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Involute spline help please

SeymourDumore

Diamond
Joined
Aug 2, 2005
Location
CT
Guys, I would like to ask for a little help.
How could I, or where could I find a tool to generate the following spline:
Specifications on the drawing:

Involute Spline per AS472-B
26 Teeth
16/32 Diametral pitch
Press. angle: 30 deg
Pitch dia : 1.625
Major dia: 1.688 +0/-.010
Minor dia: 1.495 +0/-.015

The only tool at my disposal is Autodesk Inventor, but the involute spline generator it comes with does not have an option to define the above parameters, and whatever it does create is not exactly as specified.
In the generator I can only pick from pre existing types, and by selecting ANSI B92.1 - 30 deg - Fillet root, Side fit 16/32 - Class 5 I get something that's close to what's needed, but can't say for sure.
I can of course measure the result, which is a 1.688 Major dia and a 1.500 minor dia, but don't know how to edit it to fit the specifications stated, nor do I know if the pitch dia is correct.

So, the questions:
A: How is the pitch diameter defined for involute splines?
B: While I cannot edit the profile in Inventor, I absolutely can edit it in AutoCAD. If I want to achieve the 1.683 major and the 1.4875 minor, can I just trim the OD and extend the spline down on the ID?
Or, do I need to scale the whole thing down by .005, which would move my Pitch dia as well.


On Edit:

OK, just did exactly that, created the spline, made a 2D drawing if it, exported it and ...
The profile of the "tooth" is an arc!
I do not believe that to be correct. I thought those should be also a spline from minor to major using a specific calculation.
It is likely just how Inventor's "generator" works, which is not a true representation of the gear form, just a simulation of it.

Back to square one: Is there a tool out there to create a 2D spline that's accurate to the specifications above?

Thank You
 
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Guys, I would like to ask for a little help.
How could I, or where could I find a tool to generate the following spline:
Specifications on the drawing:

Involute Spline per AS472-B
26 Teeth
16/32 Diametral pitch
Press. angle: 30 deg
Pitch dia : 1.625
Major dia: 1.688 +0/-.010
Minor dia: 1.495 +0/-.015

I made one with DP16, n=26. Rename gear.txt to gear.x_t (parasolid text) and see if that works for you. The major and minor diameters might not be right, because by default my software connects the involute segments with straight lines, but if the face is correct, you should be able to copy it and trim or extend to the proper size. With some work I might be able to get it to match your spec exactly. PM me if you want me to try.
 

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The "16" refers to the diametral pitch of the teeth. The "32" refers to the depth of the tooth form (addendum plus dedendum). For lack of anything else, Machinery Handbook will cover the basics for you.
 
The "16" refers to the diametral pitch of the teeth. The "32" refers to the depth of the tooth form (addendum plus dedendum). For lack of anything else, Machinery Handbook will cover the basics for you.
Good to know, thanks. That makes sense now. Gear design isn't something I've done a lot of.
 
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I made one with DP16, n=26. Rename gear.txt to gear.x_t (parasolid text) and see if that works for you. The major and minor diameters might not be right, because by default my software connects the involute segments with straight lines, but if the face is correct, you should be able to copy it and trim or extend to the proper size. With some work I might be able to get it to match your spec exactly. PM me if you want me to try.
Thank you!
Unfortunately I got stuck at Inventor 2021 ( not by real choice ), and cannot open the new Parasolid version.
STEP ( for the time being ) is OK, but importing the current Parasolid format is not supported.
 
At my old job I had Geartrax and it worked great.

I don't do enough of this kind of thing to justify buying it again, so the last time I needed an involute spline I just googled for a pdf of ansi b92.1 and modelled it myself.

Cost me about an hour of my life, but wasn't a big deal.
 


Last time I did this I actually tried your second link and had some issues with it that caused me to abandon it. Unfortunately I can't remember what they were...

Never tried the first one though...
 
Here's a .STP version.
Thank you, and now the mystery deepens ....

The file you've sent is eerily similar ( might as well say identical ) to what my customer sent me in DXF.
Unfortunately, the Minor dia is 1.469, the major is 1.750.
Obviously one can truncate the major down, but there is no way to enlarge the minor.

