I may not be understanding something from the first post. Why are you not machining the holes at the same time you cut the profile?
That is what I would like to do. There is no way to hold the part if I want to machine all four sides AND the holes in one operation. That is my original question, how would I hold this?
I'm certainly not a "tolerancing" authority, but I'm pretty sure that True Position Error tolerances are properly expressed as magnitudes, not plus-or-minus values.
If my belief is correct, the method of reducing the measured locations of the holes to derive and evaluate the actual True Position Error needs to be reviewed and, if necessary, corrected.
You are correct. My mistake, it is TP of .0005, no Max material (or M with a circle around it)
You don't say how old your machine is, or how hard it's been run. If it's old and worn, you can pretty much forget it. If it's young and fresh, it can be done:
First thing I would do is have the machine laser calibrated. I have Productivity Quality do mine, costs about $1500 IIRC. They map the errors in the machine and adjust the compensation tables in the control. You also need a very consistent ambient temperature in the shop, so the machine doesn't grow and warp with temperature changes; plus or minus a degree or two is ideal. No direct sunlight hitting the machine through windows. Then you should at least have consistency, with a decent setup and torque wrenches. If you can get a consistent result but it's out of tolerance, then add Kentucky windage (fudge factors) in your program to bring it in.
If you have multiple different machines, run the tight tolerance stuff on the smallest machine that will fit the part (provided it's of suitable quality); smaller machines have less thermal growth.
It is a 2021 Haas VF2SS. I don't have the means to calibrate it with lasers, I asked my local Haas retailer to send a service guy to calibrate for backlash or any errors. They said the machine is spot on already. The shop isn't exactly ideal, the machines near a bay door, the boss likes to crank the heat in the morning. I used torque wrenches and found the sweet spot of tightening without warping the part, etc.
One important feature you haven't mentioned is distance between holes. Aluminum moves .0012" in 10F in 10 inches. I can hold a part in my hand and make it move out of tolerance.
I don't mean to throw shade on your machinery, but I wouldn't trust a CMM in a shop that uses Haas machines for any +-.0005 features. +-.002, yea, maybe. Run your part across the CMM 4 times, each time reorienting the part 90 degrees, and, if possible,4 different operators. Tell us the spread on your measurements.
I know you want to do the job in house. I understand, I get it. But if you don't have the equipment both you and your customer end up mad. Everybody loses all around.
I believe it Could be done but the CMM operator doesn't adopt new techniques very well so I have to setup my machine to compensate his style... If catch my drift... I made the part slowly to I don't think heat is the issue, and then we let it acclimate in the inspection room before it's checked. I am the only operator/setup/programmer and this is our only milling machine. We have two other lathes but I can only run one machine at a time, considering it's all small lots. This plate was only 2 pieces. I ended up making 6 of them just practicing, then the welder messed all of them up anyway. so there goes all my hard work.
I also don't understand the +-.0005 true position. What is the TP actually? If the TP is .001, the most both axes can be out at the same time is .00035. If the TP is .0005 that error is reduced to .00017. Pretty close! How close is your CMM? And how consistent is the temperature of everything?
Either way, if you are establishing the outside of the part during the boring operation that adds another level of uncertainty to the problem because the datum surfaces can move about.
Try leaving the finished part in the vise and go to position and indicate each hole. If it is not dead on there is one problem. Then take that part out and put it back in the vise. Re-indicate each hole. If they are not dead on again you have a clamping repeatability issue. If you don't have repeatability you're just chasing your tail. Are you chucking on an unfinished surface? Does your cmm measurement repeat?
I'm just amazed you can hold .0001 total on the diameter without any trouble. How the heck are you measuring that?
TP of .0005. I would like to machine all sides and the hole in one shot. My original question was how to hold it. I tried doing something similar where I would indicate the piece straight and flat at a torque that wouldn't warp the part, i think it was somewhere around 10ft/lbs. I would indicate it, and remove it and repeat with different torque values until I discovered the sweet spot. In the past, i've checked hole diameters with an air gauge but this place doesn't have one, they are checking it with the CMM.
Is there a M with a circle around it on the print in the box with the true position indicator? If so there may be bonus tolerance allowed. For any given hole, the bonus tolerance is equal to the actual size of the hole minus the smallest size of the hole.
I hate true position, it's gotta be the dumbest thing in gd&t. Especially when they use unrealistic tolerances.
There is no M for this feature. Even if there was, an extra .0001 wouldn't help that much. I also hate true position. I understand the need but I also think .0005 is
way too tight.
Aluminum part
All sides finished
Two holes drilled/bored
No mention of any coolant being used
And you are probably doing those operations one after another, as fast as you can. Making heat. Aluminum expands.
I could be wrong, but I just wonder if you might be better off doing the operations one at a time, giving the parts time to cool off between them. Or use flood coolant. Or both.
Make one or more extras. Check the dimensions produced by each operation on the first part of the batch and then adjust as needed for the remaining ones.
We use flood coolant, xtreme cut 250. It is a two piece lot and takes about ten minutes a piece to setup, then I let acclimate. The operations are separate, finishing the sides first, then the holes.