Gear over pin diameter

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jdevente
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Gear over pin diameter

Post by jdevente » Sun Oct 01, 2017 9:26 pm

Does anyone have any experience measuring an over pin diameter of a gear on a CMM?
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CrashN8
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Re: Gear over pin diameter

Post by CrashN8 » Wed Oct 04, 2017 6:21 pm

Easy... Measure two circles, then report distance between using the Maximum Distance option.

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Re: Gear over pin diameter

Post by jdevente » Thu Oct 05, 2017 1:51 pm

Sorry. I didn’t give a very good explanation of how I’ m wanting to measure. Is it possible to measure the over pin distance (M) without measuring actual pins. I know you can construct a tangent circle of a specific diameter using 2 lines in CMM Manager but the gear teeth have radii on them where the pin would touch.

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Ryan Christopher
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Re: Gear over pin diameter

Post by Ryan Christopher » Thu Oct 05, 2017 2:48 pm

!! After looking this over I see this solution is wrong, but am leaving it as an example of what not to do !!

One way might be to use a loop but it would be pretty simple one.

1. Measure a stream of diametrically opposed points inside the teeth.
2. At the first pair of points create a circle for each of them and use the circle between 2 points construction.
3. Use GetFeaturePropertyAct and some shop math to find out if the diameter is the same as the the required pin diameter*.
4. If yes, end the loop; if no continue the loop moving up to the next pair of points until you find the 'good diameter''

The biggest pain of this is that CMM-M won't let us use a point in place of a circle so we need to add a couple extra steps.


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One way that would actually find the answer...

1. Set the alignment.
2. Measure points.
3. Create constructions.
4. Evaluate the distance.
5. If dist. good keep the construction point as the solution.
6. If dist. bad iterate through the loop to the next point.
qwer.jpg
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Last edited by Ryan Christopher on Fri Oct 06, 2017 11:25 am, edited 5 times in total.
Ryan Tackes
Applications Manager, VMS Inc.
http://www.vantagemeasure.com/

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jdevente
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Re: Gear over pin diameter

Post by jdevente » Thu Oct 05, 2017 2:57 pm

ok I will try this out. Nikon should add construct a circle tangent to two circles in there construct a circle options!!!

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Re: Gear over pin diameter

Post by CrashN8 » Wed Oct 11, 2017 4:55 pm

Not a bad idea... but it will not help in this case since the involute profile of a gear tooth is not circular.

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Re: Gear over pin diameter

Post by Ryan Christopher » Mon Nov 06, 2017 1:50 pm

This vbs will find the distance from the center of the cog to the center of the pin.


