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cutting spur gears on a mill

a rogue method?

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Martin Kyte22/09/2021 12:45:35
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2558 forum posts
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Posted by Dave S on 22/09/2021 12:18:27:

I’ve gone involute for the clock because I wanted to explore the use of the “rotary Sunderland rack method” as a way to make gears.
That plus many naysayers telling me that a clock couldn’t possibly work with involute gearing as it’s not possible to gear up with involutes… I’m not sure how the gear knows

Dave

Fair enough. but as far as "how the gear knows" the system will see whatever frictional forces and wedging actions are inhearent in the design. Involutes work fine on large clocks especially where there is heaps of power. Cast Iron gearing is happy in tower clocks especially at the opposite end to the escapement and you don't immidiately think of cast iron beaing a clockmaking material. No ideal for chronometers though ;O)

regards Martin

duncan webster22/09/2021 18:52:34
3508 forum posts
63 photos

I think this shows that involute is perfectly good for clocks, in fact better fuse. After all, a fuse is a clock that goes bang at the end of its set time

brian jones 1123/09/2021 04:08:55
347 forum posts
62 photos

In 1890 they knew a thing or two and armchairs hadnt been invented

https://books.google.co.uk/books?id=dyYJAAAAIAAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

Michael Gilligan23/09/2021 07:30:24
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18925 forum posts
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That’s a good link **LINK** well found, Brian

Have you considered the three ‘conditions’ listed at 175 on p119 ?

Surely the spur gears you are producing would fail on all counts dont know

MichaelG.

Martin Connelly23/09/2021 07:49:25
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1889 forum posts
203 photos

The ancient Egyptians had armchairs.

Martin C

SillyOldDuffer23/09/2021 10:50:07
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7549 forum posts
1680 photos
Posted by brian jones 11 on 23/09/2021 04:08:55:

In 1890 they knew a thing or two and armchairs hadnt been invented

https://books.google.co.uk/books?id=dyYJAAAAIAAJ&printsec=frontcover&source=gbs_ge_summary_r&cad=0#v=onepage&q&f=false

I see not having an Armchair has let Brian down again. Having found a copy of the most excellent Grossman's Lessons in Horogogy, he hasn't read it! The Grossmans, father and son, were scientists. They say:

grossmanquote.jpg

Note the bit about the practical workman faithfully following 'the principles' in the execution of his work!

Armchairs as tools are valuable at the design stage and when things go wrong. Not necessary for repetitive work or following instructions. Interpreting a good drawing is quite easy; bad drawings stretch the poor old brain, which might need help from strong coffee or this forum!

Actually, the armchair isn't the best thinking tool available. I prefer a comfy office chair in front of a well-lit desk equipped with a computer, notebooks and pencils. At first the computer is used as a support tool rather than a thinking aid: they're good for reference; calculations; formal write-ups, and exchangeing ideas with friends etc. I learn best on paper taking notes from printed textbooks and start designs with rough pencil drawings rather than going straight to CAD. The computer is good later on at formalising and validating ideas, often exposing mistakes and allowing them to be corrected without too much aggravation.

Some problems are best thought out whilst walking, and I occasionally wake up with answers, presumably having processed them subconsciously overnight whilst asleep or doing something else entirely: like free-hobbing the 'not thinking about it' method can't be relied on though!

Going back to free-hobbing, a single gear, no matter how good looking, is useless. The acid test is making two or more gears that mesh together between designed centres. Free-hobbing struggles to do this and understanding why free-hobbing fails is an armchair job. No need to read Grossman, most shortcomings have been covered in this thread.

While free-hobbing isn't good engineering, Brian is congratulated for flushing out other methods of making gears. A thread that gets over 240 replies and 12000+ reads can't be all bad!

smiley

Dave

 

Edited By SillyOldDuffer on 23/09/2021 10:52:30

brian jones 1123/09/2021 10:50:53
347 forum posts
62 photos

The full credit must go to Duncan Webster above for his "Fuse" link and his fascinating tale of bigotry by AGMA (my instincts were right about the mafia)

Its a book for the armchair Kobo, you can down load EPUB

Horologists OMG have they got their own closet on this board somewhere? I cant imagine their x30 world and desktop lathes and they wouldnt countenance free hobbing

I need a man's lathe

https://www.youtube.com/watch?v=iWW7Ck-7oAM

notice elf n safety - he should be in a boiler suit, not a flappy shop coat.

