Thickness or flatness?
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Previous conversation was for flatness. Unless that has changed.
The flatness spec. for 1/2" ATP-5 is 0.015" and the thickness specs is 0.005".
The only thing I will say to this is that my plate had several dings near the edge or on the edge and a decent gouge in one spot, not a huge deal but that plastic film does not offer a lot of protection. I honestly didnt care as I was just super excited to have the plate lol
At least it was on the edge where you are not likely to hold your workpieces. Unfortunately, it may leave the factory in mint condition but the delivery guy/gal does not care about .015 flatness. Some people posted videos of the delivery their Shapeoko where the truck barely slowed down to drop the package in the driveway. 
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My plates first delivery was banged up. Second delivery was warped.
I am glad C3D have great shipping/packaging engineers that know how to packackage their products Just that alone helps to minimize damages caused by the shipping carriers.
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We used to say of one particular driver, that she could @#$@#% up a crowbar in a sandpile! 
Always had returns when that driver was substituting on our route.
Ohio Diesel makes nice products but the standard S3 spoil board is only mounting up with 8 bolts on 2 plates. They only wrapped mine with cardboard and 3 corners were damaged during delivery.
Ohio Diesel still havenāt learn from there customer complaints about their method of shipping / packaging the heavy aluminum plates.
I figure, they are the only ones selling aluminum plates for the XXL and therefore know that we Shapeoko owners want a aluminum plate.
I truly hope another competitor can offer a aluminum plate for the XXL and put Ohio Diesel on the bottom of the consumer lists.
What a way to do business ā¦
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Looking at your photo it looks like by the bolt holes, that you retained the crossbars? Is that the case? My midwest plate comes in monday so I am formulating my plan. Thanks!
Do you think the 7075ASHT500 has higher strength than the cast aluminum? Also, did they machine it for you? And what was your exact cut dimensions?
Yes I did keep them, I figured it wouldnāt hurt and may help with keeping the y axis extrusions in the right place.
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Im not totally sure on the strength aspect but I fortunately work full time in a large cnc machine shop so we machined it here! I attatched the .dxf I made up for someone else that asked for it as well.S.dxf (438.2 KB)
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Iāve been looking at the Ohio Diesel base plates for my ShapeOKO XXL as part of my upgrades toward cutting aluminum with hobby accuracy. I have noticed that a lot of people are now buying the extruded aluminum base plate (PwnCNC kit, etc). Both are expensive to me so Iām probably over-researching it. Does one have a structural/stability advantage over the other? It looks like the 1/2" plate option is easier to install.
Extruded base plates should sag and deflect a lot less than flat ones because they weigh less and have a higher second moment of inertia.
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I wouldnāt really want to rely on a single, relatively thin, flat plate of anything to maintain rigidity and positional accuracy over the size of the XXL baseboard & spoilboard. A nice chunk of aluminium as the top plate for a structure of, say, aluminium extrusion beams underneath providing the rigidity and adjustable levelling feet under that, now youāve got a base.
On big mills the table is generally a thick steel casting with sufficient depth to provide rigidity and stability.
Since bolting down the baseboard of my XXL itās a different machine. I deliberately included a layer of rubber as a material with a high loss-coefficient so that any vibrations that do occur get damped out quickly.
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Thanks! I should have mentioned that I plan on using the mat + torsion box combination below the metal bed and remove the 4 feet on the corners. Iāve read your thread above and several others and got a lot of valuable ideas outside of which way that I want to go for the aluminum bed material.
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Great, in that case the Aluminium sheet is moslty about a stable top surface for you to work from.
If you donāt have the ability (or a friend who works in the right place) to machine the plate flat then it might be worth considering a cast and pre-milled flat tooling plate, thatās what lots of the DIY CNC crowd seem go with as an easy way to get a reliable flat surface.
Have you checked out https://www.cnczone.com/forums/ and http://www.mycncuk.com/forums/282-Gantry-Router-Machines-Building?s=70d57618799f7f1f45dd0122ece83b86 for discussions on what people have used in home-built CNC routers?
So when I say bed, I just want to replace my stock MDF with something that will not cause me problems down the road. I currently have T-rails and waste board so I am wanting to replace all of that with an aluminum base with either threaded holes (1/2 sheet aluminum option) or T-slots (80-20 extrusion option). I would then top that with a waste board where needed or a vise when cutting aluminum. I already have all the work-holding equipment for a bench mill. From what Iām gathering, the 1/2 aluminum doesnāt seem to offer any advantage in this situation, correct? Thanks for the links! Iāve not looked closely at them for this particular question.
Aha, I think I am starting to understandā¦
A solid 1/2" plate would provide a very solid base. You would, of course, have to drill and tap it for your workholding but good taps make that a bearable task. Iāve just looked up the price of a 10mm tooling plate large enough for an XXL howeverā¦
Thereās also the 80/20 as you say, have you looked at the extrusions designed as machine bed with built in T-slots which might be cheaper but less structural. You have a rigid box underneath so it only needs to be sufficiently rigid over the spanning distances which is much easier. The other advantage of these over the solid plate is that if you mess up, bend it by over tightening a clamp or similar itās cheaper to fix.
From what Iāve experienced and measured so far the V wheels and belts are the primary constraint for the machine and unless you plan to go full HIWIN and ballscrew it would be hard to tell the difference between a well braced extrusion base and a solid chunk of metal.
HDPE on top for a spoilboard surface?