Mini lathe cross slide DRO, or sunk cost syndrome

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This project started out as a thought that went from "how hard could it be" to "well I've spent THIS much time on it I may as well finish it".

I found an online description of a clever way to attach a DRO to the cross slide of a mini lathe, which moved the DRO underneath the bed. This got the DRO out of the way better than many other approaches I've seen, so I decided to give it a try. It uses a (backwards) "C" shaped piece that attaches to the back of the carriage, extends vertically to below the bed, and then there's a horizontal section where the DRO is attached. I had a 12" iGaging DRO so I decided to use it for this project.

Unfortunately, I found that the frictional force needed to move the DRO sensor relative to the scale was too great. There's a spring between the scale and DRO body that does two things -- it makes electrical contact to the scale and makes it very "stiff" with regard to external forces. The friction resulted in about a .005" deflection of my C-shaped piece, and that was about the best I could achieve despite efforts to stiffen it up. So I decided to make a replacement body for the sensor, which would use small bearings to perform both functions. My first rendition used 6 flanged bearings, which was convenient because they could constrain the scale on two axes -- but they rubbed too much on the scale. So I ended up using two sets of bearings, four on either side of the scale and four on the top and bottom.

Like this:
Base cover sensor.JPG

The 3D-printed cover goes on top of the aluminum base. It's the first actually-useful item I printed, although I went through about 3 iterations to get it all right. The bearings are 3mm x 6mm, so I used some short 3mm dowel pins for the shafts. The side bearings are mounted using 3mm screws and washers to raise the bearings up so they don't rub on the base.

And with the scale and sensor board installed:
Scale.JPG

The circuit board is the iGaging sensor, removed from the original DRO.

The "C" shaped piece looks like this:
Mounting assembly rear view.JPG

The scale is attached to the apron with two 6mm screws like this:

Mounting assembly front.JPG

The 3D printed piece underneath the aluminum body is just a spacer to get the scale to the right height. I also printed a mounting block for the scale.

I had to fiddle around with the spacing between the sensor board and scale. At first the gap was too large so the coupling between the scale and board was too weak, producing a very unstable reading. I replaced the spacer washers with adhesive tape "shims" and now the readout is very stable, even when the motor controller is running. I added a 1uf capacitor between Vcc and Ground on the sensor board, same as what I've done on my mill's iGaging DROs. They greatly reduce the sensor's sensitivity to EMI.

If I had it to do all over again I'm not sure I would. I certainly spent a lot of time getting it working right. I still need to add some kind of swarf guard to keep junk from getting into the DRO. Maybe a soft bristle brush on either end, so the printed cover may see a few more iterations. Sunk cost, yeah.

On the flip side, I gained some design experience making 3D printed items. I used openSCAD, mostly because I found the learning curve to be easier than using a CAD program. The printer is a used Ender 3 I bought from a friend. It seems to produce fairly accurately-sized prints, at least for PLA.
 
Interesting implementation.

Not sure I would do it in the same way, but interesting all the same...
 
Interesting work. How are you going to do the cross slide X axis? There's not much room there! Been pondering putting on real scales on my mini, but the X axis always is the tough one to shoe horn in. On my 10x22 lathe I put the X over the gib adjustment, and it's ok, but inconvenient for locking the axis. The mini is a lot smaller.
 
Interesting work. How are you going to do the cross slide X axis? There's not much room there! Been pondering putting on real scales on my mini, but the X axis always is the tough one to shoe horn in. On my 10x22 lathe I put the X over the gib adjustment, and it's ok, but inconvenient for locking the axis. The mini is a lot smaller.
The work I described WAS for the X axis. You probably were looking at the Z-axis DRO, which is also visible in the next-to-last photo. The scale that runs horizontally across the photo is for the X axis. I cut a slot in the vertical support member for the scale to pass through. Kind of a kluge but the modified DRO now has so little friction that it's no longer an issue.

If you look closely, you can see a little bit of the 3D-printed cover through a slot in the lathe bed. It's a little misleading because I used some filament that is very close to the same color as the OEM cover.

My scheme puts the scale in an ideal position to collect swarf, one big disadvantage.
 
A small correction. The four horizontally-oriented bearings are 3x10mm bearings. The 8 on the top and bottom are 3x6mm. Using all 3x6 bearings would make for a smaller DRO.
 
The work I described WAS for the X axis. You probably were looking at the Z-axis DRO, which is also visible in the next-to-last photo. The scale that runs horizontally across the photo is for the X axis. I cut a slot in the vertical support member for the scale to pass through. Kind of a kluge but the modified DRO now has so little friction that it's no longer an issue.

If you look closely, you can see a little bit of the 3D-printed cover through a slot in the lathe bed. It's a little misleading because I used some filament that is very close to the same color as the OEM cover.

My scheme puts the scale in an ideal position to collect swarf, one big disadvantage.
My bad then. Didn't understand what I was looking at apparently. I'll look at it again.
 
I saw that concept, but after I had gone in a different direction, keeping the X-Axis scale high and fully covered:

Mini-Lathe DRO Completed Install.jpg

Additional photos, drawings, details, etc. are in the January-February 2024 issue of The Home Shop Machinist; a digital copy is available here.
 
I saw the same, or similar, under-bed DRO project online, and though it a mostly good idea even if somewhat complex.

