How to measure face of a cone on a surface plate

JC Price · Apr 14, 2018

Please see sketch below of a part I am making on a manual lathe in small quantities from 304 stainless. There are two critical dimensions, the diameter of the upper circular face and the taper angle. The tolerances are shown on the sketch. Currently these dimensions are being measured optically but I would like to develop an alternative method using hard gauges on a surface plate. What is the best way to do it?

dcsipo · Apr 14, 2018

JC Price said:
Please see sketch below of a part I am making on a manual lathe in small quantities from 304 stainless. There are two critical dimensions, the diameter of the upper circular face and the taper angle. The tolerances are shown on the sketch. Currently these dimensions are being measured optically but I would like to develop an alternative method using hard gauges on a surface plate. What is the best way to do it?

View attachment 225763

Why not make a hardened lapped female version of the taper and just blue it up and rub it on the part? Don't even have to remove it from the chuck to check. You can detect errors on the order of film thickness of the blue.

dee
;-D

JC Price · Apr 14, 2018

dcsipo said:
Why not make a hardened lapped female version of the taper and just blue it up and rub it on the part? Don't even have to remove it from the chuck to check. You can detect errors on the order of film thickness of the blue.

dee
;-D

That's a neat idea, but I would still have to measure the critical dimensions of the female version, which seems harder. It would be nice to be able to measure the part on the lathe. So far I have avoided doing that by using a custom step collet on the lathe.

Renardiere · Apr 14, 2018

If you hold a tight tolerance on the overall diameter and length of the component you could make a gauge which is bored to a good fit to that diameter. Drop a small ball bearing of known diameter down into the angle between the vertical wall of the gauge and the slope of the cone. Use a depth gauge to measure the height of the ball relative to the height of the component. Can then use trig to confirm the angle of the slope of the cone and therefore the diameter of the truncated face.

JC Price · Apr 14, 2018

Renardiere said:
If you hold a tight tolerance on the overall diameter and length of the component you could make a gauge which is bored to a good fit to that diameter. Drop a small ball bearing of known diameter down into the angle between the vertical wall of the gauge and the slope of the cone. Use a depth gauge to measure the height of the ball relative to the height of the component. Can then use trig to confirm the angle of the slope of the cone and therefore the diameter of the truncated face.

That seems like another interesting idea, and it could be done with the part on the lathe. I do have a tight-tolerance right cylinder before I start cutting the taper. I think it would be necessary to measure the depth of two balls of different sizes relative to the circular face. I won't be able to infer both the taper angle and the face diameter from one depth measurement.

Larry Dickman · Apr 14, 2018

make a set up part and bore a 1/4 hole in the center of the face. Put the part on a sine plate with a tooling ball in the hole and measure down to it.

JC Price · Apr 14, 2018

Larry Dickman said:
make a set up part and bore a 1/4 hole in the center of the face. Put the part on a sine plate with a tooling ball in the hole and measure down to it.

I understand that I could mount the bottom face of the part on a sine plate set to the complement of the taper angle, and then slide an indicator mount around on the surface plate to check the taper angle. Sorry, I don't understand what you are saying about the tooling ball.

Larry Dickman · Apr 14, 2018

JC Price said:
I understand that I could mount the bottom face of the part on a sine plate set to the complement of the taper angle, and then slide an indicator mount around on the surface plate to check the taper angle. Sorry, I don't understand what you are saying about the tooling ball.

take a sketch like this

add a tooling ball to the face, and rotate the part on a sine plate like this,

drawing it up in cad makes it easy. obviously the dimension you need is going to depend on the dimensions of the tooling ball you use and the dimensions of the part.

JC Price · Apr 14, 2018

Thanks very much Larry, I think I see now what you are getting at. First, I mount a tooling ball exactly on the part's axis either resting on the face or a known gap from the face. Then I put the part on a sine plate and check that the upper surface of the taper is level, thus measuring the taper angle. Now I measure down from the upper surface of the taper to the ball and with some trig I can compute the face diameter. This all makes sense, but I don't see a good way to mount the ball exactly on the axis while leaving the side of it clear for the depth measurement.

JC Price · Apr 14, 2018

Maybe the simplest approach would be to combine the two methods suggested above and do the measurements in two steps, as shown in the sketch below. In step 1, I just put the part on a sine plate and measure the taper angle. I don't think this really has to be done on every part since it is determined by the lathe compound angle and probably won't drift much as long as the setup is not changed. In step 2, I put the part in a close-fitting bore and put a ball between the bore ID and the taper, then measure the ball depth relative to the circular face. Only one ball size is needed since the angle is already known. That is a simpler fixture to make than one that holds the ball on the axis.

dcsipo · Apr 14, 2018

JC Price said:
That's a neat idea, but I would still have to measure the critical dimensions of the female version, which seems harder. It would be nice to be able to measure the part on the lathe. So far I have avoided doing that by using a custom step collet on the lathe.

