Pultra lead screw

Does anyone by any chance have or know where I might get a lead screw for a Pultra lathe crosslide, it’s a very fine thread so probably 40 tpi because according to Chris at Smart&Brown they were either 20 or 40 tpi

I think it best if you measure the tpi and then repair that feed screw nut.

On my Pultra 1750 all the dials are marked 0 to 100 and the screws are 6mm diameter and 1mm pitch. Possibly 0BA as other threads and screws are BA. I doubt spares are available, but shouldn't be difficult to make a new one.

Andrew

Thanks for replying both, my Pultra 17/70 crosslide is imperial, I have measured the screw and it’s 0.246” and 40 tpi

and the grub screw threads are 6 BA

and yes I could make one if I could use the crosslide .

Dell

Forgive me asking at this late stage, Dell …

Is it the screw or the nut that you need to make, or both ?

Thread title and text seem at odds with the photos

Incidentally, that nut appears to be engraved D.2,5
… Which I would guess identifies it as being for a 1/4” Diameter screw.

Can’t get at mine at the moment or I would check whether it’s a common feature.

MichaelG.

Thanks Michael

Please forgive am oil man

it’s the nut but I understand that both should be changed as a set but if I can find or get a nut made that would be better than nothing, I thought about the D .25 but I would have thought it would have been D .250 and I should have said the the dial is 0 to 25 so 25 thou per revolution , so that points to 1/4” X 40 tpi.

Dell

Edited By Dell on 04/10/2022 18:38:42

.

More guessing from me …

I reckon there might just be enough wall thickness there to bore it out and insert a 40tpi bush retained with some Loctite 638 or similar.

MichaelG.

.

Edit: __ Taps seem very reasonably priced: 

https://www.tracytools.com/1-4-x-40-tpi-me

Edited By Michael Gilligan on 04/10/2022 19:01:02

I have already ordered a couple of taps and a 9/32” end mill as I am going to sleeve it ( the same as when I bush a clock plate and re tap it then if is works I can then make a new one..

thanks Dell

Dell, it may be too late but I would advise purchasing the HSS taps rather than the carbon steel, the HSS are made to a better standard IMO. I have had both from Tracytools

Hi John

thanks for that but yes to late now but if it is the correct thread then I will order HSS to make a new one.

I am surprised. If you intend to repair that feed screw nut, why then make a new one?

Good question, although if I can sleeve it I am belt and brasses so a complete new one will make me happier, also I need the repaired one to make a new one using the crosslide,

Well it was definitely 1/4” 40 tpi thread , I opened out the hole to 9/32” I couldn’t go any larger otherwise I was in danger of breaking through to other holes turned a bush up to be a very tight fit using a graver ( I couldn’t use the crosslide) ha , pressed it into hole, drilled hole to 5.5mm ,started tapping and promptly turned the bush out so a rethink was in order, as I already had some silver solder paste I cleaned everything up and smeared a small amount of the paste round the bush pressed it back in and heated until solder flowed that did the trick, finished cutting the thread cleaned everything and put crosslide back together, no play whatsoever.
so now to make a new replacement but what metal to use brass or bronze.
Dell

Well done, Sir

MichaelG.

All the Pultra cross slides i've seen have the feed nuts made in two parts to allow for backlash elimination The grubscrews adjust the distance between the threaded parts, and the main screws lock everythig together. The thick part is approx. 7.5mm deep, the narrow part is approx.  4 mm deep with a 1.5mm boss. 

Dave. 

Edited By david bennett 8 on 06/10/2022 20:56:58

Edited By david bennett 8 on 06/10/2022 21:23:00

P.S. use bronze for the nut.

Dave.

I couldn’t use the crosslide

Interesting! From that, I assume that lathe does not have a compound slide?

.

An interesting assumption ^^^
… I regret that your logic escapes me.

MichaelG.

That’s odd my nut is one piece and the dials are different, maybe the difference is yours are metric and my one is imperial.

Dell, If the logic also escapes you, too, I can PM you to explain how simple it can be.