After thinking about the effort needed and possible flex that may occur ( just what is needed on a mii-lathe 8^) ) I decided not to attempt this.

I very much admire the effort and good work you have accomplished.
 
This project started out as a thought that went from "how hard could it be" to "well I've spent THIS much time on it I may as well finish it".

I found an online description of a clever way to attach a DRO to the cross slide of a mini lathe, which moved the DRO underneath the bed. This got the DRO out of the way better than many other approaches I've seen, so I decided to give it a try. It uses a (backwards) "C" shaped piece that attaches to the back of the carriage, extends vertically to below the bed, and then there's a horizontal section where the DRO is attached. I had a 12" iGaging DRO so I decided to use it for this project.

Unfortunately, I found that the frictional force needed to move the DRO sensor relative to the scale was too great. There's a spring between the scale and DRO body that does two things -- it makes electrical contact to the scale and makes it very "stiff" with regard to external forces. The friction resulted in about a .005" deflection of my C-shaped piece, and that was about the best I could achieve despite efforts to stiffen it up. So I decided to make a replacement body for the sensor, which would use small bearings to perform both functions. My first rendition used 6 flanged bearings, which was convenient because they could constrain the scale on two axes -- but they rubbed too much on the scale. So I ended up using two sets of bearings, four on either side of the scale and four on the top and bottom.

Like this:
View attachment 490159
The 3D-printed cover goes on top of the aluminum base. It's the first actually-useful item I printed, although I went through about 3 iterations to get it all right. The bearings are 3mm x 6mm, so I used some short 3mm dowel pins for the shafts. The side bearings are mounted using 3mm screws and washers to raise the bearings up so they don't rub on the base.

And with the scale and sensor board installed:
View attachment 490160
The circuit board is the iGaging sensor, removed from the original DRO.

The "C" shaped piece looks like this:
View attachment 490161
The scale is attached to the apron with two 6mm screws like this:

View attachment 490162
The 3D printed piece underneath the aluminum body is just a spacer to get the scale to the right height. I also printed a mounting block for the scale.

I had to fiddle around with the spacing between the sensor board and scale. At first the gap was too large so the coupling between the scale and board was too weak, producing a very unstable reading. I replaced the spacer washers with adhesive tape "shims" and now the readout is very stable, even when the motor controller is running. I added a 1uf capacitor between Vcc and Ground on the sensor board, same as what I've done on my mill's iGaging DROs. They greatly reduce the sensor's sensitivity to EMI.

If I had it to do all over again I'm not sure I would. I certainly spent a lot of time getting it working right. I still need to add some kind of swarf guard to keep junk from getting into the DRO. Maybe a soft bristle brush on either end, so the printed cover may see a few more iterations. Sunk cost, yeah.

On the flip side, I gained some design experience making 3D printed items. I used openSCAD, mostly because I found the learning curve to be easier than using a CAD program. The printer is a used Ender 3 I bought from a friend. It seems to produce fairly accurately-sized prints, at least for PLA.
Got a re-look at this. Interesting, now that I think I understand it. I had to extend my backsplash on my 10x22 when I added the X axis. I can see that would happen for this implementation as well. Hope this works out well for you - it seems like it was quite an effort to get it going.

I'd like a better solution for my 10x22, but I haven't found it yet. Going underneath was a possibility that I hadn't serious considered. I would have to make sure that all the fasteners were accessible from the top side, as the lathe is heavy enough that I can't just flip it, like I would with my mini-lathe. For both of my lathes I need to retain a back splash as I am right up against a stone wall and need to keep the swarf in a cleanable zone.

My mini has rotary encoders which really aren't the same as DRO's. Someday, I'd like to fix that. I need to mull over your solution to see what ideas I can adapt. One of the encoders is damaged, due to inadvertent fouling during threading. I had repaired it long ago, but the repair failed. (Insert has pulled out of the plastic, which is hard to repair as the hole is wallowed out.) On the round-tuit list.
 
Got a re-look at this. Interesting, now that I think I understand it. I had to extend my backsplash on my 10x22 when I added the X axis. I can see that would happen for this implementation as well. Hope this works out well for you - it seems like it was quite an effort to get it going.

I'd like a better solution for my 10x22, but I haven't found it yet. Going underneath was a possibility that I hadn't serious considered. I would have to make sure that all the fasteners were accessible from the top side, as the lathe is heavy enough that I can't just flip it, like I would with my mini-lathe. For both of my lathes I need to retain a back splash as I am right up against a stone wall and need to keep the swarf in a cleanable zone.

My mini has rotary encoders which really aren't the same as DRO's. Someday, I'd like to fix that. I need to mull over your solution to see what ideas I can adapt. One of the encoders is damaged, due to inadvertent fouling during threading. I had repaired it long ago, but the repair failed. (Insert has pulled out of the plastic, which is hard to repair as the hole is wallowed out.) On the round-tuit list.
While the "C" shaped piece mounting points are on the top, the block that attaches the scale to the apron is a different story. There's enough room beneath the half nut engagement lever to attach something there, but I chose to keep the front clear of additional protrubances.

Of course, it all depends on your particular lathe. I had thought about a rotary encoder, but only after I'd run into my DRO's friction-related problem.
 
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