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Thread: What to do, what to do...
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10th August 2013, 10:31 PM #1Philomath in training
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What to do, what to do...
One of the long term jobs that I have lined up is to renew the compound and cross slide screws and nuts on my lathe. The lathe has suffered from poor lubrication in the past and while the screws are worn in one location, the nuts are just worn. The photo is of the old compound nut, old compound screw and on the left the new (purchased) nut. The purchased nut is slightly shorter than the old nut but around the same diameter. There is a little extra clearance in the slide but not much (a few mm)
P1010838 (Medium).JPG
My plan is to cut a new screw using the new nut to get the clearance right but I'm still debating how best to mount the nut. I'd like to keep the original nut rather than try and doctor it so a new mounting is needed. The question I have for the forum at large is how-
At the moment I can think of several options and I'd like some opinions on what is likely to be the best (easiest to do while adding least to the backlash present).
Current options under consideration are
- Make up a mount that will match to profile of the nut and then silver solder the nut to the mount. Maybe add a couple of dowels or screws to improve shear strength. Possibly put a groove in the nut and a matching rib on the base (for shear strength again).
- Machine some flats on the nut and then make up a U shaped base so that the nut just sits in the U but is constrained from moving axially or rotating
- I'm also wondering whether a gimbal type mounting may be worth trying - horizontal pins on a U shaped bracket with the base of the U able to pivot around a vertical axis.
My main concern with a soldered joint is I could introduce distortion or misalignment into the set up. The other two options are to allow any slight misalignment not to influence things, but add complexity and are potentially weaker.
Another question is whether I should cut the nut in two and then mount the two halves so I have an anti-backlash set up. (Arguably not worth doing as I don't often use the compound but that is normally because of the backlash it currently has). It's worth mentioning that the cross slide also needs doing and has a similar arrangement so anything done on the compound is likely to be a dress rehearsal for the cross slide.
Michael
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10th August 2013 10:31 PM # ADSGoogle Adsense Advertisement
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10th August 2013, 11:18 PM #2
Hi Michael,
You could machine 2 flat sides (opposite to each other), and then solder on an oversized spigot, put it in the 4 jaw, using the ends and your 2 new flats, and true the spigot.
I don't like option 2 so much, i think the U will wear the bronze nut and end up adding more backlash. Maybe.....
A gimbal i like, but is it really necessary? with correct alignment option one will be easier and last longer.
The thing i found hardest with the Mars was the R/L alignment. Vertical was far easier.
If your going for the split i would go horizontal and add springs to push the 2 halves of the nut together rather than the vertical split. That way there is no way the cutting forces should overcome the spring.
Just my thoughts on it anyway.
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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10th August 2013, 11:25 PM #3
You could do what I did. Talk about it a lot on the forum then get hold of a new lathe!
Looks very similar to my cross slide. Is there any extra clearance outside the original nut? If so make the mount bigger so nut can be mounted inside, but I guess you would have thought of this if it was possible.
I would go with option 1. Any added complexity is just adding wear points in my opinion.
Dean
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11th August 2013, 12:14 AM #4GOLD MEMBER
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Hi Michael,
Would it be possible to machine the new nut down and then bore the old one, put the new nut in the freezer and warm the old one and then assemble, as extra security you could cross drill the unit so that it crosses the join line and fit a pin hammered in and peen on both ends over.
These could be done in 3 places (2 at the bottom and 1 on top), no distortion and a secure fit. I have done this before to repair similar set ups.
Kryn
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11th August 2013, 08:42 AM #5Philomath in training
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It could be done that way Kryn, but I'd like to keep the original nut intact as a reference in case I never need to do this again. My history with shrink fits has never been that good and with only one go I'd be concerned that I'd have no back up. (Should have bought a second nut so it could sit and gather dust for the next 20 years).
Michael
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11th August 2013, 09:20 AM #6Pink 10EE owner
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Is it off the CVA?
Light red, the colour of choice for the discerning man.
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11th August 2013, 10:13 AM #7.
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Michael,
How about replicating the shape of the existing nut in steel but making it slightly oversize ( taking advantage of those few extra millimeters of clearance ) and boring it out to suit the new nut which probably would require a reduction in diameter. Then gluing the components together with something like Loctite Super Bearing Mount. A portion of the bore would require an interference fit with the "nut" to provide alignment, the remainder of the bore would be slightly oversize to accommodate the adhesive. I don't know how compatible bronze, steel and Loctite are, but if my suggestion has any appeal I'm happy to decant some of the SMT into a small container and post it over with your Swiss Delights.
BT
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11th August 2013, 11:08 AM #8SENIOR MEMBER
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I agree with Bob .
Provided you have the space, I would make the block as large as possible in steel and bore it out to take the nut/cylinder.
Lightly press in the cylinder and cross pin it through the circumference or Loctite with a small thrust flange at the handle end.
The other option is to make the existing block adjustable by slotting it vertically and adding two small tensioning bolts lengthways ala the way Chinese lathes do it.
Rob
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11th August 2013, 11:10 AM #9Philomath in training
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Yes
Thanks Bob - I have some bearing mount stuff (I use it occasionally to make up for the inadequacy of my fitting skills). It's another option to investigate, although the tricky bit then becomes hanging onto the nut to get a concentric OD. I'd probably put something like a roll pin in as a scotch key to hold it. If I went at 90 degrees to the axis it may also lock things axially too (that is, use it as a cotter pin).
Michael
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11th August 2013, 11:14 AM #10SENIOR MEMBER
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Holding onto the cylinder shouldn't be a problem provided you use a live centre at the other end.
Just pinch the headstock end in a collet about 2 mm and that can form a locating flange for the turned down job.
Rob
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11th August 2013, 01:43 PM #11
Hi Michael,
Is this the next installment of this earlier thread? https://www.woodworkforums.com/f65/do...e-taps-173173/
I'd cut a thread on the outside of the new nut and screw it into a block of bronze, a bit of loctite wouldn't hurt... set it up in the 4 jaw then machine the spigot.
Regards
Ray
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11th August 2013, 05:28 PM #12GOLD MEMBER
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nuts
hi what sort of lathe ido you have?
aaron
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11th August 2013, 08:28 PM #13Philomath in training
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11th August 2013, 08:40 PM #14
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11th August 2013, 09:31 PM #15Philomath in training
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Dean, it's a Murphy's law thing. As soon as I modify or discard a piece of the machine, I run the risk of needing the thing in it's original state.
The mill I had before the Sajo was a Tom Senior. It was damaged in transit by a careless shipper so I replaced the bend handles with new round ones rather than the original 3 ball ones. 5 years later when I sold it I mentioned that I had the original (but damaged) handles still and the buyer wanted them - I got to keep the good ones, he wanted the damaged ones.
Michael