Zyto cross slide screw

[Brian WoodParticipant @brianwood45127]

Actually a very good , practical solution Michael. My Churchill lathe has just such an arrangement for the top slide, the other motion screws are ACME.

Brian

[ianday1972Participant @ianday1972]

Thanks for all the great suggestions. I think I’ll have a look at knocking up an anti backlash arrangement first and see how that goes.

I’ve found 3/8 10tpi acme tap and dies on RDG tools website which will be about £35 if I go down the route of drilling for a larger size. There should be room for it. If I cock that up I could mill out the existing “nut” and add a proper nut to the far end of the lower slide.

I quite like the idea of converting to 3/8 BSF 20tpi. That would be fairly simple and give good control over the slide in use. I might have to incorporate a nut on the handle for attaching an electric screwdriver for any big movements or i might be twiddling that handle all day :-))

Perhaps I’ll post and let you know the outcome. Thanks again.

[Martin of Wick]

On Martin of Wick Said:

 

If you opt for a complete replacement, be careful in assuming you can bore out the existing unit to fit, as you only have a couple of mm ‘spare’ metal beneath the thread on the casting. You will need to check the OD of the Myford feed nut. If it means that boring out to fit a nut will break through the casting, this is not necessarily fatal as long as there is sufficient space between the crosslide and the saddle casting to accommodate the protruding nut (you may even be able to file a small flat in the replacement nut to assist with fitting).

 

I have an old Randa with a 5/16″ 12tpi square (I think, don’t think it was Acme) cross slide thread.  The wear and backlash made it unusable in places.

The cheapest substitute I could find was a metric 8mm trapezoidal screw and nut from China on ebay.

The screw was hardened to some extent but I was able to reduce the end with carbide tooling.

The nut did fit just within the existing casting.  I don’t have a mill so I didn’t set the nut into the casting.  Losing a few mm of cross slide travel was acceptable to get consistent cross slide operation.

The old screw had a circular disk nut threaded 1/4BSF with 120 divisions for the 83thou per rev 12tpi so I was already used to doing mental arithmetic.  The 2mm lead is about 79 thou so using 0.67 thou per div instead of 0.7 isn’t any more difficult.  To use the old disk I drilled it out to match the 6mm reduced diameter and put a 6mm drill stop on it with a 1mm pin to fix it.

I left the outer excess length on the new screw in case I need to revisit or change it but so far it works ok.

Not sure how well the brass nut will wear but 8mm trapezoidal replacements are easily obtained and fitted.

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