No. of divisions

[NobbyParticipant @nobby]

Hi.

How is the dial divided up please. I want to add one to my s7 Mk1 Mine looks about 7/8″ per rev.
Regards Nobby

[NobbyParticipant @nobby]

[John Stevenson 1Participant @johnstevenson1]

Nobby,

Can’t answer 100% correctly on how many divisions but I do know it has internal gearing so the dial move a set length per turn and not once per turn.

 

Robin has more info than I have.

 

John S.

[adyParticipant @ady]

Is that a wee brush on the handle side of the dial to keep the gremlins out?

 

I just put a digital vernier on my cross slide.

Doesn’t look as nice but backlash is eliminated and cuts are good for 1-200ths of a mm

Edited By ady on 11/09/2011 02:08:13

[JasonBModerator @jasonb]

I think its a straight knurl not a brush seal

 

J

[NobbyParticipant @nobby]

Hi Ady

Thank you for reply .I know I can use the the handwheel on the leadscrew 125 divisions but you have to turn the gears as well . I suppose I could go digital? some how

Regards Nobby

[Anthony RhodesParticipant @anthonyrhodes37318]

Posted by Nobby on 11/09/2011 00:21:35:

Hi.

How is the dial divided up please. I want to add one to my s7 Mk1 Mine looks about 7/8″ per rev.
Regards Nobby

Nobby,

 

It would probably be useful if you were to mention the article published in the latest issue of Home Shop MAchinist, September-October 2011, p. 26 – 35. There was also an earlier version of the article published in Engineering in Miniature but I don’t know the daye or issue number for that release.

 

This is an article by Graham Meek. It tells how to build a micrometer dial for the carriage handwheel. The example discussed specifically was for a Myford Auper7 but he points out that the principles can be applied to any lathe.

 

The special feature of this design is that, since the carriage traverses an inconvenient distance for each revolution of the hand wheel. ther is an internal gear system which makes the micrometer dial rotate at a differen rate than does the handwheel so tha it reads actual distance traversed instead of a decimal value of the rotation of the hand wheel.

 

Per Gray’s article the carriage travel per revolution of the hand wheel is .866″. It would be inconvenient to have a micrometer dial marked out in 86.6 divisions to indicate 0.01″ units. The internal gearing makes the dial rotate more slowly than the hand wheel so that when the handwheel has rotated one full revolution the dial will have rotated .866 revolutions by which means it reads the actual distance traversed rather than parts of a revolution of the hand wheel.

 

The picture at the start of this thread is straight out of the article and is marked with 100 divisions with each 5th mark a bit longer than the singles and each 10th mark noted with numbers for tenths of an inch. Gray gives the gearing to accomplish the reduced rotation of the dial for correct decimal inches and also provides the same information to read out in millimeters with divisions down to 1/4 mm.

 

In the article Gray states that the the gearing has an error of 0.43% (actually 4.35/1000 on a dial marked in hundreths). It would be possible to get that down to 0.17% error but it would require very special gears which can only be cut by hobbing. (J.S. original gearing 26/28 x 26/28, better 26/28 x 27/29. 27 on 26 pitch circle, 29 on 28 pitch circle.) This would actually fit because the gears would be the same size as the ones Gray specifies, I can generat numbers which can get he error down to .077% but I don’t know if the gears could be fitted within the mechanism as designed.

 

So, to recap, 100 divisions indicating .01″ or 100 divisons indicating .25 mm used with alternative gearing.

 

Anthony

Edited By Anthony Rhodes on 18/09/2011 05:10:36

[Anthony RhodesParticipant @anthonyrhodes37318]

 

In the article Gray states that the the gearing has an error of 0.43% (actually 4.35/1000 on a dial marked in hundreths). It would be possible to get that down to 0.17% error but it would require very special gears which can only be cut by hobbing. (J.S. original gearing 26/28 x 26/28, better 26/28 x 27/29. 27 on 26 pitch circle, 29 on 28 pitch circle.) This would actually fit because the gears would be the same size as the ones Gray specifies, I can generat numbers which can get he error down to .077% but I don’t know if the gears could be fitted within the mechanism as designed.

