Flexispeed meteor-II lathe Cross-Slide / lead-screw specs.

[Johan ViljoenParticipant @johanviljoen49340]

Hello all, I'm busy restoring a Flexispeed meteor-II lathe. The Cross-Slide lead-screw is quite badly damaged.

And herewith starts my challenge. (I'm not very clued-up in the imperial sizes)

I've measured the OD of the lead-screw thread @ 0.188 with 24tpi. My best guess would be that this should give me a 3/16 – 24 BSW thread.

,,, I bought the taps & die. The tap fits perfectly into the Cross-Slide. But the die does not fit the "good" lead-screw at all. (however, the "good" lead-screw also fits the cross-slide perfectly)

"forcing the die onto the 1st 1 1/2 threads, I took a photo,,, definitely Not good.

(,,, not sure how to add the photos)

Any suggestions as to what's going on here most welcome. (I've used FEW taps & dies)

Thanks, Johan

[Johan ViljoenParticipant @johanviljoen49340]

[Michael GilliganParticipant @michaelgilligan61133]

Let’s start with the easy bit, Johan : **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=103028&p=1

MichaelG.

[Johan ViljoenParticipant @johanviljoen49340]

[Johan ViljoenParticipant @johanviljoen49340]

Thanks Michael, that was easy enough

[Michael GilliganParticipant @michaelgilligan61133]

Is the die a ‘split’ version ?

… if so, it may need adjustment in the dieholder.

MichaelG.

[Neil AParticipant @neila]

You need to be careful with the threads on the Flexispeed Meteor 2. I found that the threads on my particular one were UNC and not Whitworth.

When I made a longer cross slide the thread I used for the lead screw was a No 10 – 24 UNC, this has a 60 degree angle against the 55 degree angle of the Whitworth. This could be why your die does not fit the good lead screw very well.

I hope this helps and does not confuses the issue.

Neil

[Michael GilliganParticipant @michaelgilligan61133]

Good point, Neil

Johan’s photo of the thread does look more like Unified than Whitworth in form

… obviously can’t be sure, but it would explain why the Tap ‘fits’ but not the die

MichaelG.

[James AlfordParticipant @jamesalford67616]

Just to underline the inconsistency with threads on the Flexispeed Meteor: I have two lead screws which have the same number of TPI, but have different thread forms. One is quite square in section, whereas the other is much more triangular. Similalry, I have a spare cross slide and the gib screws are not interchangeable between the spare and the slide on the machine.

Regards,

James.

[Andy CarlsonParticipant @andycarlson18141]

I'm surprised the fit is that bad if it is just a UNC vs BSW difference. When trying to identify some threads a while back I drew up the two forms overlaid on each other. Yes their angles and treatment of the thread peaks and troughs are different but…

1. I think it's very difficult to tell either by looking or by measuring which one is which

2. When trying off the shelf nuts and bolts together they seemed to all fit each other, both ways of mixing.

Off the shelf nuts and bolts can have a generous tolerance allowance which may account for point 2 and may be less true for your lathe parts but hopefully you get my point.

That's not to say it's fine to mix them in critical situations – one is 60 degrees and the other 55 so the thread flanks won't apply load to each other evenly… but in the majority of cases they do seem to fit together.

To me, UNC vs BSW doesn't add up to the amount of misfit that your photo shows.

I don't have any speific knowledge of the threads on the Flexi but if I were you I would also check the measurement over wires of the male thread before going any further – it may not fully resolve the question but it will be a measurement of the thread that you are dealing with at the part where it needs to engage with its friend. The link below will tell you the wire size and measurement over wires…

https://www.cgtk.co.uk/metalwork/reference/screwmeasurement

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Andy Carlson on 20/01/2021 08:10:24:

I'm surprised the fit is that bad if it is just a UNC vs BSW difference. When trying to identify some threads a while back I drew up the two forms overlaid on each other. Yes their angles and treatment of the thread peaks and troughs are different but…

[…]

To me, UNC vs BSW doesn't add up to the amount of misfit that your photo shows.

,

Andy

(a) The difference would also be between 3/16” and #10 diameters … small, but non-trivial

(b) May I ask : what ‘misfit’ do you see shown in a photo of a single item ?

MichaelG.

.
.

P.S. __ I received a useful PM, early this morning, from Mark Frampton; which gives support to the hypothesis that it is a Whitworth-UNC mismatch. [hopefully he will post something later today]

[Michael GilliganParticipant @michaelgilligan61133]

PostScript: __ There is some, hopefully useful, information in my post at the top of this recent thread: **LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=169168&p=2

MichaelG.

[Andy CarlsonParticipant @andycarlson18141]

Posted by Michael Gilligan on 20/01/2021 08:45:53:

(a) The difference would also be between 3/16” and #10 diameters … small, but non-trivial

(b) May I ask : what ‘misfit’ do you see shown in a photo of a single item ?

A… yes, I was using bigger sizes where UNC and BSW have the same nominal size

B… I was assuming that the deformation of the end-most threads in the photo was showing the misfit. Maybe that wasn't right?

I dug out my drawing again. It was just done for my own amusement some time back and never intended for sharing… or even necessarily for me to remember the full detail later, but…

Checking the dimensions again, this is for an 18 TPI thread with UNC in blue and Whit in green – the colours were less muddy until I exported to JPEG. This assumes zero tolerance (which is never the case). The male side is at the bottom. UNC chops off the peaks of both male and female threads as shown by the lines on the drawing.

