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Gear milling

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Bill Dawes10/12/2009 12:59:03
365 forum posts
Anyone done any gear cutting with a milling cutter. I did some proper gear hobbing in my apprenticeship days many moons ago but my workshop won't run to that. Not found any supplier so far that does such a cutter.
I have Tubal Caines hand little book and it states that the type of cutter determines the size of gear you can cut (or visa versa I suppose)
 
Bill D.
mgj10/12/2009 14:02:02
1008 forum posts
14 photos
Yes- its quite easy. if you need good info, Ivan Laws book from the Workshop Practise series covers all we would ever need about cutting gears on a vertical mill.
 
Tracy tools do cutters in DP sizes. They are about £16 each. You will possibly need more than one cutter because each cutter only does a limited range of teeth numbers.
 
Buy the right cutter, set up on centre height against the dividing head, apply the infeed for that DP. Cut.
 

This shows the Dore Westbury being stretched (nearly) to the limit on my Little Samson  Second motion gear. I had to hang the gear (and final drive gear which is bigger) over the edge, and then used a clamp to hold the gear against the edge of the table. So the dividing head did the dividing and the table took the cutting thrust. I forget how many cutters I bought to do the full range of gears. 3 I think.
 
There is a driving dog in the arbour by the way.

Edited By meyrick griffith-jones on 10/12/2009 14:08:48

Bill Dawes10/12/2009 21:47:05
365 forum posts
That's great, thank you very much. Had a look at Tracy Tools website and have sent off for catalogue.
 
Best regards
Bill Dawes
Nigel McBurney 126/12/2009 22:47:41
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Hi  words of warning,The majority of gear cutters that you will come across either have a  pressure angle of fourteen and a half degrees or twenty degrees,common practice for at least the last fifty years is to use twenty degrees and usually this is engraved or etched on the gear,a lot of cutters available are unmarked and others have fourteen and a half degrees etched on them and there are still a lot of them around at dealers and auto jumbles,it is of course good practice  to mesh gears which have been cut with cutters having the same pressure angle.So specify when purchasing that cutters must have twenty degrees p/a etched on them,I also understand that a lot of lathe change gears continued to use fourteen and a half p/a long after it went out of common use.when cutting on small lathe/mill set ups it is best to take two cuts on steel or cast on dp gears up to 12 dp.first cut two thirds of gear tooth depth ,second cut one third of depth. 
JasonB27/12/2009 08:01:42
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In answer to your first question about hobbing cutters then ARC Euro do them.
 
Another source for involute cutters is RDG
 
Jason
Ian S C29/12/2009 05:21:19
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7468 forum posts
230 photos
I,v only cut two or three non critical(for accuracy)gears,I used a fly cutter gound by hand,if that worked OK then the correct cutter would be a peice of cake.Ian S C
Stub Mandrel11/02/2010 22:16:28
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I've made single-point cutters using Ivan Law's method. They worked 100%:
 
Tom Walshaw (Tubal Cain)  was a sceptic and took the approach of hand-filling a cutter to match another gear of the same pitch and similar number of teeth. When I needed a 63-tooth changewheel for metric screwcutting on my lathe, I tried this using a 60-tooth changewheel as a pattern. the result was excellent IMHO:
(unsharpened but hardened cutter filed from 1/8 gauge plate)

All you need for gearcutting success is the patience to understand the instructions, do the calculations and take your time with the cutting.
 
 
Neil
TomK11/02/2010 23:07:37
76 forum posts
20 photos
Bill
If you look at the pictures in my album you will see a myford gear box I am working on
All of the gears were cut on a vertical mill using 20 DP cutters I made on my lathe.
The cutters were made from gauge plate using the button method which is decribed in  Ivan Laws book.
 
 
Stub Mandrel14/02/2010 18:04:29
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Hi Tom,
 
Those cutters look enviably good. I keep thinking of making a 'Eureka' but your buttons don't look like they were designed for one.
 
What method did you use to relieve them?
 
Neil
 

mgj14/02/2010 18:28:17
1008 forum posts
14 photos
They haven't been form relieved have they ?
 

TomK14/02/2010 20:51:26
76 forum posts
20 photos
Bill
          The cutters in the picture  are relieved at the bottom is the mandrel that was used to relieve the cutters. The cutters are first turned as blanks using the buttons to ruff out the forrm.  
The slots are then cut. The slots are used to time the the cutter on the mandrel. 1 tooth at a time is releived. You must watch the depth you feed each cut to ensure all the teeth are the same from the center.
The method I use for the first tooth is to put marking blue on circumference and relelieve this first when all the blue us removed note the reading and then rotatate each tooth and releive to that depth.
 
