Can someone tell me the best way to calibrate radius gages?

I don't know myself, but there should be some others here who can give practical help.

Hello Kat! Hello Hershal!

Welcome to the Cove! We're glad you dropped by.:bigwave:

Depending on the accuracy requirements on your instrument, it can get pretty tricky. Generally, you can place a calibrated ball with a known diameter on the measuring surface. What kind of instrument is it and what kind of accuracy is required?

Are you also measuring some kind of surface characteristics, or just radius?

Hello Kat! Hello Hershal!

Welcome to the Cove! We're glad you dropped by.:bigwave:

Depending on the accuracy requirements on your instrument, it can get pretty tricky. Generally, you can place a calibrated ball with a known diameter on the measuring surface. What kind of instrument is it and what kind of accuracy is required?

Are you also measuring some kind of surface characteristics, or just radius?

He's most likely referring to these things (http://www.freemansupply.com/StarrettRadiusGage.htm). If so, all you need to do is check them for damage periodically. They're cheaper to replace than to calibrate.

There are two approches I could sugest.
Use an optical comparitor or even a CMM to check them since they both have higher accuracy that the gauge.
With out either of these you could send them out for calibration ( must have a traceable baseline) and then using blueing lightly coat the radius surface and put in your calibration procedure for these that you will perform a visual inspection to verify the lack of wear as evidance by the blueing still being there and if the blueing is worn away you could then send it out (but might be cheaper to just replace it).
:2cents:

He's most likely referring to these things (http://www.freemansupply.com/StarrettRadiusGage.htm). If so, all you need to do is check them for damage periodically. They're cheaper to replace than to calibrate.

I agree with Jim. This type of stuff is easier and cheaper to replace than to "calibrate." Similar to tape measures. Use them for a predetermined time period, purchase new, discard old.

Stijloor.

I agree with Jim. This type of stuff is easier and cheaper to replace than to "calibrate." Similar to tape measures. Use them for a predetermined time period, purchase new, discard old.

Stijloor.

I also agree with Jim on this one. The radius gauges should be reviewed yearly for missing gauges or damage. That is it. If pieces are missing or a bit chewed up, then purchase a new radius gauges.

I don't agree with your thought on tape measures though. One could have a vernier caliper set at 1 inch, 6 inches and maybe another one set at 12 inches. The verniers have had their calibration confirmed using gauge blocks.

One would check the linearity of the tape measure using the veriers as the standard but make sure that they read the tape and not the vernier as I have seen some people try to do.

Also, on a tape, one should check whether the scales are legible and the ends are not loose or damaged.

Can someone tell me the best way to calibrate radius gages?

Hi Kat,

Welcome to cove.The easiest and cheapest way to calibrate radius gages (may or may not be the best)is to use a 'Profile Projector'.The same is also used for checking truency of thread profile. :cool:

CMM,in my opinion is not applicable,in absence of the third dimension. :notme:

Hope this helps.

Umang

Hi Kat,

Welcome to cove.The easiest and cheapest way to calibrate radius gages (may or may not be the best)is to use a 'Profile Projector'.The same is also used for checking truency of thread profile. :cool:

CMM,in my opinion is not applicable,in absence of the third dimension. :notme:

Hope this helps.

Umang

A "profile projector," or optical comparator, is indeed one possible method. I'm not sure about your comment about using a CMM, though. Just because CMMs are capable of measurement in three dimensions doesn't mean they aren't effective in two-dimensional measurement.

A "profile projector," or optical comparator, is indeed one possible method. I'm not sure about your comment about using a CMM, though. Just because CMMs are capable of measurement in three dimensions doesn't mean they aren't effective in two-dimensional measurement.

Well Jim,I am not aware,wheather CMM can be used in 2D also.I would definitely like to know the method of using CMM for 'Radius gage',and/or any other 2D profile.

