RandA Spindle thread

[Water-Mark]

I've recently aquired an old RandA 3" screwcutting lathe and i'm having some trouble identifying the headstock spindle thread.
I've been on lathes.co.uk and have found it was more than likely made by portass and rebadged but no mention of the spindle thread.

I've also found on the web an original advert with all of the specs but again no thread.

The calipers would have it as a 3/4 course thread but here is where i get stuck.

There are 6 threads in total and from the first to last tooth it measures half and inch suggesting a 12 tpi.

However i found a conversion chart and the metric pitch measures 2.5mm suggesting 10 tpi.

10 tpi is more likely but i really can't be sure as i'm not very experienced in this area.

Can anybody help before i start making a backplate?

 

[CHJ]

Sounds like a standard 3/4" 10 TPI Whitworth (55deg.) thread. (metric pitch would be 2.54mm)

The alternate could be 3/4 - 12 UN (unified 60deg thread) (12tpi) (metric pitch would be 2.117mm)


Edit:- can you measure the root diameter, is there an undercut at the rear of the thread that matches the root diameter for instance.

 

[Water-Mark]

Hi, thanks for the response.
I think it is a 3/4 10 bsw so i'll order a tap and try it in the old backplate.

The under cut measures 16mm which works out at 5/8".

 

[woodfarmer]

Assuming you have very little by way of tooling.
If it is a whitworth thread the base and tops will be a bit rounded. American threads are uncut flat tops and bottoms. But they could be worn

can you grind a bit of metal (6" nail ?) so it fits the thread form exactly.

Now set the swivel on your tool post to 60 degrees, almost certainly marked.

face off a bit of something turnable straight across, and then machine using the swivelled toolpost cut the corner off to leave a 60 degree chamfer.

rest the side of the ground edge of the bit of metal and look along the face. Ifteh thread form is 60 degrees the other edge will be straight to the face. If less, likely is whitworth form thread.

And/or use a pointy bit of wood in the toolpost and "pretend" to clean you headstock threads usingthe screwcutting function of your lathe.
you should be able to see if the pointy end of teh wood tracks evenly idf it is a 10 tpi thread or not. You might also use this method to help you figure out the exact tpi .

Hope you can understand what I am trying to say.. sadly I have forgotten the English for some of the lathe parts.

 

[Water-Mark]

Thanks for the suggestion.
I have nothing in the way tooling and unfortunately the tool post is the old clamp style and has no graduations to allow accurate positioning.

As if that wasn't bad enough i also have no way of holding any work in the lathe until i have made a back plate.

I'm not experienced in lathes or engineering so even measuring a thread accurately is proving challenging.

I don't do things by half

 

[woodfarmer]

Thanks for the suggestion.
I have nothing in the way tooling and unfortunately the tool post is the old clamp style and has no graduations to allow accurate positioning.

As if that wasn't bad enough i also have no way of holding any work in the lathe until i have made a back plate.

I'm not experienced in lathes or engineering so even measuring a thread accurately is proving challenging.

I don't do things by half

You will have grand time learning lots of new things. warco and rdg both have a selection of useful bits for lathes...

Good luck

 

[chaoticbob]

Get a thread pitch gauge? Machine Mart do them, or google will reveal numerous internet suppliers. Not expensive - drop in the ocean compared to what you're going to spend on the new toy! Happy machining,
Regards, Robin

 

[Water-Mark]

Thanks for the replies.
I ordered two thread pitch gauges and neither have arrived yet!

I took a punt and ordered a 3/4 10 bsw tap and drilled and tapped a back plate blank and it's a perfect fit.

I'm now halfway through fitting the chuck plate so getting close to having a working lathe.

 

[doorframe]

I've got a little RandA. From your description it's the same as yours. When I got it (freebie) it was just a lump of seized rust. Many hours later it's (almost) a thing of beauty. Main problem to sort out was the brass/bronze nut on the lead screw. The backlash in the lead screw was almost a whole turn, so it was not going to last any time at all, so before anything else I made a new nut from a lump of brass, using a home made tool to cut the thread. Not quite perfect, but the backlash is now negligible. The thread on the lead screw is an acme thread, and I have no idea where to get the correct tap, so my home made jobby will have to do. How is the nut on yours?

