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DIY bluetooth DRO for my mill

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vtsteam:
I once fixed a defunct mill with an Anilam Crusader DRO at the place where I worked. It kept losing position and doing weird stuff. I asked if I could have a look at it. I took the boards out of the control head and they turned out to use some unusual static memory IC's with internal batteries. Since these had aged, the batts stopped maintaining memory contents, and the DRO started having issues. I located some replacements, which had an explicit spec for ten year life, and the machine was usable again.

I later fixed a thin film deposition machine that had similar memory problems, though more easily figured out because the batts were external to the memory chips. I couldn't find replacements for those specialized batts, so I added new batt holders for a more common cell type with similar specs.

vtsteam:
Here's the new box, painted.

vtsteam:
I've finally started mounting the scales to the mill -- a typical heavy Asian round column mill drill, this one happens to be an Enco branded version, which I bought second-hand a dozen years ago from a repair facility. They also had a Bridgeport, and said they hardly ever used the mill drill -- which seemed likely from its like-new condition. The only problem with it seemed to be that the R8 collet retaining bar had broken at the top end and had been brazed together again. Not sure how that could have happened unless it was off the machine when it broke. Anyway, I considered it a good deal at the time, and I got a mill vise and a box of useful accessories into the bargain.

So, back to the scale mounting, today ..... I debated for awhile whether I wanted to mount the X scale to the front, or the back of the carriage, and finally decided on the front. That way I get full Y travel, because otherwise the scale reduces the free distance to the column.

One method of mounting a scale on the front seems to be to re-purpose the stops, which are on the front face of the table. These fit into a dovetail groove that runs the full length of the table. There are two stops, retained by Allen screws into dovetail nuts, and they can be set anywhere. I think most people use them merely to prevent running the mill table too far off the end.

I happen to like those stops a lot, and use them frequently when slotting on the mill. They allow easy milling of slots with clean ends without having to keep an eye on the dial. While I imagine that with a DRO it's easier to know when to stop at either end of a slot, you can do it by number. Nevertheless, I'd rather have a physical stop, and not have to constantly check the readings at all. It definitely speeds up the work when it takes say 20 passes to fully mill a deep slot.

So, though replacing or repurposing those stops to support the scale would make installation easy, I didn't want to do that. Instead, I decided today to make a second set of dovetail nuts (kind of like tee-nuts), and some solid stand-offs to support the scale and use the same dovetail slot that the stops slide in. That way I can retain the stops, and still support the scale by that simple method, and there would be no need to drill a hole in the table. The standoffs would be long enough to space the scale far enough away from the stops, so I can get an Allen wrench in there to tighten or loosen them when I need to. The standoffs would be at the extreme ends of the table -- the stops are free to slide and position in the rest of the length of the table.

I decided therefore that the standoffs should be 1.25" long, and made from some 1"x1" solid aluminum bar stock cutoffs  from a scrap barrel that I won at a machine shop auction.

I measured the dovetail nuts that the stops used, and they turned out to be 1/2" wide, and had 15 degree tapers to fit the dovetail slot. I milled these dimensions into some hot-rolled steel strip and sawed off two inch-long nuts, and tapped them 1/4" -20.  I also drilled the 1-1/4" aluminum stand-offs 1/4" and countersunk the ends. By evening I was able to screw the standoffs onto the table using the dovetail nuts, and it looked quite sturdy, clean and simple. Happy to get that particular slide mount figured out.

 

PekkaNF:
I want to see pictures of that!

I have probably same mill/drill on green colour and I was wondering the same things. I put the scale on the front:
https://www.madmodder.net/index.php/topic,12813.msg153772.html#msg153772

There are ramblings about the location of X-linear scale and factors starting at the end of page#1. I noticed that I had my nose hard at the machine and didn't notice that thread became more of a build log than actual structured content on OP.

My main drivers were:
1: To maintain full travel of the axis
2: To protect the magnetic scale
3: To put magnetic scale onto moving part to minimize reader head cable movement.

Only compromise was with X-axis stops.....I though it hard and there has been very few ocacions, where one (and once even two) stops would have somewhat usefull, but:
1: Hard stops are way more usefull with dials, DRO actually helps a lot
2: Plan "B" is to build stops on the bottom of table dowetail ....sort of clamps that clamp on the table dovetail and bump into a saddle.  Haven't needed it yet / Haven't build it yet.

Pekka

vtsteam:
Hi Pekka, very nice looking mill and photos compared to mine!  :palm:

I initially thought the same as you about maintaining full travel, but after playing around with the parts and positions of the stops and mounts, I realized I don't actually use or even want full travel on the X axis, end to end. Why? I normally position my stops to prevent over-travel.

There is not much support of the table as it nears the maximum possible travel. The table has 14" of support normally. If cranked over to the bitter end, that is reduced to only 7". If one has a 70 pound vise near the far end, plus the table weight itself, that is putting heck of a lot of stress on that cantilever for only 7" of support. The table is cast iron, not a great material in tension.

Also, because it is a round column mill drill (which has its well know disadvantages) it also has one advantage in that the head can be swung over to either side a couple inches with little loss of Y travel, to compensate for a far off-center part location on the table, thus compensating for any loss in travel caused by the scale or reader. And in fact that allows more table support -- for two inches of head swing you get 9" of table support instead of 7"

The only possible disadvantage for me personally would be if I were to try to surface a very long piece -- like the head of my tractor engine -- which I did a few years ago (some of you may remember the thread here), But at that time I actually wasn't aware that my table stops had been set conservatively, and I still managed to skim the head true by use of a large diameter homemade fly cutter (also documented there). Another possibility which didn't occur to me then was that I could have made up a column stop, so that swinging the head did not lose vertical position.

Anyway, I don't want to give up the advantage of the stops (or the carriage clamps) so simply spacing the scale out from the table is a very simple solution. The spacers are very simple to make. See photos below, and one where I'm holding a short scale up to give the relative positions of the spacer, an Allen wrench for adjusting a stop, and the table clamps.

All fit, and I believe actual table travel with the stops unscrewed from their dovetail nuts will be about the same as it would have been if there was no scale and the table stops were positioned at the ends of the dovetails. Well minus the length of the reader head, which is unavoidable in any DRO setup, unless the scales are longer than the table.

Although for my setup when you think about it, the reader head isn't much wider than the central stop bracket on the mill already.

In sum, I think I will see very little difference in useful table length with this setup, and any loss of extreme travel can be compensated for.

Phew.....sorry, pretty long winded for a very simple setup!  :loco:

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