Author Topic: Skew Bevel gears  (Read 4114 times)

Offline stevehuckss396

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Skew Bevel gears
« on: May 30, 2016, 09:44:43 PM »
Hello everyone.

I'm trying to wrap my head around the skew bevel gear concept. I have a spreadsheet with all the calculations and have studied the article. I think my trouble is in the setup. When I try to rough cut the teeth I cant seem to get to the correct position. The math says the center line of the offset is .4513 then plus or minus .036.

the cuts are made where i think they are supposed to be but they are obviously wrong. First cut was made and then rotate half the pitch and second cut is made.

Can anyone who has cut the skew gears shed a little light on what I might be doing wrong? Did you find something in the article that was a misprint? I cant seem to make sense of this deal. I fully understand how to do it but none of the numbers seem to work. The second cut is way to far from center and on the wrong side of the first cut.
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Offline Maryak

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Re: Skew Bevel gears
« Reply #1 on: May 30, 2016, 11:12:48 PM »
Hi Steve,

Steamer, (Dave Piper) made a spreadsheet - attached and I did one from Machinerys Handbook - attached.

I have never cut a skewed bevel gear but it did manage to produce a reasonable CAD drawing of the set

Anyway HTH

Regards
Bob
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Offline stevehuckss396

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Re: Skew Bevel gears
« Reply #2 on: May 30, 2016, 11:32:05 PM »
Hi Steve,

Steamer, (Dave Piper) made a spreadsheet - attached and I did one from Machinerys Handbook - attached.

I have never cut a skewed bevel gear but it did manage to produce a reasonable CAD drawing of the set

Anyway HTH

Regards
Bob



Thanks bob!

Like i said in the post up there, I think the math is correct. Problem i'm having is the placement of the roughing and finish cuts. Daves spreadsheet leaves out 3 steps. The sheet I posted includes the steps. In those steps are the layout of the cuts from center line of the gear. I can't figure out where my error is.
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Offline Maryak

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Re: Skew Bevel gears
« Reply #3 on: May 31, 2016, 06:43:33 AM »
Hi Steve,

Just had a closer look at your jpg and if cut 1 is the upper and cut 2 is the lower then my 1st thought is your indexing in the wrong direction. Why, well again if my assumptions are correct then cut 2 would be on the other side of cut 1 and the tooth would be narrower on the inner as it should be rather than wider as drawn.

HTH

Regards
Bob
Если вы у Тетушки были яйца, она была бы Дядюшкой

Online steamer

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Re: Skew Bevel gears
« Reply #4 on: May 31, 2016, 06:50:14 AM »
Hey Steve ,
When you get the chance fill ms in on what I missed...
Dave
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Offline Jasonb

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Re: Skew Bevel gears
« Reply #5 on: May 31, 2016, 07:43:36 AM »
Spreadsheet says offset is .4153 your text says .4513 is that just a typo in your post or the figure you are using?

Also not sure where your "moving half the pitch" comes from?

« Last Edit: May 31, 2016, 08:26:10 AM by Jasonb »

Offline Noitoen

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Re: Skew Bevel gears
« Reply #6 on: May 31, 2016, 08:03:34 AM »
Just looking at the image, looks like everything looks correct for the opposite (left) side of the gear.

Online steamer

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Re: Skew Bevel gears
« Reply #7 on: May 31, 2016, 01:33:37 PM »
OK  My spreadsheet has yellow fields as data inputs   There are 5 of them.  That is all that is required to complete the calculations.

Compared my spreadsheet to the calculations..  I don't see the skipped steps you mention Steve,

Again   YELLOW    input
            GREEN     output    Don't touch the output.

All the math is shown to the far right from the publication...

Additionally, if I put in the 5 inputs from the example....I get the same answers as the example.


Confused......


I've changed the input variables to reflect the example calculations shown on the spreadsheet, if you compare...and convert to English...(sorry Marv....the original was in English for the person it was written for was working in English... )   They match well.

( if you input the dimensions in MM and keep your units consistent, you get MM as output on the spreadsheet by the way.)


Dave   
« Last Edit: May 31, 2016, 01:56:12 PM by steamer »
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Offline stevehuckss396

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Re: Skew Bevel gears
« Reply #8 on: May 31, 2016, 08:52:51 PM »
Hey Steve ,
When you get the chance fill ms in on what I missed...
Dave

Thelre are a few more steps. Calculating the width of the rough cutter, depth of cut. I'll scan the page when I get home. I think there is nine steps and your sheet stops at six or seven.
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Offline stevehuckss396

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Re: Skew Bevel gears
« Reply #9 on: May 31, 2016, 08:54:17 PM »
Spreadsheet says offset is .4153 your text says .4513 is that just a typo in your post or the figure you are using?

Also not sure where your "moving half the pitch" comes from?

Typo
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Offline stevehuckss396

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Re: Skew Bevel gears
« Reply #10 on: May 31, 2016, 08:56:45 PM »
Hi Steve,

Just had a closer look at your jpg and if cut 1 is the upper and cut 2 is the lower then my 1st thought is your indexing in the wrong direction. Why, well again if my assumptions are correct then cut 2 would be on the other side of cut 1 and the tooth would be narrower on the inner as it should be rather than wider as drawn.

HTH

Regards
Bob

After the first cut the blank is rotated so the first cut moves down or further from center.
« Last Edit: June 01, 2016, 12:51:22 AM by stevehuckss396 »
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Offline stevehuckss396

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Re: Skew Bevel gears
« Reply #11 on: June 01, 2016, 12:50:15 AM »
Hello Steamer!

The copy of your spreadsheet that I have only goes to step 6. The text in live steam goes to step 9.

Step 7 deals with the roughing cutter dimensions and cutting depth

step 8 is the height setting guage

Step 9 is the horizontal cutting dimensions.


Again I believe all the math to be correct. I was asking because I was hoping someone found an error in the article or I was making some kind of mistake on the setup.
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Offline gbritnell

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Re: Skew Bevel gears
« Reply #12 on: June 01, 2016, 02:18:16 AM »
Hi Steve,
When I sent you all the scans from the article there were some correction to the mathematics on one of the pages.  I think that I had sent them to Dave when he did the spreadsheet but I can't be sure. I have a layout drawing done in Autocad 2004. If you can open it and use it you're welcome to it. Email me and I will send it to you.
gbritnell
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Online steamer

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Re: Skew Bevel gears
« Reply #13 on: June 01, 2016, 02:20:58 AM »
No Problem Steve, just if there's something wrong I want to fix it....

Dave
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Online steamer

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Re: Skew Bevel gears
« Reply #14 on: June 01, 2016, 02:28:08 AM »
Send me the associated pages, and I'll update the spreadsheet to solve for those last steps...

Dave
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Damned ijjit!