 

Did some more thinking about this. It turns out that almost ideal gearing is 26/30 x 28/28 (the extra 28/28 is necessary to return the same axis as the original drive). Results in an error of .077%. The question is whether the 30 will fit?

 

I believe the original gear train for the metric dial was 29/31 x 29/31 which had an error of 0.54%. Alternative gearing 33/29 x 31/31 results in an error of 0.012%. Same question, will the 33 fit?

 

Anthony

[John Stevenson 1Participant @johnstevenson1]

What DP are the gears ?

 

You can just get a 30T on a 28 blank, not a pretty tooth form but still an involute and workable.

This has been draw in in 20 DP just for reference, on the right is a big standard 28T gear, on the left is a corrected gear with 30 teeth on the same blank.

 

Click on picture to enlarge.

 

John S.

Edited By John Stevenson on 18/09/2011 09:18:57

[NobbyParticipant @nobby]

Hi Tony & John

Thank you for info on this . I wont be able to change gearing on the apron . I will give it some more thought. Meanwhile i will try and upgrade the adjustable carriage stop to indicate .001″ I have a platform under the stop with fixed rule & for loading home made gauges to save using my best slips. Posted in one of my albums.

What’s .866 ” in metric ? that’s a thought

Regards Nobby

[Anthony RhodesParticipant @anthonyrhodes37318]

Posted by John Stevenson on 18/09/2011 09:18:09:

What DP are the gears ?

 

You can just get a 30T on a 28 blank, not a pretty tooth form but still an involute and workable.

——————————

 

John S.

Edited By John Stevenson on 18/09/2011 09:18:57

John,

 

That was my first thought but it probably isn’t necessary.

 

The inch version of the micrometer dial uses 36 DP gears. The first and last gears in the train are coaxial with the hand wheel shaft. Original train is 26/28 x 26/28. New train would be 28/28 x 26/30. Increases the radius occupied by the train by one tooth depth (0.027777777″). I expect it would fit within thedesign as is but I haven’t actually checked.

 

Same story with the metric version which uses 40 DP gears. Original train is 29/31 x 29/31. New train would be 31/31 x 29/33. Again increases the radius occupied by one tooth depth (0.025″).

 

There is some benefit for amateur construction to not have to deal with special form gears.

 

Anthony

[Anthony RhodesParticipant @anthonyrhodes37318]

Posted by Nobby on 18/09/2011 16:16:00:
Hi Tony & John

Thank you for info on this . I wont be able to change gearing on the apron . I will give it some more thought. Meanwhile i will try and upgrade the adjustable carriage stop to indicate .001″ I have a platform under the stop with fixed rule & for loading home made gauges to save using my best slips. Posted in one of my albums.

What’s .866 ” in metric ? that’s a thought

Regards Nobby

Nobby,

 

.866″ x 25.4 = 21.9964 mm but the rotation you want to deal with is related to 25 mm, not 1″. The new factor is 0.879856 of 25 mm.

 

Anthony

[John Stevenson 1Participant @johnstevenson1]

Nobby,

You don’t have to change gears in the apron, the gears in question are inside the handwheel.

 

John S.

[John Stevenson 1Participant @johnstevenson1]

You can get 0.866 with a 13/15 setup, or multiples of.

 

John S.

[Anthony RhodesParticipant @anthonyrhodes37318]

As John says, the gears are inside the handwheel. The mechanism is a variation on the concept used to provide both inch and metric micrometer dials on the cross feed screw. Not common on inexpensive lathes but not at all unusual on machines such as Hardinge, Nonarch, Clausing, Nardini (I believe), etc.

 

John, your correct of course about the 13/15, just half the tooth counts of the 26/30, but many people aren’t happy with very low tooth counts and two of the gears are coaxial to the hand wheel shaft. On the other hand, it occurs to me, the drive could be from A to 15 followed by 13 to B where A and B are the same tooth count and the 13 and 15 are both cut to a 14 pitch circle, or A, 13, and 15 are all cut to standard pitch circles and B is cut to a -2 pitch circle.

