Mini-MIll Z axis DRO

*Mini-Mill: Adding A Z Axis DRO*

Adding a Z axis DRO on the mini-mill.
Having decided to go ahead and put DROs on the mill, I did some shopping and picked a 12 inch vertical unit for the Z axis. In the future, perhaps I will CNC the whole mill, and I've been thinking of that as the project goes on. I've got an option, of course, I can either put the scales on the left hand side of the column, or the right hand side. The left hand side will need the torsion spring taken off, and the right side has to dodge all the handles on that side. I decided to put it on the right side because I found that it could dodge the complicated stuff.
	The whole scale can be mounted with two pieces of aluminum angle. This is about 1 1/2 inch by 1/8 inch thick aluminum angle, so it's moderately sturdy. There was nothing where the bolts go through, so I drilled and tapped for two M6-1.0 bolts. Might as well have everything on the mill metric.
	On the bottom, the bracket is mounted similarly. I wanted the brackets to hold the scale behind the Z axis feed. Cast iron does well for tapping, and I was moderately careful to clean up afterwards, although this picture doesn't show it.
	Holding the scale in place with a clamp allows me to see just what will fit and what will not, and to check clearances. The brackets are lined with the back of the column, and the scale has slop in the mounting holes to go left/right.
	Determining the maximum upwards position of the scale. I want to clear the handles, and still have the scale up as high as possible.
	The scale can go quite low, but there's enough clearance at the bottom so the scale does not bottom out on the runner.
	Here's the overall view. If you think that stuff looks close, you're right. If I'd been working a bit differently, I'd have put the scale on the side, but facing to the right. However, without a readout, I can't see what's going on, so it's better like this.
	Mounting the scale is relatively easy, you need a bracket and a piece of metal. The original bracket can't be used, because it goes in the wrong direction. The mounting point would have to be behind the scale.
	Viewed from the back, the new mounting bracket is a good fit.
	Just to think of clearances, the gib locking knob is just far enough back that the end of the handle will just clear the scale. I'd have liked more clearance, but it does work. I can always reset the handle a bit. As a note, the screw going through the scale is M5-0.8.
	The flat plate of metal joins the mill head to the bracket. Since the head edge and the column are just about flush, the plate has to be milled back a bit for clearance. The plate also covers one of the gib screws, so that has to be fixed. One screw is sufficient to hold the bracket in place. It's an M6.0-1.0.
	The bracket front has to be milled down because the piece of metal is too thick, and the bracket needed to be thinned a bit. No big deal, I machined to a little more than I needed, and allowed the slots in the scale to take up the adjustment. The bracket that holds the scale bracket is fastened with M5.0 hardware. Take care that it is not too long, since you can clamp the head to the column if you're not careful. One M6.0 screw holds the bracket.
	Here's the bracket, side view. The metal under the screw into the headstock is solid, not hollow here, so I had to drill deeply and tap for a shorter screw.
	Front view of the Z axis scale. Finish on all the metal is made with an orbital sander.
	In the very back, you can see the nut for the torsion spring. There's about 1/16 inch clearance between the bracket and the end of the spring, but I checked that to start with.
	Here's the bracket from the side. I cut the slot too far over, picked the wrong hole to align with, but no big deal. There's enough clearance to get a socket wrench to the locking bolt for the gibs.
	One problem is that the connector for the readouts is rather close to the handle. If it becomes a problem, I'll shorten the handle sections
So here we are, I've managed to install the Z axis readout. I do find that a single unified readout would be a really nice idea, but I won't go there yet. I really need the connectors for the scales, and then I have to build the display units. I think that I will probably use 3 microprocessors, each with much the same program. I think that they will probably share a serial line and transmit all the serial data... or that might possibly be a fourth microprocessor, depends. Naturally, I have to finish the emulator to see what goes on in the system and get the program running properly. Nothing, however, keeps me from using it without an external readout. I think that if I CNC this mill, I will use these as the position readouts, and just make a closed loop feedback system.