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  1. #1
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    Default Does anyone own some ACME taps?

    One job I was going to attempt on the weekend was to tighten up the compound slide feed as there is backlash in the screw and the gib needs shimming/ replacing.
    Previously I'd bought a 3/8" 8tpi (RH) brass nut so the plan was to make up a new screw using the nut to check fit then mount and machine the nut so that I had a matched screw and nut. However, I discovered on disassembly that the screw was not 3/8" 8tpi but 1/2" 8tpi. I think that was me "remembering" the diameter while sitting at the computer at work (either that or it had grown since I looked at it. Yeah - that sounds more likely). A careless mistake as disassembly does not take all that long but the lathe was not available at the time. Unfortunately the place I bought the 3/8" nut from does not have a 1/2" 8tpi version.
    Does anyone have a 1/2" 8tpi (RH) ACME tap set that I could borrow to make a nut? Plan B is to single point and then clean up with a home made tap but that takes an afternoon's work into the realms of a weekend's work.
    On the positive side, I do have a 3/8 ACME nut that is surplus to requirements if anyone needs one...

    Michael

  2. #2
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    Default

    Ive got a 5/8 x 10tpi LH ACME if its of any use...

    Yeah, I didnt think so

  3. #3
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    Default

    I suppose you've considered making a screw to fit the nut you have? Why would it matter? Same pitch and everything.

  4. #4
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    Default

    Acme taps are damn expensive.

    Can you post a photo of the thread block so we can see how it's constructed ?

    It is sometimes possible to slit 3/4 way through the thread block (cross ways) and add a couple of screws to deform the block/thread path and take out any backlash.

    I did this on my lathe and it works extremely well.

    Some Asian lathes use this method as original set up.

    Rob

  5. #5
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    Michael,

    8 TPI sounds weird for a feed screw, 125 thou per rev. I have a 10 TPI x 1/2 Acme tap available if it's of any use. Probably as useful as Rob's 5/8".

    BT

  6. #6
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    Hi Michael,

    Here, for your consideration, is "PlanB", if you can't borrow an acme tap to make a nut, and buying a tap to make one nut is a waste of good cash reserves, what about short circuiting the process and go direct by buying a 1/2-8 acme nut?

    These guys have a good range, including some anti-backlash versions. 1/2 - 8 Right Hand Acme Lead Screws & Nuts for Power Transmission - Roton Products, Inc.

    Regards
    Ray

  7. #7
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    Default

    Quote Originally Posted by RayG View Post
    Hi Michael,

    Here, for your consideration, is "PlanB", if you can't borrow an acme tap to make a nut, and buying a tap to make one nut is a waste of good cash reserves, what about short circuiting the process and go direct by buying a 1/2-8 acme nut?

    These guys have a good range, including some anti-backlash versions. 1/2 - 8 Right Hand Acme Lead Screws & Nuts for Power Transmission - Roton Products, Inc.

    Regards
    Ray
    Wish I knew about this mob.I had to fix up my old dinosaur Denbigh that the table feed nut expired.I made a new 1 after about 2 goes the third was ok.Never had to cut an ''internal in that form before''.Out with the text books.a bit of time and a lump of cast.Final result satisfactory ,least got the mill going as is a bread and butter machine here to do cylinder heads on.next time be onto that supplier new screw and nut to match.also considered a re circulating ball and nut screw [no back lash to worry about. john.

  8. #8
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    Quote Originally Posted by Anorak Bob View Post
    Michael,

    8 TPI sounds weird for a feed screw, 125 thou per rev. I have a 10 TPI x 1/2 Acme tap available if it's of any use. Probably as useful as Rob's 5/8".

    BT
    Not so weird. One complete revolution is 1/8", 8 turns to the inch. The tailstock is similarly graduated. The cross slide measures is 250 thou per revolution, but is on diameter (so is once again 8 tpi)

    Quote Originally Posted by RayG View Post
    Hi Michael,

    Here, for your consideration, is "PlanB", if you can't borrow an acme tap to make a nut, and buying a tap to make one nut is a waste of good cash reserves, what about short circuiting the process and go direct by buying a 1/2-8 acme nut?

    These guys have a good range, including some anti-backlash versions. 1/2 - 8 Right Hand Acme Lead Screws & Nuts for Power Transmission - Roton Products, Inc.

