Author Topic: Cutting Spur Gears -- A neat technique  (Read 1445 times)

Offline xo18thfa

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Cutting Spur Gears -- A neat technique
« on: February 22, 2017, 01:24:34 AM »
Several years ago, I did a series on cutting spur gears using the methods in the “Workshop Practice Series” book #17, “Gears and Gear Cutting” by Ivan Law:



Mr Law's method works great.  You can follow his techniques without deviation.  However, recently I found another method to cut gears that approximates involute tooth using only one cutter to form gears of any size within the diametral pitch.  The method is described by "Helicron" at his website.

http://www.helicron.net/workshop/gearcutting/

I followed Helicron's technique with good results.

First step is to make the cutter tool.  My lathe is not rigid enough to make the cutter as Helicron shows.  Instead mine is a single point cutter with most of the blank removed before forming the cutting teeth.



The steel for the cutter is alloy “O1”. O1 is the most widely used tool steel and is available from McMaster Carr and other suppliers. O1 is very easy to work with and harden. Shape and form the tool to the desired size. Heat with a torch to 1400 degrees F, which is cherry red heat in room light. Plunge in oil to quench. I used some leftover salad oil from the kitchen. Leave in the oil quench about 30 seconds, it cools down slowly. Quenched tool steel is too brittle at this point and needs tempering. To temper, suspend the tool in a small pot of salad oil on the kitchen stove. Heat to 350 degrees F using a candy thermometer to check the temperature. Leave it in about 10 minutes, pull out and let air dry. The O1 steel comes out very hard and will cut just about anything.

For an upcoming project I want to cut some 48 diametral pitch gears with 52, and 16 teeth.  First, the 52-tooth gear.  These are from 1/8” thick flat brass bar.  First, make a shank from length of 1/2" diameter steel in the lathe cut and turn a 5/16” diameter boss. Thread the end to accept a nut. Gang up four pieces of brass stock on the shank.



Turn the ganged stock to the final diameter for the gear.  In this case 1.125"



To cut the gears I used my little, homemade Harold Hall dividing head.  It is a “direct indexing” head that uses the change gears from the Atlas 6” lathe for indexing.  The spindle hole is tapered with #2 Morse Taper (2MT). A 2MT collet holds cinches stock tightly in the dividing head be means of a draw bar.



Secure the 52-tooth lathe change gear to the spindle of the dividing head. Mount the dividing head to the mill table. Use a 1/2" 2MT collet to chuck the gear blanks.  Chuck the gear cutter in the mill spindle and use a height measure device to set the gear cutter height.



Adjust the depth of cut and start cutting. depth of cut on 48DP gears is 0.045".  Advance the dividing head spindle one notch on the indexing gear.



Finish the 52 tooth gears by soft soldering an appropriate hub.  Drill and tap for a set screw.



Next time we will cut the 16 tooth gear and do something with the results.
Bob Sorenson
Las Vegas, Nevada, USA

Offline bertie_bassett

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Re: Cutting Spur Gears -- A neat technique
« Reply #1 on: February 22, 2017, 01:23:41 PM »
nice work

that method is one im planning on using again in the near future to make change gears for my lathe.

last time i tried it didnt quite work, think my cutter wasnt very accurate. and had issues with working out the depth of cut

couple of questions:

a multi tooth cutter would have been easier on your lathe surely? its just a series of v's at the correct spacing. cuting just one tooth as you have must have been quite clunky as it went round and id have thought harder on your lathe?

also from memory you only need about 5 teeth, anymore dosnt help as they dont do any cutting ( unless your cutting a gear with hundreds of teeth.
a competent engineer uses the tools and knowledge available, to get a challenging job done.

 An incompetent "engineer" tells his boss that the existing equipment "can't do the job" and to get another machine

Offline AdeV

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Re: Cutting Spur Gears -- A neat technique
« Reply #2 on: February 22, 2017, 02:57:05 PM »
There used to be a series of videos on YouTube by a guy called Hobbynut, showing how he used a very similar technique to make gears on his Sherline lathe & mill. I think I downloaded them somewhere, no idea where they'd be now, I'm pretty sure they've gone now. I can't remember if his cutter required indexing, or if it was a free-running hob, though.

Even so, liked the write up on Helicron's site, that definitely gives me the confidence to have another go at gear cutting!
Cheers!
Ade.
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Location: Wallasey, Merseyside. A long way from anywhere.
Or: Zhengzhou, China. An even longer way from anywhere...
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Online John Stevenson

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Re: Cutting Spur Gears -- A neat technique
« Reply #3 on: February 22, 2017, 03:20:59 PM »
Yes those Hobbynut videos were very informative but as you say they have gone now.

There is a DVD by Jose Rodriguez on gear cutting doing the rounds, about £30 a pop.

