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Lathe Cross Slide Problem
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07-01-2014, 03:11 PM
Okay, it's time to reveal that I taught Greg everything I know ( it only took 7 minutes
 ).The other thing is, it rendered him slightly less knowledgable. That's why I moved much further away.  
Busy Bee 12-36 lathe, Busy Bee Mill drill, Busy Bee 4x6 bandsaw, Homemade 9x17 bandsaw, Ad infinitum.
07-01-2014, 04:34 PM
07-02-2014, 04:27 PM
I think this may work. I kept removing material until the nut would travel the length of the lead screw without bottoming out on the trough. That leaves only .090" from the crest of the major diameter of the thread to the bottom of the nut but I think that should be adequate. With that phase done, I moved on to mounting the nut to the cross slide and tried running it through the full travel and it's binding so badly that the hand crank won't turn at all. Not knowing if it was binding because the nut dimension is too long or too short I scratched my head for a few seconds and realized that I could loosen the mounting screws and if the binding went away then I would know the the dimension is too short. That ended up being the case so after scratching my head some more trying to figure out how much to shim the nut I had another realization (wow, two in a matter of minutes). I loosened up one screw a half a dozen turns and then started loosening the other screw 1/4 of a turn at a time and tested for binding. At 3/4 of a turn the binding had lessen to the point of just being slightly harder to turn than I liked. At a full turn it was perfect the full length of travel. Since the pitch of the mounting screw is 32TPI, it was easy enough to calculate that I needed a .03125" shim.
That's next, make the shim and test again. The problem with adding the shim is that I don't know if that extra length is going to cause the nut to rub on the trough. I guess I'll find out soon enough. Ed
07-02-2014, 06:42 PM
Got the .031" shim installed and it's still binding so I did the screw loosening process and at 1/4 turn the binding went away so now I need to make a .008" shim to add to the .031" shim. I think I'm hearing some scrapping of the nut on the trough. I'll know once I remove the nut and examine the bottom side for scratches. It appears I'm walking this fine line of keeping the nut from rubbing on the trough and getting the nut shimmed properly. I'm going to try adding the .008" shim and if that seems to do the trick and there is evidence of the nut scrapping on the trough, I'm tempted to remove the saddle and mill off .050" from the trough. I can't believe removing that amount would compromise the structural integrity of the saddle.
 Ed
07-02-2014, 07:09 PM
I think you'll be fine with taking the .050" off, Ed. It's minimal and the spindle motor would likely stall long before you had any structural failure of the cross slide.
Thanks given by: EdK
07-03-2014, 06:02 AM
Sounds like you are heading in the right direction Ed. You'll have it sorted in no time.
Hunting American dentists since 2015.
Thanks given by: EdK
07-03-2014, 06:29 AM
Ed, I suspect that when you examine the nut for scratches from the trough you'll find the marks to be on the corners that have resulted by the flat milling to reduce the nut's downward length. (boy! in the efforts to 'splain clearly I seem to have composed a confusing prattle
 ) .All that to say, rounding the corners by file or mill will eliminate the interference.
Busy Bee 12-36 lathe, Busy Bee Mill drill, Busy Bee 4x6 bandsaw, Homemade 9x17 bandsaw, Ad infinitum.
07-03-2014, 09:11 AM
(07-03-2014, 06:29 AM)stevec Wrote: Ed, I suspect that when you examine the nut for scratches from the trough you'll find the marks to be on the corners that have resulted by the flat milling to reduce the nut's downward length. (boy! in the efforts to 'splain clearly I seem to have composed a confusing prattle Steve, I was thinking the same thing while laying in bed this morning wondering if I should get up or just lay there. Anyway, I did chamfer the two corners but not much so I'm going to chamfer them heavily and see if that fixes the scrapping sound. I didn't see any scratches on the bottom of the nut so it must be the corners that are rubbing on the trough. That's a good thing since it's an easy fix.  Ed
07-03-2014, 11:33 AM
The .008" shim didn't do the job. The total travel on the cross slide is about 7" and with it cranked all the way towards the back of the lathe I can bring it forward with both screws tightened and it moves nice and smooth. Once I get to about the 4" spot it starts to bind. The binding seems to be at the same spot on the hand crank but the closer I crank it towards me the more it starts to bind overall. I can loosen the two screws slightly and it will be smooth sailing. This is getting frustrating but maybe I just need to keep going up in shim thickness and see if I can ever get smooth travel throughout the entire length. I'm taking a break from it for now.
Oh, and the scrapping sound went away when I added the .008" shim. I'm guessing it wasn't a scrapping sound but more of a binding sound because I never did find any scratch marks on the nut. Ed 
07-04-2014, 09:05 AM
That sounds like the same complaint you made in post #1. Have you checked to see that the leadscrew is parallel to the slideway?
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