Also, I'd be very interested to see some pics of how you drive yours.

 

[CHJ]

I think boring an 'Acme' style thread with a home ground tool is the best option for a split nut or lead screw follower, most frustrating thing is getting a trial fit, last one I did I spent as much time making a short length of male shaft to check the female thread bore as the nut itself.

 

[CHJ]

I took a punt and ordered a 3/4 10 bsw tap and drilled and tapped a back plate blank and it's a perfect fit.
....

Good news, nothing like being able to true up a blank backplate or faceplate in situ to give a measure of satisfaction on the accuracy front.

 

[doorframe]

It did take a few attempts. Disassembling the lathe to check the fit, then reassembling, repositioning the piece, and cutting a bit more took ages (and more than 1 complete failure!!)

 

[doorframe]

And just to add, I've still got the tool, if OP wants to borrow it.

 

[Water-Mark]

Hi, the leadscrew thread itself is actually good but the handwheel end has a lot of play and the drive pin is missing from the other end but thanks for the offer, it's always nice to know these things can be fixed.

This one has been modified and repaired several times over the years including the addition of an extra slide as can be seen in these photos.


http://s268.photobucket.com/user/minima ... x.jpg.html?
sort=3&o=0

http://s268.photobucket.com/user/minima ... sort=3&o=1

It has had a cracked headstock repair and had the tailstock modified for turning tapers.
It's driven through a .3 hp motor via a layshaft and is mounted on the heaviest lump of metal i've ever had the misfortune of trying to lift.

http://s268.photobucket.com/user/minima ... sort=3&o=2

This is the original advert for my model, is this the same as yours?

 

[woodfarmer]

Hi, the leadscrew thread itself is actually good but the handwheel end has a lot of play and the drive pin is missing from the other end but thanks for the offer, it's always nice to know these things can be fixed.

This one has been modified and repaired several times over the years including the addition of an extra slide as can be seen in these photos.


http://s268.photobucket.com/user/minima ... x.jpg.html?
sort=3&o=0

http://s268.photobucket.com/user/minima ... sort=3&o=1

It has had a cracked headstock repair and had the tailstock modified for turning tapers.
It's driven through a .3 hp motor via a layshaft and is mounted on the heaviest lump of metal i've ever had the misfortune of trying to lift.

http://s268.photobucket.com/user/minima ... sort=3&o=2

This is the original advert for my model, is this the same as yours?

You could get a lot for less than a Fiver in those days

 

[CHJ]

...You could get a lot for less than a Fiver in those days

You also got a lot less in the pay packet, don't know what date the advert is but even in 1962/3 wages were something like £14.00 a week.
Which was just a few shillings less than the monthly mortgage for a new three bedroom semi but about the same as renting similar local authority house.

 

[dickm]

You could get a lot for less than a Fiver in those days

...Yes, but I'll bet you'd have had to pay £4-19-6 for a Drummond, not 4 guineas!

 

[doorframe]

The hand wheels on mine are slightly different. Your pulley wheels in your pics are V type, whereas mine are flat type, as in the old b/w pic. I have tuned a V pulley add-on but it's not really working, and giving me a bit of vibration. I need to to go back to flat belt.

I'll try to get some pics later when SWIMBO gets home with her camera.

 

[doorframe]

Here's mine...

This is the drive...

You can see the mod I did to take a V belt...

And the new lead screw nut (follower?)...

I use a small 3ph motor with an inverter...

It'll never turn out any masterpieces, at least not with me at the helm, but it does for all my metal turning needs.

Good luck with yours. :wink:

 

[Water-Mark]

Clever stuff.
I'd never seen one before i bought mine but now it seams there's two or three on ebay every week.

Looks like my first attempt might be scrap as the chuck still has a wobble and i've already taken off more metal than i'd have liked.

Good job i bought a pair.