View Full Version : Tailstock Taper Lock: Good / Bad?

Paul Alciatore
02-29-2008, 09:53 PM
The other thread on a tailstock taper attachment brought a old question back into my mind. Please keep in mind that I have a SB9 and the tailstock taper is a 2MT.

Back when I first got the lathe I tried drilling some fairly large holes (3/4", 1") with the tailstock and had the tapers start rotating. So I added a couple of set screws at a point in the tailstock ram where they would contact the tang on the tapers. I offset them from center so they would bear on the sides of the tang to best oppose the rotation of the taper. This has seemed to work well so far and I have drilled a number of similar holes since then with no problems. I did have to add a pin on the tapers of a couple of attachments that did not have a tang to allow easy extraction, but that is the only drawback I can see.

What I am wondering is, should I have done this? Are there any drawbacks or hidden dangers in doing this? Do I have a disaster waiting to happen?

02-29-2008, 10:04 PM
There are mixed opinions on this. Mine is that you should use an external device to restrain the drill in the lighter lathe tailstocks to prevent shearing or otherwise damaging the small key that is used to locate them.

A lathe dog clamped to the shank of the drill, with the tail allowed to slide on the compound is the usual method of accomplishing this.

02-29-2008, 10:05 PM
Paul, I don't know either but I think some kind of lock would be good.
I routinely drill 1" to 1 1/2" holes with my 14X40.
I've spun a couple. So what would be worse? Spinning a taper...or shearing a key or a locator bolt or whatever? I think..(ultimately) that you should damm near be able to stall the lathe before this happens. Just dreaming I guess.

02-29-2008, 10:38 PM
Paul, it won't hurt anything as long as the drill is not to large or over loaded or hangs up. It's often done that way. The way I did it is I made a dog that clamps to the drill at the end of the flutes and an arm that goes down between the ways. That keeps the drill from spinning in the taper.

The problem with a taper drill in the tailstock is it is easily sucked out or twisted free. If it is locked in the quill with a slot for the tang or set screws and it hangs up it could shear the key in the slot in the tailstock quill. That is why I would rather hold the drill with a dead man dog between the ways or over the edge of the carriage that I described above.

It all depends on how hard the drill hangs up and how much power the lathe has if it can shear the key with the set screws. It would also damage the quill.

The problem is that taper drills really work best in radial arm drill presses and drill presses designed to use taper drills. Using them in a lathe tailstock brings out all kinds of issues if the lathe is not large and designed for the torque involved and even they can be overloaded.

It's tempting to use to large a drill and I do it from time to time but only with a dead man dog on the carriage or between the ways. I sure don't want to damage the tailstock or quill and the most that happens is the drill spins in the set screw in the dead man dog and pops out of the quill taper. It can get messy if you don't have fast reflexes to shut the lathe down. My current lathe has a foot brake that stops it instantly and I like that.

When I am using a taper drill without the deadman I keep my foot on the brake.

Bill Pace
02-29-2008, 10:57 PM
I devised/made up a locking set screw for my 12x36 Birmy after I had spun a couple.

But, I'll have to say, I'm a bit apprehensive when theres a big ole bit in there. I am careful to use the step drill method ... its a little hard on the outer edges of the bit, but I figure thats easy enough to resharpen --- I dont plan to remove it .... well,-- if I have a big ole wreck----

02-29-2008, 11:05 PM
Paul, good advice re the dogs. My preference is the boring bar for a couple of reasons. Large drills are expensive, hss tooling is not. Less torque is required. Nice n steady using auto feed . Boring bars are cheapish and relatively easy to make.

03-01-2008, 12:44 AM
I have mixed feelings as well.I believe in keeping the pilot hole if any is being used as small as possible.Usually just big enough to clear the chisel point on the largest drill.Reason I do this is because I have noticed over the years that the larger pilot holes provide a greater tendancy for the drill to snag and spin the taper.I almost never have any trouble with holes drilled from the solid or with a small pilot hole.The opposite is true of holes close to the finished drill size they seem to cause the most trouble I figure mainly from chatter and self feeding.

I have used the method JC mentions,the lathe dog will take a great deal of torque,but the drill tang or worse yet TS barrel pin won't.That's the part I don't like.Some lathes have an actual key and some just have a small pin to align the barrel and prevent rotation.

03-01-2008, 02:56 AM
I was taught just as you say, minimal steps. On small drills, spot and straight to finish size. That's good up to about 1/2, depending on the point and web. A properly thinned 1/2 split point will go right on in. If it needs a pilot hole, then only 1/32 or so above the web/chisel point, which generally means your pilot is 1/8 or larger. The only real exception is if you lack the HP to push that cut. The larger the pilot or center hole, the more chatter/dance you will have.

But my 20 VSG will push a 1'+ MT3 bit right on through 1/2" plate without even grunting, and that's pealing out chips that look like rolled up 16 ga sheet metal. Never seen a mark on the tang that indicated driving from the tang, never seen abrasions like it was trying to slip, then when I eject, it's always setting up and straight in the slot. So I don't think you'll have any problems with the minimal torque that offset center is going to see. The only problem is you don't have the extra seating force like a drill bit, but unless something is very wrong, it will be seeing FAR less torque. Also further minimized by offsetting to the rear, not the front.

As for the barrel to housing, that might be a legitimate concern, but I can't see that center ever coming remotely close to the torque loads of drill bits the tail stock was designed to handle. Plus, if your using that center, you will have the quill lock engaged anyway, so that should pretty much be a non-issue.

Edit: Oops, got my threads crossed up...