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That's how I did it:
https://www.ajawamnet.com/ajawam3/swarf/DSCN2848.JPG
https://www.ajawamnet.com/ajawam3/swarf/lathetopassylg.gif


On 5/4/2024 4:30 PM, Mark Kimball via groups.io wrote:

Some time back I started working on a DRO scheme for my lathe cross slide.? There's not a lot of room on top so many of the approaches I saw had one disadvantage or another.? As a result I came up with a scheme to put the DRO underneath the lathe and used a "C" shaped piece to transfer the cross slide motion beneath the lathe.? I had an iGaging DRO for the purpose because I bought two when I was working on my Z axis DRO setup, so I already had what I needed.? Or so I thought.

Unfortunately, the iGaging design uses a sliding contact with a fairly strong spring, which required a fair amount of force to overcome.? DRO mounting schemes that put the mounting system inline with the sensor aren't affected by this, but my C shaped piece would deflect under the force enough to cause about a .005" error.? I tried several ways to stiffen up the system but that was about the best I could manage.

So I decided to modify my DRO to reduce the amount of force needed to move the rule through the sensor.? This involved making a replacement base out of aluminum and replacing the sliding contact with bearings.? I used aluminum because the rule MUST be connected to the sensor's internal ground in order to work correctly.

My first iteration used flanged bearings because the rule needed to be constrained on two of its axes, but the flanges rubbed on the rule too much, which caused erratic variations in the force needed to slide the rule back and forth.? So I replaced the flanged bearings with conventional ones -- but then had to add bearings to the bottom and top assemblies to constrain the rule on its vertical axis.

At this point I debated on whether it really was worthwhile to continue my attempt to use an iGaging DRO, but since I already had a fair amount of time invested in this thing I forged on.? This is known as the "sunk cost" syndrome, and I admit to falling victim to it.

So after buying more bearings and? spending more machining time on the base (and 3D printing a cover, also with bearing pockets) I got this:

The top photo shows the scale, sensor, aluminum base and printed cover.? The side bearings are 3x10mm and the top/bottom are 3x6.

And here are photos of the mounting scheme:

I used a "T" extrusion in an attempt to stiffen up my "C" assembly but it didn't improve things much.? The 3D printed stuff was done with an older Ender 3 I bought from a friend.? This is the first project I've used it for.? The pieces were designed using openSCAD.? Not shown:? all the pieces that had something wrong with them :).

The scale passes through a slot I milled in the vertical piece.

At first the (re) assembled DRO had a terrible EMI problem.? I added some shielding on the back of the sensor board, which helped a teensy bit.? It turns out that the main problem was the spacing between the bottom of the sensor board and scale.? I had used some 3mm brass washers to make sure the board didn't rub against the scale, but that turned out to be a mistake.? I removed them and suddenly the noise problem disappeared.? The board still isn't rubbing so that was a solution without a problem.? I was sure that the DRO would misbehave once it was installed and the motor controller was turned on, but so far so good.

I checked the DRO vs the dial and they are very close.? That was a big unknown, since I wasn't sure if the spacing between the scale and sensor board would affect the readings.

Lipstick on a pig?? Well, probably.? If I had known what I was going to encounter along the way I think I would have just bit the bullet and found myself a DRO that would work right out of the box....

Attachments:
Base cover sensor.JPG: /g/7x12MiniLathe/attachment/119497/0
Scale.JPG: /g/7x12MiniLathe/attachment/119497/1
Mounting assembly front.JPG: /g/7x12MiniLathe/attachment/119497/2
Mounting assembly rear view.JPG: /g/7x12MiniLathe/attachment/119497/3