Extended tool holders for probes?

[Bob W.]

I am starting to do more mutliaxis probing and I am running into spindle clearance issues when trying to probe certain features at extreme angles. Does anyone know of extended holders for probes? My current probe tool holder has a gage length of about 1.5" to the probe interface. I know I could just go get a longer stylus but I would be sacrificing accuracy in the process. I am looking for a gage length of 3-4" to the probe interface.

[THEE THAINZ™]

 If your using an OMP60M 200mm extension P/N is A-4038-1028 cost is around $840.00   OMP 40 and 400 do not list any extensions. Western is an authorized RENISHAW dealer.

[Bob W.]

I ultimately need three of these. If there isn't something off the shelf I will probably just buy Command cat40 tool holder blanks and make them myself. I am surprised these aren't more common. I did check with Western first and Parlec quoted it as custom with the price a little higher than you mentioned above.

[MIL-TFP-41]

Pretty easy to homebrew your own....get one of THESE & cut to suit. very easy geometry to duplicate.

 

[Mgrenier]

I don't know about your probe but Renishaw has some adapters that mount on C8.  Our OMP60 and RMP 60 have that.  You can than just add capto extensions.

 

HTH

[GoetzInd]

 

 

I don't know about your probe but Renishaw has some adapters that mount on C8.  Our OMP60 and RMP 60 have that.  You can than just add capto extensions

 

Good idea. Would probably do C4 though for clearance and cost though.  Having a few cat40 to c4 adapters and extensions would be nice to have in other situations as well.

 

Mike

[THEE THAINZ™]

   There are Long carbon fiber stems with Ruby, Stainless extensions, or Carbon fiber extensions in the length you mentioned from RENISHAW. Do you have M2,M3 M4 or M5 styli? The price ranges from $110.00 to $420.00 depending on what you want and which styli.

[Bob W.]

There are Long carbon fiber stems with Ruby, Stainless extensions, or Carbon fiber extensions in the length you mentioned from RENISHAW. Do you have M2,M3 M4 or M5 styli? The price ranges from $110.00 to $420.00 depending on what you want and which styli.

The longer the stem, the less accurate the probe. I don't want to sacrifice accuracy so I want to keep the probe stylus the same length and move the probe out further.

[crazy^millman]

The longer the stem, the less accurate the probe. I don't want to sacrifice accuracy so I want to keep the probe stylus the same length and move the probe out further.

 

Spoken like someone who gets the real idea. Seen carbon fiber shafts bend. I only recommend ceramic shafts for machine probes.

[Bob W.]

I liken it to installing a 3" tip on a dial test indicator. If the original accuracy of the test indicator was .0001" with a 1/2" tip the accuracy just dropped to .0006" with a 3" tip...

[THEE THAINZ™]

Great analogy, I have just started down the road of probing and it's times like this that I enjoy visiting this site. Lots of good info with helpful advice. I've been fortunate to date to have both help from the forum and good contacts made over the years to help me stay on track

[Joe788]

I liken it to installing a 3" tip on a dial test indicator. If the original accuracy of the test indicator was .0001" with a 1/2" tip the accuracy just dropped to .0006" with a 3" tip...

 

I think it also depends on what probe you have. I remember sitting in on a Renishaw seminar years ago, where they explained the MP700 strain gage probe was created for just this reason. The gage length on all of our MP700s is right at 10 inches. 6 for the probe and 4 for the stylus, and we don't see any problems.

[crazy^millman]

I think it also depends on what probe you have. I remember sitting in on a Renishaw seminar years ago, where they explained the MP700 strain gage probe was created for just this reason. The gage length on all of our MP700s is right at 10 inches. 6 for the probe and 4 for the stylus, and we don't see any problems.

 

Joe the problem you can run into with longer probes is false triggers. When you go to probe you need to run slower with a long probe. The shorter the probe the faster you can do the probing process. The mass of the probe itself can interfere with probe hits. Why it is always best to calibrate your probe at the speeds you take your probe hits. Funny people will go by the recommended 5 imp when calibrating their probes then go off probing on a machine at 40 to 100 imp and say yes we are getting good results. Really? So you calibrated your probe at 100 ipm and checked your NIST traceable artifact in the machine at those speeds and got the same results at 5 imp with a very long probe? Not trying to say you are not seeing everything Joe, just making a general statement about things I have seen done over the years that can lead to getting wrong or misleading answers.

[Joe788]

Joe the problem you can run into with longer probes is false triggers. When you go to probe you need to run slower with a long probe. The shorter the probe the faster you can do the probing process. The mass of the probe itself can interfere with probe hits. Why it is always best to calibrate your probe at the speeds you take your probe hits. Funny people will go by the recommended 5 imp when calibrating their probes then go off probing on a machine at 40 to 100 imp and say yes we are getting good results. Really? So you calibrated your probe at 100 ipm and checked your NIST traceable artifact in the machine at those speeds and got the same results at 5 imp with a very long probe? Not trying to say you are not seeing everything Joe, just making a general statement about things I have seen done over the years that can lead to getting wrong or misleading answers.

