Author Topic: 32 DP Involute Gear Cutter  (Read 6025 times)

Offline DLM

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32 DP Involute Gear Cutter
« on: September 17, 2013, 03:07:56 AM »
I want to make a 32 DP #4 cutter 14 1/2 pressure angle. I have the book Gears & Gear Cutting by Ivan Law.
In chapter 12 it  it goes in great detail about making cutters & tools to make the
cutters, but the problem is the two charts he has in the book are for 20 deg. & 30 deg. pres. angle. For the diameter for the involute disk to make the 30 deg.is .406
& for the 20 deg.is .320 so would it be right to use .313 for the 14 1/2 deg..
The 14 1/2 should be a smaller diameter than the 20 deg.
Where i come up with the .313 is the tooth tip width  32 dp x 14 1/2 pa is .030 &
32 dp x 20 pa is .023 that is .007 so that is what i took off of the 20 deg. disk.
If anyone has any different ideas let me know or has a chart with the spec. for a
14 1/2 deg. tool. Thanks Don

Offline steamer

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Re: 32 DP Involute Gear Cutter
« Reply #1 on: September 17, 2013, 03:29:04 AM »
Hi Don,

How many teeth do you want to cut?   My Friend Gail has a great spread sheet that will spit that stuff out....I can give you the output if you want

When you get a chance, please post an introduction in the introduce yourself section.

Thanks!

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

Offline DLM

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Re: 32 DP Involute Gear Cutter
« Reply #2 on: September 17, 2013, 03:30:38 PM »
The cutter is 1 1/2 in. in diameter and has 12 teeth

I am cutting a 8 tooth 60 deg. & a 16 tooth 30 deg. helical gears.

Don

Offline steamer

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Re: 32 DP Involute Gear Cutter
« Reply #3 on: September 17, 2013, 05:11:15 PM »
Hey Don,

I don't know the limit of smallest number of teeth with a "standard" cutter...but I think you may be coming up on it.   I'll check my references tonight or tomorrow but that tooth count may result in undercutting....

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

Online Jo

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Re: 32 DP Involute Gear Cutter
« Reply #4 on: September 17, 2013, 05:39:41 PM »
The limit is 12 teeth with a standard cutter. The 8 tooth will have to be done on a gear cutting machine.

Jo
Usus est optimum magister

Offline tangler

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Re: 32 DP Involute Gear Cutter
« Reply #5 on: September 22, 2013, 06:28:06 PM »
Don,

Sorry to come to this discussion a bit late, I've been away from regular internet access.  Are you aware that in order to mill a 60 degree 32 DP helical gear you need 64 DP gear cutter (DP / Cos (a) - where a is the helix angle) and for the 30 degree gear you will need a 36.95 DP cutter?  For the first gear you will need a cutter for 64 teeth and for the second gear a cutter for 25 teeth.  Machinery's Handbook explains the calculations for milling helical gears. 

For spur gears, increasing the pressure angle to 30 degrees will decrease undercutting of the tooth and allow you to make usable gears with smaller numbers of teeth.

Hope this helps,

Rod

Edit: typo - changed x to / in equation
« Last Edit: September 22, 2013, 08:58:41 PM by tangler »

Offline cfellows

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Re: 32 DP Involute Gear Cutter
« Reply #6 on: September 22, 2013, 06:57:15 PM »
I believe you can use standard 32DP cutters for your gears.  You apparently already know what number of cutters you need?  And, contrary to what Jo says, for helical gears, you can go quite a bit below 12 teeth depending on the helical angle.  I made 6 tooth helical gear using a standard cutter, although I don't remember which number it used.

Chuck
So many projects, so little time...

Offline cfellows

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Re: 32 DP Involute Gear Cutter
« Reply #7 on: September 22, 2013, 07:01:15 PM »
Here's a link to the graph which tells you which number of cutter you need.  Again, information you probably already have.  Unfortunately, I've never made my own cutters, so I can't answer your original question...



Chuck
So many projects, so little time...

Offline IanR

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Re: 32 DP Involute Gear Cutter
« Reply #8 on: September 22, 2013, 09:34:30 PM »
Hope this is what you need. Took me a while to find out where on my computer I'd hidden it, and longer to find out how to post it.

Offline tangler

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Re: 32 DP Involute Gear Cutter
« Reply #9 on: September 22, 2013, 11:53:27 PM »
Chuck,

It is with some trepidation that I disagree with such an experienced and successful engineer as yourself but I think I am right about the need to use cutters of a different DP, depending on the helix angle.  Choosing the number of teeth of that cutter is an additional factor that needs to be taken into account.  My early attempts at producing helical gears were always unsuccessful, the teeth were too thin.  I was trying to reproduce a set of commercial gears 45 degree skew which were, presumably, hobbed.  I therefore had a pair of gears to compare my attempts with.  It was only after a considerable amount of further study into the subject that I finally twigged what the issues were.  Machinery's Handbook is quite specific although it is buried in a lot of other stuff about designing helical gears for various situations:



(Machinery's Handbook 25, page 1985)


The normal pitch is the distance between adjacent teeth at right angles to the tooth - as the helix angle increases this distance gets less and hence the cutter must be thinner than would be used on a spur gear.  Since we are using a disc cutter to machine the helix this tends to thin the teeth even more either side of the contact point, which is why the diameter of the cutter is one of the factors which needs to taken into account when choosing which number cutter to use.  I guess all this is why these gears should really be hobbed.  In the case of 45 degree gears we can use a pair of cutters from the same set.  In this case, using 32DP cutters would produce a pair of 22.6 DP gears.  I think we are fortunate that we only need our gears to maintain timing of the cam shaft, so questions of noise and power loss from less than perfect gears are of little consequence.  Our home made gears seem to work well enough for our purposes.  Don, however is quite specific about the gears he wishes to make.

My helical gear cutting adventures were hampered the maximum lead I can arrange with the change gears on my lathe.  Your helical fixture will remove that limitation  :ThumbsUp:.

I ought to add that I have submitted an article on this subject to Model Engineer.  I am not sure if it will be published, the editor has some concerns on whether the subject matter is too abstruse.

Best wishes,

Rod


Offline IanR

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Re: 32 DP Involute Gear Cutter
« Reply #10 on: September 23, 2013, 03:56:15 PM »
My understanding is that if you use 32DP cutters, the normal pitch will be 32DP, but the transverse pitch, which is what you see if looking at the side of the gear, will be some odd number.

Offline tangler

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Re: 32 DP Involute Gear Cutter
« Reply #11 on: September 23, 2013, 06:55:42 PM »
Folks,

I'm in some difficulty here.  The quote from Machinery's Handbook is unequivocal yet I clearly don't fully understand all the issues.  For a pair of meshing gears at right angles the normal tooth form must be similar for both gears, so my initial post is nonsense and my calculations are wrong  :-[.  The calcs work for 45 degree helixes but fall apart when considering a pair of gears such as 30 and 60 degrees, suggesting I have made a systematic error.  Perhaps I'd better buy the gears for the Wyvern

Please accept my apologies and disregard my posts. :toilet_claw:

Rod