Thanks, HBM and Troy!
Sorry for the long delay, everyone - my day job ate my face. Today was my first full day off work this month.
So of course I used it to make some progress.
First was some paint touch up over the scars from mounting the linear rail in the back cabinet.
On the left side, where the drill had kissed the floor, here it is all sanded out and covered up.
In the center of the rail, a bit of black in the holes make them less conspicuous.
Back on the outside front of the rear cabinet, I spent a while looking at and thinking about the gap I had in the center of the 25mm linear rail due to the cabinetry being a bit cupped. I wondered what the relative stiffness was, between that roughly inch sized hardened steel rod and the 3/4" plywood structure. I tried setting my camera up on a tripod, looking down at it, and recording video, then tightening all the screws down to pull the gap out.
Reviewed the video. It didn't look like the rail flexed. It looked like the plywood flexed.
Hmm.
I set up a ridiculous lashup to set the dial indicator I use on my lathe and mill to reference on the center of the rail, and then very carefully worked the screws back and forth, from slacked out such that the gap was as big as it gets, to totally tight with the gap pulled flush.
Conclusion: Under full screw tension, at the center, the plywood structure pulls about 0.2" out, and the rail pulls about 0.006" in.
I think I can live with six thou of possible curve over a 24" long run. I think that's as nothing. So heck with building spacers to go under it - I'm just going to crank it down and let the steel bar be the truss that straightens out the wooden box here. I'll revisit that if the control panel balks moving across it, but given the panel is going to be a wooden structure about 42" long between the rails, I think it's fine.
I got my hands on the materials I'm going to be constructing the playfield axle from.
1.5" OD, 1" ID, 0.25" wall thickness 6061 aluminum tubing will be the spine of the axle, with lathe turned endcaps made out of 1.5" solid round stock.
I think this'll be a strong enough axle to support the big panel and the flipper buttons (they end up pointing pretty much through it's centerline) and the TV mount assembly while being motorized. Opinions welcome!
I plan to make the endcaps a three-section spigot. In my head, they'll have a 1" diameter spud that fits inside the tube, then out to a short fat 1.5" diameter flange that matches the OD of the tube, and then back in to a 0.75" diameter spigot that goes into the bearings. The bearings have two set screws to grab the spigot, and I'll drill through the tubing to countersink some small screws, tapped into the spud side.
(Come to think of it, that whole endcap description will probably make a lot more sense if you just look at them while I make them. When I get to the part where I make them.)
I also got the first coat of red paint on the lockdown bar assembly. Needs another couple coats, sanding, polishing, etc - but here's roughly how it'll look on the machine.
Sorry for all the seamlines, but these three pieces disassemble for service. Also, the top is just set on for the photo, I think I can finagle the fit a little better.
A need for another small detail like the red stripes on the rear hatch arises here. Looking down on the profile of the lockdown bar, you can see the red part matches the front-back depth of the front cabinet, which is slightly deeper than the lockdown bar is...
This means it sticks out the back a bit. Looking down on it from the pinball player perspective, that red is far too conspicuous - that's going to show a lot in the necessary gap between the lockdown bar and the pinball playfield. (Some gap has absolutely got to be there for the rotation of the playfield to clear the front cabinet.)
I plan to fix this by painting the top edge - basically, the whole part you can see red in the above picture - black. That shouldn't look bad from the side when you are in the cockpit, and should fix the problem when looking down at it as a pinball player.
Lastly, I also got the first coat of red on the axle bearing pillow blocks.
Needs more coats, but they are going to match nice.
It looks like the actual position for both bearing blocks lands wholly within the red parts of the front and rear cabinets, so they don't have to get a fiddly black lower section at all, they just go solid red.
I'll need to take the monitors out of the back cabinet for drilling and mounting the bearing blocks, and I'm triple and quadruple checking my math for where they land on the surfaces to get a 3' horizontal yaw and a 3' vertical pitch and the correct rotational centerline... that part is going to be kind of scary, I gotta admit.