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cutting spur gears on a mill

a rogue method?

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John P25/09/2021 18:22:51
328 forum posts
226 photos

Posted by brian jones 11 24/09/2021 14:41:58


ll you needed to know about CP and the Base Bitch
https://www.geartechnology.com/articles/0992/Base_Pitch_Tables/
this past post went into the problems of measuring a gear (as opposed to calcs + suck it and see)
You cant just use calipers / disc mic and measure PCD just like that
https://www.model-engineer.co.uk/forums/postings.asp?th=166048

If you have two gears meshed together you can deduce the pcd from distance between centres
then there's the eyeball method

======================================
The last 2 lines is where Brian's methods of measuring all fall down.
Whilst it is true you can deduce the PCD from the distance between
centres it is of little use if you are making a pair of gears to fit
between pre determined and existing fixed centres ,you would need to be able
to measure the gears with some accuracy before they are removed
from the machine on which they are cut.

Still we have seen from his methods of working from

posting on 13 / 9 / 2021 12:30:19

Difficult to make two gears that will mesh together from fixed centres.
Drill your centers afterwards.

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


With regard to eyeballing the pressure angle , here is
a small gear the OD is 18.970 mm or .7468", the span across
2 teeth is 6.112 mm as can be best determined from the
micrometer reading.
Now is it possible to eyeball the pressure angle as suggested
by BJ 11 or will a guess do .

14.5 pa or 20deg pa.jpg

There are only 2 options 14.5 deg pa or 20 deg pa.
Here are the required inputs for the Ondrives gear tooth
calculator only the input for pa is missing , give it a try
and see which one of the two that it is and how close the
answer is to the micrometer reading. The results for both
are very close but one is a clear leader.

ondrives.jpg


Seeing Andrew's posting 23/09/2021 21:25:25

When I started making gears I spent some time faffing about with gear verniers
I didn't find them easy to use and the results were indifferent. Now I just calculate
the theoretical values and machine to those.
-----------------------------------

I can understand this point of view with the gear tooth calipers ,they always
seemed to me to be a hit and miss method , the span measurement seems to offer
a slightly more accurate solution ,the Ondrives also does give the measurement
across 2 pins which is likely to be the most accurate method obviously the requirement
to grind 2 suitable pins is just more to do.

Hobbing can be different to using form cutters in as much you can keep cutting in
and still retain the tooth form which you can't do with form cutters.Only one of the hob
cutters that i have has the infeed marked on ,using the general recommendation for
cut depth does not work either ,eg in Gears and gear cutting the tooth depth cut
for 20 dp is .108 inch both my 20 dp hobs need to infeed by .1115 inch
to cut to standard form.All of the hobs that Arc Euro used to sell were Topping
cut hobs and still did not conform to standard cut depths,all of this you find out
in time until it is no longer a problem ,being able to measure is just a help.


I suppose it could be time to reflect on the heading of this
thread
cutting spur gears on a mill

and on the first lines

" I have seen vids of using diving head for use with a milling form tool for cutting
a spur gear say 3" dia, 1/4" thick with say 80 teeth
OMG what a painfully slow process as you mill each one"

All of this diversion into the discussion of wind turbines etc has seen a complete
lack of gears made, maybe we will be getting on to hot air engines very soon,
should be enough of it to keep one running until the sun goes dim.

John

Just seen this from BJ: "Maureen has my secret weapon in her jaws I must get on"

Stay tuned for the next thrilling installment!.

John




duncan webster25/09/2021 19:01:31
3508 forum posts
63 photos

ANSI isn't a government organisation, and it doesn't develop standards. To quote the interweb 'The American National Standards Institute (ANSI) is a private, non-profit organization that administers and coordinates the U.S. voluntary standards and conformity assessment system'. The actual standards are written by the Standard Development Organisations, one of which is probably AGMA. Perhaps the OP would like people who don't understand gearing to write the standards, politicians say. If it was all secret the standards wouldn't be on sale.

BSI is much the same, but I believe it co-ordinates industry experts in the actual writing of standards, or it did until ISO took over. Except for safety related equipment, no-one is forced to follow these standards, but they make life a lot easier for industry (both makers and users), who can buy specify say a 100*50*10 channel to BS4-2004. The First BS was for tram rails in 1901 or thereabouts, co-ordinated by John Woolfe Barry of Tower Bridge fame

brian jones 1125/09/2021 19:21:37
347 forum posts
62 photos

What astonishes me JP that in this day of unbelievable high tech gadgetry at such low cost, we havent seen a means of laser scanning the gear you showed in your pic above cos thats the degree of measurement needed. Feed the data into an app and get a best estimate of what you have.

After all thats what the big boys do when making big gears, they measure to microns across a diameter of 10 meters

thats cooking on gas

John P25/09/2021 19:44:03
328 forum posts
226 photos

Posted by brian jones 11 25/09/2021 19:21:37


What astonishes me JP that in this day of unbelievable high tech gadgetry at such
low cost, we havent seen a means of laser scanning the gear you showed in your
pic above cos thats the degree of measurement needed. Feed the data into an
app and get a best estimate of what you have.