Don't bother it's absolute $hite
He's using some home made mill made from licorice root and drinking straws, the video is out of focus and any close up could be a shop of anything [ probably blancmange ]

But the biggest fook up is he gets Pi wrong all the way thru all his calculations so all his calculations are off.

Since when is Pi 3 416 ??
John Stevenson

Offline PekkaNF

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Re: Cutting Spur Gears -- A neat technique
« Reply #4 on: February 22, 2017, 04:13:15 PM »
....
Since when is Pi 3 416 ??

Imperial PI? Metric is standard :lol:

Pekka

Offline sparky961

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Re: Cutting Spur Gears -- A neat technique
« Reply #5 on: February 22, 2017, 07:33:20 PM »
Quenched tool steel is too brittle at this point and needs tempering.

In practice I've found that no tempering is needed when working with brass or other soft metals like aluminum.

In fact, for a one-off tool that's going to see little use you can often get away without tempering the tool for most materials found in the home shop.

Offline xo18thfa

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Re: Cutting Spur Gears -- A neat technique
« Reply #6 on: February 22, 2017, 10:15:19 PM »
nice work

that method is one im planning on using again in the near future to make change gears for my lathe.

last time i tried it didnt quite work, think my cutter wasnt very accurate. and had issues with working out the depth of cut

couple of questions:

a multi tooth cutter would have been easier on your lathe surely? its just a series of v's at the correct spacing. cuting just one tooth as you have must have been quite clunky as it went round and id have thought harder on your lathe?

also from memory you only need about 5 teeth, anymore dosnt help as they dont do any cutting ( unless your cutting a gear with hundreds of teeth.

I tried the multi tooth cutter using helicron's method.  My little lathe started to chatter a lot and the attempt failed.  The single point tool bumped too, but less.  I'll re-visit the tool making method again.  Yes, 5 or 6 teeth are enough.  I did not know what to expect.

According to Mr Law (in his book), depth of cut = 2.157/DP (DP is diametral pitch)

Thanks, Bob
Bob Sorenson
Las Vegas, Nevada, USA

Offline xo18thfa

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Re: Cutting Spur Gears -- A neat technique
« Reply #7 on: February 22, 2017, 10:19:31 PM »
Quenched tool steel is too brittle at this point and needs tempering.

In practice I've found that no tempering is needed when working with brass or other soft metals like aluminum.

In fact, for a one-off tool that's going to see little use you can often get away without tempering the tool for most materials found in the home shop.

Good to know.  That saves a step.  Wife gets upset when I use her cooking oil anyway
Bob Sorenson
Las Vegas, Nevada, USA

Offline Lew_Merrick_PE

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Re: Cutting Spur Gears -- A neat technique
« Reply #8 on: February 23, 2017, 11:57:05 AM »
Quenched tool steel is too brittle at this point and needs tempering.

In practice I've found that no tempering is needed when working with brass or other soft metals like aluminum.

In fact, for a one-off tool that's going to see little use you can often get away without tempering the tool for most materials found in the home shop.

There are two steps to heat treating steel.  1) Hardening and 2) tempering.  The first (hardening) takes the surface of the steel to a Body-Centered-Cubic crystalline form (which is why "hard steel" grows in size).  And tempering "relieves the stresses" generated by such a transformation which makes it more resistant to breakage.

Offline sparky961

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Re: Cutting Spur Gears -- A neat technique
« Reply #9 on: February 23, 2017, 07:31:37 PM »
There are two steps to heat treating steel.  1) Hardening and 2) tempering.  The first (hardening) takes the surface of the steel to a Body-Centered-Cubic crystalline form (which is why "hard steel" grows in size).  And tempering "relieves the stresses" generated by such a transformation which makes it more resistant to breakage.

No arguments here.  What you've said is correct.  Though I doubt most home shop machinists care what form of crystal the steel is, as long as it does the job.

What I was pointing out was merely a shortcut that you can often get away with - kinda like sex without birth control.

I didn't think it necessary to add the obvious: "Don't come crying to me if your tool shatters" (or if the baby is crying).

Offline PekkaNF

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Re: Cutting Spur Gears -- A neat technique
« Reply #10 on: February 24, 2017, 08:07:07 AM »
Often tool steels temper ok, without complete cycling...Ie. Hardening, but you don't let it cool completely, just when water does not boil anymore, lift it out and let residual heat to do tempering. Some guy's at the knife making class were pretty good at this.

I did the two step process and first blade went fine, second had wery thin blade and I got bit bluish near tang and straw on the tip. I was aiming in-between, but it became ok knife. Not perfect, but not dog either.

Pekka

Offline xo18thfa

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Re: Cutting Spur Gears -- A neat technique
« Reply #11 on: February 24, 2017, 09:27:00 PM »
The 16-tooth pinion cuts in the same general manner as the 52’s. The notable difference is that the hub is integral, rather then hub less.

