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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!!!
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  • My take on this is
    1. In a normal alignment the minimum requirements for your level, rotate, and origin are
    Level-3, Rotate-2, and Origin-1.
    You can use circles to establish your rotate, but you will need two circles. Imagine a flat part with two holes. If you pin one of those holes you can still rotate the part freely on a single pivot but if you pin both holes, the part will be secured and unable to rotate.

    2. I think it matters what you mean by Datum Simulator. Simulating the datum does “reduce error” within the datum feature but it should not help the location of a feature unless you have allowance for datum shift (bonus tolerance on a datum). The only times I have ever simulated a datum is when the datum is too small to take hits on or when my available fixturing does not allow me to take hits on that feature (Flat part with datum -A- facing down). If the feature is available to take hits on then I do, 100% of the time. If the person training you is simulating more datums than he is actually checking either you are in very special work that probably meets one of the conditions that I listed or you have a programmer that might be trying to cheat parts in.
    P.S. as I stated before I have simulated a datum before so I will not cast any stones, If your programmer is doing something unethical that is for you to decide because I don’t work close enough to have an opinion.

    3. If you have the means to go to the hexagon school it is a good option but there is only so much you can learn in a few weeks of classroom training. My best advice is to stay on the user forum and when you have questions feel free to post about it and ask the other programmers questions as well.

    Hope this helps! Good luck!
Reply
  • My take on this is
    1. In a normal alignment the minimum requirements for your level, rotate, and origin are
    Level-3, Rotate-2, and Origin-1.
    You can use circles to establish your rotate, but you will need two circles. Imagine a flat part with two holes. If you pin one of those holes you can still rotate the part freely on a single pivot but if you pin both holes, the part will be secured and unable to rotate.

    2. I think it matters what you mean by Datum Simulator. Simulating the datum does “reduce error” within the datum feature but it should not help the location of a feature unless you have allowance for datum shift (bonus tolerance on a datum). The only times I have ever simulated a datum is when the datum is too small to take hits on or when my available fixturing does not allow me to take hits on that feature (Flat part with datum -A- facing down). If the feature is available to take hits on then I do, 100% of the time. If the person training you is simulating more datums than he is actually checking either you are in very special work that probably meets one of the conditions that I listed or you have a programmer that might be trying to cheat parts in.
    P.S. as I stated before I have simulated a datum before so I will not cast any stones, If your programmer is doing something unethical that is for you to decide because I don’t work close enough to have an opinion.

    3. If you have the means to go to the hexagon school it is a good option but there is only so much you can learn in a few weeks of classroom training. My best advice is to stay on the user forum and when you have questions feel free to post about it and ask the other programmers questions as well.

    Hope this helps! Good luck!
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