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Modding and Mounting Digital Scales

Described here are some modifications to scales and digital calipers. Especially how to make a mini scale, how to protect the scales from coolant and chips and how to mount the scales to a lathe or a mill.

If you have any hints on mounting scales you your tools, I'll be glad to add them to a link-list. Drop me an eMail!

A Mini-Scale:

Scales come in different lengths but for a lathe's compound, they are much to long, much to big and still not protected from coolant and chips.

It started with analyzing how I can make the original PCB smaller. As I had some remaining, I used an ALDI-caliper and ripped it apart.

By moving a capacitor to a different place, flipping the x-tal over and rewiring all the traces I have cut off, I succeeded in making it considerably narrower. Of course, the LCD went into the waste bin. We don't need that.

This is the original unmodified PCB.
Here is the PCB with one C moved around, the x-tal flipped over and some rewiring. For the rewiring, I used vero-wire whose isolation melts and evaporates when soldered (at 400°C). And I needed to use a magnifying glass. When I was young …

Next step was to build a metal housing for the parts to fit in. After some tinkering, I came to the following solution:

The upper part is in reality the lower part in which the PCB and carrier will slide in. The long slot is for the brass carrier that holds the PCB. The carrier has a tongue going through the slot. That tongue will be screwed to the compound.
In the middle is the upper part of the housing. In a pocked of that part the coupling PCB is clued in (with contact cement). That capacitor strip can be easily peeled off the calipers body. You also can simply cut to length.
The lower two parts are the PCB (cut to size) and the brass carrier. The cables are already connected, but the PCB is not yet glued to the carrier.

You bet that I milled those parts with my DRO. The "TGC Tool geometry correction" was very useful!

Here you see how the PCB is sliding in the top part.

That's how the PCB got glued to the brass carrier. I ruined two scales with gluing them to the slide. They worked for about 4 days and then they quit life. Seems to have something to do with the gluing. I don't know.
So I changed the way the PCB is fixed to the slide. Basically, I made a frame out of Tuffnol that was glued to the slide. On top of that frame (milled to the propper height) the PCB was glued onto with super glue. This works.

Here you can see the frame on the brass slide and the PCB (a bit different to the photos above) with the modifications.

This is a look into the pocket formed by the frame. Note the wire connecting the PCB's plus to the slide. This connection is very important! Missing on that photo is the capacitor between plus and minus on the PCB. If possible (space), use a 1µF tantalum.

Here the assembled electronic pickup is half put into the slot of the lower part of the case.

These are the two parts making the case of my digital scale. In the top is the lower part (seen from below). The second part is the upper part. You see a thick tongue that will fix the case to the tool rest.

Here the case (top view) is assembled with the cable coming out from the bottom. The tongue of the carrier is pointing downwards.

The whole assembly is 115mm long. The main part of the case is 22mm wide and 10mm thick. The tongue to screw the mini scale onto is 55mm long, and 10mm thick/wide. The travel of the scale is nearly 50mm.

A Midi-Scale:

This scale wasn't that much a challenge, because it is huge compared to the mini-scale.
I used the rectangular aluminium tube (40 * 30 * 2mm) shown below, but mounting was a bit difficult. In that tube came a digital caliper cut to length (with an angle grinder, no need for respect).

This is the mounting bracket that is screwed (3 holes) to the cross slide. Into the slot on the raised rectangle goes the scales beam. There is a little screw coming down from top to hold the beam in the slot. The assembly is made out of CRS. The rectangular plate was hole welded from the back with a MAG. The cover plate seen on the photo below looks basically like the rectangular plate above.

These are all parts of the midi scale. Top is the aluminium tube seen from the bottom side. The slot is for the sideres tongue. Left side of the tube is the bracket described before. It is glued and screwed to the tube. Right of the tube is the cover for the backside (aluminium). Below is the digital caliper ("useless" parts cut off) and the tongue glued to the scale's slide.

