Member postings for Sam Stones

I was totally wrong Bazyle.

Rotating meshed identical 8 leaf pinions through 45 degrees in steps of 3 degrees, the pressure angle plot is parabolic, symmetrical about the vertical centre line, and dipping from about 22 degrees to 5.5 degrees (and back again).

The trace of the line of contact wobbles slightly, tracking at an average of about 13.7 degrees.

As with previous results and following the BS 978:Part 2 design parameters, the 'wobble' results from the radius of one tooth contacting the flank of the opposing tooth for at least 50% of the trace.

Although I can't see where this could be useful, I'll prepare the results as before.

Sam

A good idea Michael, I'll do that.

The large 290 tooth wheel and an 8 'leaf' (pin) lantern should provide a good comparison.

At a practical level, and since pinions with few leaves (teeth) are usually solid, I wonder if lantern pinions would be too challenging, even strong enough?

Bazyle ...

Being symmetrical, I'd say 'Yes, it has to be a flat line; appearing horizontal the way I've constructed the other pairs of 'gears''.

Sam

Edited By Sam Stones on 15/04/2019 20:26:14

Thank you David.

This business of teeth making rolling contact has been discussed here. **LINK**

I felt the need pose the question because I couldn't accept that two contact points on the faces of gear teeth through travelling along their own vector lines could not be rolling but sliding (skidding). As was mentioned, true rolling only takes place where the PCD's converge. Unless I didn't understand the explanation.

Does this help David?

Sam

Edited By Sam Stones on 15/04/2019 04:58:14

Would 'Alafotgu!' interpret to mean 'I shall have for to go!' in old and posh English?

Sam

To bring this thread to a close, here is the last graphic ...

Once again, the appearance of straight lines and cross-overs (seen in the previous 290 tooth 8 leaf wheel/pinion combination), confirm that the scans were relatively accurate. The pale blue line ends abruptly, the result of the entering pinion tooth colliding with the next wheel tooth.

That is where I should sign off.

Sam

This is the next pair of gears in the large wheel skeleton clock designed by John Wilding.

They comprise a 198-tooth wheel, and a 7-tooth (leaf) pinion. Again I constructed their profile according to BS 978:Part 2 supported by notes from other places, e.g.

Meadows & Passmore … http://www.m-p.co.uk/muk/acrobat/tech/cutters.pdf

and Thornton’s … https://watchmaking.weebly.com/uploads/1/1/7/9/1179986/pp_thornton_information.pdf

As before, a result of a previous forum post, I investigated the interaction between corresponding teeth at varying depths. Choosing to rotate the pinion one whole tooth (about 51° in steps of 3° ‘pushed’ along by a wheel tooth, I traced the respective points of contact. With one less pinion tooth (i.e. 7 versus the previous 8), 17 steps of the pinion were required for a full trace.

The depth of meshing from where the two PCD’s made contact was scanned at decreasing depths. They were … the ‘correct’ (on Centre-line as designed) condition followed by 0.1mm, 0.25mm, 0.5mm, and 1.0mm; i.e. five conditions in total.

At the worst condition (shallow by 1.0mm) the entering pinion tooth can be seen to clash while the exiting tooth is still engaged. Clearly, although the trace is incomplete, this condition is irrelevant.

To continue with this thread, here are the five traces similar to those for the 290/8 wheel/pinion combination. To avoid an unwieldy post, I aim to add the final image(s) shortly.

Sam

Edited By Sam Stones on 13/04/2019 00:58:33

I'm pleased to know, Bill.

How will you fix it, cos it seems like a design or manufacturing fault.

I reckon Big Clive would be interested to pull it apart, see ...  http://bigclive.com

Sam

Edited By Sam Stones on 12/04/2019 22:49:29

Back in 2010 when I set about finishing my skeleton clock that had stood for more than thirty years, I received an enormous amount of help from this forum. In many respects, that is why I like to plough back some of my ‘discoveries’, and will continue to do so.

As the forum records show John, you were amongst many who helped me.

As an aside, I’m sending you a PM.

Sam

In ’72 Les, my move to Melbourne was payed for by my employer, a multinational.

