Pultra model P

[Phil PParticipant @philp]

Just seen this thread on Pultra leadscrew nuts, there is a photo showing the split version.
It looks to be on the later 1750 style though, so maybe I got mixed up with which Pultra they are fitted to.
I would think it a very easy mod to carry out on a model P though.

https://www.mig-welding.co.uk/forum/threads/pultra-crosslide-leadscrew-nut.124409/

 

Phil P

[Michael Gilligan]

On Michael Gilligan Said:

The fact is that the <strong style=”font-family: Verdana, Arial, Helvetica, sans-serif; font-size: 14px;”>shape of the Whitworth thread lends itself rather well to running sweetly in a lead-screw arrangement.

Just to elaborate a little [because I consider the matter important, and this is a good place to post it] … The 55° angle and rounded crests are perfectly adequate for modest loads.

The use of square, Acme, and buttress threads was motivated by other factors … all before the days of Finite Element Analysis, but would make a worthy subject for that.

In ‘instrument’ work [microscopes, Pultras, and such] the lead-screw was made as near perfect as possible and then a slightly tight-fitting nut would be lapped to fit.

The shape of the Whitworth thread means that this can produce a sweetly-running pair that is almost sealed against the ingress of dust … because the lubricant film is only as thick as the lapping compound was !

Time, use, and abuse, ride rough-shod over such niceties of course.

 

[ steps down from soap-box ]

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

With apologies for the filthy state of it … this is a short section of lead-screw on a Pultra vertical slide that I have for restoration.

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It has a negligible level of wear, and I don’t think there can be much doubt that this is a Whitworth form thread.

MichaelG.

[mark smith 20Participant @marksmith20]

Talking of split anti backlash nuts in later 1750/ 1780 pultras.  i just relised that this must work in a similar way as if you look at the photo the central mounting boss is also threaded for the leadscrew ,so by adjusting the bronze nut in or out must take up any slack. I didnt realise both were threaded. Is the central mounting boss threaded on later pultras? There wouldnt be any need if the nut was split.

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