Repeatable method to measure a taper on a part


Tim Mosher

Hello, this is my first time in this forum, so please forgive any blunders I may make.
I am seeking advice on a repeatable method to measure a taper on a part. It is a 3 degree taper, and I must hold a .1043 to .1053 range when outside diameters are measured, over a 1.000 inch range. The diameter at the large end of the taper is .6880, in case this helps.
Optical comparators just are not cutting it, and neither is a sine bar technique, using a tenth dial indicator. I am by nature an ndt specialist, and dimensional is not my forte'. Any suggestions? I work for a very small company, so buying a cmm is out-lol
Thank you!--By the way-if anyone needs feedback on an ndt question, I would be glad to help

Thank you all for your replies. We came up with a different method of measuring this taper, and it seems to be working rather well. We manufactured an internal 3 degree taper to match the part being inspected.(Visualize it as a hollow cone)Then we wire-edm-ed slots the exact width of the blades of our digital blade mics, exactly 1 inch apart. We slide this cone over the part,then we simply take the diameters obtained with the mikes, and subtract the difference to get our tolerance reading. Our customer still thinks an optical comparator with auto edge detection is the correct method to measure this, but I have been reluctant to agree with him that his method is as repeatable, or as accurate, as ours, so, an R&R study is underway.(He refuses to perform one on his comparator for this part, but he IS the customer!)

[This message has been edited by Tim Mosher (edited 11 June 2000).]

[This message has been edited by Tim Mosher (edited 05 July 2000).]

Jerry Eldred

Forum Moderator
Super Moderator
I'm not really a dimensional guru, so I will 'officially' pass on giving advice (don't want to give bad advice). My first thought was CMM. But you mentioned it was cost prohibitive.

I'll try to at least take a stab at a couple of thoughts (but PLEASE take these with a grain of salt).

My other thought was some sort of go-no-go fixture at uper and lower spec limits, and have a subcontractor measure a couple of standards with a CMM, and have that periodically calibrated.

I'm being deliberately vague because without seeing visually exactly what you are measuring, it is difficult to envision accurately your need. If there is something visual you could email me, I'd be happy to show it to some of our dimensional gurus and see what they think. email at: [email protected]



Use gage pins ( Rolls )
This is defined in the Hand Book if you need more help

Tim Mosher

Thank you both for your replies.
I will seek to get permission to send a photo of the part to you Jerry. As this is a customer's part, and since it is a biomedical product,(they are a very proprietary lot-lol) I'm not sure I will have much luck.
Carl, I never thought about gage pins, but I will investigate this methodology further. Thank you.

[This message has been edited by Tim Mosher (edited 12 June 2000).]

Atul Khandekar

You could use something like a Tool Presetter instead of a CMM. Most tool presetters have an RS 232 compatible outputs. It is very easy to develop a small software program to acquire readings from the instrument.( Probe radius compensation etc etc handled through software) With these readings you can then do all kinds of statistical / graphical analysis.

The overall cost of this solution (presetter + computer + software) would work out MUCH CHEAPER that a CMM.

Hope this helps.


Paul Williams

You might try using thread wires. You would probably have to come up with a jig to hold the wire centerlines in a plane perpendicular to the centerline of the taper, and a micrometer type slide to index either the part or the wires along the centerline of the taper. You can then calculate the taper diameter based on the thread wire diameter and the geometry of the part. The jigs shouldn't cost more than three or four hundred dollars.
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