Author Topic: Lantern Pinion Questions  (Read 33289 times)

Offline dcunningham2

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Lantern Pinion Questions
« on: February 19, 2007, 10:47:06 PM »
Okay, given the overwhelming response I did not receive to my earlier questions on modules and gears, I thought I would try some more questions, if only for the comedic value of watching them also get ignored.

So anyway, I'm trying to design a clock and I'm leaning towards lantern pinions for ease of fabrication, and several questions come to mind:
1.  What is ideal tooth profile to engage with a lantern pinion?  Cycloidal, involute, or some other shape?
2.  Is there a recommended dimension for the diameter of a lantern pinion "flank" or cylinder as a percentage of module?  Would I be better to match the maximum width of a pinion flank (giving me ample clearance), match the radius of curvature of the tip of a pinion flank, or go with some other dimension?
3.  I'm assuming I should locate the centers of the cylinders on the pitch center of the pinion -- is this correct?
4.  Any other considerations when working with lantern gears?

Was just kidding about the ignoring part -- I really would like to get answers, if anyone has an opinion.  Thanks!
Dave Cunningham
dcunninghamatbluevardotcom

Offline Reid Heilig

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Lantern Pinions
« Reply #1 on: February 20, 2007, 05:59:41 AM »
If your goal is ease of fabrication maybe you should go back to pinions with  leaves  and then research some of the historical clocks to see how it was done.  I am a rank novice at building wooden works clocks but I have spent years researching the early clocks, have visited for 3 days the German Clock museum in the Black Forest and have many reference books both in English and German and no where do I find answers to or discussions of your questions. I would suggest you try to find some old books on clock design and maybe these questions will be answered in them. I am sorry I can not answer these questions. Reid Heilig

Offline Reid Heilig

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« Reply #2 on: February 20, 2007, 06:20:36 AM »
Have you contacted either "Cog Counters" or the grandfather and guru of American wooden works clocks-George Bruno? Maybe from one or both you can have your questions answered. There are by the way many more than 17 people interested in building these clocks-just ask Cog Counters how many members they have. Reid

Offline jrbeall

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Lantern Pinion Questions
« Reply #3 on: February 20, 2007, 07:42:33 AM »
Dave,  I am sorry no one has answered your previous questions but maybe that is because we don't feel competent to take on such penetrating, technical queries.  I have never made any lantern pinions but I have thought about it a little and I am sure I would use cycloidal wheels and I guess I would just draw a pair on my cad and then drag them into mesh until they looked about right and that would be it.  I think the module formula for pinion tooth width would give you the diameter of the pinion wires and you could just treat it like a standard leaf pinion.  I have never been one to get more technical than I am forced to so probably most if what I do is not really quite correct.  But it is close and after all we are working with wood.

Dave

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Lantern Pinion Questions
« Reply #4 on: February 20, 2007, 11:18:28 AM »
Hi Dave, i remember reading an article many years ago but cannot remember the author. It related to lantern pinions in both domestic clocks and turret clocks, i will try and find the article which might be some use to you, regards Dave ps dont worry about being ignored on the net, i am getting quite used to it myself

Offline jss

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Lantern Pinion Questions
« Reply #5 on: February 20, 2007, 07:33:27 PM »
the following is quoted from
".......Clocks Design and Construction by Laurie Penman
copyright 1984
LANTERN PINIONS
Fig. 31 shows a lantern pinion, a design which is often found in cheap clocks. In point of fact it is a very good pinion so long as a few criteria are met.
1.  It should not be used to drive a wheel.
2.  The rods, or trundles, should be of hard, polished steel.
3.  The ends of the pinion must be locked firmly in relation to one another so that there is no chance of the rods skewing. if possible turn a spool shaped body to serve as both ends.
4.  The rods must be held in the pinion by swaging the ends, or using an adhesive.
   The pinion will run quite satisfactorily on the normal form of wheel tooth, although a hypocycloidal form would be more correct.
One of the advantages of using the lantern form is that in terms of frictional losses it behaves in the same manner as a solid pinion with two more leaves. In other words if an eight leaved lantern is used in a train, it will show much the same freedom as a ten leaved solid pinion.
     Tower clocks have wheels and pinions so large that it is relatively easy to make the lantern pinion in the form of a cluste­of rollers instead of simple rods. It is doubtful whether much difference can be proved in friction, but because of the con­tinual rolling of the leaves, the wear is spread around the periphery of each arc the pitting associated with pinions is avoided.
The pitch circle of the rods may be taken as the pitch circle of the pinion for ­calculating centre distances. The rod, should allow clearance in the gash between each wheel tooth, 1.25x module should work quite well, but the system is not critical as long as there is no binding in the wheel and the above criteria are observed.      ..."

