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One point Alignment using CAD

Virgil UK
Just recently I have been running larger samples of parts. The time has come for me to automate my program even more. One way of doing this is a "one-point" alignment on the part. I have tried this before but have fallen foul, I think it was because I wanted to keep the CAD datum where it was. Does anybody have any info on this or can suggest some options for me achieving this?

Many thanks in advance.
  • Are you wanting to just do a single point start for your program. Are you using a fixture? Or are you inspecting multiple parts at a time
  • Keep the cad datum where it is, no need to EVER change it.

    Set the part/fixture up on the table, put directions in the program (pix too if needed) on how to set it up.

    Then, simply do a READ POINT (or single touch point) with directions of WHERE to do it. Set XYZ origins and offests, do CAD=PART, then go into DCC and measure an alignment close to where the point is, then do a real one using all the correct datums or pick-up features of the fixture.
  • Thanks Vertman, just a single point to start.

    Thank You Matthew I will try this to measure the next part.
  • Sorry to be a pain Matthew, but when you say, "Set XYZ origins and offests", what exactly am I setting/offsetting to?
  • Sorry to be a pain Matthew, but when you say, "Set XYZ origins and offests", what exactly am I setting/offsetting to?

    Lets say you are using a fixture ("You are using a fixture") and you know that the front-left corner of the fixture is X1200, Y-250, Z75 to part cad position. Directions would state, "Place probe 1mm above front-left corner of the fixture, hit DONE" (this is for a read point). Pcdmis will record, as a point, the location of the probe when the DONE button is pressed and it is then an XYZ FEATURE (point). You then align to the point, setting the XYZ origins to it. IF your fixture sits X+ to X+, Y+ to Y+, Z+ to Z+, then all you need to do is use the point as XYZ origin, then origin_offset wach axis, X-1200, Y250, Z-75, and you are ROUGHLY aligned. Close enough for the CMM to go into DCC mode and measure features on the fixture. I would start with points CLOSE to the corner to get a better rough alignment, do 3 points on the top, 2 on the front, one on the side, then construct a plane & a line. Level & origin to the plane, rotate & origin to the line, origin to the last point. THEN, now that you are roughly aligned to the actual fixture, measure whatever on the fixture you need to align it, be it 3 widly spaced tooling balls, or 4 corners and the entire side and a second side, or whatever. Could ya follow this? Start small, (single read point), go a little bigger (align on the corner where the read point was), then go HUGE (cover as much area as you can) for the final alignment.
  • Thanks Matthew, I think I follow.
    Sort of how I used to do it in the old days! My problem will be that I have very little square or flat features. I'm measuring twin NGV's, I will have to calculate how to get back to point, Y, (intersection of datums), from my first point and secondary alignments.
  • Thanks Matthew, I think I follow.
    Sort of how I used to do it in the old days! My problem will be that I have very little square or flat features. I'm measuring twin NGV's, I will have to calculate how to get back to point, Y, (intersection of datums), from my first point and secondary alignments.

    The example of the fixture base IS just one example.

    Another "good" read point location is "Place probe in the center of hole <thishole>". As long as you know the operator can get the probe close to a specific point-in-space to the part, you can use that point-in-space as the read point. Set up is the biggest worry when using read points for initial alignment which is why you need to 'start small' then go big. When using a hole, I would add yet another alignment, that being JUST the hole, using 3 surface sample hits, then setting origin to that feature, then expanding out.

  • [soapbox]

    I do this all of the time. In fact it is the only way I write new programs, and whenever possible I rewrite the beginning of older programs. I prefer to start with the tip centered on a hole, but there are couple of programs where I start with the tip approximately .5" above and centered on a key or slot. I often take a photo of the tip positioned for the readpoint and store it in the folder with the program for future reference if needed. I also have a full screen user comment that states where the tip should be positioned and warns that DCC begins when the done button is pressed.

    I begin with a large prehit/retract, (usually .3, double my goto .15"), and slowish move speed. I make that read point, X,Y,Z zero then measure the hole to refine two axis, (another alignment), then move out & take a 3 point plane around the hole to level and refine the other axis.(another alignment). Now I tighten the prehit/retract and bump up the speed. Depending on the part I either then measure that same hole again now that I have leveled to the surface, or in that last alignment I offset the X,Y,Z orgins to where I want them to be in relation to the hole & plane and then I begin what would be the first DCC alignment in a program that began with manual hits.

    HTH It sounds complex, but after you do it 5 times, it is just as easy as a manual alignment and you save the time and hassle of manual hits every time you execute the program. I do not understand why they don't emphatically teach this method in the pc-demon classes. They touch on it, but only briefly.

    [/soapbox]




  • [soapbox]

    I do this all of the time. In fact it is the only way I write new programs, and whenever possible I rewrite the beginning of older programs. I prefer to start with the tip centered on a hole, but there are couple of programs where I start with the tip approximately .5" above and centered on a key or slot. I often take a photo of the tip positioned for the readpoint and store it in the folder with the program for future reference if needed. I also have a full screen user comment that states where the tip should be positioned and warns that DCC begins when the done button is pressed.

    I begin with a large prehit/retract, (usually .3, double my goto .15"), and slowish move speed. I make that read point, X,Y,Z zero then measure the hole to refine two axis, (another alignment), then move out & take a 3 point plane around the hole to level and refine the other axis.(another alignment). Now I tighten the prehit/retract and bump up the speed. Depending on the part I either then measure that same hole again now that I have leveled to the surface, or in that last alignment I offset the X,Y,Z orgins to where I want them to be in relation to the hole & plane and then I begin what would be the first DCC alignment in a program that began with manual hits.

    HTH It sounds complex, but after you do it 5 times, it is just as easy as a manual alignment and you save the time and hassle of manual hits every time you execute the program. I do not understand why they don't emphatically teach this method in the pc-demon classes. They touch on it, but only briefly.

    [/soapbox]





    +42

    Pretty much exactly how I program. This method works like a charm, the CMM does all the work.
  • +1 here. One touch set ups were the way I was taught right off the bat even before I went to the PcD classes. I strictly program offline off the CAD model so I'll bring my model in (usually in local coordinates) and put an operator comment in with instructions how to line the datums up with the machine axes or otherwise set up the part. Then I'll program my datums with auto features and the necessary Move To's. If I'm picking up datums on a curved surface or using datum target points, I'll pick up a my datums a couple of times. When that's all said and done, I'll jump back up to the top of the program between the Op comment and first datum feature and find a feature on the model that's easy to identify. Usually it'll be a hole on the floor so I'll have an operator comment to take a "touch just Y pos of the pilot hole on the floor". I set X, Y, and Z on this touch, let the Demon auto update everything below and go to DCC. I'll then level my part, let the Demon auto update, rotate and update and finally set my origin and update. Sounds more complicated than it really is but it makes the Demon earn its keep by doing a lot of the heavy lifting.
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