Connecting Cables

As I decided to use RJ12 connectors (telephone cables) and to solder one end of the cable directly to the scale, I needed a way to make that connection secure. I solved this together with the plate that moves the slide on the scale. The sheet metal (aluminium) is about 3mm thick and has a slot milled in, that will guide and protect the cable. You'll soon see why. That plate is just stiff regarding to the lengthwise axis of the scale. That is what you want. It can bend in all other axes and thus compensate slight misalignment.

The slot where the cable is in is covered with some thin (0.1mm) brass to further protect the cable. That slot was filled with epoxy, the cable put into, covered with epoxy and then the brass sheet clamped over while curing the glue.

The cable is coming out in the back and is traced to the 4 connectors where they were just soldered onto. I used some hot glue to stop the cable from moving. You also can see the two capacitors for the scale's power supply that went into the battery compartment.

Protecting Scales

If have cut some 30 * 40 * 2mm aluminium rectangular tube to length and slotted it, so that the tongue with the cable can reach through that slot and the slide move free on the scale. A tube 25 * 40 would have been better, but my dealer didn't have it on stock. You will notice the missing caps on the end of the tube. I have put them there later. They can be readily bought.
When you fix that whole assembly to your lathe/mill, you have to properly align it! I won't go into detail about that. You also will have to drill some holes and tap them. But if you do have a mill, you will be able to handle that job.

See the first picture in the next section how it looks. The tube is very good in protecting the scales from coolant and chips. I had no problem at all within more than 3 months. Coolant was running over the body but never into the scales.

Mounting Scales on a lathe

The mini-scale I made was intended to be used on my -I call it a- lathe. She's a EMCO Compakt 8 built around 1985. Length between centers is 450mm, diameter over bed is 210mm. Little room to mount the scales.
BTW: I welded that table when I was jobbing during hollydays at a steel construction company. The yellow paint was some spray I found in a army scrap yard during my military time. Must be some air force color.

The cables on the photos are not in their final state. They need protection and better routing!

Here is the mini scale mounted on the compound. It fits quite nice and doens't come too much in the way.

The compound seen from above. You can see a shim between compound and scale. I made it intentionaly that way, to make the scale's case easier to fabricate.

This is an overview of the carriage's and cross slide's scales looking from the lathe's back. The long horizontal tube is for the carriage, the other tube for the cross slide. The carriage's scale is screwed to the lathe in the middle (next photo) and on the very left. The lathe's bed had already milled two faces that came handy for the horizontal scale.

Here you can better see the middle mounting of the carriage's scale. It is done with a L-shaped (reverse) bracket. Coming from the carriage and reaching over the scale is a massive C-shaped bracket to move the slide of the scale. I needed it to make more and more stiff. Any bend would be bad. The C was made out of CRS, the rib was again hole welded from the back. That C is screwed with 2 M5 to the carriage.
The other thing here is the cross slide's scale. The body is screwed to the carriage with 3 M5s. To move the scales slide, I needed some kind of "stick". It was screwed to the cross slide and is basically a (mounting) plate, some angle iron milled to size and a flat reaching down to the scales slide. Yes, some paint wouldn't be bad.

Here you can see better the three parts mounted to the carriage and the cross slide. Also, how the scales slides are moved.

Top view of all the scales. The way I mounted them involved quite some work and tinkering. But this way I didn't loose any travel and the tail stock still can get directly to the carriage.

View from the tail stock.

Mounting Scales on a mill

That ugly yellow tube on the left is for the cooling fluid. The lever to clamp the Y-axis will be modified. As it is now, it is just good enough to clamp the axis.
I haven't yet made photos of the other axes.

There is a modification to the housing I will add when I do get dirt problems. I will add a "brush curtain" in the tube that will keep water and swarf out of it. All scales were mounted in such a way, that the slot in the tube is pointing down or away from where the chips will come flying from. This point is really worth thinking about!

There you can see how I mounted the laptop. There is a black tube coming down from the ceiling that holds the laptop on an arm. That arm can be swung to the back to go out of the way. The mounting for the laptop was welded out of some tube (round and square) and flat that did the job.