Author Topic: Cutting Spur Gears  (Read 3060 times)

Offline xo18thfa

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Cutting Spur Gears
« on: March 29, 2017, 04:39:57 AM »
Several years ago, I did an experiment 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 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 is the 16 tooth gear and do something with the results.
Bob Sorenson
Las Vegas, NV, USA

Offline gerritv

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Re: Cutting Spur Gears
« Reply #1 on: March 29, 2017, 01:19:11 PM »
A great write up.

It will help when I get my Eureka relieving tool done and try my first gear cutting.

Gerrit
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Offline Don1966

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Re: Cutting Spur Gears
« Reply #2 on: March 29, 2017, 03:31:34 PM »
Very nice write up and I am familiar with the web site very good information. If you haven't download my spreadsheet on making gears here is the link... http://www.modelenginemaker.com/index.php/topic,6012.0.html
you'll find multi gear calculation sheets and hob and cutter calculation sheets.

Don

Offline 90LX_Notch

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Re: Cutting Spur Gears
« Reply #3 on: March 29, 2017, 05:22:39 PM »
Nice Bob.  I plan on making a cutter when I make the gears for the "Tiny".   Strictly I.C. had an article about making a cutter along the same lines as yours.  I'll have to look at the site you referenced above.

-Bob
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Offline steamer

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Re: Cutting Spur Gears
« Reply #4 on: March 29, 2017, 11:54:09 PM »
Very Nicely done Bob, that same tool can make skew gears too.

Dave
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Offline xo18thfa

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Re: Cutting Spur Gears
« Reply #5 on: March 31, 2017, 01:59:27 AM »
This is a good method.  I like it.  The cutter I made has way more teeth then you need.  Only need 5 teeth at the most.  The 52 tooth gear uses all 5 teeth.  Tooth 1 and 5 just barely contact the blank.  3 teeth would be enough for probably 40 or less teeth on the gear.  Last night I was searching around and found a better way to make the cutter.  So hat will be the next try.

Did not know that cutter can do skew gears too.  That's definitely and experiment.  Law's book shows how to make bevel gears, have not looked into that yet either.

Don:  Thanks for the spreadsheet.  The worm drive is very interesting.  The next project is a new dividing head.  The one I used for this gear cutting project has two fatal flaws.  Maybe the new one can have a more traditional worm drive arrangement.

Thanks again
Bob Sorenson
Las Vegas, NV, USA

Offline steamer

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Re: Cutting Spur Gears
« Reply #6 on: March 31, 2017, 03:55:41 AM »
Go Here

http://modelenginenews.org/

Click on "Engines"   then "Projects" and then click on the "Feeny" build.    He goes through the whole process using a very similar method..

Dave
"Mister M'Andrew, don't you think steam spoils romance at sea?"
Damned ijjit!

Offline xo18thfa

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Re: Cutting Spur Gears
« Reply #7 on: April 01, 2017, 03:38:51 AM »
Thanks for that link Dave.  Going to look into that.

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, NV, USA

Offline Don1966

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Re: Cutting Spur Gears
« Reply #8 on: April 02, 2017, 09:56:55 PM »
Impressive work Bob!.... :ThumbsUp:


Don

Offline xo18thfa

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Re: Cutting Spur Gears
« Reply #9 on: April 05, 2017, 07:35:55 PM »
Thanks Don.  Take care.
Bob Sorenson
Las Vegas, NV, USA

Offline Brendon M

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Re: Cutting Spur Gears
« Reply #10 on: April 06, 2017, 09:24:35 AM »
This was very interesting to read. Thank you for taking the time to explain.
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