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Thread: crossslide leadscrew nut
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18th May 2014, 03:53 PM #1
crossslide leadscrew nut
_PAS5603.jpg_PAS5605.jpgHi, I'm trying to remove some slack from the leadscrew on the carriage of my AL 320 lathe and just discovered that the bronze leadscrew nut cannot be tightened against the bottom of the compound slide because the part of the nut that goes through the slide is longer by .43mm than the thickness of the slide so when you tighten the screw into the nut it just wobbles around, question is, is this so the nut can self align with the leadscrew or should it be fixed tightly to remove play?, Leroy,
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18th May 2014, 04:22 PM #2SENIOR MEMBER
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My CQ9325 has the same setup and it pulls up hard against the base of the topslide.
All the adjustment is done by pinching the thread with the two screws in the bronze/brass block.
Try putting a shim between the block and the cross slide and see what effect it has, as you fully traverse the slide.
RobThe worst that can happen is you will fail.
But at least you tried.
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18th May 2014, 06:38 PM #3GOLD MEMBER
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Which way around does that nut go?
Stuart
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18th May 2014, 07:13 PM #4
crosslide leadscrew nut
the black spacer with the Philips screw goes in the hole on top of the slide and the round section on the bronze nut fits into the hole from underneath with the two adjustment screws facing the rear of the lathe, the problem was the round section on the nut was too long so could not be tightened to the slide, Rob's suggestion of shims worked and has taken all play out of the crosslide, I was going to machine the extra metal from the nut so that it lined up as it should, not sure how critical these dimensions are but as I had to assemble it to see if the shims worked I'll wait till next time I have it apart Leroy
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18th May 2014, 07:23 PM #5GOLD MEMBER
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18th May 2014, 07:42 PM #6SENIOR MEMBER
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18th May 2014, 08:27 PM #7GOLD MEMBER
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18th May 2014, 08:41 PM #8Philomath in training
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If the nut when it could slide up and down in the cross slide hole was loose on the screw and now that you have fixed it's position it is tight, to me that seems you have fixed the problem by pushing things out of alignment. If the fit of the nut boss in the cross slide hole was a smooth sliding fit then whether it was fixed or not did not matter as it would automatically adjust it's position to accommodate any error in the screw (eg a slight bend).
If the nut boss was loose in the hole then a better solution may be to either sleeve the hole or the boss so that it is a smooth sliding fit.
Michael
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18th May 2014, 08:52 PM #9SENIOR MEMBER
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The worst that can happen is you will fail.
But at least you tried.
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19th May 2014, 08:41 PM #10Awaiting Email Confirmation
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Leroy,
came across a similar problem on my lathe, except the brass nut did not contain the pin, the pin was separate and basically allowed for a crappy screw alignment when manufactured due to it sliding piston style in the cross slide.
when checking the piston pin it moved about 0.3mm in the cross slide which would cause more wear over time, solved it by first adding the 2 grub screws and machined a new flanged bolt pin to fit tightly in the cross slide.
it helped but found out that the cross slide screw was not centered in the other axis.
needed to make up another flanged pin, except drilled the bolt hole about 0.4 mm off center so that the other axis could now be adjusted.
definitely improved the feel, as it didn't get any tight-spots along the slides travel.
looking at the photos of your cross slide it seems as if there's not much room to add the 2 grub screws similar to what many lathes use, even the screw oil hole is in the way for one of the screws as well as the nut not being long enough.
the other option is to use 4, M4 grub screws on the corners of the brass nut, looks as if there's room, "images attached"
fig 1, shows the 4 grub screws and flanged pin, note the optional flanged pin on the right (light and dark blue) has an off centered bolt hole which allows for adjustment if the screw is not parallel along that axis).
fig 2, bottom view, displays the brass nut pin cut off.
fig 3, no explanation needed.
fig 4, top view and shows the optional flanged pin with the off center bolt hole.
cslide-1.JPGcslide-2.JPGcslide-3.JPGcslide-4.JPG
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19th May 2014, 09:50 PM #11
crossslide leadscrew nut
Just to recap, the original problem was a lot of play in the crosslide back and forth and a tightening as it neared the end of the screw, both of these problems were fixed by adding shims between the nut and the slide, it now slides very smoothly with no binding even with the gibs tightened more than before, there is only 2.5 thou. backlash in the crosslide now, I'm thinking about drilling and tapping a hole through the nut so as to expand the gap instead of compressing it, not sure if the results would be worth the effort, or leave well enough alone, anyone's opinion is welcome, Leroy
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19th May 2014, 09:50 PM #12SENIOR MEMBER
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Can we at least call the roundy part on a square nut a journal. Thats the round male round part that floats up / or down in the female bore in the cross slide. 0.43 millimeters, you may as well call half half a mill. Its a huge amount. Randomly shoveling shims in, wheres the basis in that?
Get rid of all the shims, wind the slide back until its allmost hitting the housing at the bearing end. Thats the point where it's the most self aligned, with the nut closest to the anchor point via bearings. The other end of your screw doesnt have a housing /bearings. Then depth mic the top of your nut journal, to find out where your nut really wants to sit.
If you were in my caper, you would measure it @ 0, 90, 180. 270, and put it in the middle to average bend/ run out.
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19th May 2014, 10:34 PM #13Philomath in training
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20th May 2014, 12:14 PM #14SENIOR MEMBER
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This indicates that the original looseness/ poor fit was caused by too much metal being machined from the top square section of the nut, also making the journal too long.
The shims have obviously positioned the thread block on the correct alignment.
That's why I said try adding shims first, rather than simply grind a bit off the top of the journal. If shims had made it worse, then you could attack the journal length.
I'd just superglue the shim to the block so it can't dislodge and leave it as is.
Spreading or compressing the slit block would appear to have the same effect as I see it. All the thread canting will still be in the thin section, regardless.
RobThe worst that can happen is you will fail.
But at least you tried.
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20th May 2014, 12:31 PM #15
As I see it you want the large part of the thread taking the thrust away from the work. There is more likely to be more load pushing the slide out than in. So if the slit is at the back of the nut you want to compress it not jack the two halves apart. I think thats right.....
Ew1915 17"x50" LeBlond heavy duty Lathe, 24" Queen city shaper, 1970's G Vernier FV.3.TO Universal Mill, 1958 Blohm HFS 6 surface grinder, 1942 Rivett 715 Lathe, 14"x40" Antrac Lathe, Startrite H225 Bandsaw, 1949 Hercus Camelback Drill press, 1947 Holbrook C10 Lathe.
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