 

Aside from needing the coaxial gears to be large enough to fit over the center shaft, there’s no preference for large or small DP. Looking at the drawings in the article it appears to me as if two 20 tooth 24 DP gears axial to the hand wheel shaft and and a cluster of 24 DP 15 and 13 tooth gears both cut to a pitch circle of 0.700″ would be an ideal solution. This gives 28/15 x 13/28 = 0.86666666666666 = perfect result.

 

Your thoughts?

 

Anthony

[John Stevenson 1Participant @johnstevenson1]

Anthony PM sent

[NobbyParticipant @nobby]

Hi John

Cheers mate .

Regard Nobby

 

[NobbyParticipant @nobby]

Hi Rob

I misunderstood the from the start .I just wanted to put a dial direct on the standard handwheel on my S7 Mk. 1

I have another problem now with Srewcutting 10 TPI on my 1912 Drummond .

I will post thread & see if you our anybody can help Its driving me mad ????

Regards Nobby

[adyParticipant @ady]

10tpi

 

8tpi leadscrew? 8 x 1.25 = 10tpi

so.

20/25

or

40 headstock 50 leadscrew?

 

[Anthony RhodesParticipant @anthonyrhodes37318]

Posted by ady on 21/09/2011 23:46:45:

10tpi

 

8tpi leadscrew? 8 x 1.25 = 10tpi

so.

20/25

or

40 headstock 50 leadscrew?

ady,

 

I started to respond to this but suddenly realized I’d confused theissue and you had it correct in the first place.

 

20/25 x .125″ = .10″ = 10 TPI. Any 4/5 ratio will do.

 

Edited By Anthony Rhodes on 22/09/2011 02:13:30

Edited By Anthony Rhodes on 22/09/2011 03:23:50

[NobbyParticipant @nobby]

Hi Andy & Guys
The gear train was no problem 40 – 60 idle- 50 leadscrew as photo .When engaging screwcutting lever photo on a test peice After disengaging lever the the 2’nd cut did not line up . On my Exe lathe I sold there was no problem . I know i can use the revering trick I have no reverse on this lathe . I suppose if I put the pedal back on I could use this trick Can I add a threading indicator some how . ?
Regards Nobby

[Anthony RhodesParticipant @anthonyrhodes37318]

Posted by Nobby on 22/09/2011 11:49:54:
Hi Andy & Guys
The gear train was no problem 40 – 60 idle- 50 leadscrew as photo .When engaging screwcutting lever photo on a test peice After disengaging lever the the 2’nd cut did not line up . On my Exe lathe I sold there was no problem . I know i can use the revering trick I have no reverse on this lathe . I suppose if I put the pedal back on I could use this trick Can I add a threading indicator some how . ?
Regards Nobby

Nobby,

 

For the dog clutch to pick up all threads reliably it has to be before any changes in ratio and have a single dog. This is how the Exe is setup and is not how the Drummond is setup.

 

Reversable motors are common, reverse pedalling would work, and a hand crank you insert in the back end of the spindle is another solution.

 

Yes, you can install a threading dial. Look at any Myford or Boxford or most other lathes to see how they are set up. Most are for 8 TPI, does have to match right hand or left hand leadscrew thread. Usually mounted on right side of apron, needs to be able to be swung into and out of engagement with the leadscrew and hold in either position. When mounting you may have to shim the dial away from the side of theapron until the graduations on the dial line up with the witness mark when the split nuts are closed.

 

Anthony

 

[NobbyParticipant @nobby]

Hi Andy & Guys

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

[Anthony RhodesParticipant @anthonyrhodes37318]

Posted by Nobby on 23/09/2011 00:42:31:

Hi Andy & Guys

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

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

Nobby,

 

Try “Anthony”. Thanks for the photo.

 

Anthony

[NobbyParticipant @nobby]

Sorry Anthony

Great idea saved me some trouble.

Nobby

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