Lathe DRO

[RobinParticipant @robin]

JasonB: Extending to the chuck is easy. The question is, can you extend the centre slightly past the tool tip ready to make that between centre cut and still have good support on the tailstock barrel?

ChrisB: My saddle started hitting the feed clutch barrel as soon as I removed the clock spring from the lead screw. Luckily it hits an unused part of the split nut T slot so I can relieve it without emptying the oil from the apron.

[MeunierParticipant @meunier]

Posted by JasonB on 20/04/2021 19:22:58:

Posted by ChrisB on 20/04/2021 19:17:10:

where the carriage can move further to the right and touch the headstock

Edited By JasonB on 20/04/2021 19:28:19

I think your right and left have become confused after SOD's tailstock episode.
DaveD

[JasonBModerator @jasonb]

Robin I mostly use a revolving ctr so that gives me extra length. Will take a photo later

[RobinParticipant @robin]

I see the prices of the triple angle revolving centres are coming down at last. A credible alternative to the half dead centre?

Perhaps an answer to the insert threading tool, set at 30 degrees, forcing a risky top slide extension below the chuck

Edit: Replacement picture, I got rid of most of the overhang but the tailstock is all the way out and the toolpost is blocking all but the fanciest of revolving centres…

Edited By Robin on 21/04/2021 10:28:52

[Ian PParticipant @ianp]

Forgive my ignorance, but what are 'triple angle revolving centres'?

If prices are coming down, are they a better bet than Pork Bellies?

IanP

[RobinParticipant @robin]

Ian P: I have no idea, I saw "8 Type Live Center Morse Turning Revolving Bearing MT2 MT3 Taper Triple" on e-Bay for £17.35 and took a wild guess.

I meant the ones with the spindly nose that doesn't get in the way so much

[JasonBModerator @jasonb]

Here you go

Standard revolving ctr, with the DCMY tool shown I can happily get down to 3.0mm dia for things like valve stems

Like this I can use the full travel of the topslide to give fine positioning when doing things like cutting a series of cylinder fins

reverting to the stock toolpost would reduce tailstock extension by another 12mm if needed.

[ChrisBParticipant @chrisb35596]

Posted by JasonB on 20/04/2021 20:20:04:

Shear pin on mine. Also no Leadscrew spring cover or boxing sticking out the back where the motor goes.

You just got me my next project Jason!

Some time back I got myself a lathe collet chuck, prepared a piece of steel for the backplate…bolted the blank backplate to the spindle and proceeded with the machining. Little did I know that the tool post would not reach the spindle! I managed, but it was one of those simple jobs turning into a nightmare.

Spent the morning fiddling with the lathe, and result! I was wrong about the WM280 tailstock reach

[JasonBModerator @jasonb]

It's not just backplates when it helps but handy for faceplate work too.

[ChrisBParticipant @chrisb35596]

Posted by JasonB on 21/04/2021 15:40:49:

It's not just backplates when it helps but handy for faceplate work too.

True and also with the collet chuck, working close to the chuck I have to extend most of the topslide.

And the issue with saddle travel would have been easy to fix at production level, the apron gearbox casting is already shaped quarter round to clear the feed shaft, they just needed to add 1/8" more to clear the clutch.

I had no intention of removing the apron, so I turned down the clutch just enough to get some clearance.

[Jim Smith 8Participant @jimsmith8]

I've got my scale working O.K now on the cross slide, but the standard size 150mm £30 scale had to be dismantled, electronics and wiring removed, then replaced after making it smaller. Then I found doing a simple turing and boring job the DRO numbers don't give the right answers I expected. It was after that I pushed the WM280V compound tool post hard towards the rear and heard a 'clunk' which measured about 0.65mm. It explained why my turning finish wasn't so good with more tooling marks than I expected. My final 20mm bore size calculated from a starting ID of 19mm and DRO readings divide/2 didn't work out.

Now I know all about the compound X leadscrew and threaded block on these Chinese lathes and how when first assembled and set up 'wrongly' they can wear the LH Acme threaded brass block. I'll post some info later. I've now got the compound backlash down to 1/2 thou and no clunk. Turning a fine finish on some ali looks a lot better and I can turn a thou.off a 25mm bar reasonably confidently and repeatable for a cheap lathe.

Edited By Jim Smith 8 on 22/06/2021 19:56:38

[Jim Smith 8Participant @jimsmith8]

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

[Jim Smith 8Participant @jimsmith8]

Posted by ChrisB on 21/04/2021 14:39:27:

Posted by JasonB on 20/04/2021 20:20:04:

Shear pin on mine. Also no Leadscrew spring cover or boxing sticking out the back where the motor goes.

You just got me my next project Jason!

Some time back I got myself a lathe collet chuck, prepared a piece of steel for the backplate…bolted the blank backplate to the spindle and proceeded with the machining. Little did I know that the tool post would not reach the spindle! I managed, but it was one of those simple jobs turning into a nightmare.

Spent the morning fiddling with the lathe, and result! I was wrong about the WM280 tailstock reach

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

[Nigel Graham 2Participant @nigelgraham2]

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.

.

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.

.

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…

[Author]

Posts