Author Topic: 0.6 module involute cutters  (Read 2096 times)

Offline pgp001

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Re: 0.6 module involute cutters
« Reply #30 on: September 29, 2018, 11:54:15 AM »
Mike

I am curious as to why you need a 2.25:1 ratio, generally people are wanting a 2:1 ratio for cam drives etc.

Phil

Online Vixen

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Re: 0.6 module involute cutters
« Reply #31 on: September 29, 2018, 01:02:11 PM »
Hello Phil,

Thanks for your kind offer to cut the gears.

The magneto drive for a big radial engine is full of mystery and magic. First off, a full size aircraft magneto usually has a four pole rotor and nine ignition leads. The drive to the magneto rotor must ensure there is one magnetic pole crossing for each spark. To achieve this, the magneto rotor turns at 1.125 time crankshaft speed to get a whole number of sparks per revolution.

The distributor part of the magneto, which feeds the nine spark plugs, is gear driven from the magneto rotor shaft and has the 2.25:1 reduction ratio. When you divide the 2.25: 1 gear reduction by the 1.125 speed up, you get the magic 2:1 ratio you were expecting i.e. all nine cylinder fire once for two crankshaft revolutions

Another problem with a magneto ignition system is, if you don't turn the engine over fast enough, you don't get any sparks to start the engine. The solution was often a additional hand cranked magneto in the cockpit, to give the pilot something else to do while he was trying to juggle the priming pump, the throttle and the ignition advance settings.

They certainly had a lot of mechanical design considerations to deal with back in those days. Today we would use a magnetic trigger off the flywheel and a box of fancy ECU electronics to do the same thing and more.

The cam ring drive is another mystery and another entirely separate story

Cheers

Mike  :old:
« Last Edit: September 29, 2018, 01:21:43 PM by Vixen »
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Offline Jasonb

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Re: 0.6 module involute cutters
« Reply #32 on: September 29, 2018, 01:10:23 PM »
Mike, what formula did you use to calculate the cut diameters as the one for the 63T is quite a bit smaller than what I came up with from Ivan's book?

Online Vixen

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Re: 0.6 module involute cutters
« Reply #33 on: September 29, 2018, 01:31:29 PM »
Jason,

I based my 0.6 module calcs of Zepherin's information, which is very similar to method as shown In Ivan laws book Fig 89. i.e. 20* pressure angle, tangent to the PCD etc.

I cannot explain why the 1 DP table corrected to 42.33 DP does not give the same result, but I did notice it. My calculations/ drawing  tie in with Dan Rowe's Gear Wheel Designer CAD drawing. I am happy my module calculations and CAD drawings are correct.

Cheers

Mike
« Last Edit: September 29, 2018, 02:25:28 PM by Vixen »
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Offline Jasonb

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Re: 0.6 module involute cutters
« Reply #34 on: September 29, 2018, 02:53:15 PM »
It may be that the tabel in Law's book shows cutters to cover a range of teeth rather than calculating for the exact tooth count

Online Vixen

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Re: 0.6 module involute cutters
« Reply #35 on: September 29, 2018, 02:59:20 PM »
Jason,

Agreed, the table does not specify the actual tooth count used, only a range and we know the circle diameters are dependant on tooth count.

The tooth face is only a very small part of the cutting (or button) circle. You have quite a bit out of latitude with the circle diameter before it makes any noticable (measurable) difference to the tooth profile.

Lots of useful information in his book though, I was interested in his ideas for single point cutters.

Mike
« Last Edit: September 29, 2018, 03:14:39 PM by Vixen »
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Offline Stuart

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Re: 0.6 module involute cutters
« Reply #36 on: September 29, 2018, 03:42:23 PM »
I makes me very happy that as a community across the big ball can take the time and effort to help each other when a cry for help/advice it posted

Well done to all
My aim is for a accurate part with a good finish

Offline Zephyrin

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Re: 0.6 module involute cutters
« Reply #37 on: September 29, 2018, 03:50:24 PM »
Hi Vixen
I'm sorry for the poor picture i've posted, how come it becomes so unreadable I dont know...
And yes, the geometry of method i described is exactly the "buttons" method but without buttons...

Buttons method come from the days where people made tools to do a tool to make a jig to hold a support for the part to be machined...
even if an epicycloide is replaced by a small circular arc the gears will be truly functional.

PS: I know perfectly were Toucy and Auxerre are; when much younger, I spend lot of my holidays in Auxerre, where my grandfather had a pharmacy business.
I used to pickup mushrooms in the fall in a forest close to Toucy, mainly cepes (Boletus edulis & Boletus rufus), good old days.
the world is a small village...

Online Vixen

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Re: 0.6 module involute cutters
« Reply #38 on: September 29, 2018, 03:59:07 PM »
I makes me very happy that as a community across the big ball can take the time and effort to help each other when a cry for help/advice it posted

Well done to all

Plus 1 to that. I truly appreciate the help and support of everyone on the MEM forum :praise2: :praise2: :praise2:

We can all teach and learn from each other, we pull ourselves up with our own bootstraps.

Mike
« Last Edit: September 29, 2018, 04:10:44 PM by Vixen »
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Online Vixen

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Re: 0.6 module involute cutters
« Reply #39 on: September 29, 2018, 04:06:29 PM »
Hi Vixen
I'm sorry for the poor picture i've posted, how come it becomes so unreadable I dont know...

the world is a small village...

Hi Francois-Marie,

Your picture came out clear and sharp this end, no problems.

Great websites, lots of interesting engines

Mike

It is the journey that matters, not the destination