What did you use as the parameters for the spline?
Were you able to plug in the diameters, or picked one form from the database?
I am only asking because I'm now wondering if the drawing meant to say that it is a modified spline with reduced major and increased minor dia.

At this point I'll just let the customer come up with the form and not waste any more of anyone's time.

Thank you all!
 
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Thank you, and now the mystery deepens ....

The file you've sent is eerily similar ( might as well say identical ) to what my customer sent me in DXF.
Unfortunately, the Minor dia is 1.469, the major is 1.750.
Obviously one can truncate the major down, but there is no way to enlarge the minor.

What did you use as the parameters for the spline?
Were you able to plug in the diameters, or picked one form from the database?
I am only asking because I'm now wondering if the drawing meant to say that it is a modified spline with reduced major and increased minor dia.

At this point I'll just let the customer come up with the form and not waste any more of anyone's time.

Thank you all!
Best to clarify with the customer. Such a severely truncated design doesn't seem like it would mesh properly. I'd have to simulate it to see.

The parameters I entered were in a predefined spur gear profile: Module 1/16", Pressure angle 30, Teeth 26. There is a "Shift Coefficient" input that appears to adjust the major/minor diameter . The Involute curve command itself takes inputs of starting diameter, end diameter, center point and passing point. In order to get those values I'd have to reverse engineer the predefined gear template that the software came with and do the math in the formulas.

Here's what the shift does: I would guess that it's useful for adjusting the mesh tolerance of the gear, but I don't really know.
1718211204348.png1718211261934.png1718211234693.png
 
I'm now wondering if the drawing meant to say that it is a modified spline with reduced major and increased minor dia.

The profiles posted so far don't look like the splines I know. I'm used to something more like this where the teeth have involute flanks, but are truncated at both the minor and major diameters:
spline.png

If you've got the involute profile with correct pitch diameter, pressure angle, and number of teeth is it not just a matter of truncating with major and minor circles and then filleting? I think maybe that's what @gregormarwick was getting at when he said that he has drawn them himself. Formulas for diameters are here: https://www.engineersedge.com/gears/involute_spline_13649.htm

But, I've never cut a spline. I only know that they don't look like gears.
 
You can certainly use the 16 DP 30 deg profile and adjust the addendum and dedendum to arrive at your specified OD and root diameter. The profile shift amount will allow you to adjust the tooth thickness. This will not create any root radius obviously. I don't recall that you ever indicated if this was either a flat root or full fillet spline. That needs to come from your customer if it was not specified.
 
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I don't recall that you ever indicated if this was either a flat root or full fillet spline. That needs to come from your customer if it was not specified.
Fillet-root splines have standard radii for a given spline, and this creates the minor diameter. A flat-root spline will have a different minor diameter than a fillet-root spline.

Also, I have seen different fillet radii than standard specified! This again changes the minor diameter, which for a spline is established by the "whole depth", which is a measurement of the tooth depth.

The whole depth ("WD") should be listed along with spline pitch and pressure angle to more completely describe the spline....a minimum for manufacturing purposes.

ToolCat
 
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This thing isn't a gear, rather a removal tool that fits into a part with an internal spline.
It is absolutely possible that the Major is truncated down in order to assure that it fits into the part to be removed, but then there is the question of why is the minor truncated-up?

As far as flat, radius or full fillet, all that's indicated on the print is what I've posted. Pitch, minor, major, press. angle and # of teeth.
I could cut the damned thing no matter what ( WireEDM ), but I need to know what first!
Seems like my customer is stuck too and trying to figure out what their customer wants.
 
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It is absolutely possible that the Major is truncated down in order to assure that it fits into the part to be removed, but then there is the question of why is the minor truncated-up?

I'm guessing because only truncating the major down on the male results in sharp teeth on the female:
single truncation.png
I avoid sharp-toothed females.

But, truncating both gives this:
dual truncation.png

Truncation isn't about fit, right? There needs to be clearance all around the teeth. Isn't truncation more about making the teeth strong?
 








 
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