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How to inspect this feature? Arc on part with center off some distance

cosmos_275

Hot Rolled
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Jun 9, 2015
Can anyone tell me a good method for checking this feature? Is an optical comparator the best equipment to use shy of a CMM? What I've done before is turn a custom pin and use with with the height gauge to get the location, but that doesn't do very well for radius as finding a .005" discrepancy seems very iffy.

EX.jpg
(drawn in metric)

Anyone know a good book on inspection techniques? I've looked in my area for classes but can't find any.

Thanks
 
That's pretty big feature for a comparator. You're not going to be able to use an overlay.
You might have some luck by picking up 3 points on the radius and drawing it up on the computer.
Fit your radius to the points and see where the center comes out.
 
can you probe it on a machine? If not, you could put it on a mill, zero at the (theo) center of the arc, then pick up a couple points on the arc with an edge finder.
 
I have a Haimer 3D taster, but unless I'm missing something, I can only accurately pick up flat faces in X or Y (or z).

So, an overlay on a comparator would be for the diameter? I'd like to get one at some point. I imagine I could get three points with the comparator then throw it in CAD to find the measured center.

This is just an example. I see stuff like this from time to time doing job shop work and I'm trying to improve.

Thanks
 
You can pick up angles or arcs with the 3D Taster, you just have to account for the offset made by the probe diameter. If you were using cad and your mill as a cmm you would pick up 3 locations on the arc and draw a circle that is the probe diameter at each point. Construct an arc tangent to each probe tip circle and you'll have the radius and center location.
 
I’ve made my own overlays before. You could make one to check the radius but you won’t be able to check to the center because even at 10X the center of the radius overlay won’t fit on the screen. Some comparators have an edge finder attachment where you sweep across the shadow of the radius and it picks up the points and calculates the radius and center but I haven’t found them to be that accurate.
 
I had one inspector that would have dialed to the virtual center point, then measured from there to points on the radius. Comparator. If they didn't have a GeoCheck, they'd trig out the hypotenuse.
 
0.005" == 0.1 mm.
Any di swung at the right point should easily qualify 0.1 mm, much better usually.

Optionally, laser cut templates, even plastic, of under and net and oversize might qualify the part.

If the part is big, printing optical reference cards, and a good digital camera, could easily prove edge size/geometry.
Internal round ridge geometry is another thing.

Likewise, turning milling or laser a gage part in thin sheet steel might prove part size/form to 0.1 mm.
 
Can anyone tell me a good method for checking this feature? Is an optical comparator the best equipment to use shy of a CMM? What I've done before is turn a custom pin and use with with the height gauge to get the location, but that doesn't do very well for radius as finding a .005" discrepancy seems very iffy.

View attachment 265827
(drawn in metric)

Thanks

How many and what are the tolerances? What's the material and thickness?
 
How many and what are the tolerances? What's the material and thickness?

This is just an example. I see stuff like this from time to time doing job shop work.

Quantities are usually low.

Seems like next time I will chuck up a dial indicator, set the radius off a know edge (side of vise), go to theo center and sweep.

Thanks all for the input
 
This is just an example. I see stuff like this from time to time doing job shop work.

Quantities are usually low.

Seems like next time I will chuck up a dial indicator, set the radius off a know edge (side of vise), go to theo center and sweep.

Thanks all for the input

And what will you be measuring if you do that? You have 3 dimensions on your drawing.

There's an easy way to measure all three so think harder.
 
Can anyone tell me a good method for checking this feature? Is an optical comparator the best equipment to use shy of a CMM? What I've done before is turn a custom pin and use with with the height gauge to get the location, but that doesn't do very well for radius as finding a .005" discrepancy seems very iffy.

View attachment 265827
(drawn in metric)

This post annoys me. Before measuring tell me how this would be made.

Add to that the fact that the dimensions are without tolerances makes measuring senseless.
 
Gordon,
The op says within .005 (inches here I will guess from the ").
Let's assume milled profile and at 5 you'd want .001 or .0025 worst case on rad size and center location for a check.
How would you do it?
Not much of an arc there to do a three point pickup on either rad size or projected center.
Best fit 10 point means a special box or a lot of CAD work.
Just for giggles assume the OP has other parts with differing rad sizes and positions so special fit rolls or masters are impractical.
Bob
 
Gordon,
The op says within .005 (inches here I will guess from the ").
Let's assume milled profile and at 5 you'd want .001 or .0025 worst case on rad size and center location for a check.
How would you do it?
Not much of an arc there to do a three point pickup on either rad size or projected center.
Best fit 10 point means a special box or a lot of CAD work.
Just for giggles assume the OP has other parts with differing rad sizes and positions so special fit rolls or masters are impractical.
Bob

I think I'm repeating myself but I wouldn't "do it" with the information given by the OP.

Even as a theoretical question, which it is, I'd want to know more than just being given 3 dimensions.

I can certainly understand why you write "assuming" and "just for giggles" but I'm not going to assume or do anything for giggles. A drawing in metric and then a dimension (0.005") in inches.

I asked the OP questions but got no answers. I can understand why I haven't gotten an answer. It's all theoretical and as theoretical task I could give many options. I suggest he asks his teacher at school if he's in doubt.

What's drawn is something that going to be placed on or fit something so what is it that's important?

The distance from the edge for the arc radius?
The arc diameter?
Me? I'd want more dimensions than just those 3 plus tolerances.

IRL things like:
Quantity, material and material thickness, how it was made, etc., etc, would be known.
What is available to measure?
 
If it was a structural part, I would use d1 to check square, d2 to check radius, S1, S2, S2, S4 I hope are self explanatory. you could add a vertical (perpendicular to s3) layout to assist d2 location easy enough.rr.jpg
 
Easy to do with either a comparator or CMM with just the dims on the drawing, other than tolerance which was stated in the op. Material thickness and all that other stuff is irrelevant. Origin on lower left corner of the part (in this example). Move to theoretical center point of arc and re-zero. Measure straight line distance to multiple points at both ends and the center of the arc. I would do at least 5 points. If those measurements are within your arc radius callout and tolerance, you're good to go. If the numbers vary significantly from one end of the arc to the other, then the position (not size necessarily) of the arc itself is off. I have to measure quite a few parts like this at my day job on a regular basis.

Sent from my SM-N960U using Tapatalk
 
Gordon, I agree missing dimensions, like height and width. Forget tolerances or units, that is irrelevant on how to measure "this shape".
 
Gordon, I agree missing dimensions, like height and width. Forget tolerances or units, that is irrelevant on how to measure "this shape".

What you regard as "irrelevant" isn't irrelevant to me. It's the difference between theoretical and practical. Theoretically and practically there are many ways of measuring the part.

This thread is yet again one of those where somebody wants help but is too lazy (or worse) to give enough information to give a sensible answer.

I'm still far from certain what the "shape" is he's wanting to measure. Given tolerances for all 3 dimensions can alter "the shape".
 
I am trying to see how thickness maters. Assuming that all cuts are perpendicular to shape, and part is flat... but that is something that should be checked before going thru effort of shape checking.
I now am curious on how you change measuring thin (say paper thick) vs thick (1")? can we say 3" long x 2" tall? How that would differ from 3' x 2' or even 30' x 20'. +- 2 ticks on dial calibers or tape measure.
 








 
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