New CRP4848 build - tramming puzzle

[good-ham]

I ordered the 4848 Pro kit from the awesome guys at CNC Router Parts almost a year ago, and receive it a few weeks later. As so often happens, work and life went nuts between the time I ordered it and the time I received it, leaving the boxes of awesomeness gathering dust in my garage until just a few weeks ago. I finally built the machine (pictures and a time-lapse to follow), but have run into something that has me completely baffled.

After completing the build I set about making sure that everything was level, square, and in tram so I could start cutting stuff. To tram it, I put a very solid slab of marble on the top, on top of which I have a stack of several 12x12 glass sheets with cards shimming the edges to make sure they are in the same plane as the X & Y axis movement. I have it pretty close as shown in the pictures below. When I move anywhere on the plate, both dial indicators stay within .0005" of where I zeroed them. Incidentally, I individually zeroed them to the same spot on the table when I first put the indicator rig in the machine.



So I rotate the indicators to face the right side of the machine and see the dial now closest to the front of the machine drop by around 10 thou, and the other go up by almost the same. Ran the gantry forward and back to make sure I wasn't measuring some inconsistency in the surface, and the readings held steady.



OK, so my router is nodding in a little and I'll have to shim it. No worries. ...then I rotate it to face the left side of the machine just to verify. I should see the readings on the dials swap readings more or less right? Yeah, except they didn't. As I rotated them through the original position they both returned to zero, then went back to the SAME values. e.g. the one that read +10 thou lowered to 0 then went back UP to +10 rather than continuing down to -10 as I would expect:



So now I'm completely baffled! I should say that I'm new to this, so perhaps I'm just an idiot and am missing something silly obvious. <crossing fingers> It seems to me that the same indicator is indicating I'm out of tram in opposite directions depending on how it is rotated.

I can't think of any possible geometry that should return these results. I'd think the dial indicator was out of square or something, except that it returns to zero when rotated 90 degrees. I'd think the glass was out of plane, except that I can move the x and y axis to move the indicators all over them and they maintain their respective readings for a given rotation. Can someone explain to me what I'm missing.

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[Jim Dawson]

Very nice tram indicator setup. But would not be my first choice for tramming the spindle. I have a piece of welding rod brazed into a 1/2 slug that goes in the spindle. It sweeps about a 30 inch circle on the table. Using a piece of paper under the pointer (0.003) as a feeler gauge you can tell exactly where you are at. I can get within about 0.002 in 15 inches this way, much closer than 0.0005 in 3 inches.

[ifeliciano]

This wont answer your question, but it might make things simpler. CNCRP posted a video on how to level and tram your machine.

[ger21]

You don't want to shim your glass.
You want to first surface your spoilboard, so that it's parallel to the machines travel.
Then place your marble, and one piece of glass on the marble.
Now, tram your spindle to the glass, by adjusting as needed.

[good-ham]

Hey, Jim,

Thanks for the reply. I really love the simplicity of your setup! Absolutely something I'll look into simulating in the future. Given that I'm new to this, I opted for the feeler gauge rig because it eliminated the possible variable that I wouldn't know to account for in my infinite ignorance. I'm lacking the experience at the moment to know what the difference in feel would be on something like your setup (you accept drive-by apprentices? ), but can read a dial well enough. Since .002 over 15 inches is roughly .0004 at 3 inches I should be able to get close enough locally, though. I like that your setup accounts for a wider area, though. Thanks again!

[good-ham]

Thanks, ifeliciano! I'd seen that that had come out, but already had the gauges by then. Figured I'd try it that way first.

Thanks to you as well, Gerry! So, I'll end up doing that and trying again no doubt. I saw the method I'm using on youtube and I get the logic and it makes sense to me from a logic perspective, so I thought I'd give it a try to check for gross errors before cutting anything. To be honest, the main reason I posted is that I truly found the readings I'm getting completely baffling. I can't think of any component in the system that could be adjusted to create readouts that flip with direction like that. I was hoping someone here with more experience than me could weigh in and explain what I'm seeing more as a learning opportunity. I'll surface the board tram after as suggested.

Thanks again to everyone for their quick answers!