 

I'd have to go look, but I think our second touch is 2.4ipm.  You're right about those false triggers though. On some programs we have to put a 1 second dwell after the initial rapid move, or it'll trip the protected positioning.

[crazy^millman]

Well most probing routines will only allow the real probe hit to be taken a slow speed it is the approach hit that tells the cycle about where to take a hit and then the 2nd hit is the real hit taking by the cycle. I talking a little off topic about it, but like to make people think about the process throwing out off the wall ideas. We sometimes need to get out of our comfort zones and see do we really understand the process or are we just thinking we understand it?

 

Anyone who knows probing cycles will see that response and go he is off his rocker, but those that think they know will go hum yeah that makes perfect sense.

 

Sorry just how I like to get people to think. Helps me to have off the walls ideas and see where they might lead.

[specv]

I guess I will have to disagree with this analogy:

 

I liken it to installing a 3" tip on a dial test indicator. If the original accuracy of the test indicator was .0001" with a 1/2" tip the accuracy just dropped to .0006" with a 3" tip... 

 

A indicator is made to accept a certain length stylus and has a gear ratio that is calculated for that length. so if you change the stylus length on a indicator and don't change the ratio then of course you will change the accuracy.

 

Now a machine probe is different, when you change the probe length (stylus) you re-calibrate the probe and give it new values. so if the probe flexes, it will flex the same each time with each hit. we use 6+ in styli in our machines and hold .001 tp on probed diameters that were cut from previous lathe ops daily.  

[specv]

Bob, what is the model of your probe?  

[Bob W.]

Bob, what is the model of your probe?

Renishaw OMP-400. I wouldn't be concerned about the probe tip flex. The issue that drives the inaccuracy is the precision and repeatability of the probe's trigger mechanism. If the probe repeats to .00005" with a 2" stylus the best it can repeat to with a 6" stylus would be .00015". This is the same with the test indicator where the internal gearing inaccuracies and periodic errors will be magnified with a longer indicator tip. I know it is splitting hairs but I would prefer to move the probe out in lieu of a longer probe tip. Just a matter of preference.

[The Cathedral]

I think you're on the right track for your probe. Like Joe788 said, the strain-gauge model is designed to overcome this, but you have the triple mechanical trigger model (which is what we have here as well.) When I was researching probes, the renishaw salesman showed me an accuracy graph on the mechanical model. It was tri-lobed--when you hit a point that was "between" two triggers, your accuracy would drop. Add in extra length and it drops even further. The accuracy of the strain gauge was a much better, more circular readout, but they are priced for their accuracy.

[specv]

That makes sense Bob. According to the Renishaw website the OMP400 is a strain gage style. or it that just the new version?

[THEE THAINZ™]

The OMP60M is a modular version of the OMP60. It has interchangeable extensions that fit between the transmission module and the probe module. It comes in lengths up to 200mm. This would allow you to keep the current styli length that you are using. The only draw back is the purchase price close to $8500 when all said and done.

[Joe788]

Renishaw OMP-400. I wouldn't be concerned about the probe tip flex. The issue that drives the inaccuracy is the precision and repeatability of the probe's trigger mechanism. If the probe repeats to .00005" with a 2" stylus the best it can repeat to with a 6" stylus would be .00015". This is the same with the test indicator where the internal gearing inaccuracies and periodic errors will be magnified with a longer indicator tip. I know it is splitting hairs but I would prefer to move the probe out in lieu of a longer probe tip. Just a matter of preference.

 

It's a little different with a strain gage style probe - since it's just ON/OFF. The trigger repeatability on a Renishaw strain gage probe is .25 micron for a 2 inch stylus, and .35 micron for a 4 inch stylus - so it's really just a .0001mm difference, or .00000039 inches.

[Guest]

You can't compare old probe technology to new strain gage technology.

 

Besides, you DO NOT get that .00005" probe accuracy. You get that accuracy stacked on top of your machines accuracy plus whatever peripherals. It all stacks. You want to get the most accuracy possible out of your machine tool, run it in Metric.

 

[Bob W.]

It's a little different with a strain gage style probe - since it's just ON/OFF. The trigger repeatability on a Renishaw strain gage probe is .25 micron for a 2 inch stylus, and .35 micron for a 4 inch stylus - so it's really just a .0001mm difference, or .00000039 inches.

If that is the case I'll just get the probe tip extension. I really like my 4mm probe tips so the extension is the way to go. The two A51s have strain gage probes so accuracy will not be much of an issue. Thanks for chiming in, I learned something new :-)

[Bob W.]

You can't compare old probe technology to new strain gage technology.

 

Besides, you DO NOT get that .00005" probe accuracy. You get that accuracy stacked on top of your machines accuracy plus whatever peripherals. It all stacks. You want to get the most accuracy possible out of your machine tool, run it in Metric.

 

I know these machines are native metric but it there a tangible difference that you have seen from running in English versus metric? How difficult would it be to change everything over? I have reams or production programs stored on the machine and they are all in English. Changing to metric would be a daunting task.