TP-2 Pressure Settings - CMM Machine for Inspection of Parts

[Jeenan]

Hi every one, I have a little question for you all...

Here is a little explanation of the problem.....

We use CMM machine for inspection of parts with Renishaw PH-9 & TP-2
The Question is: AT WHAT PRESSURE TO SET THE TP-2??

- Renishaw set it @ .07-.08 newtons when they sell the TP-2
- It fits MOST of the application, BUT when we use long styli or extension or any strange set up, we may have FALSE TRIGGERING.....

So now, how do we make sure we have the GOOD pressure (without having too much...), who should set the pressure.....

One way we thought was:

- Determine how many turns (from completely unscrew) represent .07-.08 newtons
- The operator of the machine should make sure that BEFORE he uses the machine he got the good pressure, by unscrewing the pressure and apllying the amount of turns determine here above
- In case of FALSE TRIGGERING, he put a little more pressure (someting like 1-1.5 turns), Requalify the probe & try again for FALSE TRIGGERING.....

What do you think??
Are we looking too deep and trying to kill a mosquito with a nuclear bomb.....
Should we just put .10 newton for all test??
Should Metrology (when inspecting the machine) put back the pressure to .07 newtons and let the operator 'crank it up' as he needs it??

I hope I make it clear.....

A lot of questions but not much answers......

Thanks and have good & safe holidays........

 

[bobdoering]

Is it pressure or approach speed that should be adjusted to eliminate false triggering?

 

[True Position]

Your best solution might be to just look for light probes and balanced configurations if you can't get the false triggering down. QMark sells most of their items with graphite shafts that can help quite a bit with this problem.

 

[Jeenan]

Hi everyone......the question here is not to change ALL the instrumentation....

It's WHO should adjust the pressure???

Thanks!!!

 

[Sturmkind]

I would think that the CMM operator would be the one to set the pressure (ours are because of exactly the reasons you describe).

The Renishaw manual http://resources.renishaw.com/download/(ec15a1ef15cc4b03aba20570ba1e9020)?lang=en&inline=true states on page 15 that the factory setting is for general use but that pressure may need to be increased for long extensions or heavier probe. They have a very good illustration of the method for verifying Max./Min. pressure directions and show the use of a force gage which may save some time rather than guessing at turns (whose threads will wear over time).

I am not associated with Renishaw in any way.

It has been noted that the TP2 design is subject to both lobing and hysteresis (inability to return to the true original probe starting position). Renishaw claims that the design of the TP20 mitigates these issues but I have no personal experience or data with the TP20 series of probes.

I hope this helps!

 

[falconer65]

By classification, I would not have an operator assume that responsibility. Any qualified person you trust with the $$$$ probe can do it. A gage would give a number to aim for, but not necessary if common sense is used.

The pressure just has to be low enough it does not move or deform your parts. After every adjustment the probe would need to be re-certified. And it would be a good idea to check accuracy with a ring gage and jo blocks.

This is the brute force method. I assume from previous posts that you have troubleshooted other avenues.

I had a TP6 I wrung an extra year out of by turning up the pressure. What it really needed was replacement/rebuild. Due to the CMM being a constraint I was able to upgrade to scanning.

Good luck!
Erik