After doing this I decided that trying to determine UNC-ness or BSW-ness of an unidentified thread by fitting it to a known nut or bolt was probably not going to be very informative with real world tolerances in play.

Hopefully the OP is making progress.

[Howard LewisParticipant @howardlewis46836]

From personal experience, I can say that a BSW bolt into UNC will not go.

Our Chief Engineer would not countenance anything other than BSW and BSF. When we came across UNC threads in Clayton Dewandre unloader valves the tappings had to be tapped out to BSW for the bolts that we had in stock

If the Leadscrew is UNC then it should be cleaned up with a UNC Die. Ideally the die should be adjusted using a good quality UNC bolt as a gauge.

If the BSW Tap goes into the leadscrew nut, either the nut bis worn, or someone has already put a BSW Tap through it.

Before buying a UNC die, try a good quality UNC nut on the thread.

Butb if the nut has already been modified to BSW, you might as well set up the Dies on a good BSW bolt and modify the thread to match the nut.

Not an ideal situation, but you have to live with what is there, unless you can obtain or make prototype replacements.

Howard

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Howard Lewis on 20/01/2021 19:47:34:

From personal experience, I can say that a BSW bolt into UNC will not go.

.

It depends upon the UNC ‘Tolerance Class’ class, Howard … that’s why I posted the link earlier

Perhaps the most notorious example is that the ISO standard for photographic tripod screws is 1/4” 20 UNC, to such a sloppy tolerance that it fits the 1/4” Whitworth socket in a camera.

[ yes, I know that’s the other way round to your example ]

MichaelG.

[Howard LewisParticipant @howardlewis46836]

Maybe the camera thread, which has been 1/4 BSW since LONG before I was born, (and 3/8 BSW for larger cameras. STILL used on professioinal tripods today ) is why the ISO UNC standard is so sloppy that "one size fits all"?

We could screw UNC bolts, IF we had any, into BSW tappings, but had to retap UNC tappings to use the BSW bolts so beloved of our Chief Engineer at the time.

You think I'm a Luddite?

He made us change all the 5/16 UNF propshaft bolts with Nyloc nuts to 5/16 BSF with castellated nuts and split pins before a new vehicle was put into service. Because the holes were out of line, they slackened in service and the depots the had to tighten, redrill and repin before the MOT inspector got to see them!.

Howard

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Howard Lewis on 20/01/2021 21:54:02:

.

You think I'm a Luddite?

.

Not at all, Howard … Whitworth remains a superhero

MichaelG.

[Howard LewisParticipant @howardlewis46836]

Without Maudslay inventing the micrometer and Whitworth standardising screw threads where would be be?

Yes, we owe them a huge debt of gratitude.

the Greeks had a word for it but the British have standards for many things.

Howard

Proof reader wanted

Edited By Howard Lewis on 21/01/2021 19:42:49

[Johan ViljoenParticipant @johanviljoen49340]

Posted by Andy Carlson on 20/01/2021 19:20:42:

Posted by Michael Gilligan on 20/01/2021 08:45:53:

(a) The difference would also be between 3/16” and #10 diameters … small, but non-trivial

(b) May I ask : what ‘misfit’ do you see shown in a photo of a single item ?

A… yes, I was using bigger sizes where UNC and BSW have the same nominal size

B… I was assuming that the deformation of the end-most threads in the photo was showing the misfit. Maybe that wasn't right?

I dug out my drawing again. It was just done for my own amusement some time back and never intended for sharing… or even necessarily for me to remember the full detail later, but…

Checking the dimensions again, this is for an 18 TPI thread with UNC in blue and Whit in green – the colours were less muddy until I exported to JPEG. This assumes zero tolerance (which is never the case). The male side is at the bottom. UNC chops off the peaks of both male and female threads as shown by the lines on the drawing.

After doing this I decided that trying to determine UNC-ness or BSW-ness of an unidentified thread by fitting it to a known nut or bolt was probably not going to be very informative with real world tolerances in play.

Hopefully the OP is making progress.

B… I was assuming that the deformation of the end-most threads in the photo was showing the misfit. Maybe that wasn't right? This is exactly the misfit.

Also, I've now tried the UNC#10 -24tpi, better but not 100%.

,, I'll keep at it. thanks for all the input so far

[Andy CarlsonParticipant @andycarlson18141]

Posted by Johan Viljoen on 22/01/2021 17:56:01:

I'll keep at it. thanks for all the input so far

Well done.

If you haven't tried it then I'd still recommend measuring over wires. It will give you a bit more info, it's a better check than measuring the OD and it's not too difficult to do -.just find something that is a consistent diameter and in the right ball park, The sweary man from the Admiralty who taught me how to do thread cutting recommended using chopped up paper clips for the job we were doing. That was for a different sized thread so they may or may not be in the right ball park for your job.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Johan Viljoen on 22/01/2021 17:56:01:

Posted by Andy Carlson on 20/01/2021 19:20:42:

B… I was assuming that the deformation of the end-most threads in the photo was showing the misfit. Maybe that wasn't right? This is exactly the misfit.

.

My apologies to you both … I had assumed that the ‘deformation’ was evidence of slight chamfering to ease engagement [noting that this is a fairly small diameter] :

If it’s been done by the die, then the die [or its adjustment] is suspect.

MichaelG.

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