Stuck Morse taper
I have an older Jet JWL1236 lathe(blue) with a spur center stuck in the headstock. No rust, just stuck. Drift pin will not loosen it. I'm afraid to whack the pin too hard and damage the bearings. I've tried penetrating oil and a heat gun. Any suggestions? I have a hydraulic press and have considered removing the spindle and pressing out the spur center if that's an option.
Every time that I can remember when we have suggested hitting it really hard it has been successful. I don't remember anyone complaining about bearing problems afterwords. Can't say for sure if it would hurt them. If you've tried penetrating oil then I think a really sharp wack should do it.
I am assuming that it has a hole through the spindle in order to do this. There are some lathes out there that have solid spindles. On these a nut had to be installed before putting the drive center in. I have removed drive centers from this sort of lathe by cutting a nut in half that had the appropriate thread. Then install the nut behind the drive center and C clamp it together. Then just unscrew it and it pops the drive center out. You could do that on yours if you don't want to knock it out. You do need a way to lock the spindle in order to do this.
Try CRC Freezeoff, you can find it at your local NAPA store. This stuff will freeze and lubricate at same time and expand the metal to releave pressure and should let center come out without to much effort.
Turn it with a wrench!
turning is much easier than beating it out. I have not seen one that won't turn free.
Most spur drives are square enough to hold with Wrench.
If you can't get a hold with a box wrench, a pipe wrench probably will hold.
And big vice grips will always do it.
Why did it sticking he first place? Dust or wood chips re the most common cause cleans the center and the taper.
Also, check with your pinky finger for any scoring in the taper.
Scoring can be remove with some stiff 80 grit sand paper rolled into a taper. Turn on the lathes and run it in and out.
Last edited by hockenbery; 11-08-2011 at 07:46 AM.
I had one of those Jets a long time ago and had a stuck spur drive a few times.
I think the spur MT was a bit small and it would jamb from time to time.Most of the time a good wack will remove it.
I stopped having a problem with jambed spur drives when I started to wax the MT and the spur drive on a regular basis, like weekly. Wax on Wax off.
No, the spur will not slip, and neither will the live center. I've been doing this for over 20 years and have never had one slip.
The slightest bit of dust or rust can, and will cause a drive to stick.
Another good practice is to remove the drive and live center when not turning.
if you have not had any luck yet take a small hammer and tap on the side of the spur drive head part next to the spurs ( not talking about a heavy blow) just tap it light one side then the other ( all sides just little taps one side then the other all the way around with your oil in there will help loosen it, then try your knock out bar.
I would not try to twist it too much because it might damage the spindle inside by scraching it causing slipping failure.
Keeping them clean and with light oil and not trying to put so much pressure with the tail stock will help it from not getting so tight
Had that happen to me on my old 1236. I used the split-nut technique to which I added a "U" washer to get a better grip on the spur's shoulder. Popped'er right out. I then trashed the KO bar and made of a nut with washer welded to it and ground flat. This goes on before the spur is inserted, so removing the spur is simply a matter of spinning the nut off which removes the spur. I borrowed this idea from a Poolwood solid spindle lathe, and use it on my Stubby because my spindle is blocked for a vacuum system. Attached is pic of the nut. Easy to weld or just braze on the washer.
Last edited by Mark Mandell; 11-08-2011 at 01:20 PM.
John, you gave the best advice, by far. Here is the reason: When you use the knockout bar (and a hammer only if absolutely necessary) every time that you hit the back end of the drive center, the energy is being dissipated somewhere.
Originally Posted by john lucas
First let's consider the case where we only apply light to moderate taps and stuck drive center doesn't move. In this situation 100% of the kinetic energy must pass through the bearings and into the headstock structure. Since the bearing assembly is the only part of this entire energy dissipation path that has any "compliance" (engineering term basically meaning yielding under applied load), the end result is almost the same as taking a hammer and tapping directly on a bearing.
