Turn Off Lathe Backing Plate...Tips?

[G-ManBart]

I went to remove the chuck from my Sheldon lathe (13 x 36) which has a 2-1/4 - 8 thread-on chuck and it's stuck...I mean really stuck. I haven't been using this particular lathe long and haven't removed the chuck previously. I had the exact same model lathe, minus a taper attachment previously, and had the chuck off of that several times with no issues. I've tried all of the "this always works" tricks I've been able to find and it's not looking good....stuff like 1" hex in the chuck and gave it some impact gun hits did nothing. I took the chuck off the backing plate so I could get heat (propane torch) to the right area, as well as get Kroil on the threads. I made a 36" long bar that I drilled to bolt to two of the face plate holes and that's giving me decent leverage. I made a split collar sized for the far end of the spindle and welded a 24" bar to that so I could pull on the back plate while pushing on the spindle after getting it hot...no luck. At this point the only thing I have left to do is to try some different ways of locking the spindle (I know not to use back gear) a bit better than I can right now. I could try going hotter with an oxy/acetylene....that works well for smaller stuck bolts/nuts. I figure I'll give it another day or so of heat/Kroil/etc and see if anything works.

If not, it looks like I'm going to have to turn off the backing plate, which is doubly annoying because it's 8.25" not 8" and so far the only options I've found are about $300, which is more than what the chuck is probably worth (old Cushman likely original to the machine).

If I have to turn it off, are there any tips/tricks I should know? I'm dreading that many cast iron chips flying...ugh.

 

[twhite]

I went to remove the chuck from my Sheldon lathe (13 x 36) which has a 2-1/4 - 8 thread-on chuck and it's stuck...I mean really stuck. I haven't been using this particular lathe long and haven't removed the chuck previously. I had the exact same model lathe, minus a taper attachment previously, and had the chuck off of that several times with no issues. I've tried all of the "this always works" tricks I've been able to find and it's not looking good....stuff like 1" hex in the chuck and gave it some impact gun hits did nothing. I took the chuck off the backing plate so I could get heat (propane torch) to the right area, as well as get Kroil on the threads. I made a 36" long bar that I drilled to bolt to two of the face plate holes and that's giving me decent leverage. I made a split collar sized for the far end of the spindle and welded a 24" bar to that so I could pull on the back plate while pushing on the spindle after getting it hot...no luck. At this point the only thing I have left to do is to try some different ways of locking the spindle (I know not to use back gear) a bit better than I can right now. I could try going hotter with an oxy/acetylene....that works well for smaller stuck bolts/nuts. I figure I'll give it another day or so of heat/Kroil/etc and see if anything works.

If not, it looks like I'm going to have to turn off the backing plate, which is doubly annoying because it's 8.25" not 8" and so far the only options I've found are about $300, which is more than what the chuck is probably worth (old Cushman likely original to the machine).

If I have to turn it off, are there any tips/tricks I should know? I'm dreading that many cast iron chips flying...ugh.

That really sucks. If you have flat a belt pulley. You can use a strap wrench to try and keep the spindle from turning. Then use your hex stock in the vise. That might be one way. It might be helpful to have a second person assist.


Cutting oil is my blood.

 

[matthewsx]

Patience and persistence win in the long run. I've never had to cut one off but that's always an option, I'll let others give advice on that though....

John

 

[DavidR8]

Have you tried chucking a long flat bar across the face of the chuck and a block of wood on the ways and giving it an almighty clockwise heave and letting the bar hit the wood block to see if it will jar it loose?
I had to do this to my South Bend 10 to get the 3-jaw off the first time. Nothing else worked.

 

[SLK001]

Lock your spindle, then chuck up a long bar sticking out horizontally from the chuck, the longer the better (or use the chuck mounting holes to attach your bar). Hang as much weight on the end of the bar as you can. Walk away. The next day, your chuck should be loose, if it is ever to loosen.

If it isn't loose from above, get a reciprocating saw with a short blade (cut one off if you have to) and cut a slot right across the diameter (but don't cut close to your spindle's threads). Spread the slot with a cold chisel and the cast iron should split cleanly in half. As the CI is cut, it should loosen from the death grip, so keep trying to remove it as you progress thru your cutting.

 

[Jake M]

I'm going to assume that this is in good condition, and "stuck", and that it's not rusted, corroded, and frozen in place. That means you have to throw out 99 percent of the ways that "always work" for getting stuck things apart. Good clean metal that's stuck is the way it is by an entirely different mechanism than things exposed to the elements, heat cycling, badly dissimilar metals, etc.

If you've got enough pressure against the thread that it won't move at this point, stop spraying the Kroil, or any oil. It's not gonna get where you need it until after the chuck is off. (If there were a gap there, it wouldn't be stuck.....). It's just making smoke.

Persistance usually gets things of that nature to move eventually. Constant "bumping" is what got it on as tight as it is in the first place, and will eventually get it to come loose.