After all thats what the big boys do when making big gears, they measure to
microns across a diameter of 10 meters

thats cooking on gas

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

The micrometer was only £25, i guess that your eyeball
measuring system of measuring PA has failed on this
occasion.

Gas supply failure!

Andrew Johnston25/09/2021 20:13:48
avatar
6264 forum posts
677 photos

Posted by brian jones 11 on 25/09/2021 19:21:37:

After all thats what the big boys do when making big gears, they measure to microns across a diameter of 10 meters

thats cooking on gas

Never mind gas, it smells more like bullsit. smile o

If we assume a coefficient of expansion of 10x10^-6 per degree C for steel then for a 10m diameter gear the diameter could change by 10x10x10^6 for one degree C, that's 100 microns. So there would be little point in measuring to microns. Alternatively, one would need to hold the temperature to one hundredth of a degree C, or less, for micron resolution to be useful. That's better temperature control than national standards laboratories.

With the involute system it's the shape of the tooth that is important, small variations in centre to centre distance are less critical, and don't affect the smooth meshing. So there wouldn't be any need to measure across a 10m diameter gear to microns.

Andrew

Andrew Johnston25/09/2021 20:39:12
avatar
6264 forum posts
677 photos

Posted by brian jones 11 on 25/09/2021 15:48:26:

.....the Crown and bevel pinion, without the benefit of CNC how does one make those pieces......

I'm beginning to suspect that the OP is actually the greatest gear expert who ever lived, and is just messing with us for his own amusement. But I'll do my best to answer the question for other forum members who might be interested.

A crown gear (aka a contrate gear) is simply a bevel gear where the pitch cone angle is 90 degrees. So they can be made with any of the methods used for bevel gears. In practice the face width of crown gear is small so the change in shape of the tooth form is very small and they can be satisfactorily cut, one tooth at a time, with an involute cutter.

There are two approximate methods for cutting bevel gears on a milling machine with involute cutters. One, the parallel depth method, uses standard involute cutters. The other produces tapered teeth in two dimensions rather than one, but needs special (narrow) involute cutters. Both methods require three passes around the gear. The second method creates gear teeth which lack curvature at the small end which needs correcting. I've never made bevel gears using the parallel depth method, but these test gears were cut using the second method 45+ years ago as part of my training:

Old Bevel Gears

No CNC used, all manual machines.

The first bevel gear planers were introduced in the 19th century by Gleason in the US. They used two reciprocating rack like cutters to form each tooth. Early machines followed templates but later machines eliminated the need for the template. If the OP thinks cutting one tooth at a time is slow he should watch a video of a bevel gear planer! I've not used one, but have seen one in action. Apparently they're difficult to set up and are temperamental.

Straight tooth bevel gears fell out of fashion to some extent, being replaced by spiral and hypoid bevel gears, which can be (approximately) cut using vertical rack like inserts in a circular holder. It's a much faster operation than planing. More recently Gleason have introduced the Coniflex straight tooth bevel gear. These can be cut with one, or two, circular discs with radial inserted teeth that form the teeth. They are much faster than the bevel gear planers, and presumably less temperamental as they are, of course, CNC.

Andrew

Michael Gilligan25/09/2021 22:29:04
avatar
18924 forum posts
942 photos

For info.

The George B. Grant ‘Treatise’ is available in PDF, here: **LINK**

https://ia800909.us.archive.org/4/items/treatiseongearwh00granrich/treatiseongearwh00granrich.pdf

MichaelG.

.

Incidentally : Brian would be advised to read section 35

Edited By Michael Gilligan on 25/09/2021 22:35:40

John Haine26/09/2021 09:02:26
4170 forum posts
242 photos

Good find Michael. I had a quick re-read of Ivan Law's little book on Gears and Gearcutting last night, and it's also a recommended read.

Michael Gilligan26/09/2021 09:51:13
avatar
18924 forum posts
942 photos
Posted by John Haine on 26/09/2021 09:02:26:

Good find Michael.

.

It’s an absolute gem … and it appears it always was:

.

5b058403-1d92-4116-ac16-85c7261dc304.jpeg

.

It was a bargain then ^^^ and now it’s free !

MichaelG.

Michael Gilligan26/09/2021 10:12:20
avatar
18924 forum posts
942 photos

1c9d7020-dd6e-4edd-b0cc-b637f3fc6087.jpeg

ega26/09/2021 11:13:25
2255 forum posts
186 photos

In trying to answer my own question about Brunel, I found a chapter on Gearing and Millwork in J W Roe's "English and American Tool Builders" which briefly touches on the history of epicyclic and involute gearing and contains some interesting comparisons between the two. A footnote says that "Diametral pitch, which is credited to John George Bodmer, was long known as Manchester pitch."

I have a paid-for reprint of this fascinating work but do wonder if it is lurking somewhere gratis on the internet!

