cross slide micrometer wheel

[CotswoldsPhilParticipant @cotswoldsphil]

Hi Robin and all,

Sorry for the tardy reply…

The DRO in the photo does not power down when static, once on it stays on – you have to long-press the on/off/reset button to turn it off. The battery is an LR44 which seems to last a reasonable time; even the cheap ones. I tend to just turn it on when I need it, it's always there ready.

As I mentioned, the only issue (for me) is that these particular DRO's (from Axminster – usual disclaimer) are not liquid proof. I may have been lucky, it got wet and started behaving oddly so I took the back off, dried it out and all has been well since.

Phil (CP)

[CotswoldsPhilParticipant @cotswoldsphil]

Following on from Neils post, here is a crossslide index wheel I made for an ML7 years ago to replace the 'orible die-cast one. As Neil indicates the feedscrew is 10tpi so there are 100 divisions on the dial. A piece of clock-spring between the inner and outer components adds the necessary friction.

Phil (CP)

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 07/11/2014 11:43:16:

So, as the thread is 10 tpi, why not just make a 100 division handwheel, 1 div=1 thou or 2.54mm within 1.6%,, i.e. over 10mm the error will only be 0.016mm.

.

Neil,

Only Robin can say for sure, but [from my reading of his posts] he wants better than that.

… i.e. convenience and precision when working to the final [metric] "gnat's wotsit"

My preference for 127 un-numbered divisions on a re-settable micrometer dial, stands.

MichaelG.

Edited By Michael Gilligan on 07/11/2014 12:15:28

[John Stevenson 1Participant @johnstevenson1]

Jesus H Christ with a Bridgeport.

If it's that important then just buy a new metric screw and nut.

You will have wasted more time and effort kludging everything up and still have a chance of errors and scrap work on anything you do.

[Neil WyattModerator @neilwyatt]

Sorry, over 10mm the error is 0.16mm.

Bearing in mind my lathe is the 'other way round' using 40 divisions to turn 1mm into '40' thou I have never, ever encountered a significant error when applying a finishing cut

My preference is to avoid an 'awkward' step in the dial at all costs, as if you overlook it and work past it, you will either add or lose a few thou.

I also plan to replace the brain-damaging 75 division dials (0.02mm/div, which doesn't work in for me for some reason) on my mill with 60-division ones, although the DROs mean I keep making excuses to put this off.

An interesting paradox is that my mini-lath has a 16 tpi leadscrew, I use this with a 64-divison dial, 1 grad = 0.97 thou, a 3% error. A metric 1.5mm pitch leadscrew would let me use a more convenient 60 divisions with half the error when working in imperial…

Neil

[Jon GibbsParticipant @jongibbs59756]

Posted by Jon Gibbs on 07/11/2014 11:51:11:

I think if you can accurately set the top-slide at 23.19 degrees to the lathe bed then 10 thou on the top slide would result in an advance the inward feed by 0.1mm.

Sine(23.19) = 0.39378 which is almost exactly 10/25.4.

To set this angle precisely it would be necessary to check for a 0.500" advance for a movement of 1.270" advance of the topslide using this set-up.

Just realized that 51.94 degrees would also work and give the 100/127 reduction.

In this case you'd have 0.2mm for each 10 thou advance on the topslide so you'd have to keep multiplying by two but not too hard to do.

…but John S's words of wisdom are still ringing in my ears … not to mention the expletive

Jon

[Neil WyattModerator @neilwyatt]

Just a thought… an article in the next MEW will point out that the topslide screws of old ML7s are NOT screwcut and can have significant errors so there's not really much point having a solution that claims to offer accuracy over any significant distance.

Neil

[Robin teslarParticipant @robinteslar]

Posted by Michael Gilligan on 07/11/2014 09:05:58:

Posted by Robin teslar on 07/11/2014 08:20:50:

BUT when you are turning down a diameter towards the last few cuts then you re-zero the dial each time so its not really that limiting.

.

Robin,

… if I understand your likely working practice correctly: I would probably make a simple re-settable dial for the Myford [there have been several designs published] and engrave it with 127 un-numbered divisions.

MichaelG.

A valid point MG

I have never worked with an un-numbered scale but its worth having a feel of this – would I lose my way?

Dont know till I try

The OP has certainly produced some interesting observations and I am totally blown away by the geared scales but as said maybe too much play would detract from the benefit. I'll just knock up a test sample

BTW messing around with an ML7 is what floats the boat. I could have bought a modern machine with full DRO for less that the total cost of my old Myford but it wouldnt be the same as when I started out in a machine shop

So I recycled a jam jar lid from the kitchen pedal bin and here we have an un-numbered 254 grad scale. The print needs adjustment but it can work and cost me nothing

Robin

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Neil Wyatt on 07/11/2014 17:26:34:

Just a thought… an article in the next MEW will point out that the topslide screws of old ML7s are NOT screwcut and can have significant errors so there's not really much point having a solution that claims to offer accuracy over any significant distance.

.

I wait with 'bated breath … and a screwcutting project on the To Do List.

MichaelG.

[Author]

Posts