' TANGENT CIRCLE CENTER FINDER
' circle from 2pts and radius version 17-11-03A
'===================================================================
' Creates a circle center point from a group of points by searching
' for a circle center at a specified radius tangent to the
' measured points.
' 1. This assumes that points are on an xy plane.
' 2. The x value will always calculate out to zero.
' 3. The y value is the output being sought after.
' 4. Measure points with probe comp turned off.
' 5. The order of points should be towards y positive.
' 6a. Set the y axis through the middle of the channel.
' 6b. Measure only the right (x positive) side of the channel.
' 6c. This routine assumes symmetry.
'===================================================================
' Ryan Tackes VMS Inc. : ryan@vantagemeasure.com : November 3, 2017
'===================================================================
' \/ EXPLINATION OF VARIABLES \/
'===================================================================
Option Explicit
'cird = diameter of the tangent circle
'cirr = radius of the tangent circle
'pr = probe radius
'pd = probe diameter
'prfix = prefix of the point names
'startpt = ordinal of the first point being evaluated
'endpt = ordinal of the last point being evaluated
'i = loop variable
'x1 = measured point 1 x value
'y1 = measured point 1 y value
'x2 = measured point 2 x value
'y2 = measured point 2 y value
'x3 = midpoint x value of (x1, y1) and (x2, y2)
'y3 = midpoint y value of (x1, y1) and (x2, y2)
'q = distance between (x1, y1) and (x2, y2)
'outx = x output value of the center of the tangent circle
' outx = x3 + sqr((cirr^2-(q/2)^2)*(y1-y2))/q
'outy = y output value of the center of the tangent circle
' outy = y3 + sqr((cirr^2-(q/2)^2)*(x2-x1))/q
'x4 = evaluation point x value
'y4 = evaluation point y value
'evaldist = dist from calculated center to the next point to see if loop should continue
'===================================================================
' \/ DECLARATION OF VARIABLES (lazy) \/
'===================================================================
Dim cird As Double
Dim cirr As Double
Dim pr As Double
Dim pd As Double
Dim prfix as String
Dim startpt As Double
Dim endpt As Double
Dim i as Double
Dim x1 As Double
Dim y1 As Double
Dim x2 As Double
Dim y2 As Double
Dim x3 As Double
Dim y3 As Double
Dim q As Double
Dim outx As Double
Dim outy As Double
Dim x4 As Double
Dim y4 As Double
Dim evaldist As Double
'===================================================================
' \/ DEFINE THESE VARIABLES \/
'===================================================================
'\/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/
'\/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/ \/
' enter the tangent circle diameter
cird = 1.2500
'
' enter the prefix name of the points
prfix = "POINT"
'
' enter the start point number of the point set
startpt = 2
'
' enter the end point number of the point set
endpt = 17
'/\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\
'/\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\ /\
'===================================================================
' \/ CONSTANTS - DO NOT CHANGE \/
'===================================================================
pd = GetActiveProbeDiameter()
pr = pd/2
cirr = cird/2
cirr = .625 - pr
endpt = endpt - 1
'===================================================================
' \/ EVALUATION - DO NOT CHANGE \/
'===================================================================
'
' extract values from the point on the right side
for i = startpt to endpt
x1 = GetFeaturePropertyAct(prfix & i, 1)
y1 = GetFeaturePropertyAct(prfix & i, 2)
'
' create the point on the left side as a mirror of the first point
x2 = x1 * -1
y2 = y1
'
' calculate the midpoint between the first two points
x3 = (x1 + x2)/2
y3 = (y1 + y2)/2
'
' calculate the distance between the first two points
q = sqr((x2-x1)^2 + (y2-y1)^2)
'
'calculate the x value of the tangent circle
outx = x3 + (sqr((cirr^2-(q/2)^2))*(y1-y2))/q
'
'calculate the y value of the tangent circle
outy = abs((y3 + (sqr(cirr^2-(q/2)^2)))*(x2-x1)/q)
'
' extract values from the next point in the sequence
x4 = GetFeaturePropertyAct(prfix & i+1, 1)
y4 = GetFeaturePropertyAct(prfix & i+1, 2)
'
' compare the distance between(x4, y4) and the tangent circle radius
' escape the loop when the dist is greater than the radius.
evaldist = sqr((outx-x4)^2 + (outy-y4)^2)
If evaldist > cirr Then
Exit For
Else
End If
next i
'===================================================================
' END
'===================================================================
Ryan Tackes
Applications Manager, VMS Inc.
http://www.vantagemeasure.com/

Bill K
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Re: Gear over pin diameter

Post by Bill K » Fri Mar 20, 2020 1:11 pm

Oh man, I know this post is old... But I can't help myself :)
I personally wouldn't do this. I don't know how tight your MOW tolerance is but measuring it without pins are going to give you erroneous results. Heck, dedicated gear analyzers with rotary tables and analog scanning heads will report tooth thickness and MOW but nobody in the industry goes by those reported numbers because they're not accurate. I've had this discussion with an instructor (school) on the AGMA board, engineers at some of the biggest names in aerospace.
Anyway, the reason I'm even here is that google found this thread when I was searching for something (I forget what). I currently have a gear on my CMM and I'm doing a MOW check and I'm using wires. We would use a mic (best results) but this thing is a 6DP gear with 100 teeth and a 16.5" MOW :) So with something this big a CMM with pins IS a good idea. But pins are used.

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