Change out the 52 tooth indexing gear on the dividing head and replace it with a 32 tooth.  During machining, skip every other tooth to get 16 divisions.

A 16 tooth, 48DP gear has a rough stock diameter of exactly 3/8” which is convenient. Use a 3/8” collet to chuck some 3/8” stock.  Cut as before.



With the dividing head set up I did some 32 tooth gears too.



Chuck the 16 tooth gear in the lathe and turn a hub. Tap for some set screws and it’s done.



These gears are going into a scaled up Ernest Glaser “Cracker”



They mesh perfectly. The chassis rolls smooth as silk.



Observations:

- Helicron's method is a great way for cutting gears. Simple to follow, simple to do.  A single cutter rather then a set of 7 or 8 is so much better.

- My lathe is not rigid enough to make the cutter blank as he shows.  So I went with the single tooth cutter.  Perhaps feeding the lathe bit in at an angle would be better then plunging straight in as I did.

- Overall grade: A-
Bob Sorenson
Las Vegas, Nevada, USA

Offline sparky961

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Re: Cutting Spur Gears -- A neat technique
« Reply #12 on: February 24, 2017, 10:21:07 PM »
Nice work.  I definitely like the idea of using a rack-shaped cutter over the use of a specially shaped single point tool.  Are you able to get an extreme close-up picture of the resulting tooth profile?

As for the lathe not being rigid enough to cut the cull diameter, this is possible - even likely.  But, I wonder if you couldn't get the result you were looking for either by turning the speed (RPM) way down.  Feed as quickly as your lathe will allow with a sharp tool.  Another possibility is to rough out the grooves a bit first with another tool then come and finish using the above parameters.

... Or go CNC and peck at it using a few plunges.  Too finicky for manual, though some might attempt it.

Offline PekkaNF

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Re: Cutting Spur Gears -- A neat technique
« Reply #13 on: February 25, 2017, 03:57:40 AM »
Those gears look very nice. Very good work and very nice info.

That method looks worth trying...hmm..where do I need some gears?

Pekka

Offline krv3000

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Re: Cutting Spur Gears -- A neat technique
« Reply #14 on: February 25, 2017, 02:29:16 PM »
I see a project for me one of them dividing heads

Offline xo18thfa

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Re: Cutting Spur Gears -- A neat technique
« Reply #15 on: February 26, 2017, 08:54:39 PM »
Thanks for the kind words.

Here are the best pics I could get with this camera.  Holding these gears up to the light with a commercial gear shows they are pretty close.  You can see the flat cuts of the "approximate involute" but it does not seem to affect the performance.  I have a set of these in a "Cracker" loco that's been run hard and no appearance of wear.





I like this method.  Going to try 32 DP gear next.

The dividing head is Harold Hall's design.  It has a #2 Morse Taper spindle which is not a good idea. Morse Tapers do not quick release.  They go in tight and need a hammer blow on the draw bar to loosen.  I have a set of castings for George Thomas' "Versatile Dividing Head".  Going to set that one up with a straight shank ER-25 collet.  I think that will work better.  It will also be direct dividing with change gears or plates.
Bob Sorenson
Las Vegas, Nevada, USA

Offline awemawson

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Re: Cutting Spur Gears -- A neat technique
« Reply #16 on: February 27, 2017, 03:01:16 AM »
Very nicely done  :thumbup:

I'm tempted to have a try just for the fun of it despite not at the moment needing any gears.
Andrew Mawson
East Sussex

Offline Biggles

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Re: Cutting Spur Gears -- A neat technique
« Reply #17 on: February 27, 2017, 01:10:52 PM »
Propar Job!  :)

Offline sparky961

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Re: Cutting Spur Gears -- A neat technique
« Reply #18 on: February 27, 2017, 09:25:57 PM »
Again, very nice. I'm in the same boat as others though... don't need any gears at the moment.

Offline SeaCat

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Re: Cutting Spur Gears -- A neat technique
« Reply #19 on: April 22, 2017, 06:26:59 PM »
Bob, very nice gears and a very nice application you have made for them.  A very useful method of gear making which I have noted down - I have some gears to make sometime soon including an internal gear and this looks like solving the problem of the making of the spur gears at least.

Yes, I can see that the gears have a series of straight lines on the teeth - had the been steel gears I would have suggested you make a "running in board", where the gears are mounted on spindles on a temporary board and one gear driven to drive the rest and run for ten minutes or so with grinding paste to grind the gears into one another, which would take off the rough edges, such as they are, not very rough really.  But being brass this would not work as the grinding paste would only inbed itself into the brass for every more.  Perhaps if they are run with plenty of lub they will bed themselves in, if you are worried about it.  Not sure I would be much!

Chris