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gear cutting help needed

Our machining class needs information on generating single point (fly) cutters with involute geometry to cut spur change gears.

Eyeball grinding of the tool ala Gingery produces entirely useable gears but we are looking for something more exact.

Ivan Law in his book " Gears and Gear Cutting " [see

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for details] [another US source for UK workshop practice series of books is
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] shows a technique to generate very close circular approximations to the involute curve for both single point and circular form tools by using two circular cutters of specific diameters spaced a given distance apart. The tool blank is then fed to a specific depth between the circular cutters to generate the correct involute form.

Data take from Gears and Gear Cutting by Ivan Law ISBN

0-85242-911-8 Data to generate circular approximation of involute curve For 20 degree pressure angle gears Base table for 1" diametrical pitch gears Inch Cutter # Teeth Diameter C/C In Feed Width 1 135-R 51.300 49.600 17.790 4.000 2 55-134 32.150 31.600 11.470 4.000 3 35-54 15.070 15.510 5.870 4.000 4 26-34 10.260 11.030 4.270 4.000 5 21-25 8.550 9.400 3.710 4.000 6 17-20 7.800 8.700 3.440 4.000 dimensions in inches Table for DP gears 25.400 The problem is that both charts show C/C spacing distances LESS than the specified diameter of the two circular cutters for the form tools for larger numbers of teeth.

Has any one used this technique? If so how are the #1 and #2 cutters formed?

We will be making 1.0 m/m module change gears out of 6061 T6 and/or phenolic / micarta, and possibly a 127 tooth metric conversion gear.

Given that it takes some time to hand grind a form cutter and this is a introductory machining class, we would like to minimize tool breakage. Has anyone tried using a slotting saw to remove most of the material and then cleaning up the slot using the form cutter?

Using the advise from these NGs, our first attempts were done using a spin indexer to make a 40T gear with entirely satisfactory results. We just purchased a rotary table to produce the gears the spin indexer can't divide. This is a WT

1990-0015 (see at
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)

Any advise would be appreciated.

GmcD

Reply to
F. George McDuffee
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Very common practice, even when using form milling cutters. Saves some wear and tear on the cutters.

Greybeard

Reply to
Greybeard

This subject is exhaustively covered in the British metalworking mags.

I know a guy who wrote a program to plot out an involute curve at 20X actual size, and then he plotted that on a transparency and put it on the screen of his optical comparator. He made a single-point tool and used a round lap to remove metal, comparing with the transparency often. He said it went really well and he made a whole set of gears for a lathe. He did all of this at home, but then he's a really good machinist compared to me. Seems like something you could do at a school where they have programming guys, plotters, and optical comparators around.

GWE

F. George McDuffee wrote:

Reply to
Grant Erwin

I think there might be a small market for 127 tooth 1 module gears among the owners of mini-lathes.

Like me.

Reply to
jtaylor

Did you try compound gearing for a 80/63 ratio? That is maybe close enough for hobbiest work anyhow. Since 80 = 20 * 4 and 63 = 21 * 3 you can build a compound gear train from a 20 tooth, 21 tooth, and another pair of gears with a

3:4 ratio. Finding 20 tooth, 21 tooth, and either 15 tooth or 25 tooth gears should be easier than finding 127 tooth gears. 80/63 = 1.2698 Basically this gets you within .0015 percent.

Maybe someone will have enough ambition to develop electronic gearing for a mini lathe. Even if it doesn't have the ball screws for CNC threading, it could work with electronic gearing and a stepper driving the lead screw... But I digress.

Pete

Reply to
3t3d

They're available from Ametric in 15mm face width...

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Ned Simmons

Reply to
Ned Simmons

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Reply to
Martin H. Eastburn

Correct. You have to grind flats on the two cutters so they won't interfere with each other. The radius given by the formula is needed only where the two "circular cutters" actually cut.

-Dave

Reply to
Dave Plumpe

"Has anyone tried using a slotting saw to remove

This is a very old approach in watchmaking and it is still the preferred approach for cutting pinions. Pinion cutters for clock/watches are very dear (can't be had from MSC) and every effort is made to spare them.

In the very early days (1700) the wheel was divided with a slitting saw and then a special file was used to shape the teeth. Later, this evolved into the "rounding up" tool; a self indexing tool that is used to modify an already divided wheel. When I have a wheel that does not conform to current cutters (tooth is shorter or longer) then I divide the wheel and use the rounding up tool to shape the tooth. Only when the wheel is too large for the tool will I make a fly cutter.

BTW, in watchmaking/clockmaking we make fly cutters in the lathe out of round stock. Since we use hand gravers (ala wood turning), we turn the end of the rod to a profile that is an exact fit between two good teeth of the wheel we are replacing. File the profile to the center line, harden and temper. Grind relief on the tip and polish. Takes about 30 minutes.

Reply to
???

