Potts type milling spindle column advice needed

[StewartParticipant @gaunless]

Hi all.

I have some machined castings for a ‘Potts type’ milling spindle, minus the column. Everything else is there including the spindle cartridge and other bits of hardware etc.

I would like to get it up and running, but I need to make a column for ir. It needs to be 45mm O/D and either tube, or solid bar drilled through.

I have some 44.5mm mild steel tube with a 3.5mm wall, which would be perfect, but it’s just a shade sloppy with the fit. It needs to be a good sliding fit in the cast iron part that clamps around it (that part that the angle-adjustable spindle holder can be attached to) so I think 45mm would be ideal. The part mentioned above has a keyseat already machined into the bore, so my idea was to attach a key to the new column, rather than milling a keyseat in the column as well, which would be difficult as I don’t have a milling machine. (I can mill in my lathe but it wouldn’t have the necessary capacity).

My question is, what is the best material to use for this column?

I have a material stockist very local to me (M-Machine is 10 miles away).

Thanks

Stew.

[howardbParticipant @howardb]

If M-Machine is close to you, ask them if they have stock of 45 mm dia centreless ground carbon steel shafting.

Ask them what dimensional limit it is produced to – ie h6 or h7 is common.

Better than just using ordinary bright drawn bar.

I wouldn’t drill it through, possible risk of distortion if it’s for a machine tool application.

[JasonBModerator @jasonb]

The hole through the middle does make it easy to fit to the cross slide, I doubt a 10mm dia hole would cause any distortion. It’s unlikely to see a lot of up and down movement so if you can turn parallel EN1A in 1 7/8 or 48mm would do. 50mm black EN3 is distortion worries you.

You could use the carriage to plane a keyway along the side of the column with it held in the 3 jaw and with tailstock support. Mighyt even be able to clamp the part made potts spindle onto the cross slide and pack it upto height then use that to make it’s own column keyway.

[bernard towersParticipant @bernardtowers37738]

If you had the simple cross drilling jig (MEW in the distant past) it could be clamped to that. Its one of those tools I find that I cannot do without.

[howardbParticipant @howardb]

“The hole through the middle does make it easy to fit to the cross slide, I doubt a 10mm dia hole would cause any distortion”

I was thinking more in terms of drilling a larger hole to lighten it – 1″ or 1 1/2″ maybe.

[bernard towersParticipant @bernardtowers37738]

I think keeping it as heavy as you can will be a benefit to stability/finish etc.

[DiogenesParticipant @diogenes]

Yes, agree strongly – steel needs mass to help damp it’s ‘ringy’-ness..

[JasonBModerator @jasonb]

Can’t really see any need to lighten it. If it were needed then just start with a bit of thick wall seamless tube, M-Machine has plenty of choice. I’ve used that several times and even turning OD and ID to final size not seen any movement

[BazyleParticipant @bazyle]

I thought they have a location groove down the side of the column, so would need really thick tube.

Is the design still copyright or patent? Would have expected castings to be still available from one of our regular suppliers. Sure it would be popular.

[StewartParticipant @gaunless]

Hi Guys.

Some great advice there. Thank you.

Once I purchase some suitable material for the new column, I was going to simply screw on a long key to the column. This key would then sit into the existing keyway that is cut into the casting that goes around the column. (The part that moves up and down the Y axis). This would save me the hassle of cutting a keyseat into my new column, and I can then keep the internal diameter a little thinner. Can anyone check me on this and suggest why this method wouldn’t work well? I understand the need for mass and rigidity though.

I’ve also seen versions where the casting has a short key the width of the casting screwed into the keyway in the casting, and this then slides in a keyseat in the column. It seems there are a few ways of skinning this particular cat. All it’s doing is stopping the casting from rotating, and keeping it aligned in the Y axis.

(By the way, if anyone knows the correct name for the casting that moves up and down the Y axis on the column, I’d absolutely love to know!!).

That’s the plan at the moment anyway.

Stew.

[StewartParticipant @gaunless]

I think Hemingway offered castings, but stopped some time ago.

[cedric 1Participant @cedric]

<p style=”text-align: left;”>A bit of mild steel should do the job for the column. It is not under super high stress.</p>
 Key screwed onto the column might not be rigid enough under side loading though. It would put all the load onto the small mounting screws which by nature will have clearance in their holes. Maybe some dowel pins for location might help, maybe. And concave radius the key to sit firmly on the column.

It really would be better to mill the proper keyway though. Could be done clamped to the cross slide with a slot drill held in the lathe chuck. I  do a lot of milling like that quite successfully.

