[Fish]

Has anyone here made a CMM? I've looked at MaxNC's stuff - could be a good starting point. I've got two spare Renishaw probes kicking around...hmmmm. Any feedback? Anyone interested in getting involved?

[Klox]

Fish,
I'm sorry to sound like freshly baked bread, but whats a CMM?

Klox

[Jennifer]

Coordinate Measuring Machine...freshly baked bread sounds better...

[Wjman]

Klox,
A CMM is a Coordinate Measuring Machine, we use one at work to measure components or possibly a repair job on a press tool that we did not make in the first place.
Mark...

[cbcnc]

Hi,

So let me ask a question about a CMM; I already know about FBB and it does sound good.
Would you use a probe that has a make or break contact and use your software to read out the coords? Then what do you do with the coords? How would you save them and use them?
Or would a probe attached to an encoder and a seperate input work?
I really know nothing about them and I've thought I might like to experiment.

Thanks,
Chris

[Wjman]

Hi there,
With our CMM we have a software package that allows us to measure Distances X,Y,Z, Radii, circumferences, Angles, from a certain datum (Resettable at anytime), pretty much anything you can think of. When we "Digitize" a workpiece, the coords are stored by the software, and then we can input them as a series of points and basically "join up the dots, rads, angles, or whatever" We have still to work out how we might save them as a DXF of points, but our method seems to work.
BTW the probe seems to be a make or break contact, when it is "unarmed it moves rapid" but when it is "Armed" it is ready to sense the slightest touch, stop, and then record it.
I don't know how accurate a probe attached to an encoder and a seperate input would work.
I've just been watching the guy service our CMM, And from what I can see the whole assembly runs on air bearings (Basically air pushed through grooves in feet at the bottom of the "Y" axis which meet the granite table), sort of like a hovercraft. Both axes are driven back and forth by a series of bearings which are set at (looks like 2 angles) to a rotating rod, which spins CW/CCW creating backwards and forwards motion.
Forgive me for my ignorance but what is "FBB?"
Mark...

[cbcnc]

Thanks Mark.

FBB - Freshly Baked Bread

Very interesting.
So a CMM is a dedicated machine for measuring. Is the mechanism a combination of XYZ and vector or just XYZ that can be interpolated to angles, radii and so on?
What kind of accuracy can you expect? It sounds pretty tight if you are using granite, air bearings, etc.
I wonder if someone could point me to some pictures on the web?

Chris

[Klox]

Hey guys the term i know for CMM is "digitise". Sorry for the language barrier....South African English, British English and American English are for sure 3 different languages...LOL

May your FBB's taste very deliciously today!!!

Klox

[Klox]

Toast avaible also!

(flame2)

LOL!!

Klox

[cbcnc]

:cheers:
Here's a toast in any language! Got any good beer in Pretoria?


Chris

[Klox]

Yes! and Malt!

Klox

[abasir]

cbcnc,

Here is the link out of Google
http://www.mitutoyo.com/Products/cmm/literature.html
lookup the Crysta Plus datasheet for some detailed pictures, etc.

[Wjman]

Chris
FBB,
DOH!, I wouldn't mind but I read the post and never clicked.
The mechanism is a combination of XY and Z, and the software has assorted functions that can work out angles, rads etc. As for the accuracy, I guess it could be accurate to a few microns
(=/-0.005mm) in the right conditions. Although not in our shop, what with all the dust. BTW Hi Klox!,
Mark...

[Wjman]

Also check this page http://www.cmmxyz.com/70CC/404.html
It looks like our exact machine.
Mark...

[Fish]

Hey Wjman,

CMM's will give you a cloud of points, referenced to whatever datum you choose. Some CAD/CAM packages can take the "cloud" and create a solid from it. Think of reverse engineeering. Remember that the points are actually from the centre of the ball on the end of the probe used to measure, so the resulting part is bigger. Once the solid has been created, ann offset of the surface is done to achieve the actual size.

A good CMM, in a temperature controlled and dust free "Clean Room" will be able to reliably measure to an accuracy of 0.0002", day in, day out.

Hey, if you can't measure it, you can't make it.

My question still remains though, has anyone made, or thought of making a CMM.

Fish

[balsaman]

Gang,

I reopened the thread. Not sure how it got closed. Mods, if it was closed for a particular reason let me know. If not, it stays open.

Carry on. Don't mind me.

Eric

[SRT]

.

[cbcnc]

Wow, CMM's are way more sophisticated than I imagined. Thanks for the education guys. I think that I want the Brown and Sharpe "Alpha Gantry".
http://www.cmmxyz.com/25CC/333.html

Chris

[Klox]

CBCNC,
I checked out the link, the Brown & Sharpe looks impressive! It looks a bit small to me! (just joking!). Now that we are back on track on the topic of CMM's, let's not get side tracked again....

As far as i know CMM's measure by means of a probe, i know some measure by laser. What's the pros and cons of each type?
Let's say cost, accuracy, etc.....

Klox

[balsaman]

Originally posted by SRT
Message wouldn't delete, again?

I am pretty sure the user does not have the ability to delete his own posts. Only Moderators can delete a post, and we generally don't/won't.

Eric