Author Topic: Novel CNC gear cutting using a slitting saw and 4th axis  (Read 1839 times)

Offline cfellows

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Novel CNC gear cutting using a slitting saw and 4th axis
« on: February 09, 2018, 01:07:02 PM »
I ran across this video showing how to cut pretty much any involute gear pitch and pressure angle using a vertical mill with a slitting saw cutter and a 4th axis. 

<a href="https://www.youtube.com/watch?v=HI27vSoxCeo" target="_blank">http://www.youtube.com/watch?v=HI27vSoxCeo</a>

Anybody else tried this guys method or anybody elses similar method?

Chuck
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Offline gerritv

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Re: Novel CNC gear cutting using a slitting saw and 4th axis
« Reply #1 on: February 09, 2018, 01:25:49 PM »
Nicely done implementation.
There seems to be a spate of methods creating involute teeth lately.

The best I have seeing is this series, he is waiting to publish the details in a magazine: <a href="https://www.youtube.com/watch?v=fMY8zUs3bZI" target="_blank">http://www.youtube.com/watch?v=fMY8zUs3bZI</a>

There is also the shaper method: <a href="https://www.youtube.com/watch?v=7kgUR7CIfwM" target="_blank">http://www.youtube.com/watch?v=7kgUR7CIfwM</a> based on an article in Model Engineer in the Sept 14, 1950 issue
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Offline Brian Rupnow

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Re: Novel CNC gear cutting using a slitting saw and 4th axis
« Reply #2 on: February 09, 2018, 06:47:57 PM »
That is interesting Chuck. I have no intention of going cnc, but it certainly is interesting to see what it can do. Hope you are feeling well.--Brian

Offline tvoght

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Re: Novel CNC gear cutting using a slitting saw and 4th axis
« Reply #3 on: February 09, 2018, 07:13:58 PM »

Interesting.

I've been wanting to try a similar method using the CNC with 4th axis. The method would use a trapezoidal rack form cutter like the one we've seen Chris use recently on the Marion 91 project. I'm thinking to use an off-the-shelf #1 involute cutter (135 teeth to rack).


It should be possible to cut any gear in a given pitch with just the rack cutter for that pitch.


--Tim

Offline cfellows

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Re: Novel CNC gear cutting using a slitting saw and 4th axis
« Reply #4 on: February 09, 2018, 08:49:24 PM »
Interesting.
I've been wanting to try a similar method using the CNC with 4th axis. The method would use a trapezoidal rack form cutter like the one we've seen Chris use recently on the Marion 91 project. I'm thinking to use an off-the-shelf #1 involute cutter (135 teeth to rack).
It should be possible to cut any gear in a given pitch with just the rack cutter for that pitch.
--Tim

I had thought of trying to find a trapezoidal end mill or round milling cutter.  Never occured to me to use a standard rack involute cutter.  I should think you would want a pretty small pitch size to accommodate smaller gears.  I was actually looking on youtube for videos detailing cutting gears when I came across the video I posted.  Being able to just use a slitting saw really increases your options on pressure angle, pitch size, etc.  I'm actually contemplating the purchase of gearotica.  $120 is a bit steep, but with it, you can cut pretty much any gear you want.

Chuck
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Offline cfellows

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Re: Novel CNC gear cutting using a slitting saw and 4th axis
« Reply #5 on: February 09, 2018, 09:04:25 PM »
That is interesting Chuck. I have no intention of going cnc, but it certainly is interesting to see what it can do. Hope you are feeling well.--Brian

Oh, come on Brian, be adventurous!  Ok, well I know you already are adventurous, and CNC can be expensive.  But it sure is fun and greatly expands your capabilities, especially with a 4th axis.  If I had the last 15 or 20 years to live over, knowing what I know now, I would find a way to buy a Tormach PCNC1100.  I know that they are pricey, probably $8000 - $10,000, but I think they are a dandy CNC mill, very accurate, and quite capable.  My homebrew CNC set-up started life as an Enco Mill/Drill which, as I recall, cost me around $750 20+ years ago.  The hardware upgrade which included ball screws, stepper motors and controller, and miscellaneous stuff was probably around $800.  The PC and software was around $400.  And, there was a considerable amount of work to dismantling, machining parts, and fitting it all back together.  The result is certainly worth  the cost and effort, but the milling envelope is about 5" x 16" and it's accuracy is only fair at + or - .002".

