Stuck Chuck Follow Up

[porthos]

ok guys still have a stuck chuck. I can get it off, but not as easy as it should be. here is some more info. I have a n area at the back of the back plate that is rubbing against the spindle face appx. 30% of the surface area. as per what Brain Coral mentioned. I took another skim cut off that surface with no change. I wonder if the back plate is just not square when I screw it on backwards to make this skim cut because the threads are just not holding square because there is no shoulder to lock on in this backwards set up? I read somewhere in backplate fitting about scraping the back surface where it is rubbing. by the way I'm checking this "rub" area with dykem blue, and a .001 feeler gauge. the feeler gauge goes in about 70% of the radius. Sorry for the long message, but there's a lot more and I'm a newbe. I have the part of the rear hub from the back plate that I cut off . What if I got this piece surface ground and used that as a spacer. when I reinstalled the back plate backwards it would but up against the spindle face square. i'll probably try that. MORE. when I cut the front of the back plate for the lip that goes in the recess of the chuck I took a little too much off (oops) it falls right in. I can't measure the difference because it's so close. but this might be part or all of my runout. the fellow who drilled the holes in my baclplate (he has a Bridgeport) said that I should be able to center for runout by only installing 3 of the 6 bolts that hold the backplate on and tapping with a plastic mallet to center it. it ain't workin. I approached him with this thought that I had. I have a starrett spring loaded prick punch. I had tested it previously and it makes a consistent .003 high indentation . what if I prick punch the circumference of the hub uniformely (6) places. I think that this would center the 2 pieces. he said not to do it. the 2 pieces don't have that much clearance, but they wouldn't be hard to mate together. I thind that it's worth a try. but , my biggest concern is the sticking. thanks for all the help so far

porthos

 

[4GSR]

Sounds like some one before you did a sloppy job of making a back plate. Your heading in the right direction fixing it, if you can get the bearing face back to square with the thread. Flipping the back plate around to the other side and facing off is probably just duplicating the same problem to that side. I don't know what thread your spindle is, but if it is a common thread like 1-1/2-8 or 2-3/8-8, I would suggest buying a new back plate from LMS and start over with something that you know is correct & good. Just my honest opinion.

 

[joshua43214]

I am having some trouble following you. It sounds like you are talking about several different things all at once. Among other things, you did not mention what kind of lathe you have, and where the faceplate came from. Breaking the post up into paragraphs and separating different things with double spaces would help some too.

What I gather it:
Your backing plate is not making full contact with the spindle face. It is only making about 30% contact.
You are trying to square the mating surface on the backing plate by screwing it on backwards and skimming the back face.
You cut the boss for the chuck too small.
You are trying to center the chuck on the plate and are not able to eliminate the run out.

For the first point, the threads and the mating surface need to be pretty square. How square they need to be depends on how loose the thread is. The threads should be just loose enough to allow the backing plate to register on both the spindle face, and the spindle boss (assuming you have one). Ideally, the threads and the register should be cut on one set up to they are square. If they are out of square - it can be difficult to get them square again unless you have extra tooling.
It sounds to me like both faces of the backing plate are not square with the threads. All you are doing my cutting it again, is just duplicating the issue. Try to add a spacer will just do the same thing.
Your best bet is to make a threaded plug that matches your spindle, with about 3"-4" extra unthreaded material. Mount the backplate on a faceplate or another chuck. Wrap the threads on the plug with Teflon tape until it is a tight fit on the threads of the backing plate, and screw it on til it almost bottoms out (do not run the plug all the way in). The idea here is to create a reference surface for the threads. Now sweep the plug with a dial test indicator and shim or knock the backing plate until the thread bore is as close as you can get it to parallel with the bed. Remove the plug and skim the register on the backing plate. Your threads and backing plate should now be square.
An alternative method is to put transfer dye on the spindle. Thread the backing plate on backwards and seat it onto the dye. Scrape or power sand the dye off the backing plate, and repeat until you get full contact with the plate on backwards. You should now be able to skim the mating face and have it come out pretty square. The results will depend on your patience. I would suggest skimming the chuck side, and threading it backwards again to re-skim the mating surface and bore the register for the spindle boss. Then make a finish skim on the chuck side and make the chuck boss.

As for trying to center the chuck on the backing plate. You have the cart in front of the horse so to speak. If the chuck is not square with the spindle, it is a waste of time to try and center the chuck on the plate. Get the plate square on the spindle, then worry about getting the chuck centered on the plate. If you do manage to succeed in centering the chuck on a plate that is not square, you have just introduced even more error into the whole thing.

EDIT: I forgot to mention that I agree with 4gsr about it probably being best to just get a new mounting plate.

