I use a P type and restore Pultra lathes, the guide on the bottom of the crosslide is normally fixed by two pins and a bolt into a T nut, as for the leadscrew nut I have sleeved the original nut and silver soldered then re threaded with tap from Tracy tools and I have also made new nuts.

Pultra lead screw

Cant see you being a customer for a mini lathe Dell!!!

Is there a missing tapered gib?

On 16 October 2024 at 12:57 mark smith 

Dell, would you do anything about the out of line guide ?? Once i notice these things i usually get an itch to fix them.

Another thing is why do they only have one guide strip to seat on the bed??

 

Yes if was me I would correct the guide , I had to make one not so long ago , if you notice a lot of plain turning lathes only have one guide probably for ease & quickness of fitting.

the thread is 1/4” X 40tpi.

check everything is tight at the front end of the crosslide & compound because they can come loose because 1mm seems a lot.

I wonder if that solid leadscrew nut is original ?
The ones on my model P from memory were split into two halves with adjusting screws to take out the backlash.

You slackened off the two cheese head screws, then tightened a couple of grub screws to push the two halves apart along the thread axis, then re-tightened the cheese head screws.

Phil P

Thanks Mark

… still looks like a perfectly reasonable Whitworth thread-form to me.

MichaelG.

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https://en.wikipedia.org/wiki/British_Standard_Whitworth#/media/File:Whitworth_Thread.svg

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https://www.rolledthreads.com/a-quick-guide-to-acme-threads/

Go compare.

On 16 October 2024 at 16:53 mark smith 20 Said:

Jason ive dismantled the compound slide firstly and the leadscrew is moving around 0.45mm back and forth in the nut. So less than 1mm but feels like it.

Better to express the backlash in terms of dial graduations, not guestimates.   1mm, if true, means something is seriously wrong.   Before rushing to fix this, be aware that rather high-levels of backlash are acceptable in a lathe because the operator can easily compensate for it.   Backlash is perhaps best tolerated until the amount of compensation becomes annoying; that’s because adjusting the nut to reduce it wears the nut out.

Judging by the lead-screw photo, my guess is that the nut either needs adjusting, or is worn out and should be replaced.  A good photo of the inside of the nut would help decide.

Dell but what is the thread form , minature acme or what?

Dell says the thread is 40tpi Model Engineer and I believe him, though it might seem an odd choice at first.    ME is a Whitworth form thread that doesn’t follow the BSW and BSF standards in terms of diameter.    Nor does ME have to!  In this example, BSW and BSF both apply to nuts and bolts, not lead-screws.   It happens that ME standardised 40TPI on several diameters, one of which I guess happens to be a good choice for the Pultra.   In theory ACME, being designed to transmit power, is a better choice for lead-screws, but the Pultra is a small precision lathe, not a metal muncher.  40TPI ME is a good compromise I think.

Dave