Bevel and pinion gear cutting

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JohnR
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Bevel and pinion gear cutting

Post by JohnR » Tue Apr 06, 2021 9:49 am

I am the point of cutting my gears for my 1 1/2" Shay.
My question is with regards to the three cuts with the cutter. The first being down the
middle and the second and third cut offset both sides of the first cut.
How do I determine the offset amount ?
I will be making 25 and 50 tooth gears at 16 DP.
I have Ivan Laws book but cannot read the formulas as the printing is blurred ( also trifocals
do not help).
Any help would be appreciated.

John

Russ Hanscom
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Re: Bevel and pinion gear cutting

Post by Russ Hanscom » Tue Apr 06, 2021 1:55 pm

I have the Law book, and if what you want is on page 106, mine is clear.

Give me an email address and I will send you a pdf of the page.

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Rich_Carlstedt
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Re: Bevel and pinion gear cutting

Post by Rich_Carlstedt » Tue Apr 06, 2021 3:53 pm

John
I addressed some of that in a earlier Chaski Post
viewtopic.php?f=4&t=108880&p=417280&hil ... ng#p417280

Hope that helps as well
Rich

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Re: Bevel and pinion gear cutting

Post by JohnR » Mon Apr 19, 2021 2:04 pm

Gentleman
My apologies for not responding back until now.
I have a question with regards to cutter selection.
The angle is approximately 26.5 deg.
Applying the formula found in Ivan Laws book I come up
with the use of a #2 cutter ( 55 tooth ) for a 25 tooth
tooth bevel gear.
Is this right?
Again thank you for your help.

JohnR

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Rich_Carlstedt
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Re: Bevel and pinion gear cutting

Post by Rich_Carlstedt » Mon Apr 19, 2021 9:47 pm

John
I can understand why the formulas are not clear, as Ivan Laws used numbers that confuse the reader,
He should NOT have used the same number of teeth as he does pitch (20 and 20) in his examples - this is confusing
when the formulas do not designate which is to be used but instead just have the number 20 listed.

John, Really should have more info , but using what you posted, I get this data,
You are right, the angles are 26.56 for the Pinion ( small) gear and 63,44 for the large

Cutter size is 1/.447= 2.23 x 25 teeth= 55.9 , so use a #2 cutter for the small gear and the large gear is 1/.8944 x 50 = 55.9 , so the same cutter for it
Pitch diameter (PD) , Small end of small Gear is 1.562 and small end of large gear is 3.125
Diameter of small end of small gear is 1.6179 and the large gear is 3.2368
Your Chordal Thickness is .0981, so the offset you will use is .049 for both gears
When you offset , you want 1/4 of the Pitch or 1/4 x 360 x 25 = 3.6 Degrees for the small gear
and 1.8 Degrees for the large gear
Hope this helps

Rich

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Re: Bevel and pinion gear cutting

Post by JohnR » Tue Apr 20, 2021 9:15 am

Thank you Rich

JohnR

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Re: Bevel and pinion gear cutting

Post by JohnR » Thu May 13, 2021 7:58 pm

Rich
Again thank you for the information.
The degree offsets are for the second and third cut starting points ( 1/4 of the pitch).
Assuming the second cut is advanced in a clockwise direction the cutter would be offset
up or counterclockwise direction of .049".
At this time I would cut all teeth and upon completion return the gear back to zero
degrees.
The third cut would be the direct opposite with starting point ( 1/4 of the pitch ) being in a counterclockwise
direction.
The cutter would be offset down .049"or in a clockwise direction.
Sound right ?

JohnR

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Rich_Carlstedt
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Re: Bevel and pinion gear cutting

Post by Rich_Carlstedt » Thu May 13, 2021 11:06 pm

Sorry John. Saying clockwise doesn't help because I don't know which side of the clock you are cutting on.
I mean a 3 O'clock clockwise cut is down and if cutting at 9 O'clock, and going clockwise - thats up ??
What you want to look at is where is the "Gullet " is going . The Gullet being formed where the material was removed in the center pass
When the Gullet goes downward, you lower the cutter, and visa-versa
So say the first pass was at 3 O'Clock on the gear and now you rotate it clockwise and the Gullet is at 3:15 .
It is Lower, and that means you lower your cutter .049" ( This is calculated on how much the gullet moved for the 1/4 pitch change and is based on the small tooth pitch center only !)

Yes, you got the process right . Cut all the teeth First and then do the 2 nd pass as a offset and 1/4 pitch change.
Then go back to the original for both ( but don't cut ) , and then go the other way in the third pass

The amount you lower (or raise) can be checked with the cutter POWER OFF.
After you rotate the gear blank , if you manually bring the cutter into the gullet on the INSIDE of the bevel gear and it should match !
This confirms that cutter will only remove material from the tooth as it goes outward toward the larger diameter and that your move of .049" is correct

Hope this helps
Rich

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Re: Bevel and pinion gear cutting

Post by JohnR » Fri May 14, 2021 7:25 am

Rich
Thank you for the clarification.

JohnR

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Re: Bevel and pinion gear cutting

Post by JohnR » Mon May 24, 2021 11:16 am

Any recommendations for speed and feed of cutter.
Cutter #2 16dp. 2.5 dia. 14 tooth.
Machine to be used Series 1 Bridgeport CNC.
Also can I cut full depth or should i stagger the
depth of cut.

Thank you

JohnR

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Rich_Carlstedt
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Re: Bevel and pinion gear cutting

Post by Rich_Carlstedt » Tue May 25, 2021 10:51 pm

John don't know what the material is so lets start with Steel
I would run 100-125 RPM and go full depth of cut- don't do partial depths ( It tends to wear the cutter tips only !)
I would shoot for .001" feed per tooth to start, not knowing the rigidity of the part holding
That means .014" per revolution and at 100 RPM , which becomes 1.4 IPM
For Cast Iron , I would increase to 150 RPM
and for Bronze go to 300..but watch the chip load --too many variable Bronzes out there and cutter sharpness is a factor
Rich

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