Pete Rimmer26/09/2021 11:19:00
1069 forum posts
69 photos
Posted by ega on 26/09/2021 11:13:25:

In trying to answer my own question about Brunel, I found a chapter on Gearing and Millwork in J W Roe's "English and American Tool Builders" which briefly touches on the history of epicyclic and involute gearing and contains some interesting comparisons between the two. A footnote says that "Diametral pitch, which is credited to John George Bodmer, was long known as Manchester pitch."

I have a paid-for reprint of this fascinating work but do wonder if it is lurking somewhere gratis on the internet!

Yep:

**LINK**

A fascinating read and the archive version is handily scanned so as to be searchable. It seems that the DP system was originated by (Austrian born) Bodmer here in England but adopted and popularised by Brown & Sharpe.

Edited By Pete Rimmer on 26/09/2021 11:56:34

John P26/09/2021 11:28:49
328 forum posts
226 photos

Posted by brian jones 11 25/09/2021 15:48:26

Looking at the Crown and bevel pinion, without the
benefit of CNC how does one make those pieces

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

It would be worth Brian getting a copy of
Gears and gear cutting and reading through it.
Making parallel depth bevel gears is not that difficult
if you follow the the instructions in the book.


I have made several sets of parallel depth gears over the
years ,if you set up and mark the centre they can be done
in just two passes ( which would obviously please one
particular poster on here ,or maybe not).
I had always been a bit skeptical as the the long term use
and how much power they would transmit until the last set
that i made.
Material selection is obviously of importance ,so a rummage
around in the scrap box and a couple of likely rusty candidates
emerged.
The job was a pair of gears to replace the stripped bevel gears
in a detail sander (Wickes).
I was unable to get the exact tooth count of the original gears
but the gears that were made are close enough.
The cut gears were lapped together for a while with some
Timesaver green label fine abrasive, cleaned and sandblasted
then soaked in some Kasenit in a sealed tin for an hour .
Here is the finished job ,the pinion runs at about 18 to 19000
rpm and surprisingly reasonably quiet.

detail sander.jpg


I wonder if Brian has looked in at this forum post and the link
to this amazing piece of work.
Do you think that the gears have been
cut one tooth at a time
https://www.model-engineer.co.uk/forums/postings.asp?th=174884

John




ega26/09/2021 11:46:45
2255 forum posts
186 photos

Pete Rimmer:

No sooner asked than answered! Thank you. I did try a search on the Internet Archive before posting and must try harder next time.

Having the PDF version allowed me to conclude that there is nothing relevant to this thread in relation to either Brunel but the the father's history makes fascinating reading.

brian jones 1126/09/2021 13:07:40
347 forum posts
62 photos

Kerriste PR that was his French father MIB

fascinating piece of history showing the lengths industry went devise machinery for making guns (and clocks)

There's another hour gone perusing the past

Quam tempus fuggit

WaM

BTW any Horologists here

ever get your hands on one of those pioneer Wall clocks from the 1650s, they had the dial above and a painted glass picture below. You often see them in period wild west movies

**LINK**

I could tell it was cheap and nasty just by the back of case. Mass produced, did they stamp gears out of sheet back then, they were like something in a childs toy. It didnt keep good time for long

brian jones 1126/09/2021 13:43:53
347 forum posts
62 photos

PR

Ive got IKB's biography on my Kobo and must browse (if this board stops distracting me)

A few things I remember from earlier accounts is that

a) He was a 5' short **** and invented the fashion for very tall top hats

b) He tried to push for a 7' gauge for the Bristol GWR railway arguing it provided much greater speed and stabilty but the Armchairs and the gauge wars slapped him down what a game changer that would have been

c) In Victorian times at the height of the Empire it was necessary to raise funds from investors so he became something of a fair ground showman and mountebank and not very good at budgets

d) he died young at 53 but evidence of his genius are still in use today

Michael Gilligan26/09/2021 13:45:39
avatar
18924 forum posts
942 photos
Posted by Pete Rimmer on 26/09/2021 11:19:00:
Posted by ega on 26/09/2021 11:13:25:

In trying to answer my own question about Brunel, I found a chapter […]

I have a paid-for reprint of this fascinating work but do wonder if it is lurking somewhere gratis on the internet!

Yep:

**LINK**

A fascinating read and the archive version is handily scanned so as to be searchable. […]

.

Thanks to both of you yes

Given the origins of many ‘engineering’ developments:

I was mildly amused by the Author’s connection with the ‘Museum of Peaceful Arts’

MichaelG.

roy entwistle26/09/2021 13:47:53
1407 forum posts

ever get your hands on one of those pioneer Wall clocks from the 1650s, they had the dial above and a painted glass picture below. You often see them in period wild west movies

**LINK**

1650 ?

Roy

brian jones 1126/09/2021 13:52:21
347 forum posts
62 photos

sorry Roy I meant the 1850s

ega26/09/2021 15:05:20
2255 forum posts
186 photos

MichaelG:

Oddly enough, my hard copy title page does not mention that museum; the author is just described as "Assistant Professor of Machine Design, Sheffield Scientific School, Yale University".

I am reminded of the saying translated from the Latin: They make a wilderness and call it peace.

I wonder how many chairs of machine design existed in UK at the time (1916).

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