I have a question about tapping using a lathe. I've got a SB 11" lathe with a non-keyed tail stock; IOW the chuck arbor is not prevented from rotating in the tailstock except by friction. I tried to use a tap mounted in the arbor mounted drill chuck that was inserted in the tailstock of my lathe. After drilling the appropriate sized hole for the tap (1/2" x 13), I tried to tap the hole (using a very slow speed) and found that I ended up turning the arbor in the tailstock. I ended up finishing the threads by hand.
Is there a technique that allows a better/tighter fit between the arbor and that tailstock or is this just a natural limitation of a lathe with the type of tail stock I've got? IOW, is this tap just too big for my lathe? I sprayed the arbor and the inside of the tailstock with brake cleaner and wiped them off. I had no problem drilling the holes using the tailstock - just the tap caused the problem.
#2 or #3 Morse? If it's a #2, it's entirely possible the taper is just too small to overcome the torque.
One thing you could do is check the fit to see if it is making good contact. I've seen shanks that have enough damage that they make contact in only a few narrow bands, not providing enough friction to resist the torque of heavier operations such as tapping. If you find everything to be in order, and your tailstock has a #2 taper, you may have to resign yourself to the fact that you are asking more of the machine than it may be able to provide.
Tap isn't too big for the lathe, but it is too big for the taper to hold. Clamp a lathe dog on the shank of the tap, and rest the tail on the carriage or compound. This is standard procedure when using large drills.
I don't have a lathe dog currently so I can't measure it to see if it'll reach from the tap to the ways. Will a standard lathe dog for an 11" lathe work?
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What you're looking for is an interruption of contact, so you might be able to simply put a line along the length of the taper with a grease pencil, then push it in and turn it. If the line smears everywhere, it's making good contact. If you find the line interrupted here and there, it's likely not making good contact at all. A lathe that doesn't have a tang drive often suffers from this problem. At some point, something spins, be it a drill or a chuck, and it will leave a few streaks that remain high. It has happened on my lathe more than once. If you find such a problem with yours, you may find it won't clean out all the way with a three cornered scraper. If so, one of the things you can do is chuck up the quill and spin it in your lathe, then concentrate on the bad spot with a scraper. My quill is hardened and ground, so it doesn't do any damage. If that doesn't work, you might try using some polishing cloth on the tip of a small item so you don't polish the general area, changing the taper. If necessary, kill the area so it will then not interfere with the balance of the taper. You're much better of to be using the accurate (undisturbed)portion, perhaps
85% of the length, instead of the minor amount that may be causing the problem.
If you use bluing, one of the big problems with it is getting too much on so the reading isn't very reliable. Be sure to use a very thin film of it, and it might be wise to put it in the socket, then see if it transfers to the male taper, otherwise it can be quite hard to see.
The other thing to check is if your tapers match well. If you find the taper to be off, you might be able to polish it enough to improve contact, but I'd be very careful to make sure that you're error is in the tailstock, not the male piece. I purchased a live center off ebay that doesn't match perfectly, but making it work will be no chore, I just haven't got to it yet. Same problem, a slight error in the taper. I know the taper in my tailstock to be good because I've never had the problem with anything else in the 36 years I've owned the machine.
From your original post, it seems that you are holding the tap in a TS 3-jaw chuck?
A workaround would be to use a tap in a tap wrench (the handle of which should reach out to the top of the lathe carriage--or if not add a pipe nipple as a cheater). Use a tap that has a center punch hole on its back end--some do, some don't--and mate your TS center tip to this (greased for a solid center).
Line up the setup, and put some pressure on the TS wheel, then rotate the tap handle clockwise (by hand) and spin the HS chuck counterclockwise a bit to start the tap. (Pleanty of cutting oil on.) Turn the TS in to take up the slack, and repeat a few times, always keeping the pressure of the TS center on the tap end. Once you get the feel of it, you can go to intermittent power, keeping the pressure of the TS on the setup as you go.
Once you have the tap engaged concentric, you can also take the setup off, and finish by hand in the vise.
I've done many 1/2 by 13 threads this way on a 9-inch lathe with a 2MT center. Frank Morrison
Hold the tap in a bar type tap wrench, use a center in the tailstock to center the tap. Let one of the handles of the tap wrench rest on the carriage. Use lathe's lowest spindle speed or turn the spindle by hand while advancing the tailstock ram to maintain some pressure on the tap.
The solution when the taper has been reamed out too far is of course to face some off the front.
The final, and most important warning is, NEVER turn that taper reamer backwards during use.
Jim
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Peter; If the tailstock taper is damaged the best solution is to get yourself a matching reamer and use that to clean it up. These reamers are not all that expensive. One *major* caviat - Be aggressive when you apply the reamer and
*major major* caviat; Remove the absolute minimum you can get away with! It is truly amazing how much the linear register can change with minor removal of metal in this situation.(don't ask how I know) Regards. Ken.
This is the fastest way that I have found. The tap is in the chuck. The piece being tapped is moved against the chuck then backed into an oversized collet in a collet block on the toolpost. Then the hole to be taped is brought forward onto the tap. The piece being tapped was held from turning with vise grips with a copper shim to stop marring. I was able to tap at about 128 RPM. The pieces went in and out very quickly with about zero danger or possibility of mistake.
That's an interesting way to do it. The piece I was working on this time was rectangular and was held in a four jaw chuck so a collet wouldn't work (if I'm understanding your example).
Fair enough, if it will not work for your situation Peter, but the collet serves only to align the outboard end of the stock being tapped and it does not care if the stock being aligned is round, hex or square.
For that matter it is not necessary to use a collet / block. A rocker type toolpost with something the right height clamped in it could serve to align any shaped stock (round, square, rectangular or irregular shaped parts. Just so long as it does align the part in the required attitude.
I made a tool from am ordinary tap holder intended for hand tapping. I drilled and reamed a 3/8" longitudinal hole in a piece of round stock about 2" long. I then bored the hole out to a decent sliding fit over the cylindrical back end of the tap holder. I cross drilled this so I could replace the handle through the sleeve.
For use, I chuck a piece of 3/8" drill rod in the tailstock and slide the tool on to it with the tap installed. All the torque is on the cross handle. The rod in the tailstock is just a guide.
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