Stuck McDougal Lathe spindle adaptor
I'm new to the Home Shop Machinist and have never asked a question before. I have a McDougal 20" lathe in very good condition, but cannot remove the adaptor or backing plate, threaded on to the spindle nose. I have tried, gingerly, heating, pounding on the collar portion of the adaptor plate, and an 8 foot long cheater bar, all to no avail. Does anyone know if there is some hidden locking mechanism (because the lathe has quite an effective brake) or some other device used to lock on a chuck? I have a face plate, same serial number as the lathe, and see no evidence of any locking devise in its bore. ANY thoughts of suggestions would be much appreciated!
Are you sure that it has a threaded spindle? Gary P. Hansen
Now, like Gary asked, are you SURE that lathe has a threaded spindle? You mentioned gently pounding on the collar, I would expect that that lathe may have a tapered spindle mount which would have a threaded collar that holds the chuck / faceplate on the tapered spindle. It this is the case the collar will have notches around it for a spanner type wrench. Check it carefully, I would be surprised if a lathe that large had a threaded spindle.
Stuck McDougal Lathe Spindle adaptor
Hi Gary and Robin and Thanks for your interest and response.
Yes, I am sure this is a threaded spindle nose. Robin, I am familiar with the spindle you describe (an L1 ? like an old Colchester) with the large tightening collar behind the chuck. This does not have that. I have a faceplate, same serial number as the lathe, and I can look inside the center hole and see the threads. This is the same design as used on a Southbend or Logan; threads and a registering i.d. matching the o.d. behind the threads on the lathe spindle. And yes, Robin, one would assume because of the size of the lathe (10 H.P. and the fact it has a brake, there would have to be some way of keeping the chuck on the lathe when quickly stopping the spindle from a high RPM. The three jaw, which was mounted to the threaded adaptor plate weighs some 100+ pounds and is 15 inches in diameter. I would not want to see that go flying across the shop floor! This leads me to believe there has to be some locking mechanism, something probably unusual as the lathe was made in Canada around WWII, and has some other unusual features. Yet, there are no set screws, keys, keyways, internal locking rings, or anything visible on the adaptor or the removed faceplate. My next thought is there might be some way a lock works from the rear of the spindle, where the feed gears get their drive from. I will check into that on Monday and let you guys and the others know what I find.
Any other thoughts?
It sounds like you have a good handle on the mechanics of your lathe. I was indeed referring to the L-x spindles, thats what my 17 inch Leblond has. Just to let you know, I have seen a large chuck (13 inch or so) unscrew from a spindle when the operator bumped the machine into reverse to stop it. BAD MOVE, lots of dancing to save the toes. No saving the work piece or the tooling . If there is a locking mechanism it would have to either bind on the spindle threads or on the register area on the back of the chuck. I have never seen anything like that though. If it has been assembled for a long time it might just be tight or possibly a little rust or corrosion. I would spray the thread and register area with a good penetrating oil, both from the inside and back. After doing this for a few days I would again try to unscrew it with a little help, possibly a heavy bar in the chuck and some impact to knock it loose. I really don't know the proper way to do this and I really don't like the idea of pounding on the chuck or spindle. Another thing that might help is a little heat on the collar area (a heat gun and let the machine run slowly for a long time or a light torch?) then quickly pack the spindle bore with dry ice to cool it, then try the impact thing again. I don't know if any of this will help but it might. You might want to post this question on the general board, there are a lot of people there that don't actively look at the other boards, but there is a lot of knowledge there.
Inertia can be your enemy or friend in this case. Since the chuck is heavy, having much more rotary inertia than the spindle, jarring it does not work very well. One technique I have used successfully is to find a hardwood or soft metal block about the length of the center height. Hold it between the ways and the chuck so it will hit a chuck jaw when the chuck is turned backward. Loosen all possible belts or gears from the spindle. Rotate the chuck sharply backward so the jaw hits the block, keeping your fingers out of the way. This is kinda hard on the chuck and jaw but you can adjust the force as needed. The sudden stop of the chuck will usually cause the spindle to unscrew and come loose.
A heavy metal plate with three slots to go over the jaws and a short stub for hammering would likely work. Also a heavy band clamp around the chuck with a stub for hammering should work if you can get it tight enough. For hammering, you need something very rigid, so short levers tend to work better than long ones.
If you can manage it, a little dry ice or a blast from a CO2 extinguisher thru the spindle might contract it enough to help.
I had the same problem with the chuck adapter on my Bradford lathe when I got it. When a threaded backing plate has been on a lathe for years, they can get really stuck.
I tried literally everything everyone has mentioned in this thread and more, with the exception of using a heavy inertia plate - that's too elaborate for me. I tired heating the adapter and packing the spindle with dry ice. I used a cheater across the chuck jaws and pounded on it as hard as I dared - which is pretty hard. Nothing. Not a wimpy cheater either - 6 feet of 1.5" x 2.5" cold rolled steel - zero perceivable flex. I tried to rattle it off with an air hammer on the cheater. Nothing. I chucked hex stock in the 3 Jaw and hit it with my good IR impact wrench. Nothing. Eventually I gave up and just used the 3 jaw for a long time, but after reading several threads regarding stuck chucks on threaded lathe spindles on a different forum I decided to just machine the adapter off. It was a good plan.
Just start machining. When you get close take shallow cuts until you will see the clearance at the major diameter of the threads on the backing plate. Stop machining when you see this. Unless you are taking giant cuts, there is very little danger of hitting the spindle becuase there is a good amount of clearance on a large coarse thread. Use HSS and even if you do hit the spindle it probably won't cut it since the spindle should be hard tool steel.
Having a face plate makes your life easier. You can buy a blank chuck backing plate and machine it to fit. Just bolt it to the face plate, center it up, bore and thread. It's an easy job and gives a good sense of accomplishment.
When you have the chuck backing plate threaded and bored, spin it lightly onto the spindle and machine it to fit the chuck. You'll have to pull it off again to drill the holes for the mounting bolts.
Check page 1651 of the MSC big book for rough chuck backing plates. You will have to get the one meant for a 16" 4 jaw and machine it to fit your 15" chuck. It's not cheap, but your back gear is irreplaceable.
Don't forget to clean and oil your spindle whenever you swap the chuck. It goes a long ways towards preventing future stucks.