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Best procedure Profilometer usage? made a "jig"... did'nt work as planned...

Jeffers1

Plastic
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Sep 6, 2012
Location
South East WI, USA
Best procedure Profilometer usage? made a "jig"... did'nt work as planned...

2012-10-17_10-40-29_133.jpg2012-10-17_10-41-21_166.jpg2012-10-17_10-40-35_319.jpg2012-10-17_10-40-42_312.jpg2012-10-17_10-40-48_667.jpgLooking for advice, need to verify a 16ra (in) finish at a 1.125" Ø bore. Feel really good about the process and yield acceptable parts. Problem is it usually times takes passes with profilometer to get that acceptable reading. Is that fair and typical to everyone reading? So that said I designed and fabbed a "bracket or jig" with a Fowler Pocket Surf attached that aligns the "probe" the same every time location wise. That said I believe the probe is on center and aligned right where it needs to be and repeatable within .020 (probably .010"). Still get readings all over the place from 12-58 and everything in between (mostly 18-35)... This is a tough feature to produce Gray Iron casting, bore approx. 7.5" deep, but this isn't a 50 finish either. Customer agrees they have the same troubles verifying this finish and similar requirements on similar parts too that even they machine in house. Talked to another customer too about the situation and they too agree these finishes can be a challenge to verify and get consistent readings. I will try to post a pic of the Jig shortly.. Understand I probably need to achieve a 4-8 to be capable of a 16 but any insight or tricks otherwise would be appreciated...
 
I haven't used a Pocket Surf. Is it OK to use it in the vertical position? At least one profilometer I've used could only be used in the "normal" position, for similar reasons that most dial indicators can't be used upside down.
 
Not a bad idea, so I tried it results were; 19,20,30,63 in that order. That was attaching taking a reading, then loosen resnug and repeat 4x. The new plan is to machine this design into a larger plate that acually covers the surface of the part and align with "reamed" holes rather than the "slots" on the bracket that is shown. New plate should be here this morning and machined by noon. I'll update then... Anyone with any advice or history and resolve with similar situation I'm all ears...
Thanks again
Jeff
 
I had an application similar where I had a bore on the end of a face. I ended up ordering Mahr's Bore Adapter Kit EAS-2839. Then I put two holes in the face plates that lined up with some threaded holes on the face of the bore. Then I used some shoulder screws to locate the assembly on the bore face. I had excellent repeatability. *** This was in horizontal position, but should work fine in vertical as well ***

It seems that you're already using the shoulder screws and the knee should be fine. How is the PocketSurf attach to the knee?
 
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We attach our Mitutoyo to an old height gage and get very repeatable readings. Are you sure your unit is stable and rigid during use? I can't tell if you are just relying on gravity, or you have it clamped to the workpiece.
 
The ht. stand attachment is our typical setup too, but with the smaller Ø its so important to get the probe aligned and centered with the bore in question, I was certain this setup would be successful and repeatable. It is certainly a more ridgid setup than that of the ht. stand just not as consistent as I am aiming for. As luck would have it the 8x8 angle plate ordered didn't arrive either so the project will be on hold another day. I'm not overly confident it will improve the results but it won't hurt to try..
 
You should have better results when the angle plate arrives and you can accurately locate & ream two ( or three ) holes to locate on. Spring for the precision finished shoulder screws as well. Gauge location repeatability is one issue and actual surface finish capability is the other. If you can't put that profilometer back in the *exact* place every time, then you're fighting a losing battle ( or you're putting more pressure on machining that hole consistently).

Work with the gauge first. Get your new plate it and put on all snug, take a reading. Remove gauge & plate, put back on, take a reading. When these readings start to be consistent on the same part, you can prove repeatability of the gauge. Then you can start testing multiple parts, and prove reproducibility of the process.
 
Some dial indicators state that they should only be used in a vertical position with the indicating tip at the bottom.
I can't claim that you're wrong. I've never encountered such a restriction in over 50 years of working with these things, but I've not seen every product on the market.

If so, it's defective. You can never guarantee that the instrument is absolutely vertical, so using it will introduce an unknown and unquantifiable error in the measurement.

It should be replaced with a DI that's not defective.

- Leigh
 
It should be replaced with a DI that's not defective.
I'm sure Mitutoyo and Interrapid will be delighted to learn they have defective DI designs. Really, this is a documented behavior. Using a DI upside down is not guarantee to repeat properly because gravity is fighting the return spring.
 
I can't claim that you're wrong. I've never encountered such a restriction in over 50 years of working with these things, but I've not seen every product on the market.

If so, it's defective. You can never guarantee that the instrument is absolutely vertical, so using it will introduce an unknown and unquantifiable error in the measurement.

It should be replaced with a DI that's not defective.

- Leigh
This is from a Mitutoyo catalog, these are long travel indicators, but still, there is the warning.

vertical.jpg
 
I expect that restriction is due to the length of the stem and friction with the sleeve.

My previous comment was regarding normal 1" DIs, not long-throw instruments.

- Leigh
 
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Back to the surface finish repeatability. After re reading, I would say there may be a problem with your profilomiter. Seems like you are doing everything correctly, and you should get very repeatable results. Does it repeat if you measure a flat block with no fixturing required?
 
Yes, the profilometer repeats on a flat surface and too is accurate to the test plate.. FWIW we just happened to have our annual calibration circus and the profilometer got a pass... I think the biggest challenge here is related to the diameter (1.125") and finding that "sweet spot" in the bore... Could it be a matter of a different kind of "stylus/tip" on the profilometer or different type of profilometer altogether? Anyone have any luck finding support for their profilometer? I tried Fowler once and that seemed to be a lost cause.... I plan to try Mahr/Federal this afternoon and see if I might find a local Rep.... Hope to see the bigger angle plate today too and cut it yet this afternoon.. My mind still says if I place the probe the same every time, good or bad the results should repeat. Also shouldn't the "built in" play aid the probe to kind of fall into the tangent of the bore as long is it is placed relatively close? I feel I'm about as close as a guy can get..
Thanks
Jeff
 








 
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