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A Couple Newbie CMM Questions

zoebear
Good evening everyone!

I’m extremely new to CMMs, GD&T, and pretty much anything to do with this whole world. (>4 months) My employer found themselves in a tight spot when our old CMM Operator/Programmer left for another company. The previous employee was the only one who /really/ knew how to run a CMM and program it - of course there was one “back up” who got very small amounts of training.

So I’m interested in learning and I’ve gotten the job title and was trained on what could be - due to the current situation in the real world - no one is having in class training so I’m stuck with online videos and tutorials and this lovely forum.

I have a couple of random questions I’ve compiled since getting my job - they will be newbie questions and they will probably make people mad but I checked search and couldn’t find what I’m looking for.

1. I’ve noticed that an alignment shouldn’t have a circle as a rotation. Why is this? I have noticed nearly every single program made at my company has a circle - or even circle(s) as the rotational alignment.

2. What is the benefits of having a datum simulator? I understand a simulator is the perfect datum and that it reduces chances of positional tolerances to be out - but why exactly would I use them instead of taking hits from the actual physical part? Would it help if the part were (hypothetically) .005 in out?

3. What is the best method to learning programming for PC-DMIS without any type of real training or mentor? I have watched a lot of videos and I check the forum every day just for random knowledge. Are there any book, video, website suggestions anyone may have?

Thanks for any help and I’m sorry this post is super lengthy!!!
  • 1. A circle can’t be used for rotation because there’s nothing to grab hold of. Use a plane, a line or a cylinder.

    2. Explain Datum Simulator? Do you mean using a CAD model to program with?

    3. Please get the training. It’s not that expensive and it’s much better than watching a video or asking one of us. We will help you all we can but only when we have time.
  • in reply to Darrollh
    Thanks for the feedback! Would that mean any program made with a circle in the alignment is kinda garbage??

    I do everything with a CAD model but most of our programs just take datum hits on the actual part. I have an engineer telling me it would be more accurate if I were to use, for example, surface plates - as datum simulators and bank the part into those and take hits from that instead of the actual part. Which I feel like doesn’t make sense because wouldn’t that just cause extra error? I know datum simulators are “perfect” because our parts have a low and high point and who’s to say where those are - but I guess I just don’t understand how that would really make a significant difference.
  • The only time I use a circle is for an origin or for a read point.
  • What I do is this. I make sure I set up the part like it’s being machined. That way you get the same results.
  • in reply to Darrollh
    If the alignment is only using one circle then yes that is wrong, if it is asking to rotate using two circles then that is perfectly OK as it is the same as constructing a line between the circles and rotating to that.
  • CMMXYZ on you tube has a lot of well made videos. Their company also offers online pc dmis level 1 and 2 course. Have not used that but based on the quality of their free you tube videos I think it would be a pretty safe bet. CMMXYZ .com is the main web site.
  • 1. A circle can’t be used for rotation because there’s nothing to grab hold of. Use a plane, a line or a cylinder.
    Why not? First example is with 2 circles second example is with a circle and a point. The software shows circle but that is how the DEMON shows it. 
    AUTO =ALIGNMENT/START,RECALL:STARTUP,LIST=YES
ALIGNMENT/LEVEL,YMINUS,A_DATUM
ALIGNMENT/[B]ROTATE_CIRCLE[/B],ZPLUS,TO,D_PIN,AND,F_PIN,ABOUT,YPLUS
ALIGNMENT/TRANS,XAXIS,F_PIN
ALIGNMENT/TRANS,ZAXIS,F_PIN
ALIGNMENT/TRANS,YAXIS,A_DATUM
ALIGNMENT/END


    AUTO =ALIGNMENT/START,RECALL:STARTUP,LIST=YES
ALIGNMENT/LEVEL,YMINUS,A_DATUM
ALIGNMENT/[B]ROTATE_CIRCLE[/B],XPLUS,TO,D_PIN,AND,140_G_PNT,ABOUT,Y PLUS
ALIGNMENT/TRANS,XAXIS,F_PIN
ALIGNMENT/TRANS,ZAXIS,F_PIN
ALIGNMENT/TRANS,YAXIS,A_DATUM
ALIGNMENT/END


    2. Explain Datum Simulator? Do you mean using a CAD model to program with? A datum simulator is a perfect geometric feature such as a surface plate, precision gage pins, angle plate. sine bar/plate, master ring. Anything that is known to be as near perfect as possible, see 1.3.17 (page 3 of the 2009 release) see 4.5.2 for datum simulator requirements, (page 53 of the 2009 release) of the GD&T standard

    3. Please get the training. It’s not that expensive and it’s much better than watching a video or asking one of us. We will help you all we can but only when we have time.
    Tec-Ease is one of the better places for GD&T training in regards to using it with CMMs. It is cheap considering the world of knowledge Don Day has in his head and resources he has.
  • Hi,
    I like this: "2. What is the benefits of having a datum simulator?". Maybe this good sounds in a books or at least from lips of expert who would have tricky ides, but when beginner asking like this is not easy understand whats going on. I think if there is no expert who can tech is the best go to courses. Forums and books are ok with good background otherwise could be that after gaining experience appears that all programs are wrong.
  • in reply to Darius11
    at some point you will come across a time when a datum simulator is the way to measure a feature and get good results. I've measured some small parts where datum A was a small hole, a gage pin inserted into the hole was the only way we could get correct and repeatable results because of poor form and/or lack of PREHIT/RETRACT distance. I've also used parallels or a 1-2-3 block or an angle plate for datum features because the part was not flat or straight enough for reliable measurement
  • Start by doing the courses offered through this site, start at the beginning Try to get into a class (Hexagon) or better yet see if the company will pony up to bring in a consultant / contractor for 1 on 1, if you do this put a big "DO Not Disturb" sign up and honor it. A circle can be used in an alignment, but a circle is a 2D feature, is work plane dependent and for alignment purposes you are using the center point (location) of that circle as the element used in the alignment. there are times when a datum simulator makes sense and when it does not, that will come with experience and practicality of what your trying to measure, correlation of results is huge to having bye in on the CMM accuracy and results. If you have some experience here great, if you do not find the crotchety old grey haired dude that is the toolmaker or reasonable facsimile and find out what kind of coffee he likes and plan on buying him a few dozen and hope he eventually becomes willing to share some "good fundamentals" and then some of his wisdom. Most people on this forum started where you are today, enjoy a chuckle, try to find what works for you and gives you results that can be repeated
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