Umang :bigwave:

Well Jim,I am not aware,wheather CMM can be used in 2D also.I would definitely like to know the method of using CMM for 'Radius gage',and/or any other 2D profile.

Umang :bigwave:

Just set the gage in a holder such as a vise, tell the software that you're measuring a radius or circle and take several points along the radius in question.

Just set the gage in a holder such as a vise, tell the software that you're measuring a radius or circle and take several points along the radius in question.

Sounds intresting,theoriticaly(to me,I may be wrong).
Could you please demonstrate the method,or explain the exact process of calibrating a radius gage using CMM? :confused:

Umang

Sounds intresting,theoriticaly(to me,I may be wrong).
Could you please demonstrate the method,or explain the exact process of calibrating a radius gage using CMM? :confused:

Umang

Do what I said earlier, then compare the result to the nominal size (and required tolerance) of the radius gage.

Do what I said earlier, then compare the result to the nominal size (and required tolerance) of the radius gage.

I am not able to comprehend what you are saying.
Could you please demonstrate the method,step by step,for calibrating a Radius gauge,using CMM.I would be greatful.

Umang

I am not able to comprehend what you are saying.
Could you please demonstrate the method,step by step,for calibrating a Radius gauge,using CMM.I would be greatful.


Do this:

Just set the gage in a holder such as a vise, tell the software that you're measuring a radius or circle and take several points along the radius in question.

I guess I should have finished that by saying, "Note the result."

Then this:

Do what I said earlier, then compare the result to the nominal size (and required tolerance) of the radius gage.

I don't know how else to explain it. Determine the actual size of the gage, then compare it to the nominal size, just as in any calibration process.

Added in edit: I think perhaps where you might be hung up is in the area of traceability, or the absence of a standard?

Our standard for a radius gage is when new and a visual each day of use by the user of the gage.

We calibrate them with the Optical Comparator when they are new and from there on the user checks them for wear, nicks, bends etc.

The internal auditor doesn't know if we can get by with just a "visual" on a TS audit.

We have verified they are good for at least 10 years. Maybe the best thing to do is just throw them away after ten years of use. What do you guys think?

Thanks for your suggestions.

Do this:



I guess I should have finished that by saying, "Note the result."

Then this:



I don't know how else to explain it. Determine the actual size of the gage, then compare it to the nominal size, just as in any calibration process.

Added in edit: I think perhaps where you might be hung up is in the area of traceability, or the absence of a standard?

Got your point.Thanks.
Umang :thanks:

Our standard for a radius gage is when new and a visual each day of use by the user of the gage.

We calibrate them with the Optical Comparator when they are new and from there on the user checks them for wear, nicks, bends etc.

The internal auditor doesn't know if we can get by with just a "visual" on a TS audit.

We have verified they are good for at least 10 years. Maybe the best thing to do is just throw them away after ten years of use. What do you guys think?

Thanks for your suggestions.

Does the new one comes with a certificate?If yes,then that becomes your trceable standard.Otherwise,you may use templates(drawn and filled-in with black ink).Long back I have used thread profiles,supplied by the manufacturer.You may enquire from the manufacturer of radius gauges.

'Just a visual',in my opinion,may not suffice.Others on the cove may opine on this.I feel you should periodically compare the ones in use,against a new set of gages or templates.Periodicity will have to be determined on the basis of your own experience.Normally once in a year is enough,but in cases of high usage,you may increase the frequency or may shift the cycle from periodicity to number of usages.

For example,calibration frequency of thread plug gages in my factory,use to be annual.Due to consistent quality problem,it was reduced from one year to six months then to three months.For most of the gages 3M cycle is fine,but in 20% cases the problem persisted.So for these I changed the system to number of usage,and it is working fine.

Hope this helps

Umang :cool:

Our standard for a radius gage is when new and a visual each day of use by the user of the gage.

We calibrate them with the Optical Comparator when they are new and from there on the user checks them for wear, nicks, bends etc.

