offset points

[Karen]

We are having to offset 2 points from 1 point to create a plane for leveling.
Let's say P1 is at suppose to be at 0 but the actual is .252mm. Now we go to P2 on another surface that is suppose to be 41mm from P1........it's not........it's about 40.5 mm.........then we go to P3........it is suppose to be at 47mm.......but it is 45.6 mm. Now we are suppose to create an offset point from P2 so that this point (we'll call P4) is 41mm from P1 and then another offset point (we'll call P5) is suppose to be 47mm from P1. Then we are to create a plane using P1, P4 and P5 and level. My question is, do we offset the point from the theoreticals/target nominals or do we offset the 41mm & 47mm points off from the actuals, Which in this case would be to offset P4 to equal the same nominal as P1 I would have to offset the point 40.5..........then P5 would have to be set at 45.6? Now we put the next part up there and it is actually 39.5 for P2..........now I just created the program to offset at 40.5, now I will be 1mm off? If I am understanding offsets correctly I should be offsetting the point 41mm from the theoreticals shouldn't I? What if we are not using CAD........and just taking points............if I take a point on that surface and all the theoreticals and actuals are at 40.5 mm...........do I offset the point 40.5 or the 41mm that the print says it is suppose to be? This is my alignment and I know the alignment is everything, so if I don't do it correctly it will skew my answers terribly!

Please Help ASAP!!!!!!

Thanks,
Karen

[\v/inston]

make sure you are in a working plane that is a side view to the plane (not viewing from above the plane). look at the triheadron for your direction.

[Karen]

I have it in the side view and it looks like the point went up to P1, but my concern is, do we offset the point from the actual or theoretical........it is hard to see if I am exactly with the P1.........I am not using a CAD file.I could be off .5mm.........again that would be in the offset.........offsetting it from actual to offsetting from theoretical.........there is a .5mm difference.

[bw_bob]

You are creating lets say your datum -a- for leveling are the dimensions in question basic dimensions. If they are then you use the basics for creating, offsetting and leveling

[Karen]

Yes they are basic dimensions. So then you are saying I should use the basic dimensions to offset no matter what the nominal is for the actual? I would then be offsetting my point by 41mm even though the actual point is .5 mm off from where it should be? This is what I thought I should do, but I was second guessing myself.......co worker did it the other way and offset the point by only 40.5 because that is where the point actually was. My concern there was, when you put the next part up there, maybe it is more at nominal and then we are only offsetting it by 40.5 mm instead of 41mm like the print says.
At any rate, I was doing it correctly then?............always offset the amount the basic dimension says it is suppose to be regardless of the actual. Use this rule for both CAD and no CAD programs?

Thanks for any input!
Karen

[Matthew D. Hoedeman]

If you are trying to create a plane for a level and you know the NOMINAL amount the points are offset (different) by, then you offset the ACTUAL measured points offset by the nominal difference.

[Virgil UK]

Stick to nominals and do an iterative alignment, this should do all the calcs and necessary stuff for you.


Darren.

[Karen]

offsets

But then what happens to the next 30 pc I have to do...........they are not all going to be the same "difference" off.........that is why I thought I should use the nominal off the print and offset it the same on each part and if each part varies, then so be it...........if I only offset it 40.5 mm and then next part is closer to the print nominal it will show that part out, when in fact it may be in tolerance, correct?
Or do we have to offset each part differently everytime? That doesn't sound right? I was trying to look at it, as if the points were all suppose to be on the same plane............and then you level that plane...........well if the next part is warped, the plane is not going to be too level, and the results will show that, but the next part could be flat again.

I should mention we are dealing with plastic here............they warp, bulge, twist,,,,,,,,,,,,,,,etc etc etc.

[Matthew D. Hoedeman]

BUT, those 3 points are your datums, correct? If they are, then they are, by definition, ZERO, even if they are checking off nominal to a previous alignment, so you have to offset from the actuals. And yes, every part will be different. But, datums are datums and unless you can clamp the part down on those datums, to force them to zero, then the rest of the part IS going to vary, depending on HOW those datums check in the free state. Ah, the life of plastics!

[#2#]

I am a little confused by the problem and I suspect others may be also. This is what I think I understand...

You have a part which has three datum targets. One of them is on the datum plane. The other two are at some point offset from the datum plane. Your drawing shows basic dimensions from the two targets to the datum plane.

Now, you want to create the datum plane from these three points correct?

[Karen]

But what would have happened if the very first part I put up there was at nominal........I got Lucky that time and got a flat plastic piece (yeah right).......but then every part from there on, to the end would be 41mm offset...............like the print says...........so now I am still back to the correct way............offset from print or offset from part.....do you see my dilemma.......it sounds like it all depends on that very first part?

[bw_bob]

I am a little confused by the problem and I suspect others may be also. This is what I think I understand...

You have a part which has three datum targets. One of them is on the datum plane. The other two are at some point offset from the datum plane. Your drawing shows basic dimensions from the two targets to the datum plane.

Now, you want to create the datum plane from these three points correct?

That is correct.You use the basic dimensions from your datum for offsetting to create your plane.

[#2#]

That is correct.You use the basic dimensions from your datum for offsetting to create your plane.

Ah, but if you create an offset point isn't that dependent on your current alignment?

If this plane is the first thing she is trying to create then she would need it to be perfectly placed on the machine to get the plane correct.

I propose that she create a plane using her three measured points. Then, using the basic dimensions available she will have to do a little math and rotate her axis/axes to that plane but offset by an angle determined by the math.

[Matthew D. Hoedeman]

In this case, the best bet would actually be the ITERATIVE alignment, no worry about the offseting or anything.

[Karen]

offsets

You are not confused at all....................that is what I am saying, I have 3 target points and 2 of them are offset from the one point...........I deal with plastic and each part may vary with warp and sink.............I wanted to make sure how to correclty offset...........offset to the print (regardless of the actuals) or offset from the part even though the next part may not have sink or warp.

In a perfect world I would be offsetting to the print and the 2 points would be exactly where the print says it is suppose to go.......but in the plastic world.......it can be so confusing..............At any rate, I have been doing it as if I was in a perfect world and offsetting as the print says, but is that correct.

Which is the best way.............I guess it depends on who you talk to huh?