OBTW SOD

sometimes I feel its whack-a-mole time

12000 views have we gone viral - like Covid?

Certainly given the fustian Mew Board a throgging

Edited By brian jones 11 on 23/09/2021 11:07:30

Edited By brian jones 11 on 23/09/2021 11:11:38

Andrew Johnston23/09/2021 11:08:51
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6264 forum posts
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Posted by SillyOldDuffer on 23/09/2021 10:50:07:
A thread that gets over 240 replies and 12000+ reads can't be all bad!

Don't confuse quantity with quality. smile

Andrew

Howard Lewis23/09/2021 11:14:11
5298 forum posts
13 photos

If involute gears cannot be used to increase speeds, someone ought to tell the manufacturers of gearboxes with overdrive top gears! And probably of Norton gearboxes for lathes

They have been getting wrong for YEARS!

Howard

brian jones 1123/09/2021 11:26:35
347 forum posts
62 photos

Don't confuse quantity with quality.

Sounds like the motto of Tesco

or perhaps

Millionaire Alan Sugar and his egregious Amstrad rubbish

IMHO there have been numerous high quality insightful postings on this thread

May the freedom to rattle cages and shake the trees be long fruitful and may we be tolerant enough to sweep up the dummies spat out on the floor

Now Maureen needs my attention - Wimin

OBTW have we got any members of the err opposite gender on this board? They were good at making bullets in WWII

Howard Lewis23/09/2021 11:34:31
5298 forum posts
13 photos

There are threads on here that have been posted by those not of male gender.

And just look in awe at the work produced by Cherry Hill! Puts many men.to shame.

A while ago there were articles showing one of her workshops.

Howard

John P23/09/2021 11:41:42
328 forum posts
226 photos

Posted by brian jones 11 19/09/2021 23:06:16

Why was the concept of DP Diametral Pitch introduced when the CP
Circular pitch addresses the same size issue and is physically
realisable ie you can measure it with calipers

----------------------------------------------------------

I expect it was more to do with the folk around at the time of his
avatar setting out gears with calipers and circles of whole inches.
Maybe it goes back further than this even to the time
of wooden gears in wind mills.
Although this does raise an interesting point for model makers ,
just like using stock size threads mostly all gearing is
Dp or module and made to a standard, for the production of
small gearing and rack type rotary cutters this does not make
much sense.For model engineering applications the only considerations
for gears would be to fit in the space available the required tooth count
and to look in the correct proportions it does not matter whether
they are mod or dp or cp standard.
Pitching out a 20 dp circular rack type cutter at .1571 inch is just
plain daft, since a cutter is being made it would seem to be
more sensible to use a CP system either imperial or metric
depending if that you favor one or the other units.
Laying out the spacing between each tooth can be so much easier
using this system .The page here

dp mod cp.jpg
shows the near equivalent DP,CP ,MOD ,providing there is no intention
to link up to a commercial gear train there is little point in doing it from
a model engineering perspective.
Dividing also becomes somewhat easier from the example above of 20 dp.
eg for 20 tooth gear pitched out now at .150" CP instead of .1571 "
moving the cutter down by . 030 inch and setting the dividing head
to cut 100 divisions would ensure accurately timed cuts leaving just a
few facets on each tooth.Similar combinations of other size gears
just need to be worked out.

The chart here


rack profile.jpg

shows the basic rack dimensions
and there is enough information there to calculate the tip width
and from that a form tool can be ground to make the cutter.
There is some benefit to having cutters properly form
relieved to avoid the type of finishes noted by
Roger Best in his posting 21/09/2021 21:57:52

"I did see some very good imitations of severely worn traction engine
gears. Modelling to such realistic detail is wonderful."

