Chuck Alignment

T

tkingmo

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OK I have a problem with my little Craftsman 109. It came with a worn out 4 jaw so I purchased a NEW 3 jaw. The lathe still has the original 1/2x20 thread on the spindle. The face and the hub OD on the spindle check within .002. I mounted and faced off the back plate for the new chuck and bolted it up. There is run out of over .020 at the far end of the chuck. And a small cylinder chucked up also shows this run out. I clocked the chuck in each of its three bolt holes but I can not eliminate the excessive run out.
What are the methods to fix this? Thanks for your help.
I also have a SB Heavy 10 and a US Machine Tool vertical mill that I am learning to use so I am sure I will have more questions as I progress.
 
Have you tried taking the chuck of and moving it round one bolt hole to see if it's any better?
 
like hermedic said check all the bolts by rotating them and if they are shouldered bolts make sure they are not loose in the backing plate, you might try marking your low side and loosen bolts and bring up and retighten might get you closer:biggrin:Mac
 
irishwoodsman said:
like hermedic said check all the bolts by rotating them and if they are shouldered bolts make sure they are not loose in the backing plate, you might try marking your low side and loosen bolts and bring up and retighten might get you closer:biggrin:Mac
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Yes, I did like hermedic said "I clocked the chuck in each of its three bolt holes but I can not eliminate the excessive run out." I also loosened and tried to move the chuck. No joy. Perhaps I make the holes larger and get it aligned and then drill and tap a new hole to keep alignment?
 
You've got to find out where you're getting that runout. If you still have some after working on the register and facing the face plate, it could be coming from the back side of the chuck itself. What I do to remedy this concern is to remove the chuck jaws, (keeping track of where they belong), mount it backwards on the faceplate, attach it with threaded rod and big washers, then take a face cut on the back side of the chick to true it up. Reassemble the chuck, mindful of bolt torque, then indicate, and you should be very close to dead on.


I've tried clamping on backwards to the faceplate, but i've had better luck with the method described above.


Good luck!
 
You have a indicater by the sounds of your post. So here is the way I would start.
Remove the chuck from the back plate. Run the indicater on the face the chuck would be against. If it shows run out. Remove from spindle and clean with a tooth brush sized s/s brush, make certain no chips or swarf are in the threaded area. Reassemble check again, still have run out? You would need to leave the backing plate in place, and take a very light skim cut. I would start at the register step, and feed out wards toward the operater.

The next thing to check before you cut anything is the register step. This is the step that fits in the back side of your chuck. Now if you have allready removed the chuck, was it a snug/tight fit? or just fall right off? Either way, get the tip if your indicater on that step, check for run out. If you have run out on either of these places will cause you problems.

Other things to look for, raised treads at the back of the chuck. These can be stoned down flat. Stoning the back of the chuck looking for raised spots, should be done anyway. Look at your back plate closely for embedded chips that might hold the chuck out from the backing plate too.

You may need to take a facing cut to the back plate to true it. Also you may need to take a skim cut to the register as well if need be. If the chuck is loos on the register allready, mount the chuck, and indicate they body of the chuck, and use a dead blow hammer to shift the chuck for the min run out whiie the bolts are snug, and not tight. You can bump it around to get the min run out on the body. Once you get this far, you should have a pretty good indication of how true it is. Run the indicater on the body, and the front face.

If you can get all this sorted out, then chuck up a known piece of true running stock, and you guessed it, chck run out again. But ,,, you have dissasembled this chuck, and cleaned the scroll and all related parts first. and chips in there will affect your reading once again! Once the scroll and all related parts are cleaned, and still have bad runout. I would look for tell tale signs of a crash, if none show up, then I would haul out the toolpost grinder, or rig up your own, and regrind the chuck jaws on the lathe, but that may be past your abilitys at this point. So, get to checking this stuff out!

Good Luck ;)
 
i'm going to start the same process tomorrow, i will take some pics and start a new thread, my chuck is a er40 that uses a backing plate which i will be turning down for my er chuck, i dont have any transfer punches so i'm going to use a drill bit shank and make one to mark my holes for the attaching bolts, i guess my real question would be how much step goes into the chuck, right now i have about a 1/8 sticking out from my backing plate but my chuck has enough room for prob 3/8ths:))Mac
 
Thanks for the help guys. I had turned the backplate mounting true on the lathe before mounting the chuck to it. It does have a register. My threaded spindle is out .002 and after mounting the backplate it, the backplate is out .022. So I believe the problem is the backplate was poorly made. This is a new chuck/plate. So I trued up the backplate diameters, both OD and register OD and reassembled. The OD of the chuck is still out. So I enlarged the three mounting holes and dialed in the OD of the chuck. Then I pinned the chuck to the backplate in two places. I am within .002 now. I think I may need to make a new back plate, but I will try what I have for now. No doubt I will make mistakes along the way.
 
Blue Chips said:
Something isn't right - .022 with just the backplate mounted? Is it threading all the way on to the spindle register? It should seat with a dull thud, and not screw up tight like a pipe thread.

Nobody can make a backplate that far off! :)
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Yes it threads on and seats firmly against the hub or shoulder on the spindle. The OD of the spindle hub, about1 inch in diameter, checks out of round by .002. When I screw the back plate on it checks the .022 as does the OD of the chuck when mounted. That lead me to conclude the backing plate was machined poorly. This was so in any of the three mounting holes. So my fix was admittedly shade tree; the proper fix I would suppose is to make a new backing plate; that will come later as I dont have any material right now. Thanks.
 
How thick is the back plate? You may have the material if it's thick enough. You would have to face off the register boss on the plate and turn a new one. Move slowly when you get close to the right size. You want to have to push the chuck on with hand pressure (at room temperature), not have it slip on easily. 1/8" boss height is enough. BTW, if you have as deep a pocket in the back of the chuck body as Mac has, you can skip the first step and leave the current register in place. Just ignore it in your thinking as you work on the new register. It will help to keep the plate stiff.

Since the back plate and chuck showed the same amount of runout, this could fix it, assuming they both ran out at the same angular location. If this corrects the runout, mark both the chuck and plate with scribed lines, so that they can always be assembled to the current position. Then proceed as mentioned with jaw testing and possible grinding.

If nothing else, doing it this way will train your thinking for when you go to make a new back plate.
 
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