Offline dcunningham2

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Thanks !!
« Reply #6 on: February 20, 2007, 07:52:04 PM »
This is really helpful -- I appreciate the thoughtful responses -- I feel guilty about having made the comment about having my questions ignored -- given that my participation in this forum is at no charge, I didn't want to come across as complaining or having a sense of entitlement.  I made the comment more in a joking spirit because I know my questions can be somewhat over detailed.  As JR indicated, we're making clocks out of WOOD for crying out loud, so my interest in precision may be a little misplaced.

Thanks again!
Dave Cunningham
dcunninghamatbluevardotcom

Offline RJG

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Lantern Pinions
« Reply #7 on: February 20, 2007, 10:33:57 PM »
Mr. Cunningham.

Data Sheet 11 "Lantern Pinions and Epicycloidal Driving Wheels" in "Gears for Small Mechanisms" by W. O. Davis provides all the details necessary to design lantern pinions and their driving wheel, up to and including rack and contrate gears.

To answer your questions:

>1. What is ideal tooth profile to engage with a lantern pinion? Cycloidal, involute, or some other shape?

An Epicycloidal tooth form is suggested in the book mentioned above.

>2. Is there a recommended dimension for the diameter of a lantern pinion "flank" or cylinder as a percentage of module? Would I be better to match the maximum width of a pinion flank (giving me ample clearance), match the radius of curvature of the tip of a pinion flank, or go with some other dimension?

From Data Sheet 11, the pin diameter = 1.05 with 10 or fewer pins and 1.25 for more than 10 pins.

>3. I'm assuming I should locate the centers of the cylinders on the pitch center of the pinion -- is this correct?

Yes.

>4. Any other considerations when working with lantern gears?

Driving wheel tooth width = 1.57
     "         "     dedendum = 1.2 for heavily stressed teeth.
     "         "     dedendum = 1.4 for lightly stressed teeth.
     "         "     dedendum has radial flanks

The addendum of the driving wheel tooth and the radius of the flank of the addendum is given in the table mentioned above, and depends upon the number of pins in the pinion, and the ratio between the pinion and the wheel.  In addition, the table states "The tooth forms for driving wheels are rather taller than the teeth of wheels which engage radial flanked pinions.  The gears are often formed by stamping, and a small tip rounding aids this operation.  Where the pinion has 8 or fewer pins, this rounding should be very slight, in order to retain the maximum path of contact.  Where the pinion has 12 or more pins, the rounding may be generous, such that the working height of the addendum is reduced to 1."  Sorry, but the drawing with the table makes this clearer than I can describe.

                                    RJG

Offline rabbit

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lantern pinions
« Reply #8 on: February 21, 2007, 09:07:55 PM »
this is a great discussion thread, so i'd like to add my 2-cents worth...
the best clarification i know of is from the very old (1905) - but timeless - book The Modern Clock by Ward Goodrich. look it up if you can.
without going mathematical, it can be shown that the force required to overcome the friction of a lantern is roughly half that of a cut pinion. the main difference between lantern and cut pinions mechanically is that there is no radial flank for the curve of the wheel teeth to press against in the lantern pinion. the driving is all done on or after the line of centers. hence, the engaging friction is entirely eliminated  when the pinion is driven, as is the case with clockworks. where the pinion is the driver, this condition is reversed - the driving is all before the line of centers, and the resulting engagement friction makes the lantern unsuitable as a driver.
there is no essential proportion for the thickness of the pins. mathematically, these are taken as mere points of no thickness at all. the diameters are made simply of workable size - of course not to exceed the space between the wheel teeth. they need not be nearly as thick as a cut tooth. the pin centers are on the pitch diameter. the "barrel" serves no purpose other than to hold the two side plates, and therefore its diameter only needs to clear the wheel teeth points.
'all that said... and as "great" as they seem...my subjective opinion: i've used them many times (when i needed to); and i'll use them again; but i hate them. they're definitely not easier to make than a cut pinion. if you use brass pins, they'll blacken the teeth on the mating wheel (look close at my Pound Clock)... use wooden pins. They have to be engaged radially (as opposed to axially) - sometimes complicating assembly. i avoid them if i can.

that was more than 2-cents, huh?
and Dave, it IS only WOOD.
- rabbit

Offline dcunningham2

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Thanks again
« Reply #9 on: February 25, 2007, 04:29:10 PM »
This thread has really been helpful and has changed my opinion of lantern pinions, to say the least.  For my design, I had been leaning towards lantern pinions reluctantly, feeling like I was choosing a less aesthetic and efficient gear for ease of fabrication (one of my design constraints is to not require the use of power tools or gear cutting equipment).