    Regards
    Ray
    The original plan was just that - cut the screw to suit the nut, so it's back to the original plan. I was thinking about making my own tap but that may have to wait a while.
    The reason for the effort is two fold. I used the compound to machine a conical surface the other day and was not impressed with the quality of finish - you could see the turns in the screw, so I'd like to get that better. A good proportion of that is probably gib - that will need a scrape, but The other thing is that I've been told that these lathes left the factory with zero backlash. I don't know that that is achievable in a shed on a 55 year old machine but I'd like to see. Below is the nut and screw that came on the lathe. I can't say that it is original as the lathe had been half stripped, so it could have been a replacement. The screw is fine near the LH end but at the RH end there is around 10+ thou backlash. I tried single pointing a new nut but only got the backlash down to around 5 thou. That's enough that on a heavy cut the screw will vibrate back
    P1010678 (Medium).JPG P1010677 (Medium).JPG
    I am hoping that with a properly cut nut I can get down to less than 2 thou. I haven't decided whether to use the nut as a gauge for cutting a good screw and using that to cut my own nut or mounting the bought nut somehow and use that. Then it's on to the cross slide...

    Michael

  9. #9
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    Default Another fix

    Hi

    My Sheraton 9 " top slide had a sloppy nut and the screw was worn . I fixed it myself, a bush fix . I tinned the thread of the worn nut with some solder , the nut was held in a drill and rotated slowly while the solder was curing ... . I used the original screw and tapped the thread with it , the solder being soft , it worked OK , the repair has held up well . Maybe silver solder or some other harder filler would be a better choice .

    BTW I tried the same fix on the cross slide nut , but it was not successful , it became sloppy again after a short time. The top slide fix worked well... and it has not worn loose again , even after doing thread cutting jobs .

    Mike

  10. #10
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    I suspect the success or not of a fix like that would depend a lot on where the wear is. If the screw is a uniform profile and the nut worn it should work but if the screw has uneven wear (like the one I had) the difference will either be sloppy or chew the solder out.

    One thing I'm still tossing around is how best to mount a nut in the compound. Strictly speaking, all the nut has to do is provide an accurate location in the Z direction. Small movements in the X and Y don't matter. Similarly, the nut can rotate around the X and Y axis but must be fixed on the Z axis. The nut pictured was mounted in a hole so that it could rotate slightly around one axis (Y?) but could not rotate in X or Z. The nut was secured from underneath and the through hole was deeper than the nut spigot, so there was no vertical movement. The semi-rhetorical question is of course, would there be any benefit in giving the nut some more degrees of freedom? If the nut was given a ball shape and then held (like a hydraulic or pneumatic cylinder rod end) would that be better? Ideally it would eliminate any misalignment so any clearance to cope with these error would be removed. What am I missing here (besides the added complexity that would be needed)

    While I remember to ask - is there anyone else chasing an ACME nut (or threaded rod)? The site that Ray pointed to is in the US, so the postage will be similar for one nut or several.

    Michael

  11. #11
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    Default slotted nut

    The nuts on my milling table DM 45 , have a slot in them, you can take up the play in the nuts by squeezing the slot together with a screw . I have seen these slotted nuts fitted on some lathe cross slide as well.

    BTW I bought a some ACME screwed rod and round nuts from a UK seller ( cant remember the name ) , for the Hendey lathe . I needed metric sizes funnily enough as it is a metric Hendey, rather odd for a US built 1940 machine ... Mike

  12. #12
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    Try T.E.A Transmissions in Brisbane. Engineering trade components supplier - Special purpose engineering products - TEA Transmissions Australia

    They stock Trapezoidal but apparently have some ACME.
    John

  13. #13
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    Ueee is offline Blacksmith, Cabinetmaker, Machinist, Messmaker
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    As i see it the best way to remove the backlash is not to try and turn matching nuts and screws, but to make an adjustable nut. Not some split thing that relies on very little thread, but 2 separate nuts. Mount them in a bore (just like the nut you showed but bored out), one fixed, and the other keyed and sliding. Add a way of pulling the nuts apart, be it a jacking bolt or a large nut on the outside of the sliding nut. This way the nuts can wear and be adjusted to absolute minimum backlash. If course the hardest part is making it small enough to fit.....

    Cheers,
    Ew
    1915 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.

  14. #14
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    I was thinking about this today....whilst struggling with cross slide backlash of my own....I did some searching and found this link NEW DESIGN For Anti-Backlash Acme Nuts! the first idea has flaws but to thread the ID of the floating nut and the bore of the sleeve would work well, otherwise go to a sprung version.....

    More ideas here http://pic-designcatalog.com/images/..._3.pdf#page=10 Aim for page 3-11

    Cheers,
    Ew

    And more Adjustable cross feed nuts
    Last edited by Ueee; 2nd Jul 2013 at 10:47 PM. Reason: and...
    1915 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.

  15. #15
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    Default Even more...

    1915 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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