calibration of CMM using gage blocks?

[DrEaMcMm]

hi,
i hav trimek CMM,the problem is that its measuring the 500mm gage block's nominal value as 500.012 and the actual or measured value is 500.022.can anybody tell why its nominal value is not exact 500mm or close to it?
2nd question is that i wanna compensate ma CMM using gage block.can anyone guide me wat to do?please reply soon

[Matthew D. Hoedeman]

DO NOT TRY TO DO ANYTHING ON YOUR OWN. Anything you do will more than likely mess it up. If you think it needs to be 'adjusted', that is called a CALIBRATION and you MUST have a qualified company come in and do that for you.

Anyway, a 500mm gage block and it is only checking off by 0.010mm? Your machine is not that accurate, don't worry about it.

[Underspec]

Gage blocks have tolerances which are certified to (Check your calibration cert). Mine are +/-.00005". Another note to remember is that some CMMs are not as accurate. My gage blocks were certified using a Laseruler. That being said, your CMM would have to be accurate enough to measure something with that kind of tolerance to really get an accurate measurement. Use the 10-1 rule.

[Matthew D. Hoedeman]

Also, just because at 500mm it is checking +0.01mm does NOT mean that at 250mm it would be checking +0.005 (1/2 at 1/2 tjhe distance). It might check -0.01mm at 250mm. One value is not acceptable for determining the quality of the calibration of the CMM.

[#2#]

hi,
i hav trimek CMM,the problem is that its measuring the 500mm gage block's nominal value as 500.012 and the actual or measured value is 500.022.can anybody tell why its nominal value is not exact 500mm or close to it?
2nd question is that i wanna compensate ma CMM using gage block.can anyone guide me wat to do?please reply soon

I believe, the nominal is just a "guess" that PC-DMIS makes. You can edit that to be whatever you want.

The measured value is what you should look at. You don't have any details as to how you measured this gage block (alignment, type of features measured, etc.). If you are not happy with the 500.022 measurement perhaps you could get a better measurement through programming.

What Matt said about calibrating it yourself. Do not try it. It is, however, a good idea to occasionally run that gage block program between calibrations to make sure nothing has changed.

[DrEaMcMm]

gage blocks

tanxs 4 the reply..i also measured 500,400,300,200,150mm gage blocks and the error in reading is linear i-e small in small gage blocks and big in bigger blocks.i am jus worried abt its accuracy.cant we do the calibration at our own?

[Wes Cisco]

tanxs 4 the reply..i also measured 500,400,300,200,150mm gage blocks and the error in reading is linear i-e small in small gage blocks and big in bigger blocks.i am jus worried abt its accuracy.cant we do the calibration at our own?

No! ! ! Unless you have been trained and fully understand how error maps are generated and altered, you are only going to make things worse. Probably much worse!

[Matthew D. Hoedeman]

tanxs 4 the reply..i also measured 500,400,300,200,150mm gage blocks and the error in reading is linear i-e small in small gage blocks and big in bigger blocks.i am jus worried abt its accuracy.cant we do the calibration at our own?

That could be due to the temp. in the lab and the temp of the blocks. You have no way of knowing. What temp were trhe block measured at? What temp was teh CMM calibrated at? What temp are the blocks now? What temp is the CMM now? The list is endless. Don't try this at work!

[dwade]

I agree with all of the posts concerning the measurment error on your gage blocks and for "self calibration". Make sure that when you schedule for a service tech to come in for your next calibration to use the "enhanced" calibration method and not the basic. Then your linear measurements should be better. Ball bar calibrations do not measure for linearity, only for squareness of your CMM.

Duane

[JoeRZ]

I would take these guys advise if I were you - They know their stuff.

Also I hope your facility does not get audited because in order for your shop to be able to perform high level validation - need certification. Consider enviroment control issues + traceabilty to a known standard issues all that good stuff.

I would find some qualified techs to do all those.

Joe

[DrEaMcMm]

if the CMM is so sophisticated then how can it be so accurate?and how can i check the squarenss, perpendicularity of ma CMM?

[justncredible]

a laser is used to check that, you can do it, buy a laser and tone arm set, then map the table.

[DrEaMcMm]

actually the company has compensated it but unfortunately we hav 2 shift it on other site..all dese complication are coming after the shifting ....i neeed some document gudience for measuring perpendicularity of ma machine using square granite blocks..

[justncredible]

set the block on the table use the table as a plane and then use the block side as a plane and check it that way. Which is great if the blocks have a known value for perpendicularity to the sides, all 6 sides have to be a known.

That will not tell you anything about the mapping of the machine and if it is in spec, get a tone arm.

[DrEaMcMm]

jus consider me a infant to CMM,i hav given the task of operating it..how can i know that ma machine has gud repeatability?how can i know the value of perpendicularity to the side..weather its ll be given in certificates? or where?