill is locked in position then the full power of the DP's motor will be applied to the tang alone and it too can fail to hold.

Another problem with this is the hammering action of the tang striking the slot will be hard on any pin or key that is used to keep the ram form turning. So that pin or key is also more likely to break.

When I install a drill or chuck with a taper with a tang, I ALWAYS rotate the taper in the direction that pre-loads the tang against the slot. In this manner, both the taper and the tang are resisting the drilling forces and the two together will have a much better chance of holding than either of them would have alone. I have used drills up to one inch in diameter on my SB9 and have never broken a tang of a pin or key. I believe this is the proper way of installing a taper with a tang in a spindle or ram.

J Tiers
08-15-2016, 05:49 PM
Ok, burr up a taper drill so it won't hold, stick it in place with bubblegum, and then drill lotsa holes.

We'll see.

You first! :D

Carm
08-16-2016, 09:09 AM
"You argue that tapers that use drawbars do not have tangs and that means that only the taper itself is responsible for preventing rotation. I would say that a tang is impossible with a drawbar."

I worked at a place that had both an Arobga and a Solberga drill press. One of them (memory fails) had an X-Y table and a drawbar with a 3 Morse spindle.
Some of the tooling had tangs interrupted by the drawbar thread.
Whether it was Swedish manufacture I couldn't tell you.