Suggestions for fixing magnetic scales to cross-slide of old Pratt & Whitney Lathe?

[harrilynch]

Hello machine enthusiasts,

I'm working on a project for my university, to digitize old legacy equipment such as this 1940s-era Pratt & Whitney Lathe (12x30 size).

The goal is to attach magnetic scales for readout on the X and Z axes but I ran into issues when determining the best way to implement this on the X axis for the cross-slide.

I am wondering if anyone on this forum has experience performing something similar, and could suggest a recommendation for mounting methods and location.

I've determined that the cover on top of the cross slide is not suitable for mounting, although there is a possibility of removing it and fixing the scale/encoder on the inside. Also will need to keep in mind where to fix the encoder itself which I can create custom brackets for. Overall, I'm sure drill tapping would be necessary but would love to use pre-existing holes and such to avoid this if at all possible.

Below I will attach images of the cross-slide and its surroundings, the first image will have an approximate size of the magnetic scale I intend to use.

Any help is greatly appreciated!

 

[eKretz]

Generally, the encoder is mounted where you've drawn in the scale, and the scale is attached to the cross slide. Usually, a shield is installed over the top of the scale to help prevent coolant and chips from getting in.

 

[Doozer]

You have a late model 12C. Nice.
It is a late 1950s machine.
The cross slide has 8-5/8" of travel.
(Probably call it 9").
On the tailstock facing side of the cross slide
there is an allen head set screw for locking the
cross slide. If you measure from the edge of the
set screw threads to the underside of the compound
slide, you have a heavy 5/8". The only scale that
is that thin is a Newall MicroSyn. Maybe some
other scales are equal or less than that 5/8" dimension,
but you would have to orient the slit opening of the
encoder track sideways, towards the tailstock, instead
of facing down, like it should be (to exclude debris).
I have been afraid of Newall quality, as I have heard
a few stories of them failing lately (from friends, not
only on the damn internet). Maybe someone else has
some suggestion.
Side note... On my 12C, the oiling holes that are in the
bottom of the compound slide that are supposed to
allow oil to drip down into the cross slide, and lubricate
the dovetail ways, these holes did not line up with the
circular transfer grooves. I can't remember exactly, but
I think the problem was in the cross slide casting. I had
to drill some oil passages a bit further to get the oil
passages to line up. Check out your lathe and see if
you can detect the same problem. Another way to say
it, if you oil the Gits cups on the compound slide, the
oil should reach the cross slide ways. On my lathe,
the passages were not connected. Thus my cross slide
is the only part of my lathe with a bit of wear. Hope this
helps.

-Doozer

 

[L Vanice]

I installed a Newall on my Clausing 5900 12" lathe. The X is a Microsyn. Here are three pictures of the installation.

I had to use a woodworking router with a long straight 1/4" carbide bur to create a flat spot on the carriage to mount the reader. The two socket head screws are what the tailstock can hit, so the aluminum chip shield does not get damaged. I used a Kodak 35mm bulk film can to tame the excess length of the cables.

Larry

 

[tailstock4]

I went through some pictures of the DRO scale installation on my Pratt & Whitney 12C. I just used some existing pictures and maybe you can get some idea of what I did. I mounted the scale to an aluminum bar which is mounted to the cross-slide cover. The reader is mounted on the backside of the saddle. It works well. It also has the added benefit of allowing the tailstock to get all the way to the saddle.

The Pratt & Whitney is difficult to mount this scale in a traditional sense because of the bulge in the cross-slide. But this really isn’t the difficult axis. Mounting a scale for the bed is going to be more challenging because of the way the taper attachment attaches to the bed rather than the cross-slide. I haven’t quite decided how to do that. I’m in the process of a VFD conversion on this machine right now. When I complete this, I may also complete the DRO installation and post some pictures of both of those projects.

Here are a couple pictures of what I’m talking about with the taper attachment.



These are pictures of the current cross-slide scale mount.

 

[Doozer]

tailsotck4-

Did you modify (or add screws) the cross slide rear cover
to make it more rigid to be able to mount the DRO scale?
My cover only has 2 flat head 10-24 screws.

-Doozer

 

[eKretz]

Might have been a better idea to make a thin steel base (bar) and attach that to the solid part of the cross slide, then attach the scale to that. That's if any of that is even really necessary. Monarch CW cross slides are similar with the rear cover plate and we just mounted those to the solid part of the slide and had room. The P&W does look a bit shorter in that portion though.

 

[tailstock4]

The story of this DRO and how I mounted it was that the Sargon and this one scale was salvaged from another lathe. Because it wasn’t the DRO that I ultimately plan to end up with on this machine, I decided to mount it in a way that it would not require me to drill any holes in the cross slide. So, I just mounted it to the cover. To my surprise, it all works really well. There isn’t much deflection, and it’s accurate and repeatable. Sometime you get lucky.

 

[harrilynch]

I went through some pictures of the DRO scale installation on my Pratt & Whitney 12C. I just used some existing pictures and maybe you can get some idea of what I did. I mounted the scale to an aluminum bar which is mounted to the cross-slide cover. The reader is mounted on the backside of the saddle. It works well. It also has the added benefit of allowing the tailstock to get all the way to the saddle.

The Pratt & Whitney is difficult to mount this scale in a traditional sense because of the bulge in the cross-slide. But this really isn’t the difficult axis. Mounting a scale for the bed is going to be more challenging because of the way the taper attachment attaches to the bed rather than the cross-slide. I haven’t quite decided how to do that. I’m in the process of a VFD conversion on this machine right now. When I complete this, I may also complete the DRO installation and post some pictures of both of those projects.

Here are a couple pictures of what I’m talking about with the taper attachment.

View attachment 434122 View attachment 434124

These are pictures of the current cross-slide scale mount.
View attachment 434118 View attachment 434119 View attachment 434120 View attachment 434121 View attachment 434123

Thanks for the input and photos, your machine looks to be in great shape!

For the z-axis measurement for the carriage, we currently don't use any attachments on the backside t-slots so our intention is just to fabricate some t-nuts that fit the magnetic scale bolts and fix it that way, then use some of the machine's downward facing allen-head bolts and some brackets to fix the encoder.

Also for the cross-slide scale fixed to the cover, does the whole thing come off if you need to remove the cover for any reason? And does the vibration of the cover cause any issues in the measurement?

Thanks

 

[harrilynch]

Might have been a better idea to make a thin steel base (bar) and attach that to the solid part of the cross slide, then attach the scale to that. That's if any of that is even really necessary. Monarch CW cross slides are similar with the rear cover plate and we just mounted those to the solid part of the slide and had room. The P&W does look a bit shorter in that portion though.

A steel bar of some sort seems to be the solution