The second part is to set up the buttons and releive to the calculated depth of the form.
one tooth at a time.
 
I have put up 2 more pictures of the releiving mandrel that may help you.
 
One more point the diameter of the cutter is important, when relieving you must make sure that the tool does not foul the next tooth.
Stub Mandrel14/02/2010 21:51:47
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4311 forum posts
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Thanks Tom,
 
I'll have to try that. What diameter cutters do you use?
 
Neil
TomK14/02/2010 21:59:22
76 forum posts
20 photos
Neil Sorry I put Bills name on that reply.
The relieving mandrel I used was designed for 2 inch (50 mm) cutters.
 
This link takes you to the information to produce gear cutters using the method I used
 
 
Tom

Edited By TomK on 14/02/2010 22:17:34

mgj14/02/2010 22:16:27
1008 forum posts
14 photos
Tom my apologies- thats very neat - by how many thou has each tooth been relieved.
TomK14/02/2010 22:38:01
76 forum posts
20 photos
Meyrick
               I checked the dimesion on the cad drawings I did for this and it shows that on the cutters I made  from  the cutting edge to the trailing edge of the tooth is 0.021 inch clear.
 
I used the cad rotating fuction to check my dimesions and it shows that the tooth clearance is ok. When using the cutters there is no sign of rubbing on the cutters.
 
I have added a link to my previous post which shows a method of how this type of cutter is made. I just modified it from a 4 to a 5 tooth and used cad to work out the dimensioning
 
One other point I have only used this mandrel to make 20 dp 2 inch dia cutters I have not checked it out for other DP size cutters
 
Tom
mgj15/02/2010 18:09:31
1008 forum posts
14 photos
no wonder they looked perfectly round - neat job.
 
I was having brain fade, because I thought (without checking the job) you were using the slots to get away without form relieving - on thinnish work. Then I saw the gearbox which looks very nice.
calder percival 120/02/2010 23:14:51
19 forum posts
1 photos
Be very carefull when buying cutters from people who advertise in the model engineer and other press as a single tooth cutter costs around £180 in the trade and 8 in a set makes for a lot of money, i have bought three cutters in the last couple of years to cut gears and found that one supplied was actually a stubby tooth version sold for the same dp and pressure angle (it went back) the other two left marks up one side of the tooth and upon inspection with a glass were found to be marked on a couple of teeth. I returned both of these aswell but that did not help with the time i lost.
James Veitch05/03/2010 03:00:39
16 forum posts
Hello TomK,
Thanks for your contributions to this thread, I've found them interesting and helpful, however I have a question you might be able to help me with.
You make reference to two sources: "Gears and Gear Cutting", by Ivan Law and the web article at metalwebnews.com, "Cutting Involute Gears with Form Tools" by John Stevenson.
 
On page 114 of Law's book and in the Stevenson article there is a table to calculate dimensions for the cutting tool.  Both authors claim their tables are for DP 1 and a Pressure angle of 20 degrees.  
 
Trouble is the two tables do not match. Not even close.
 
So?  Can you or anyone else sort this out for me?
 
Thanks in advance,
Jim V.
John Stevenson05/03/2010 12:29:43
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Both sets of tables are correct if used in their entirety and not mixed up.
Where the differences are concerned is where the infeed position is calculated from.
 
In Ivan's book   [ brilliant book BTW a must read if you are into gear cutting ]   he calculates the infeed by touching the outer edge of the button on the blank, moving over to centralise then infeeds the distance in the table.
 
In the web article which was taken from calculations done by Grant in 18 ought plonk, the infeed is taken from a point where both buttons radially touch a blank of known width, [ W ], and then infeeds from this point.
 
It's not easy to spot the differences between the two methods and this causes the tables to be different.
However if you drawn these out in CAD and overlay them, the differences are minute  and both follow very closely a precise CAD drawn involute.
 
John S.
 

Edited By John Stevenson on 05/03/2010 12:30:35

TomK05/03/2010 21:48:02
76 forum posts
20 photos
James
               There is nothing I could add to  John Stevenson answer. Just do as John says and only use 1 table and don't mix them.
 
TomK

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