Heat is an option. If "normal" ways fail, one really effective way is instead of heating and then trying to unscrew it fails... ESPECIALLY if you have what you have... The "outside" part is heavier than the "inside part", is to place it under tension BEFORE heating. Because the inside part is so relatively light (less thermal mass) it heats up a LOT easier. It obviously has good intimate contact... You don't get as good of a differential expansion. Take your lever arrangements, the bars and the collar, set up one against a brace, and the other loaded up with a small ratchet strap, maybe down to the table, and put some good tension on it, as if you were actually pulling on it. The longer the ratchet strap, the better. Maybe to a low place on the stand/table? There's some stretch in it, so the longer the tensioned secton of strap is, the more "distance" you'll get. You only need this to move a whisker, then it'll go. THEN, after you have a good "preload" in the right direction, start heating the backing plate all the way around, maybe an inch out from the threads. This way, when (if) you reach the breaking point, you won't loose it (by the spindle warming) as you go for the turning weapons. You can easily loose the "window" in a fraction of a second. Another thing is the heat it's self. Propane torches are not "that" hot, and it takes a while to warm things up. You might do a lot better, with less heat applied, if you had access to a stronger heat source. Something that will heat it faster, but have you in and out in seconds instead of minutes. Another valid thing to if it's possible, which I suspect you can, is to stuff the spindle with wet rags. If there's room, and it may or may not be possible), an ice cube or two inside the wet rag. Just like there's an amazing amount of energy (heat) involved in making steam from the water (which is what you want, that energy (heat) comes right driectly out of the spindle...), there's also a similarly large energy amount involved in the transition from ice to water. All that amounts to more "differential heating", which is in the end, what separates stuck things.

The trouble with turning something like that off of there is, you take away the "handle" that you want to use to get the last bits out. Hoop stresses are a pretty amazing thing, but it leaves you with a small bit of the back plate in this case, still just as stuck as it ever was, and even if it relaxed "some", there's no way to hang on to it. So you're left turning right to exposed threads. Very, very possible to do, but every chance of it not going quite to plan.

If it does come to turning it off, it's just turning. You'll end up making a LOT of chips to get there, but the goal would be to turn it down until you just (and only just) cut into the root off the female thread, but no deeper than the gap between that and the crest of the male thread, so you'll be left with a giant heli-coil threaded onto the spindle. At that , when the heli-coil bit of metal is separated from the continuous metal, you'll have broken the "hoop" through which the pressure is applied, the fit will be relaxed, and the remaining bits will come right out.

I'd still go for the heat though, especially if there's any way you can come up with a higher and faster heat source, but cooling the spindle will greatly improve the results. And help with not burning the oil out of the front spindle bearing.

 

[stupoty]

I slit my stuck back plate off my lathe when I got it, which was handy as I managed to save it. I used a hacksaw blade held by hand (wearing rigger gloves).

8" back plate , took a while , I used wedges to crack the last inch or so to avoid damageing the thread on the spindle.

Stu

 

[Dabbler]

so here goes - just my 2 cents worth.

First I wouldn't use the spindle lock, as this can result in a broken pin or ruined gear tooth depending on you lathe.
I'm assuming you are at the 'desperate but don't want to ruin anything' stage...

Separate the back plate from the chuck. You want as little rotational mass as possible.

make a flat breaker bar to bolt to your face plate - something like 1/2" X 2" X 12" long (not too heavy or too long)
lock your spindle using your plug and fasten it like you are anchoring an ocean liner.

before I discuss the complicated bit - and just checking - (because I've made this mistake a long time ago)

make sure you are hitting in the 'twist off' direction, not the 'make this even harder' direction... Place the breaker bar in tension in the 'twist off' direction. I hang barbell weights on a wire until I have about 100-200 lbs off the end of the bolted breaker bar. It was a long time ago so I don't remember how much exactly.

You will need to evenly heat the back plate to about 300 degrees. use an infrared thermometer to ensure it is even. Don't go above 300F. Use dry ice to cool the centre of your spindle -and very quickly using a steel hammer whack the breaker bar in the twist off direction.

I had to do this for a SB9a once, and it wasn't pretty but it worked.

 

[G-ManBart]

Have you tried chucking a long flat bar across the face of the chuck and a block of wood on the ways and giving it an almighty clockwise heave and letting the bar hit the wood block to see if it will jar it loose?
I had to do this to my South Bend 10 to get the 3-jaw off the first time. Nothing else worked.

I've read about that one, but probably after I took the chuck off the backing plate. I guess I can put the chuck back on and try that one if the other methods fail and I'm down to that or turning it off...can't hurt!

 

[G-ManBart]

If it isn't loose from above, get a reciprocating saw with a short blade (cut one off if you have to) and cut a slot right across the diameter (but don't cut close to your spindle's threads). Spread the slot with a cold chisel and the cast iron should split cleanly in half. As the CI is cut, it should loosen from the death grip, so keep trying to remove it as you progress thru your cutting.

This backing plate is very tight to the headstock and doesn't have much exposed to cut. The shoulder the chuck registers on doesn't stick out very far and I'd probably only be able to remove 3/8" of the threaded section from the spindle...if I could get at it. Honestly, it would be easier to run a parting tool in there and go partial depth, then switch to a chisel. I'm just not sure it would help...but it's got me thinking.