No. of divisions

It was only a short thread about 5/8" so I fitted a crank handle As Andy suggested NobbyIi

Edited By Nobby on 23/09/2011 00:43:14

Best option is to click on the drawing, then download it for better study.

Looking at the left drawing, on the left the feed screw passes through a bearing as it extends out through the dial. Immediately to the righ of the bearing is a sleeve keyed to the spindle of the carriage handwheel on which a gear is cut. The center gear drives an outer gear on a layshaft which, via a second gear at the right end of the layshaft, passes the drive back to a aecond sleeve running on the outside of the first one. This second sleeve is attached to the micrometer dial which surounds the mechanism and thereby also serves as the housing for the mecahnism.

The unit shown is setup for metric readout but an alternative to read out in inches has already been engineered. Based on the gears provided the micrometer dial can be made to rotate faster or slower than the handwheel spindle so that instead of reading out revolutions of the handwheel it reads out distance traversed by the carriage. This can be built to read out in decimal millimeters down to 0.025 mm or decimal inches down to 0.001".

Very effective when doing precision work.

Anthony

Edited By Anthony Rhodes on 01/10/2011 06:59:29

Hi Graham
Brilliant work
Nobby

Yes. Lovely workmanship, it's an artform when you get good enough

...now it's back to hacking away with a knife and fork for me

Well I've waited 24hrs and no one has said a word so it's time for Ady1 to ask Graham

Are those dials in aluminium or steel?

How are you marking them up so they look good?

Ady1

Hi Gray
It looks  great  when fitted to the lathe.  Brilliant 

Nobby

Edited By Nobby on 23/07/2012 21:48:38

Anthony,

How have you calculated the 0.866" distance for one complete revolution of the Myford handwheel? I ask this because I make it 0.8617". I arrived at this figure based on the following:- The pitch of the Myford rack is .15708" (3.1416/20dp). The apron reduction gearing is 35/16 which equals 2.1875. One turn of the 12t gear (that engages with the rack) 12 x 0.15708" =1.885". Divide this by the 2.1875 reduction and the answer comes to 0.8617". If the 28/26 gearing is applied twice the distance moved is .99936". The only assumption I have made is that the Myford rack is 20 DP but I have no reason to think it is isn't. I can't see how any of the alternative gearing that you propose, will improve the accuracy.

Steve.

Steve.

Not had time to check your sums but I can confirm the Myford rack is 20 Dp at 14.5 degrees PA.

Edit,

Steves figures make sence to me

Steve - thanks for bringing a thread I had missed back to life.

Gray - thanks for a delightful design.

I am sorely tempted to have go - have I missed a post giving the gear sizes for the C3 version?

Neil

John,

Thanks for the confirmation about the Myford rack and checking my figures. I was starting to think that I had missed something - even more so after posting!

Gray,

I absolutely agree about theoretical figures as opposed to practical uses. If I have not completely fried my brain on this, a complete turn of the graduated dial (1" will actually move the carriage slightly more - in theory. I would suggest that (again, in theory) that this is a condition that will only improve as the rack and/or gears wear. So, if the carriage was moved from an unworn section of the rack, to a worn section, any error will reduce. I have one of your dials fitted to my S7 and it has transformed the lathe. I have not come across any situation where I would question it's accuracy. I need to do the 10" slip gauge check just to see where it sits on my lathe. I can certainly see why they are so popular and why so many have been sold over the years. My post was really just to question Anthony's figures and to make sure that there isn't a better iteration. After consulting gear ratio tables in Machinery's handbook, I feel sure that there isn't - or not one that would fit into the existing body. Thank you for your thoughts on this.

Best regards,

Steve.

Edited By Steamer1915 on 25/02/2013 18:56:19

Bit hypothetical anyway.

Although the number 0.866 is fixed in peoples mind Grays calculation of (25/28) x (26/28) = 0.862245

So 0.862245 - 0.8617 = 0.000545" Just a tad more than half a thou and allowing for wind down Wilmot lane where Myfords gear cutting equipment was located we can say this is knob on.

Don't understand your second line John. However, I've just spent half an hour or so checking the actual measurements on my S7. I clamped a small angle plate to the bed at the headstock end and made sure it was square to the carriage travel so as to avoid sine errors. Using slip piles of various lengths between 1 and 11 inches, I was able to see that the error (such as it is) was no more than 1/2 thou per inch over all measurements. That's close enough for me. In an earlier post, I alluded to the point that I thought that the actual measurement would be slightly longer than the dial reading and this has proved to be the case. Job's a gud 'un!

Steve.

With Gray's drawings, and advice I have just finished and fitted the C3 version of his handwheel dial to my Clark CL300M, one of the 'generic' mini lathes.

Important things to note for anyone trying this version are:

• The handwheel spindle is 8mm diameter (Gray warned me to watch for this, but I missed it!)
• My rack was pitched slightly differently at 0.766" for a turn of the handwheel (five teeth on the rack) but by increasing the gear pairs to be 30:30 and 34:26 I was able to get a theoretical accuracy of two thou over the inch.
• The extended handwheel just fouls the end of the cross-slide ball-ended handle. I took a 0.3mm cut off the outer surface (which then covered all my beautidful work with black dust). A fine foam backed abrasive block brought back a neat finish, but somewhat speckled compared to the original!

To my astonishment (given that I changed the gear ratio, not becauise I doubted the design) it works just as it's supposed to, with 1.002" of saddle movement for 1.000" on the dial.

Here are a few pictures, but first I'd like to thank Gray, not just for his support and great design, but for encouraging me to acheive a level of fit, finish and accuracy a step up from my usual. It's not quite toolroom yet, but I think it looks OK.

Neil

The working parts in place:

My first attempt at a sraight knurl(!) - I cut away the numbers and re-stamped them after this was taken (the bad ones are hidden):

And finally, tehdial on place on the lathe:

I have the copy of the above article which was published in Engineering in Minature a couple or so years.Very good. I never actually understood how the two gears on the small shaft were linked together, perhaps I've missed something ( a keyway perhaps) when reading the article. I hope Hemingway do a kit, If they do, might just lash out when at Harrogate show.Ted

Yes Ted,

I just pressed the gears on to a slightly oversize bush, using two wooden pads so the bush ended up slightly protruding from each gear.

My cunning plan to ream after fitting the gears gave me a perfect push fit on the PGMS stub axle, so I had to ease it a bit with emery paper in the lathe.

Neil

Nice work Neil. I'm sure you will soon wonder how you managed without it.

Steve

Here are three photos of my efforts at Gray's dial for the Myford 7 lathe. There is an Imperial and Metric version here.

Steve.