Lathe DRO

Lost my post after shunting back and forth to album so this is very trimmed down. Here's the scale I started with

I removed the chrome ends replacing them with thin ali sheet, unsoldered the cable ends and removed the circuit board electronics from the reader housing to reduce the housing height.

Then I reduced the height of the housing to end up with this:

You can see the first attempt at attaching magnets with professional Supergloo. That was unsuccessful and I (very carefully!!) drilled and tapped the box M4 with the glass in position - drill & tap depth <6.5mm. I think I could have removed the glass scale as there is no absolute reference.

I cut some ali angle to use as a bracket fixed to The tee slots to retain the scale head:

My Easson scale is only two channel so I designed a simple electronic schematic to allow me to switch from one of two scale inputs. I built it on a pcb, but it's so simple you can get the IC, wire directly to its pins, test it works then pot the lot in Epoxy:

The small project box has another magnet fixed to it so it can sit on metalwork at the back of the lathe. This simple 1 of 2 input switch can't be used for absolute scale measurements. The DRO remembers the reading from the last input and carries it over to the second input after switching, whatever position the second scale is in.

Now using the new DRO and without clocks, I can see all the slop in the compund leadscrews and poor setup of the compound gib - but that's another story. I wouldn't use this size optical DRO again. It's electronic design is old. Had they have used miniature surface mount semiconductors they could have made the sensor housing a lot smaller. Magnetic reading could be the way to go as has been suggested.

The moving 'trolley' is pretty crude to. Some small rollers inside to keep it in the extruded ali track. Once one chrome end is removed the reader trolley parts can be slid out. When moving it away carefully on the tee slots for angle taper turning, it seems strong enough to be self supporting, although I might find a clip to hold the 2 parts together? But for £30 and some work it will be useful. Most of my beginner turning is non-ferrous at the moment and I'm aware my magnets will be a 'magnet' for ferrous so I'll need to keep them clean.

Edited By Jim Smith 8 on 24/06/2021 17:08:06

Edited By Jim Smith 8 on 24/06/2021 17:09:37

This photo of the Warco 'Bad Boy' brass block saved me posting my own. If I pushed my quick change tool post hard to the rear I could hear a 'clunk' and my newly fitted DRO scale readout confirmed the table had moved. I removed the handwheel + leadscrew and block to have a good look. I held the block very loosely in a vise and turned the leadscrew end to end. There was very little binding on the Acme thread across unworn parts of the lead screw thread but I adjusted the 2 X 4mm grub screws anyway to take out any play as felt in the vise.

Then I replaced the assembly, fixed the table slide with the M8 screw in the counter bore and lightly re-adjusted the gib. Result was terrible - Binding up as the lead screw was rotated end to end. It was very tempting to play with the thread adjustment but this wouldn't have been right. I know lead screws and blocks can wear. Warco sell both as a matched pair but I was able to buy just the (expensive) brass block to take a chance.

I fitted the new block which was nice and tight on the threads in the vise without needing to adjust the grub screws. I replaced the assembly and got a similar binding result. I removed the M8 screw holding the slide to the block, loosened the gib a little and wound the block to the front. I then pulled the slide towards the front until it was sitting just over the block. I could see a gap between the top of the block and the underside of the slide, it measured 1.6mm with feeler gauges. I couldn't see any support at the far end of my leadscrew?

I then cut some shim to fit the top of the block and temporaly held it in place with a spare grub screw set level with the shim. I wound the block in to align with the table fixing hole. Tightened the M8 screw and Success, no binding along the length of travel but still a little play of 3 thou. left. This wasn't coming from the thread but end play on the leadscrew. I removed the handwheel and fitted a 3 though shim. Now all play is gone no binding or excessive friction, I can push hard on the tool holder and only see 1/2 thou change in reading. I may try to modifying my old brass leadscrew block with a saw cut to adjust the thread over more thread turns, rather than just the end 3 threads.

Next I will look at the 'Z' lead screw (or is it 'X'?) on the compound, this has a steel block. There is no measurable horizontal play, but the handwheel seems to have more backlash than I would like compared to the other one. Are these common issues with most Chinese lathes, or is it just me finding these problems? It seemed to me that getting the compound slides sorted was more important than other parts of the lathe.

I also met a problem with one of the compound gibs. After several attempts at careful adjustment I removed it. It looked bent, but wearing specs can give optical illusions. I put it on a surface block and confirmed it was bent. Therefore it becomes impossible to adjust all 4 gib screws for even contact along the length of the gib. As a last resort I hit it with a hammer on a steel block and it's now straight, but I think I might try making a new gib when I can work out how to cut/grind the edge angles without a mill.

Onwards & Upwards!

Edited By Jim Smith 8 on 25/06/2021 10:40:56

Stuart -

I have fitted and do sometimes use a leadscrew-handwheel on my Myford lathe, using the adjacent corner of the bed as a pointer, but that does give the screw and half-nuts a hard life. So as a general rule, I combine the carriage feed and compound.

Cut most of the length with the saddle travel, then (assuming it is actually set parallel) lock the saddle and trim the little bit with the top-slide. Or if working on the end of bar-stock, over-cut the length slightly and face it to length.

If I am cutting a short diameter within the range of the top-slide I sometimes use that to create the first step as a guide; then the saddle for the remaining cuts very slightly short, leaving a tiny but visible witness step, then the top-slide again just to finish to size.

I don't use dogmatic approaches, but go by which I think the best option for the particular task.

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I have fitted a Machine-DRO 3-axis system to my Myford mill; but not to either the Myford or Harrison lathes. I have looked at the idea but it seems to put a lot of vulnerable bits where they ought not go, and anyway possibly get in the way.

I don't like this x,y,z nomenclature though. It makes sense on a mill, and does correspond to geometry (Y does not go "to the sky" in maths, map-reading or CAD; but is horizontal, towards the far edge or North; so should be that for a lathe cross-slide).

It's OK on the read-out itself when you are using it and accustomed to it: X long travel, Y cross-travel, Z vertical; but when writing describing machining operations, I prefer and use the proper machine terms.

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On guards, I have to confess my lathes don't have such things, other than a crude plywood tool-tray that shelters the inverter screwed to the cabinet below the headstock, on the ML7. The electricals on the Harrison are well out of the way: the motor on a frame above the headstock, the inverter and controls on the wall above the tail end. Even so, I think I ought fit guards to both machines, if not interlocked, at least controlling the swarf, and on the L5 me due to the clutch lever position. A mass of steel string grabbed by a big, fast-spinning chuck is not nice...