I made one of these circular rack cutters around 1985,because the
cutter had no form relief the cutting action was so poor i never
pursued the idea further,seen here a pair of
timing gears and a cast crank case it was never completed.

1985.jpg

A few years later the Eureka device was published and provided
an easy solution to the making of form relived cutters.

Look in at Lathes .uk the latest submission there is a
Micron gear hobber 102 a very interesting machine,
apparently will cut gears down to 800 dp.
In the section Brief General Catalogue 1960s-70s
shows the smallest gear in the world the profile of the teeth
looks remarkedly similar to BJ 11's gears.

Finally with interest shown on here with horology and armchairs
maybe a combination project would be of interest.

John

armchair clock.jpg




brian jones 1123/09/2021 11:58:05
347 forum posts
62 photos
Posted by John P on 18/09/2021 11:40:12:

Somehow doubt if BJ 11 would be interested in cutting a rack.
This one here took over 5 hours to cut the 159 teeth.

milled rack 1.jpg

Was definitely a "OMG what a painfully slow process as you mill each one"
John

You see I knew you were doing it wrong

you need a cycloid profile for rack and pinion

https://www.geartechnology.com/articles/0115/Non-Involute_Gearing,_Function_and_Manufacturing_Compared_to_Established_Gear_Designs/

That why I suggested a motor bike chain

fascinating stuff

Whack a Mole

John P23/09/2021 13:55:08
328 forum posts
226 photos

Posted by brian jones 11 23/09/2021 11:58:05

Posted by John P on 18/09/2021 11:40:12:
Somehow doubt if BJ 11 would be interested in cutting a rack.
This one here took over 5 hours to cut the 159 teeth.

Was definitely a "OMG what a painfully slow process as you mill each one"
John
----------------------------------------------------------------------------

You see I knew you were doing it wrong
you need a cycloid profile for rack and pinion
https://www.geartechnology.com/articles/0115/Non-Involute_Gearing,
_Function_and_Manufacturing_Compared_to_Established_Gear_Designs/

That why I suggested a motor bike chain
fascinating stuff
Whack a Mole

------------------------------------------------------------

I suppose 5 hours + for cutting rack teeth passes into
insignificance in comparison 14 + years and still
counting in making the parts the rack fits to.

universal grinder11.jpg

It's called making things
John



brian jones 1123/09/2021 14:22:16
347 forum posts
62 photos

Tremendous magnum opus, 14 years longer than most marriages then.

Is it the sort of m/c to make special gear hobs?

WaM

Andrew Johnston23/09/2021 15:01:27
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6264 forum posts
677 photos
Posted by brian jones 11 on 23/09/2021 14:22:16:

Is it the sort of m/c to make special gear hobs?

Looks more like a cylindrical grinder.

Andrew

John P23/09/2021 15:13:13
328 forum posts
226 photos

I'm being generous here , Brian 5/10 but Andrew gets 10/10.

John

Andrew Johnston23/09/2021 15:22:18
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6264 forum posts
677 photos
Posted by brian jones 11 on 19/09/2021 23:06:16:

....CP Circular pitch addresses the same size issue and is physically realisable ie you can measure it with calipers...

You can't measure CP with calipers. Circular pitch is defined as the length of an arc on the pitch circle diameter. A caliper measures between two points on a line, which is also not likely to intersect the PCD at the point of measurement. Using a caliper to measure across multiple teeth doesn't give CP either. There are published tables that give theoretical values measured across multiple teeth to get pitch and backlash, but they don't give CP.

Andrew

brian jones 1123/09/2021 16:40:17
347 forum posts
62 photos

Agreed, you are measuring chordal pitch slightly less than CP

So how did they actually measure gears in late victorian times with simple tools

I think someone had some actually gear design books from that or edwardian period

Martin Kyte23/09/2021 16:57:01
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2558 forum posts
45 photos

Could I suggest that circular pitch is actually more sensible when you think of someone cutting gears with a saw and a file. or inserting teeth into a wooden gear. Once you have your pitch circle you can then mark the positions of the gears by dividers. Draw your lines and then start cutting filing or whatever.

regards Martin

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