 

[porthos]

4gsr and Joshua
thanks for the info , but, you need to understand many of us on this site are newbes . your info is somewhat understandable. but, a lot is over our heads. I have many skills but being a machinist is not yet one of them. Joshua, I get some of your ideas and will try to apply them (in my own way) . As far as a new backplate; i'll play with this some more. Because , cutting cast iron is a very messy operation on a lathe;and, if I can elilminate doing it again, I will. On that note if I did get a bad backplate (the threads are a little loose) who would recommend to buy a better quality backplate from. I have all of my reciiepts for what I bought, but this backplate is not one of them. I belive that I paid around $ 50.00 for this and I've seen them priced for around $ 100.00 . I'm not opposed to paying that. I thought that they were pretty much the same regardless of price.
As to the type of lathe. I had a previous post (2 days ago) stating that it is a south bend 10l . I just headed this posting FOLLOW UP ON STUCK CHUCK

Porthos

 

[4GSR]

Here's a chuck adapter for a 6" chuck from LMS for $40.
http://www.littlemachineshop.com/products/product_view.php?ProductID=1923&category=-1110836144
I'm not totally sure for your exact needs, other than you have a 10L SBL. But if this will not work, they do sell blank back plates for your needs. Be a perfect place to start learning how to thread.
Sounds like you have a good handle on what to do there. And yes, we tend to talk over the heads most new people without realizing we are doing so.
Sorry. I'll try to do better.
Ken

 

[joshua43214]

Sorry if I was not clear.
Even though you started a topic a few days ago, you should still provide the lathe info again. I tend to only know who owns the same tools that I do...

My lathe uses a different type of mounting than yours does, so I found some pics on Google, and I mocked up something on my lathe.

This is the plug I described. Many owners of SB lathes make one for test fitting the threads on backing plates while machining them. This plug has a spigot on one end for mounting in a collet and appears to be meant for facing both sides of the plate.

Note the slightly polished area. This corresponds to the area of the spindle called the boss. When the backing plate threads up in the spindle, the boss is what centers the plate, and the face of the spindle is what squares the plate.

Here is a mock up of what I was describing above. This is an 8" backing plate mounted in my 4jaw chuck backwards. The piece of steel round would be the threaded plug shown above. It is important that the plug is screwed in most of the way, but not bottomed out. The plug needs to be centering on the threads, this is why you put a heavy layer of Teflon tape on it. The backing plate does not need to be perfectly centered, it is ok if it off center a small amount. What you would do is mount the test indicator on the carriage and move the carriage side to side (this is called "sweeping"). Do not rotate the chuck, put it back gear or lock it so it can not rotate. Tap the backing plate with a hammer to adjust it, or use shims if you are using a faceplate. Once the plug is perfectly horizontal, you would move the indicator around to the front and repeat until the plug is square that way. Then go back to the top and re-align that. Then back to the front. You would do this until the rod is as close to being in line with the axis of the spindle as possible.
Then just face the part that mates to the spindle face. Break down the set up, and test fit the face plate. If you got the plug tight in the threads, and perfectly aligned to the bed, then the mating surface should be square to the threads. Getting the plug tight on as much of the thread as possible and patience with the indicator is the key here.

Some folks find stuff like this more painful than root canals, others just do it with out thinking about it. If you have trouble, do not take it as a mark of being a poor machinist, many pros would take forever doing this. Gun smiths are about the only folks that do this sort of thing for a living.

Before I got into all this though. I would double check to make sure the backing plate is not reaching the end of the thread before it contacts the spindle face. I am just guessing that there should be between 1/4 and 1/2 of a thread remaining on the spindle when it is snug.
Hopefully my other description for scraping the mating face made enough sense.
I hope this helps.

 

[stupoty]

Before I got into all this though. I would double check to make sure the backing plate is not reaching the end of the thread before it contacts the spindle face. I am just guessing that there should be between 1/4 and 1/2 of a thread remaining on the spindle when it is snug.
Hopefully my other description for scraping the mating face made enough sense.
I hope this helps.

Thats definetly worth checking,

I recently went a little wrong making a back plate and didnt have a big enough radius at the spindle end of the thread which was stopping it going flat, opps

Stuart

 

[mattthemuppet2]

if you want to face the spindle register on the back plate by threading it on backwards you need a spacer on the spindle that's thicker than the unthreaded part of the spindle, otherwise your reversed backplate won't sit true. a stack of washers would do or you can make your own spacer on the lathe. the more parallel the faces the better. then, once you've faced the spindle register of the backplate, you turn it around, thread it on the right way then recut the chuck register and "hub" so that they run true. then mount your chuck on the backplate and see how it looks

 

[chevydyl]

I just want to say one thing, the boss or register that is on the spindle does NOT have to be close tolerance to the backing plates register, all 3 of my backing plate registers are different sizes. And all my chucks repeat, one repeats 4 tenths, if you make that register to close in size to the spindle register you won't be able to use the chuck on any other lathe, I know that's not the intention of your project but it's something to think about, MY atlas chuck will fit a SB, and have low runout. The threads are going to engage at the same point every time, and that's why it repeats, the face being square to the threads is important because of that.