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.

[David George 1Participant @davidgeorge1]

I have made both leadscrews and nuts for an M Type lathe. The nut was made by turning and screw cutting a phosphour bronze flanged nut which was chased through with a silver steel tap hardened and tempered which i made prior to starting the nut. I have also made a few leadscrews to match the same just by screw cuting a piece of silver steel centered on the end for a rotating steady and also suported by the traveling steady.

David

[jim1956]

On jim1956 Said:

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.

Thanks Jim,Thanks for the photo’s. You have a very similar set up to me. I have ordered a trapezoidal screw set from eBay and I’ll have a good look at it when it arrives. As you say, they are very cheap and it looks like it may do the job quite well.

It looks like you broke through the casting when you fitted the nut, what was the OD of the nut/drill?

I’ve fitted the same super cheap toolholder which was a considerable time saver over the original clamp. I made up some brass bushes to fit inside mine to make things a bit tighter and take out a bit of flex.

[ianday1972Participant @ianday1972]

You’ve done a great job with those leadscrews David. Sadly your talents exceed mine by some considerable margin, as much as I’d like to have a crack at turning my own screws I haven’t progressed that far yet. I only got my lathe a few months ago and I don’t have a steady rest although it’s on the project list!

I guess I’d have to grind my own tool to cut a square thread? Again this is something I haven’t tried yet.

[ianday1972]

On ianday1972 Said:

 

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

Thanks Jim,Thanks for the photo’s. You have a very similar set up to me. I have ordered a trapezoidal screw set from eBay and I’ll have a good look at it when it arrives. As you say, they are very cheap and it looks like it may do the job quite well.

It looks like you broke through the casting when you fitted the nut, what was the OD of the nut/drill?

I’ve fitted the same super cheap toolholder which was a considerable time saver over the original clamp. I made up some brass bushes to fit inside mine to make things a bit tighter and take out a bit of flex.

My cheap Lidl calipers said the OD of the nut was between 10.15 to 10.18 mm.

I drilled out the old 5/16″ thread progressively, from 8mm to 10mm, still too small so had to use a 10.2mm drill to get it to fit.

Maybe I’m telling you something you already know but I was caught out by multi start threads.  A lot of the 8mm trapezoidal leadscrews and nuts offered on ebay are for set-ups where a stepper motor would be driving the leadscrew, they’re 4 start 2mm pitch but 8mm lead.  I’d never heard of multi start threads so I ordered based on the 2mm pitch, but the four start thread means one rev of the nut moves it 8mm.  Not suitable for a cross slide I think, it’s so low friction that if you hold it vertically the nut unwinds itself and falls off.

The ebay code (the bit after http://www.ebay.co.uk/) for a 8mm leadscrew with 2mm pitch and 2mm lead is

/itm/296058800848?var=594189715645

Regards  Jim

[Author]

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