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AR15.COM
3/31/2016 7:12:49 AM EDT
So we have a rwp dovetail fixture in a larger dovetail fixture on our trunion machine.

I'm trying to hold .02 mm true position and its at .05mm

The fixture is not perfectly centered and I feel it needs to spin true with the rotary table. It is off in y direction by .0015 inch, which is what my true pos is off. My boss says it doesn't matter because were cutting all the sides of the part.

I feel the part is rotating with a .0015 runout. He said he called the rwp people and they said it doesn't matter if its not perfect

Thoughts, am I over thinking this?
3/31/2016 7:28:22 AM EDT
[#1]
What does the print say? If you make it to the print/statement of work you will not be wrong.
3/31/2016 7:32:05 AM EDT
[#2]
I know, I have shifted the geometry in the cam system.

3/31/2016 7:47:26 AM EDT
[#3]
I assume you're machining from a rough block to a finished part so no, it wouldn't matter if the fixture was a little off. Unless you care about your finished piece not being exactly in the center of your rough block.
3/31/2016 7:50:49 AM EDT
[#4]
In theory I think it should be ok because everything will be off center but off the same....yes adjust the model to what you have measured.



That being said, centering the fixture would always be my first choice.
3/31/2016 7:58:01 AM EDT
[#5]
Provided you have enough stock on the part, which is hard not to when you are talking about .02 mm, it won't matter if it's off a little since you are machining the other 5 sides.

That's provided you aren't working to any other part features that would be already machined into the stock.
3/31/2016 8:01:54 AM EDT
[#6]
Cool.

Yes there are no finished features yet.
3/31/2016 9:57:07 AM EDT
[#7]
The boss is always right. Carry on.

Seriously though, the only way the fixture issue would present a problem is if you rotate up a full 90 in the direction adjacent to your location error to machine a feature then rotate 180 to the opposite side to machine a mating feature, say a bearing bore that had to be held dead nuts concentric with the first side. Even then it depends on where your work offsets are registered. You will probably still be within tolerance but not perfect. It really depends on the part, what you have is probably good but I'm anal like you OP and always strive for perfection.
3/31/2016 10:04:08 AM EDT
[#8]
The datum is 2 bored holes in the face when a and c are home.

The holes that are off are at a-90 c45.