Looking for suggestions to QC a difficult profile

[Stu2011]

Hello all ,

I was hoping I could get a little advice regarding the measurement of a profile seen below:

I needed to find an efficient way to measure this shroud's inner profile. This shroud profile is seen below. The tolerances we want are within .005" of specification.

I guess my question is, what is the best tool I could use to accurately measure this curved profile? Is there a method I could use to quickly measure the profile with out a lengthly process? Our dilemma has been the impellers we use with these shrouds (the impeller's profile should match the profile of the 3rd picture) have occasionally failed because they rub against the shrouds during testing...I've been trying to think of ways to measure the shrouds to ensure their manufactured quality, but I'm stumped. Any help from the experts here would be greatly appreciated .

 

[Cornilsn]

Hello all ,

I was hoping I could get a little advice regarding the measurement of a profile seen below:

I needed to find an efficient way to measure this shroud's inner profile. This shroud profile is seen below. The tolerances we want are within .005" of specification.

I guess my question is, what is the best tool I could use to accurately measure this curved profile? Is there a method I could use to quickly measure the profile with out a lengthly process? Our dilemma has been the impellers we use with these shrouds (the impeller's profile should match the profile of the 3rd picture) have occasionally failed because they rub against the shrouds during testing...I've been trying to think of ways to measure the shrouds to ensure their manufactured quality, but I'm stumped. Any help from the experts here would be greatly appreciated .

The print specifies a profile of .003 to A and B.

Is that a casting you're machining?

 

[Stu2011]

The piece is CNC'd from just a large cylinder from what I understand. Yes, I believe the tolerance for that is 0.003.

 

[sfriedberg]

I'm assuming you don't have a CMM.

One thing you might try is making a male gage and using Plastigage (or similar) to measure shroud to gage clearance. That wouldn't work so well on the cylindrical section, but you could use conventional bore gauges or internal mics for that portion.

 

[xdmp22]

How about making a guage with 1/2" x 2" or 3" x "xx" aluminum like a giant fat radius guage....you could even drill and tap through it to accept travel dial indicators in a few places where the rub spots have been......

 

[Cornilsn]

The piece is CNC'd from just a large cylinder from what I understand. Yes, I believe the tolerance for that is 0.003.

You said .005 in your original post... which isn't to print I wasn't having a dumb moment!

Anyway, CMM is the best you're going to get. An offset profile with a go-no-go gauge would be my second idea but it won't be capable for that tight of a tolerance.

 

[litlerob]

How about making a guage with 1/2" x 2" or 3" x "xx" aluminum like a giant fat radius guage....you could even drill and tap through it to accept travel dial indicators in a few places where the rub spots have been......

I like this idea, if you could build a gage that located on three points that were datum points, (I.E. A and B) to sweep the contour with the indicator, that would probably be good enough, IMO that R1.516 dimension in relation to the profile call out is asinine, to .003"? Not realistic.

I would think the best, fastest and cheapest way to inspect this part would be to simply have a mating part (or the known interference points) on some fixturing that you can throw your part on spin the impeller around, and make function more important than dimensioning.

Robert

 

[litlerob]

The piece is CNC'd from just a large cylinder from what I understand. Yes, I believe the tolerance for that is 0.003.

By the way CNC cannot be used as a verb. Computer Numeric Control.

Robert

 

[winger]

Use an indicator in the mill spindle and plot it out with 2 axis movements.
Dave

 

[FranH]

contour gage

1. A piece of flat stock 1/8 by 10 by 4
2. Mill from center (5.0) out equally the minimum radius of the inside diameter as a step about .100 deep.
3. From that step mill a 75 mm radius on each side from c/L
4. Now we have a .100 step and a 75 mm radius extending 2.95 inches in X and minimum radius plus 1.97 in Y. (Continue thru to the end of the part.
5. Grind the contour so only about .05 is left for gage thickness at the 75 mm radius.
6. Drop the gage in the part and use shim stock on each end (the .100 step) to center it to the ID.
7. A 0.004 feeler stock cannot enter either end of the radius else you are out of tolerance.

Make a second gage as above with a 50 mm radius and a 0.004 feeler gage cannot fit anywhere between the top or bottom as the ends of the 50 mm will make contact and the center will be open.

Hope I made sense.

 

[litlerob]

1. A piece of flat stock 1/8 by 10 by 4
2. Mill from center (5.0) out equally the minimum radius of the inside diameter as a step about .100 deep.
3. From that step mill a 75 mm radius on each side from c/L
4. Now we have a .100 step and a 75 mm radius extending 2.95 inches in X and minimum radius plus 1.97 in Y. (Continue thru to the end of the part.
5. Grind the contour so only about .05 is left for gage thickness at the 75 mm radius.
6. Drop the gage in the part and use shim stock on each end (the .100 step) to center it to the ID.
7. A 0.004 feeler stock cannot enter either end of the radius else you are out of tolerance.

Make a second gage as above with a 50 mm radius and a 0.004 feeler gage cannot fit anywhere between the top or bottom as the ends of the 50 mm will make contact and the center will be open.

Hope I made sense.

But the profile tolerance of the radius(which is .003"), is to Datums A and B, what would the radius' contour/tolerance have to do with it (which is unspecified as .005")? .004" feeler gage or "shim stock" is not going to verify your zone, really you would still be far from it by at least 2 times.

Robert

 

[FranH]

contour

Found "A" assume "B" is the 2.383 dim.

Swap the dimensions so that the gage rests on surface "A" and ends at the 2.383 dim. A feeler stock (rounded tip) .003 should not fit. If it does than the elipse is incorrect or its placement is axially incorrect or the diameter at the 2.383 dim is incorrect. The gage will show that. The gage rests on surf "A" and at the 2.383 dim and the contour examined from there.

To do the left side reference the "A" surface, commence the gage at the 2.383 dim and do the contour. Again .003 gage and validate its shape (radially) and position (axially). As an example if the gage fits perfectly yet forces the gage up from surface "A" .02 then the position of the contour (not its shape) need attention.

Millions of blades and vanes are qualified in a similar fashion.

 

[WILLEO6709]

might be able to air gage it, but you'd have to be able to verify a go/nogo set standard, even if you had to hire someone with a scanning cmm to calibrate the standards.

 

[Stu2011]

Thanks for all the advice guys! I really appreciate the feedback.