Trying to figure this one out before final surfacing

MR-1
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Fixture plate has a few surfacing passes on it while trying to get tram dialed. Earlier iver the weekend I got it pretty close then used an SST tram squaring dial to bring it into within about .001 across 4.5 inches on X and within about .002 across 4.5 on Y. Have another gauge coming that sweeps 6 inches where I will really try to finalize it.

I clamped in a 3/8 plate to do some test passes on with the fly cutter and got some nice finishes with very little bit of edge that would roughly match what I was seeing on the tram tool dials, like .0005 of a step between passes which would roughly match the 2 inch step overs used with the fly cutter. I was able to measure a bit of an inconsistency thanks to the clamps bowing the 3/8 plate.

Now here is where it gets weird. Last night I wanted to use a thicker 1 inch chunk of aluminum which was gonna get surfaced on both sides. I wanted to see how parallel of a piece I could make.

Those with ESP can probably figure out that I wound up with a tapered part.

Running the dial indicator across my SMW jaws across the X axis I was getting around .001 per inch of rise.

Stripped all the clamps/pallets off and decided to test the entire plate.

This does not make sense as I would figure the gantry/spindle would make the fixture plate track in plane parallel to travel.

Lets call the corners where measurements were taken
Back left A is 0
Front left B is 15.5 in forward
Back right C 14.5 in to the right of A
Front Right D 15.5 in to front of C

So
AC
BD

Measurements are as follows.

A to B was run 15.5 inches and from a Zero Z at A I am low .003 inches at B

Running from B to D, I am .006 inches high at D from A

Running back to C from D, I am .009 inches high from A.

So what is interesting to me here is comparing left side to right side, the right is .009 inches higher across 14.5 inches.

Comparing front to back, the front is .003 inches lower than the back.

Dial indicator was mounted to the side of the spindle assembly so the dial is about 5 inches to the right of the true center bore of the Spindle. But if things were truly square the dial indicator should track as zero across the face of fixture plate.

Trying to figure this one out before final surfacing of the fixture plate.

Inchecked coplanar with dial indicator and the check gaige last night. I set it on top of the linear rails and I am between .001 and .0015 so there should not be enough there to cause the error.

I am fine with the .003 front to back slope across 15 inches, that does not bother me. But the nearly .010 across 14 inches is bothering me and given the spindle travels on the X gantry I am not seeing how a slope is introduced or revealed on the dial indicator.

Tonight I am going to tape out a pretty precise set of points for refrence edges put some 246 or 123 blocks down at a square refrence without having to dodge fixture plate holes. I am then going to touch off on all 4 corners with the dial indicator held in the collet of the spindle while testing zero and gathering data.

Maybe part of it is magnified by an off set of how I was testing before?

But the work piece I faced having a taper to it from a 180 degree rotation would seem to confirm there is indeed a taper.

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Where do you have your dial indicator situated? I recommend clamping the indicator directly into a collet and then sweeping the baseplate again.

The other thing, the SMW should be reasonably flat. Does it rock on the baseplate? If the baseplate truly has a .010" flatness error, SMW pallet will rock severely on the baseplate.

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That is where I am at this weekend when I can test through the collet as opposed to mounted to a magnetic stand attacjed to the spindle.

But the facing of the back side of a test plate after first surfacing the front side results in a taper that should not be there.

The SMW stuff is measuring square and true.

My measurement examples above were off the fixture plate itself after removing the pallets.

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How much taper did the block have that you machined?

I’m guessing that the SMW pallet is going to be pretty dang flat, so you can use it as a standard to check the flatness of your baseplate. If its truly out .010 over 15", you’re going to pick up on that immediately by rocking the pallet back.

I’m certainly interested to hear your result with the indicator mounted directly in the collet.

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The thing is it appears to be flat.

The 1 inch thick piece I was surfacing was 7x10 inches. I surfaced across the Y axis with the 10inch length being along the X axis.

I wound up with about .012 difference from left side versus right side after rotating it.

Was like .982 for the right and .970 for the left.

If half the taper comes from one side and half from the other side that would be about .006 from either side. Would seem to be within reason given the ratio of a 10 inch pass made compared to the baseplate measurements across 14 inches being .009.

The thing I am scratching my head over is how I can apparently get a flat fixture plate, albeit at an angle.

Will soon be touching off on a 123 block from a known zero and moving to various points around the fixture plate. Similar to that of a BL touch on a 3D printer mapping surface imperfections.

Will have the dial indicator in a collet in the spindle.

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Sent you a PM