Now to find out that lantern pinions are efficient is quite the revelation and relief.  I'm still trying to wrap my head around the notion that lantern pinions could have less friction that a cut pinion with the same number of teeth.  

I'm still a little skeptical of this whole business of receding friction being less than advancing friction.  I know it's the convention wisdom but I'd be interested in seeing some empirical data that confirms that gear friction varies with the direction of drive.  To my way of thinking, the coefficient of friction should be the same in both directions, assuming the gear assembly is sufficiently rigid to prevent an advancing surface from "snagging".

Thanks to RJG and JSS for the specifications.  I am using them now.

One last question on pin dimensions -- the recommendations vary from 1.05 x M for an 8 pinned pinion to a general recommendation of 1.25 x M.  It seems to me that a larger dimension would be more forgiving of irregularities in the driving tooth shape because the radius of curvature of the pin is greater.  Any opinions on this?

Question to Rabbit -- you had mentioned the challenges that lantern pinions can pose during assembly because they must be engaged radially versus axially -- what is your opinion of "open" lantern pinions that consist of pins cantilevered from a single back plate?
Dave Cunningham
dcunninghamatbluevardotcom

Offline rabbit

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lantern pinions
« Reply #10 on: February 26, 2007, 07:25:59 PM »
on the friction question...  the coefficient of friction is the same in either direction, but it's a matter of the contact angle. (i'm still trying to not go mathematical.) receding friction merely causes a "drag", requiring more power to overcome; but, engagement friction can cause a "binding", stopping the clock. it's very analogous to a gear depthing issue: the same reason a "tight" depthing will run with less friction than a "loose" one. (neither being as efficient as correct depthing.)

make a lantern/gear set, and play with it. vary the depthing. turn it both directions.

and the pin diameter... i'll repeat that in theory, lantern pinion leaves are simply points. understand this and you've mastered lanterns. that's what makes them unique. (it also makes the driven gear different from a "normal" one.) the closer you come to a "point", the closer to the theoretical ideal; the smaller the pin diameter, the better. this is why you usually end up with metal pins in a wooden clock - strength requirements rule.

and, cantilevered pins from a single plate: even uglier, and bending becomes the issue.

cutting small pinions is probably the least enjoyable part of making a wooden clock to me. but i'd rather do this than resort to lanterns. (yet, all in all, they have their place.)
- rabbit

Offline RJG

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Lantern Pinions
« Reply #11 on: February 27, 2007, 11:41:52 PM »
At the risk of skating dangerously close to the boundaries of off topic, I would like to point out an exception to the "never drive a wheel with a lantern pinionl" rule.  (Not that anyone here said 'never'.)

The Samson Sieve-Grip Tractor Company of Stockton California designed and built an internal combustion agricultural tractor which used a lantern pinion to drive the rear wheels of the tractor.  General Motors bought the company, and built a few of these tractors in a plant in Pontiac, Michigan in about 1917. They hoped that it would compete with Henry Ford's "everymans tractor" which he produced in large quantities.   I located a photo of a Samson Seive-Grip tractor, and you can see it at  http://www.gmphotostore.com/prodinfo.asp?number=53216874

Apparently the tractor was not a success, and General Motors did not enter the agricultural tractor business.  I understand that the lack of success was not related to the lantern pinion final drive.  One would assume that competent engineers vetted the design for General Motors.  Is there something about the fact that the pinion engages an internal gear that changes the rule, or did they just decide that they had adequate power, and could afford some losses in the final drive?  The only advantage I can see over the usual toothed pinion was that the lantern pinion could be built with fewer "teeth" than a toothed pinion, allowing a larger reduction ratio at the wheel (as I recall, there were only 8 trundles (pins) in the lantern pinion).

If I recall correctly, the trundles in the lantern pinion on this tractor were mounted in bearings and were free to rotate (all the while bathed in dust and/or mud).

I'm sure there are other exceptions to the rule, but this one was brought to mind while viewing this thread.

                                        RJG