My lathe and all my tools along with several pieces of furniture and household valuables, were collected from my UK address and shipped by container. I have no evidence or memory of a quarantine inspection but, much to my dismay, everything was delivered to my new address on an open truck.

There was no point in cramming a container with bulky low density items, so beds, mattresses, etc. were disposed of.

Buying new here is best left to those who have commented above. I’ve been out of the action too long. Starting again, if I could afford it, I’d buy a good 2^nd hand Myford.

Sam

Good luck with your move. This is still a great country.

Edited By Sam Stones on 12/04/2019 02:46:50

Thanks for your ongoing support John, especially the link.

Your mention of torque variation and its effect on the behaviour of (any) escapement, is most valid. I’d always presumed that the time period of a pendulum (and spring/balance wheel) was a constant. This anomaly became obvious while I watched mine as it came close to running out of puff. With less torque, it was running faster, but that also seemed to relate to the mark/space ratio.

Against the drift of too many Senior’s Moments, and a similarly elderly CAD package, which still grabs my attention, I’ll try to get to grips with the contents of that link John.

To be perfectly honest, as my ailing friend in a nursing home still asserts, this level of investigation has come as something of an unexpected challenge. None of which, I had a clue about while building my one and only clock back in the 70’s. The teeth on the wheels of my version of John Stevens’ skeleton clock are vaguely similar to an involute. In contrast, and though I say it myself, my lantern pinions look quite respectable.

Having, over the past few weeks completed the (depthing) exercise including the other pair of (198/7) wheel/pinion ‘gears’, I still feel the urge to offer it here. It just needs to be in a presentable form.

What I wasn’t expecting was this rather odd set of pressure-angle curves.

It was surprising to see straight lines and a comparatively sudden change of direction, not to mention the cross-overs. So, I laboriously repeated the complete exercise with greater accuracy. This time, any errors I had made were likely to be ‘accurate’ to several decimal places.

Sure enough, the (sudden?) shift from a smooth curve to a straight line matched where the point of contact changed from the pinion radius contacting the wheel flank to wheel radius contacting the pinion flank.

Sam

Continuing with meshing about with cycloidal(?) teeth, here are two more images and their respective contact traces.

Shown close up, they indicate how the teeth mesh while reducing the depth.

My guess is that at the 1.0mm offset, the teeth are likely to jam or at least wear quickly.

In this next image, I have superimposed all five traces for comparison.

The relatively straight-line section of the ‘On C-line’ trace occurs where the flanks (sides) of the teeth and leaves make contact with the opposing tooth radii.

At this level of magnification, the CAD package presents large arcs as polylines. It was rather confusing at first while trying to determine why the PCD’s failed to coincide. They are touching in the original working file.

Some of the data I gathered makes it quite clear that the velocity ratio (thanks John) varies thus giving rise to varying torque.

This may seem insignificant, but at the slow speeds of the large and centre wheels, the torque variation could have a noticeable effect on sensitive escapements, e.g. John Stevens’ English lever mechanism. I suspect that this will not be so noticeable with Mr Wilding’s large wheeler.

More to come.

Sam

It was rather rude of me to refer to the wheel and pinion as thingies. My apologies to anyone I've offended.

Thanks John, the term velocity ratio struck a note in the depths of my memory.

More explanation is required with regards to the direction I was taking. For a start, I'm no expert in gearing or clocks. It just so happened from an earlier post and my choice to respond, that I began pondering how the teeth of John Wilding's large wheel skeleton clock would actually mesh at different depths. Like Topsy, 'It just growed'.

Before grasping the significance, I had generated the wheels and pinions for the clock. In particular, the large wheel with 290 teeth, and its corresponding pinion with 8 teeth (leaves). Similarly, the 198 tooth wheel, and the 7 tooth pinion joined the gathering collection.

Here is my rendering of the gear train in position …

I’m still preparing additional diagrams, so watch this space.

Sam

Apologies John,

The big brass thingy (large wheel) pushes the little steel thingy (pinion) to the right.

As can be seen here, and when I get around to it, you'll see how the points of contact trace unexpected(?) paths.

Thanks for your support Michael.

I'll be back.

Sam

As you will gather, I no longer make swarf and, although I considered if this should be entered into ‘What did you do today?’ I chose to give it its own title.