So now a reasonable person might be wondering why in the world would a hard sharp rap give better results when it seems like that would be worse. Here is why -- it's called transfer of momentum. Have you ever played billiards and made a hard shot where the cue ball hits another ball squarely? Hopefully you have noticed that the cue ball stops dead in its tracks and the other ball takes off at the same speed that the cue ball was traveling before the impact. What happens with a straight-on high impulse shot is that all of the momentum of the cue ball is transferred to the other ball. A similar thing happens when a very strong impulse blow is applied to the back end of a tapered drive center. Essentially all of he momentum is transferred tot he drive center and it pops free. Very little unnecessary energy gets dissipated in the bearing assembly.
Now, I need to explain what "impulse" means in the engineering sense (it has nothing to do with any particular shopping style). In a nutshell, an impulse is a transfer of energy in a pulse that is so short that the length of time approaches zero and the magnitude approaches infinity. We can't achieve a perfect impulse, but we can get a reasonable facsimile. Here is an example of two scenarios:
- In the first case, we use a very heavy sledge hammer and swing it slowly to hit the knockout bar
- In the second case, we use a typical knockout bar that weighs a bit less than one pound and swing it at very high velocity
We have sized the mass and speed of the sledge hammer and knock bar so that the kinetic energy is the same. The difference is that for the first case the energy is transferred over a long period of time with a certain peak magnitude, while in the second case, the energy is transferred in a very short length of time at a much greater peak magnitude. The total energy is the same for both cases, but the results will be different. The sledge hammer is likely to smash the headstock while the knockout bar will be more likely to pop out the stuck drive center. The main idea here is to swing the knockout rod as fast as you can. When the drive center pops loose, it will be flying at very high speed so be prepared to catch it and watch out for the sharp edges.
I have tried to avoid getting technical and mentioning anything to do with the M-word (math).
You're scaring me, Al. We left brain technical geeks fear right brain creative artists. You are correct that you can usually "wring" it loose, but at the cost of causing more galling on both the drive center and in the spindle socket.
Originally Posted by hockenbery
You are correct about the root cause of sticking. The dust dirt, grit, and grease do not directly cause sticking, but they are the reasons that a drive center will spin. Once a drive spins, it's too late. While it may not be stuck in mild cases, damage has been done and the mating tapered surfaces will be galled which means that they will no longer fit together properly.
Using 80 grit sandpaper is scaring me even more than wrenching out the stuck drive center. The tapered parts are supposed to mate together within 0.0005" and have a nearly polished finish to achieve the necessary metal-to-metal bond.
Tapping on it like that is risking causing Brinnelling to the bearings.
Originally Posted by rjones
Keep both surfaces clean, yes! However, never ever oil the tapered surfaces -- doing so will only serve to reduce the friction force that keeps them from slipping.
It is good advice about not applying excessive tailstock pressure, but not for the reason cited. The reason that it should not be done is to avoid damaging the bearings. If you are finding that the drive center is sticking because of tailstock pressure, it means that the lathe spindle bore and/or drive center shank are already damaged. If they are in good condition, this will not happen.
Guys, thanks for all of the advice. That sucker was REALLY stuck. Nothing worked, so I had to come up with another method. I removed the headstock as a complete unit, fitted an automotive bearing splitter against the spindle shoulder to avoid putting pressure on the bearings. I put the whole assembly on a hydraulic press and pressed the center out with a rod I cut to the proper length. The spur center popped right out, with no damage to the center, spindle, or bearings
Don, it sounds like you took really great care to keep from damaging the bearings and the polished surfaces that they mate with. I am glad that you were able to get things apart, but I am really surprised at how tightly things were stuck, especially considering that neither of the tapered surfaces seemed to have any damage. Are you sure that there were no narrow "scratch rings" on the tapered surface? Another possible reason for the sticking could be that the drive center taper is slightly "off" and because of that, was able to wedge tightly like a stopper in a bottle. You might want to compare that spur center's taper to another one to see if both are identical. One other thing is that a spindle socket with bell-mouth damage is subject to either sticking tapers or sometimes tapers that won't hold.
Originally Posted by Don Burts