You could make one precise version of the male part and lap the female part to it then use it to verify the others. You have an optical comparator to get the first male part right.

...I would not bother with this method unless I had more than a dozen to make.

dee
;-D

Gordon B. Clarke · Apr 15, 2018

JC Price said:
Please see sketch below of a part I am making on a manual lathe in small quantities from 304 stainless. There are two critical dimensions, the diameter of the upper circular face and the taper angle. The tolerances are shown on the sketch. Currently these dimensions are being measured optically but I would like to develop an alternative method using hard gauges on a surface plate. What is the best way to do it?

View attachment 225763

I notice you give your profession as "professor" in your profile.

When I see your drawing I believe that you are.

http://www.practicalmachinist.com/vb/search.php?searchid=15047389

What would you even want to use something like that for?

Larry Dickman · Apr 15, 2018

JC Price said:
Thanks very much Larry, I think I see now what you are getting at. First, I mount a tooling ball exactly on the part's axis either resting on the face or a known gap from the face. Then I put the part on a sine plate and check that the upper surface of the taper is level, thus measuring the taper angle. Now I measure down from the upper surface of the taper to the ball and with some trig I can compute the face diameter. This all makes sense, but I don't see a good way to mount the ball exactly on the axis while leaving the side of it clear for the depth measurement.

By tooling ball, I'm referring to something like this

Tooling Balls - MSCDirect.com

very easy to mount.

JC Price · Apr 15, 2018

Gordon B. Clarke said:
I notice you give your profession as "professor" in your profile.

When I see your drawing I believe that you are.
What would you even want to use something like that for?

Gordon, a sketch is a sketch, right? At least I did not upload a picture of a napkin :-) Half-time physics professor these days, and otherwise various R&D projects in my own shop/lab. This is related to a commercial project, so I can't explain the details, unfortunately.

Larry, thanks about the tooling ball. Got it.

Gordon B. Clarke · Apr 15, 2018

JC Price said:
Gordon, a sketch is a sketch, right?

What I was referring to in my post were your tolerances. Completely unrealistic especially with regard to how you intend making the "item".

±0.05º (3 minutes) and ±0.001". Have you even given thought to the measurement accuracy required?

This is just a sketch, right? Try making it. Make them as a solid and I'll buy one

JC Price · Apr 15, 2018

I have already made parts like this to tolerance, Gordon.

Ox · Apr 15, 2018

Personally I can't warp my head around trying to use a depth mic or whatnot in the machine - see'in's how you only have .001 total, and you are working with componants with some amount of slop...

I would likely lay it down on the flat table (ground plate would be fine - it doesn't need to be a fancy hunk of rock) and use dowel pins and measure it like a dovetail. May need to clamp the part down if it's not heavy enough.

Make sure to use one tool for all 3 surfaces, and once you have figgered out, you should be able to monitor by checking the OD frequently.

---------------------

Think Snow Eh!
Ox

JC Price · Apr 15, 2018

Ox said:
Personally I can't warp my head around trying to use a depth mic or whatnot in the machine - see'in's how you only have .001 total, and you are working with componants with some amount of slop...

I would likely lay it down on the flat table (ground plate would be fine - it doesn't need to be a fancy hunk of rock) and use dowel pins and measure it like a dovetail. May need to clamp the part down if it's not heavy enough.

Make sure to use one tool for all 3 surfaces, and once you have figgered out, you should be able to monitor by checking the OD frequently.

---------------------

Think Snow Eh!
Ox

Yes, I like that. May as well use the surface plate since it's sitting there next to the lathe anyway. So put it face down on the plate, roll gauge pins in from either side and measure across them with a mic. If the taper is known and the pin diameter is known that gives the face diameter in one measurement without any close-tolerance fixture needed. It also does not depend on the OD of the part, only the critical dimensions that I actually care about. Sweet.
PS. Don't warp your head.

Ox · Apr 15, 2018

No - it is not dependant on the OD, but if you use one tool for all 3 surfaces - once you dial in your OD to your taper/face interface, then you can check the OD much quicker for any variations. Not saying that you wouldn't maybe make some dowel pin checks along the way, but you could check every 20th part with the dowels if you watch the OD more frequently.

Say another way:

If all surfaces done with one tool - any change in the feature that you are looking at - will also show up on the easier to measure surface.

Also - you would prolly want to drag a file or a stone over the face of that part so's it's not rocking on a face-off tit.

----------------------

Think Snow Eh!
Ox

Gordon B. Clarke · Apr 15, 2018

JC Price said:
I have already made parts like this to tolerance, Gordon.

So how did you measure them and with what?

How to measure face of a cone on a surface plate

Aluminum

Diamond

Aluminum

Aluminum

Aluminum

Titanium

Aluminum

Titanium

Aluminum

Aluminum

Diamond

Banned

Titanium

Aluminum

Banned

Aluminum

Diamond

Aluminum

Diamond

Banned

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