Perhaps it would interest first-time clock makers who know about depthing. Or perhaps do not.

I didn’t either, but as Basil Fawlty once said “I think I got away with it!”

Nevertheless, I have been enticed by my own curiosity into the inner sanctum of cycloidal gear teeth and how they mesh or don’t.

According to BS 978:Part 2, found via the good services of Meadows & Passmore **LINK**

Thornton **LINK**

(and others.), cycloidal wheel and pinion teeth look like this …

The trace line in yellow (via my CAD package) required that I rotated the 8 leaf pinion through fifteen x3° steps, and follow the pinion leaf (tooth) with a wheel tooth.

Using the same laborious process, I chose to decrease the depth of mesh from the ‘PCD coincidence’ by 0.1mm; 0.25mm; 0.5mm; and 1.0mm.

If this interests anyone, I’m prepared to add more results, including the Excel graphs of the corresponding pressure angles. The latter revealed some odd and (to me at least) somethings rather unexpected.

Sam

When I was moving from machine to machine during my apprenticeship in the toolroom of a plastics factory, Adonis (nicknamed thus as a result of his vanity) was a miller on the Cincinnati next to the milling machine I began using. Whether he was self-conscious or careless I can’t be sure; he was certainly accident prone. Proof being that he managed to break a 1" diameter reamer into pieces while running the mill too fast. A sliver of the reamer hit another chap in the face some distance away. It could have hit someone in the eye!

After ‘clocking’ a hole in a work piece on the Cincinnati using a Verdict dial indicator, our hero returned the spindle from neutral into gear. Pressing the ‘Start’ button by mistake, the Verdict did a couple of turns at a speed setting of some 500 rpm or more before disintegrating. The only part ever found was the face of the indicator, folded neatly in half.

This next anecdote which again included our idol, was not so serious but nevertheless highlights the need to concentrate.

In the fifties, we made all our own sprue bushes. The taper was never a standard angle, and it was often the job of whichever apprentice was on the apprentice’s lathe to rough out from bar-stock a slightly oversize HSS blank for the reamer. On one occasion, Adonis had the job of milling the flutes in one such reamer.

Complete with centring holes and after they had been fluted, they went to Syd for hardening. A high temperature electric arc furnace provided the necessary heat. Percy, who operated the precision tool and cutter-grinder, would then grind the flutes to the appropriate dimensions. At that juncture however, and too late in the schedule for a new one to be made, Percy found that Adonis had milled the flutes left-handed. There was no choice but to continue with the LH reamer.

Perhaps I was the senior apprentice by then, but I had the job of making and reaming the sprue bush on the only small lathe that could be set to run in reverse. The drive was from an overhead counter-shaft and it was a relatively easy matter to twist the flat belt. Of concern (of course) was the need to stop instantly in case the lathe chuck began to unscrew. I doubt that exposed flat-belt drives as they were then would ever meet safety regulations these days.

Changing spindle speed on the lathe had to be done with a long stick and a flick of the wrist while the lathe was running. At the other end of the shop's counter-shaft feeding five or six other machines, was a 10 hp electric motor.

By the way, I'm talking about the early 50's.

Sam

Edited By Sam Stones on 09/04/2019 09:45:59

Right again Neil,

Stiffness = Softness

I should have stuck with the deflection for a cantilever Δ = WL³/3EI

Bill,

Your photographs of the toothbrushes show they are different designs.

As Hopper suggests, try swapping them over.

Sam

Bill,

Sight unseen, I suspect there's a sealing problem, and that a toothpaste slurry is working its way down the inside of the unit. Can you dismantle it without difficulty?

Sam

An upstairs gremlin perhaps, Bill?

Sam

Any chance of a photograph?

Absolutely Neil,

I stand corrected ...

The softness of a toothbrush bristle is proportional to …

1. The modulus of the material,
2. The cube of its length,
3. The 4^th power of its diameter.

Sam ... a not so alert pedant.

Hopper said "Who sits around thinks about this stuff anyway?"

An old fuddy duddies like me who makes swarf no more, wondering how can he stir these clever blokes with stuff of little consequence.

It's not working

I had hoped for the last lap!

Sam