Pultra lead screw

[DellParticipant @dell]

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

[DellParticipant @dell]

[not done it yetParticipant @notdoneityet]

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

[Anonymous]

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

[DellParticipant @dell]

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

[Michael GilliganParticipant @michaelgilligan61133]

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.

[DellParticipant @dell]

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

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Dell on 04/10/2022 13:25:24:

.

 

.

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

[DellParticipant @dell]

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

[JohnFParticipant @johnf59703]

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

[DellParticipant @dell]

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.

[not done it yetParticipant @notdoneityet]

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

[DellParticipant @dell]

Posted by not done it yet on 05/10/2022 08:14:42:

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,

[DellParticipant @dell]

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

[Michael GilliganParticipant @michaelgilligan61133]

Well done, Sir

MichaelG.

[david bennett 8Participant @davidbennett8]

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

[david bennett 8Participant @davidbennett8]

P.S. use bronze for the nut.

Dave.

[not done it yetParticipant @notdoneityet]

I couldn’t use the crosslide

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

[Michael GilliganParticipant @michaelgilligan61133]

Posted by not done it yet on 07/10/2022 09:13:21:

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.

[DellParticipant @dell]

Posted by david bennett 8 on 06/10/2022 20:52:53:

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

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.

[not done it yetParticipant @notdoneityet]

Posted by Michael Gilligan on 07/10/2022 11:16:13:

Posted by not done it yet on 07/10/2022 09:13:21:

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.

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

[david bennett 8Participant @davidbennett8]

Dell, mine is metric,but your nut looks rather long. I wonder if yours was made with the intention of being cut into two at a later date. If not , can you see a purpose for the grub screw holes?

dave.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by david bennett 8 on 07/10/2022 20:47:55:

[…] I wonder if yours was made with the intention of being cut into two at a later date. If not , can you see a purpose for the grub screw holes?

dave.

.

I had the same thought, Dave … but you expressed it so well that I shall just add +1

MichaelG.

[DellParticipant @dell]

Posted by Michael Gilligan on 07/10/2022 21:22:17:

Posted by david bennett 8 on 07/10/2022 20:47:55:

[…] I wonder if yours was made with the intention of being cut into two at a later date. If not , can you see a purpose for the grub screw holes?

dave.

.

I had the same thought, Dave … but you expressed it so well that I shall just add +1

the only thing I can think of is when one gets wears adjusting one grub screw over the other it puts a slight twist on the nut , so effectively putting the thread on an angle and taking up play because putting the thread on an angle tightens it up , the overall length of my nut is 11mm same as the split two together, my Pultra is mid 1940’s so perhaps the one in the picture posted earlier is later and metric.
a friend has a crosslide ( metric ) with smashed T slot on the bottom and I am hopeful he will sell it to me so I can convert my crosslide to metric and that one has split leadscrew nuts, it has bigger dials as well the same as the picture earlier, having gout in both hand it would be easier to use.

Dell

also I see the nut in picture has a shoulder on one part and a recess on the other , yes please PM me and explain, if it was a antique clock I would be fine.

MichaelG.

 

Edited By Dell on 07/10/2022 21:41:18

[david bennett 8Participant @davidbennett8]

Dell If you "search" this site for "pultra" ( stripped thread) there is one identical to yours.

dave

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