And, as I said before, it is very engaging and lots of fun.

Chuck
So many projects, so little time...

Offline tvoght

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Re: Novel CNC gear cutting using a slitting saw and 4th axis
« Reply #6 on: February 09, 2018, 09:10:18 PM »
[
... I should think you would want a pretty small pitch size to accommodate smaller gears...

Chuck


The technique I was considering would use a 24 pitch rack cutter to cut any 24 pitch gear, 32 pitch rack to cut any 32 pitch gear, etc.


If I understand Gearotica correctly, it would require a pretty small endmill to cut small gears, whether using 2.5d or 4th axis techniques.  That is, the endmill would have to be small enough to fit into the tooth root. Is that correct?


--Tim

Offline Dan Rowe

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Re: Novel CNC gear cutting using a slitting saw and 4th axis
« Reply #7 on: February 09, 2018, 10:30:59 PM »
Here is a post where Gail described generating 96DP gears with an engraving cutter.

http://www.modelenginemaker.com/index.php/topic,6649.msg136156.html#msg136156

Dan
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Offline tvoght

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Re: Novel CNC gear cutting using a slitting saw and 4th axis
« Reply #8 on: February 09, 2018, 10:49:05 PM »
Somewhat related is this well-written and detailed page from Tony Jeffree:

Gear Cutting with a rack form multi-tooth Cutter

--TIm

Offline GailinNM

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Re: Novel CNC gear cutting using a slitting saw and 4th axis
« Reply #9 on: February 10, 2018, 08:44:34 AM »
Dan  Thanks for the plug on the 96 DP gears.  Sorry that I was not able to post the method used as promised.  I had another step loss in vision and have spent much of my time working around it.  I am not legally blind in one eye and 20\200 corrected in the other.

Probably just as well that I did not post it.  I had another idea that was born out of necessity.  It uses regular cutting tools rather than the engraving cutter. 

About 3 months ago my 60 year old roll in band saw shucked out the final drive gear.  The gear has 60 teeth with 13.5PA and is is APPROXIMATELY  12 DP.  It appears that the manufacturer probably machined the frame with the center to center holes about 0.01 0 to 0.015 too close to each other and compensated by shaving the OD of the gear and cutting the teeth deeper.  So a new special gear was  necessary.   So, playing around with some math a new method was developed. 

The gear was cut on 2-1/2 D CNC Bridgeport with a unidirectional indexer.  A standard 3/32 end mill was used to cut all the teeth.  Here is a photo of a segment of the finished gear. It runs and works fine.



After watching the video that Chuck posted (thanks Chuck) I got to thinking that The same approach I used could also be used with slitting saws. All I would have to do is transpose the Y and Z in the equations. Some rough calculations show that the only requirements for the slitting saw could be that the thickness would be that it be less than 1.125/DP. This means that for 38 DP gears a 0.020 saw would work fine and a 0.010 thick saw would take me down to 96DP with ease. For  gears with a large number of teeth, say 50 or more,the indexing head would only have to be able to index for the number of teeth in a gear.  For gears with few teeth, down to about 12 or 13, it would have to be able to index  4 times the number of theeth. THAT IS 60 divisions for a 15 tooth gear.

I will try to get a general set of equations generate, or maybe a spreadsheet for the general set to do any gear.  Because of my current project it will be about 2 weeks before I get a break in it to play the math games.  Or if people are interested I can post enough about it that it could be used with a bit of CAD work to get the numbers.
Gail in NM
« Last Edit: February 10, 2018, 08:48:40 AM by GailinNM »
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