[Bazyle]

On Bazyle Said:

I thought they have a location groove down the side of the column, so would need really thick tube.

Is the design still copyright or patent? Would have expected castings to be still available from one of our regular suppliers. Sure it would be popular.

That is why I said thick wall tube

2″ OD x 1/2″ wall would still leave about 9mm wall once the OD had been turned and the keyway is only 1/8 or 5/32 by the looks of things so only half that depth for the keyway. This sort of stuff

[BazyleParticipant @bazyle]

Yes that’s thick walled! I think the original idea was a triangular groove keyway so the key can be arranged to be pushed in for positive lock on both sides against turning.

[JasonBModerator @jasonb]

Just looks like a regular rectangular one to my eye

https://www.lathes.co.uk/potts/

[half whitParticipant @half-whit]

Hi All,

Interesting read this thread. I made one of these some years ago from original potts drawings from february 1937.

There was an article in M.E. issue number 1866 which featured detailed orthographic drawings and a couple of photos. From the drawings I made casting patterns. They machined up really well with all of the milling done on the myford V.S. These were the days before I acquired my sieg mill, and in some ways machining was more challenging and often much more fun.

This original Potts attachment was made for an early Drummond M type lathe, 1921/24. The column had an extension bolt the seucure it to the tool post stud.

I no longer have the patterns, or the Potts, or the V.S., sold on when I got the seig, something I now regret!!!!

Geoff

 

[bernard towersParticipant @bernardtowers37738]

Stewart if you look carefully on the lathes site there is one with the screwed on key you can see the screws in the picture its the one after the red one.

[StewartParticipant @gaunless]

Hi. Yes, I didn’t notice that. I think it may still be sunk into a keyseat though, and the screws are just holding it in place.

[bernard towersParticipant @bernardtowers37738]

You could well be right I did that on my tailstock turret for a taig and seems to work well.The key slot was done on the aforementioned cross drilling jig.

[StewartParticipant @gaunless]

Only trouble is that none of my lathes seem to have enough capacity on the cross slide to mill the entire 150mm without turning it and going again from the other end, which would probably introduce an error.

[JasonBModerator @jasonb]

As I said earlier can’t you use the other bits to machine the slot?

Pack up the casting that goes around the column so the spindle is on lathe ctr height and put a bolt through it to clamp it to the cross slide.

Put the turned and drilled column in the 3- jaw chuck with tailstock support and lock the lathe spindle.

Then it is just a case of putting an 1/8″ or whatever is needed cutter in the spindle and feeding with the cross slide to set depth of cut and the carriage to move along the length of the column

You are basically using the spindle as it was intended to be used bit without easy height adjustment.

[JasonBModerator @jasonb]

I just mocked this up while the kettle was boiling. The Unimat 3 head usually mounts on a 28mm column but with some blocks packing it up and a bolt through the middle down to a tee slot it is set up to mill a slot along a length of bar.

[BazyleParticipant @bazyle]

You could also machine it in two parts but undersize then mount between centres and plane the edges of the slot with a tool bit moved along with the cross slide.
Above it was mentioned that the drawings had appeared in ME in 1937 which is before my collection starts. I wonder if the management would consider putting them in the archive articles or perhaps just republishing in ME&W.

[Bazyle]

On Bazyle Said:

You could also machine it in two parts but undersize then mount between centres and plane the edges of the slot with a tool bit moved along with the cross slide.
Above it was mentioned that the drawings had appeared in ME in 1937 which is before my collection starts. I wonder if the management would consider putting them in the archive articles or perhaps just republishing in ME&W.

I’d second that request.

[JasonBModerator @jasonb]

Chance of editorial management reading much on the forum is slim, but his contact details can be found on this site.

I supose with the castings no longer being available an updated article would possibly be better detailing how the parts could be fabricated, cut from solid or even containing links to files so the “castings” could be 3D printed in metal or patterns printed.

If the design were “squared up” a bit so it looked more like the image of my U3 then cutting from solid would be quite straight forward. A bit more work and a block of iron could be made to replicate the original casting shape or if you can weld reasonably well some more tube and bar would have a convincing replica.

Though I suppose some these days would opt to mount an off the shelf spindle motor with integral ER socket than build the spindle and arrange the overhead pullies, drive motor, etc . Even more would feel they had less use for one given the greater number of home wokshops with a mill compared to few back in the 30s,

 

 

Further to my suggestion to clamp the castings to the cross slide. It would also be possible to cut the keyway by just bolting the spindle casting to the vertical slide which would give you fine adjustment in all three axis and easy to mill a long keyway.

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