We have a version of the gear generation program written in lisp for auto/intelli-cad called truegear by Eugene Kalney [see

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to download as truegear.zip w/ support files and coumentation] this seems to work very well.

One problem is we don't have an optical comparator and we have a zero budget. This is not all bad in that it forces us to do machining projects that stress ingenuity over attachments.

One of my major concerns, given the current economic trends, is a situation where industry and manufacturing is forced into survival mode where replacement parts are no longer available, either because the equipment is so old, a world wide economic implosion has occurred or because the parts are only made overseas and the suppliers will no longer accept worthless American dollars. [Consider the situation of an Argentinean manufacturer who has a failure of a critical part on an old American made machine?]

It appears possible we can ad>This subject is exhaustively covered in the British metalworking mags. >

Reply to
F. George McDuffee

Several sources have suggested using a 37/47 gear combination which is susposed to produce "2/100 of 1% accuracy" [see

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We can't find a source for those gears either.

GmcD ======================================

Reply to
F. George McDuffee

My numbers are more accurate with the 80/63 than the 47/37. And most sets of gears should have a 20 and 21 tooth gears in them. I posted that because I am sure that 20, and 21 tooth gears should be cheaper, more accuarate and easier to find than the 47 and 37 tooth gears, If someone wants to go that route.

Pete

Reply to
3t3d

I'd try using a known good gear to compare the dimensions that you have on the cutter and trim the cutter as needed to nicely wipe the layout dye off of the gear.

-- Why isn't there an Ozone Hole at the NORTH Pole?

Reply to
Bob May

I am not sure but I think Scott Logan at Logan Actuator has the 37/47 gears for metric threading on Logan Lathes. Don't have a link right now but there is a web site. Don Young

Reply to
Don Young

"Bob May" once again asked in message news: snipped-for-privacy@news-1.nethere.net...

Why, Bob? Do you want one?

from

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"The difference between ozone content in the two polar regions is caused by dissimilar weather patterns. The Antarctic continent is a very large land mass surrounded by oceans. This symmetrical condition produces very low stratospheric temperatures within a meteorologically isolated region, the so-called polar vortex, which extends from about 65°S to the pole. The cold temperatures lead in turn to the formation of clouds, known as polar stratospheric clouds. These clouds provide surfaces that promote production of forms of chlorine and bromine that are chemically active and can rapidly destroy ozone. The conditions that maintain elevated levels of chemically active chlorine and bromine persist into September and October in Antarctica, when sunlight returns over the region to initiate ozone depletion.

The winter meteorological conditions in the Northern Hemisphere, just like in the Southern Hemisphere, lead to the formation of an isolated region bounded by strong winds, in which the temperature is also cold enough for polar stratospheric clouds to form. However, the geographic symmetry about the North Pole is less than about the South Pole. As a result, large-scale weather systems disturb the wind flow, making it less stable over the Arctic region than over the Antarctic continent. These disturbances prevent the temperature in the Arctic stratosphere from being as cold as in the Antarctic stratosphere, and fewer polar stratospheric clouds are therefore formed. Nevertheless, chemically active chlorine and bromine compounds are also formed over the Arctic, as they are over Antarctica, from reactions at the surface of the clouds. But the cold conditions rarely persist into March, when sufficient sunlight is available to initiate large ozone depletion."

...but whadd'a they know?

Reply to
Jeff R.

Nice website Dewey. You appear to be a true craftsman. Did you serve an apprenticeship? I can appreciate working with small stuff. I used to run a factory that made dental handpiece motors. Spindles, chucks, impellers, all with seemingly zero tolerance. At a half million rpm .001 run out will waste a bearing in a short period of time.

Reply to
Bill Roberto

Also available from Ametric..

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Ned Simmons

Reply to
Ned Simmons

A cylindrical cutter with multiple rows of teeth(about 5) in the shape of a rack of the desired pitch (easily made on the lathe) will generate involute gear teeth of good quality. There is info available on this gear cutting method if you are interested.

Randy

Reply to
R. O'Brian

We carry those gears. Our online store is temporarily down for maintenance, but you can call our office [(815)943-9500] for details.

We have two different sets available, both 16DP, 14-1/2 NPA.

One set is 7/16" wide with a 5/8" bore and 5/32" keyway. These are designed for Logan 9", 10", 11" and some 12" Lathes.

The other set is 5/8" wide with a 15/16" bore and 5/32" keyway. These are designed for Logan 14" and some 12" Lathes.

We also have available 100T and 127T gears with the same specs for mathematically correct transposition. These gears are, of course, substantially larger and more expensive.

The 37T gears are $60.50 each, the 47T gears are $74.50 each.

The 100T gears are $162.25 each, and the 127T gears are $213.25 each.

Reply to
Scott S. Logan

Would greatly appreciate the information -- URLs? Books?

How do you get the clearance for the teeth? Simple eccentric offset with only one "gash"?

Thanks

GmcD

Reply to
F. George McDuffee

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