Machine speed issue

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  • Machine speed issue

    I noticed something kind of scary last night, while trying to measure a hot part. Normally, when we calibrate to the sphere, it is at one speed, maybe movespeed of 50 and touchspeed of 2. Now most of the time, the movespeed and touchspeed are set a little bit lower in programs that are used, like 40 and 2. I knew that different speeds than what the stylus was calibrated to makes a difference, but, we have never seen that much deviation on my B&S machine when going a hair slower (we do this because the machine errors if it goes much faster). On my DEA, the probe was calibrated to movespeed 70, touchspeed 4 (I don't know where the 4 came from, that was what was in there when I bought it). I set the touchspeed at 2 in the program with no changes on movespeed, I then measured a part that I knew to be good, noticed about .010" deviations!!! So I adjusted the touchspeed to 4 and ran it again and the part came out fine. Is this something in DEA machines that they are this picky, or is it something that happens as the movespeed increases?? Like I said, that sort of movespeed is new to me as well. I've never needed to use fly mode on my xcel, does fly mode have any effect on measurements?
    Last edited by dccfreak; 08-18-2006, 07:34 AM.
    DCCFreak

  • #2
    What is the make, model and build year of your DEA?

    It has always been and will always be my highly tainted opinion (I have been too close to this fire) that DEA machines (especially the mid 90s ones) are sensisitive to pre-hit distance and move/tocuhspeed combinations.

    Your Xcel has special dampers built into the system (one in the Z-ram and one at the end of the X-beam) to lower that sensitivity. Xcels ought to run very nicely with fly.


    Jan.
    Last edited by Jan d.; 08-18-2006, 08:02 AM.
    ***************************
    PC-DMIS/NC 2010MR3; 15 December 2010; running on 18 machine tools.
    Romer Infinite; PC-DMIS 2010 MR3; 15 December 2010.

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    • #3
      I haven't seen our fly mode to affect anything, other than the machine taking forever to do something without it. Actually, I would not consider speed/software issues unless I was done with many more basic checks.

      I would consider other monsters. False triggers, loose TP, ..... Oh,.... have you experienced the loose ruby yet? I had a programmer crash one, not realize the ruby was damaged, and continue to find severe deviations.

      Oh, had you read the thread about cleaning tables? I mentioned something about a film from cleaning with a 2-ply rag. Check the scales. Once in a while, we see things like this from cleaning the scales, but forgetting to wipe then a second time with a clean rag.

      http://baggy3.info/signani3.gif
      Last edited by Paul Barriage; 08-18-2006, 08:01 AM.
      http://baggy3.info/signani3.gif
      Excercise your mind,..... muscle works better than fat!!

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      • #4
        My DEA is a 1996 Scirocco. I have only had it for about a month, but, I seem to like it so far, but, I am still learning about it as far as its squeaks and rattles.

        I am much more comfortable with my Xcel at this point, but, this Scirocco is smoking fast and I would like to take advantage of it if is going to be safe. Particularly, I want to feel good about both of these machines because they are at different plant locations and it is a pain running back and forth. I plan to do a study with an artifact between both machines very soon, but, I was wondering about the speed differences. Basically, it seems to me that I need to adhere to the exact parameters I calibrate to for running programs on the DEA. Now, the prehit on the calibration is set at .1968" and I am doing 3 levels with 13 hits. If I use the exact movespeed and touchspeed, how much prehit/retract is safe in the proggy? I usually try to stay around .05 - .1" depending on features. I rarely ever use any styli over 40mm long and 3mm dia.

        Thanks for your answers
        Brad
        DCCFreak

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        • #5
          You are right: if you use EXACTLY the same touch and move speed as the ones you calibrate with, you will probably be OK.

          If you want to see the issue with pre-hit distance, write a program that makes a long (>20") Y-move at your planned fast speed. Move at full speed to your prehit distance, and touch a gauge block. Retract and make the long move at full speed again. Loop the program to do this many times. Output the actual position in Y. Now vary your hit speed and your move speed. You'll see the Y position wander all over the place. Similar issues will come up when you change the pre-hit distance (though less pronounced).

          But if you keep the prehit distance, the move and touch speeds constant though, the machine will repeat remarkably well.

          It has always been DEA's contention that that is how you ought to run your machine, that is how they teach you to run the machine and that is therefore the way it is. PERIOD. And they are not really wrong in that. They are trading off a (maybe remote) accuracy issue for speed. On CMM's it is really hard to get both! Scirocco is made for speed, as you found out. It is actually a great machine, just know what the limitations are.

          Your Xcel is better at that kind of an exercise because it is designed differently. B&S, at the time, traded speed for accuracy. Simple as that. The result is a somewhat slower machine that is less sensitive to pre-hit distance and speed variations.

          Yes, yes, yes, I am still shedding tears over the fact that Xcel is not being produced anymore. I believe it was the best machine ever! Those who know me, will know why.



          Jan.
          ***************************
          PC-DMIS/NC 2010MR3; 15 December 2010; running on 18 machine tools.
          Romer Infinite; PC-DMIS 2010 MR3; 15 December 2010.

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          • #6
            On my DEA Scirocco I run it at 100% both qualifying probes and running parts, I have done this from day one. The touch speed is set to 2% and I have never had any deviation issues. The important thing is to keep the qual speed and run speed the same!! As far as pre-hit distance goes I run at .15 unless I have to reduce it for clearance and I usually have fly set at .2 .
            sigpic Eye Yam Sofa King We Todd It.

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