The internal auditor doesn't know if we can get by with just a "visual" on a TS audit.

We have verified they are good for at least 10 years. Maybe the best thing to do is just throw them away after ten years of use. What do you guys think?

Thanks for your suggestions.

It seems to me as though you have got a reasonable approach here. What your internal auditor says has little bearing on the situation. Are they competent in this subject? If you perform enough optical verifications to build data, I'm sure a visual check, run a thumb nail around the profile etc. would suffice for a verification (not calibration) in between times. The use of radius gauges is not necessarily a very precise verification of a part anyway. I'd suggest that if it is, a quick trip to the cmm is likely to be more effective.
BTW - the first cmm's were only 2 D 'X' and 'Y' axis with no 'Z'. So they could be used to check a radius gauge.

Don't throw them away after 10 years. Put them on an optical projector or on the cmm and check them. I rather doubt they'll be off by much.......

Don't throw them away after 10 years. Put them on an optical projector or on the cmm and check them. I rather doubt they'll be off by much.......

Agreed. :agree1::yes:

My initial post on the subject had to deal with a totally different type of radius gauges. Namely, they were indicating-type meters that would ascertain the radius of different size material.

I am not familar with these more economical type instruments. Obviously the advice given on this seems to be fairly consistent, and a sound approach.

Like you Andy, I just can't bring myself to dispose of any instrument without taking some kind of readings first. Otherwise, it's possible to have been taking measurements with an instrument that contained error, but you would not know about it. As you stated, chances are they are not off, but you never know...

These are really good suggestions. The Quality Manager decided to leave our procedure as is but 1 1/2 years later the internal auditor gave us internal non-conformance for not addressing the problem. Looks like we will putting some of these solutions into action.

We are now faced with similar problems such as using:

Mandrels/arbors used for checking run out on Bench Centers
Gage wires for measuring dimension over pins. I don't know how we will ever control these.
Air plugs used on air amplifiers for checking bore diameters.

All of these are used for measuring/passing parts. Any suggestions on these?

Thanks
Kat.

We calibrate our radius gages mathematically using an optical comparator to trace a line (chord) from one point along the curve of the radius gage to another in order to define an arc, then measuring the height of the arc from the midpoint of the chord. Plenty of math pages with ways of determining the radius of an arc abound on the net, one such is http://www.mathopenref.com/arcradius.html.

The process is as follows: First mount the radius gage in a vise on the comparator so that the high point on the arc of the radius gage is at the top (think of a rising sun). Then pick a point on the left edge of the arc, and center the cross hairs on it. Zero the X-axis counter, then crank the X-axis horizontally to the right edge of the arc. Note the distance, this is the width of the chord (W). Now crank the X-axis back to exactly half the distance across the arc. Zero the Y-axis counter, then crank the Y-axis vertically to the top edge of the arc. This is the height (H) at the midpoint of the arc. Then plug W and H into the formula R=(H/2)+((W^2)/(8*H)) to get the radius.

Your method, and your optical comparator may vary, but the math is the same. I don't see why it couldn't be done with a CMM for larger radiuses.

Of course, the uncertainty of the radius would be based totally on the measurements W and H, i.e. take the uncertainty of W and H and run it through the same formula to get the uncertainty in terms of the radius. The larger the "bite" into the arc, the more length you have to work with above the uncertainty of the optical comparator.

The only problem with this method is that it assumes that the arc is "perfect" and doesn't take into account any wear; for instance, if there's a flat spot between any of the edges that are being measured. In this case it's better to do a visual inspection, i.e. mate it up to a known good master radius gage, or lay a circle template drawn by a compass on the optical comparator screen, etc.

Thanks to everyone for all the wonerful suggestions. Just as soon as I thought I was going to put these solutions to work, the Quality Managers got the internal auditor to drop the non-conformance. I hope they know what they are doing. I will keep these in my file just in case the TS auditor nails us for it. Thanks again for all your help!

Kat