Really good to know, Thanks!
Seeing so many aluminum base plates on this forum make the .02" flex in my MDF base plate look like a mile XD
With so many unofficial options for the base plate though, I wonder who has the flattest and most over engineered base on this forum.
Pretty sure the “flattest” award goes to @RichCournoyer.
And there is no such thing as “over-engineered” so I could not say 
So the extruded aluminum looks sweet, but it’s not exactly cheap. It’s also 14 pieces–a few years ago I bought a couple of “flat aluminum plates” that have T-slots on both sides from Misumi. You could get the job done with four of these, 250mm x 1000mm at $62 each. Anyone thought of that?
That being said, I am much more inclined to begin with the step of removing the leveling feet and letting the bed rest on the bench top. In reading the thread, do I need to put anything under the machine?
I left the three cross-members on, do people take those off? I think I’ve read that people remove them.
@Julien from your picture it looks like you don’t use those three cross-members underneath your baseboard? That’s a great way to re-purpose the baseboard and commemorate its service.
@WillAdams was definitely the one I saw mention the HF mats; and I meant anti-fatigue, could you imagine mats that induced fatigue? probably a tough sell haha. When I had my SO resting on my work bench without the mat it was significantly louder.
I have the SO3, so I wouldn’t know anything about cross-members
The three cross straps are structural and should be left in place.
Yes the fatigue mats are made by the same people who make headache pills, seasick pills, and diarrhea pills.
I put adhesive rubber feet under my XL and was surprised how much quieter it is.
Probably also as good as the other mats mentioned. https://www.mcmaster.com/95495k722
The Misumi T-Slot HFSQN4-15250-500 was very popular for the Shapeoko 2 when two pieces fit the machine as if made for it:
(esp. during Misumi’s “Reddit-150” promo)
I don’t know that anyone has done it for an SO3 or XL or XXL — the cost stacks up pretty quickly — I believe that in addition to the pieces running front–back you’d need additional structure going side–side. I tried working up a B.O.M. for extrusion and parts available from Fastenal/Grainger (trying to avoid the added expense of shipping) but have instead continued w/ my weird T-track/MDF/PVC hybrid (at least I went to the effort to spray my MDF baseboard w/ spare urethane).
https://forum.shapeoko.com/viewtopic.php?f=37&t=8332&p=65068#p65068
(though things have changed since then, integrating the C3D T-track in addition to what I was using — only had 2 track left over)
Possibly longer lasting/better would be something like:
Yes. I actually have 4 of the Misumi 250mm wide extrusions leaning up against the wall in my shed because I was going to go that route before I went all in on the Ohio Diesel Parts bed. I think it would have worked well, but I do not like the “traditional” way of clamping using really long t-nuts and knurled nuts to clamp (like the Incra Build it clamps do) , so I bought Misumi T-nuts that fit the extrusion and then went to McMaster-Carr and bought 3/4" long all thread and ~7/8" long threaded couplers and was going to make an adapter so I could use the many 1/4-20 SHCS I already have.
Pretty much like this:
I am debating whether to sell all of the Misumi extrusion as a set to someone who wanted to use it for their bed, or keep a small piece for really small work and make the adapters so I can precisely clamp things that are difficult to clamp with 1.5" hole spacing.
EDIT: If anyone was wondering, it was $59.98/ea for 1,066mm (~42.00") long pieces of the HFSQN4-1520 Extrusion plus ~$38.00 shipping to Washington state.
Yeah, the side–side arrangement is probably easier to make work, but I find it less pleasing aesthetically (as well as from a practicality standpoint).
While I’ll be getting some more expensive setup, I am going to try a budget-friendly, non-committal solution that will allow adjustment.
A bolt threaded through the bench-top right under each of the supporting steel planks making the base of the Shapeoko should allow easy adjustment of sagging with a twist of the wrench.
I used 1 1/4” MDF for the top of my table that my XXL sits on. It stays dead flat. Add a piece of that to the top of your table and then secure your Shapeco to that. My XXL, after surfacing has stayed flat within .003”. Flatness measured with a dial indicator in the collet over a 2” square piece of tool steel moved around the table in 6” increments.
That makes a lot of sense! Your table provides good and stable support for the already compressed and stable MDF (unless it gets wet!). Did you actually surface it or a spoil board that sits on and is totally supported by it?
The top of my table is 1 1/4” MDF. It’s coated with deft, top and bottom. I have installed another layer of 3/4” MDF(as a spoil board)and t-slots on top of the stock MDF panel that came with my machine. I then resurfaced the t-slot top to within .003”. The machine is heavy enough that careful adjustment of the leveling feet and careful surfacing will yield a flat and parallel surface to the carriage travels!
This is a torsion box table top.
Start with flat. You’ll never go back. 
Is your Shapeoko bolted to it? Does your spoil board sit on it or on the Shapeoko?
Okay a dampening May sounds good.
How do you avoid grinding into the aluminum? You use MDF between alum and workpiece?
