Hi all - thank you for all the helpful, positive and supporting commentary - I am learning a ton!
I’m working with small scale manufacturing in 1/4 bamboo, so my tolerances are rather small. A 0.02" deep embossed text carved on the right of the board needs to be the same depth ask on the left 
. It is not. I have squared, trammed, rebuilt, refaced, and adjusted as per suggestions - and there’s still a difference between heights at different parts of the bed.
I read a lot about issues with MDF sagging and aluminum beds.
The solution appears to be an aluminum bed to replace the MDF, however, that doesn’t make sense to me and I was hoping for clarification as well as suggestions.
My problem with the bed is the opposite: The steel frame underneath the MDF seems to be popping up, not slopping. The middle left side is 1mm above the sides, not below. I checked and there’s no debris under the MDF.
Further, even with sagging, the ‘sagging MDF’ does not sit well with me as 3/4 MDF does not simply become thinner in the middle. I believe that the issue is the steel frame under the MDF that sags (especially on the XXL).
My question is, has anyone built a bet to go under the MDF bed out of extruded aluminum, maybe 80/20, etc. so that the MDF itself has a solid foundation to sit on?
I think that a base that is more of a table that supports the entire bed, not just the legs, would do a better job at providing a truly flat surface Han a large sheet of aluminum.
Has anyone done that, thought about it or has some plans/BOM for something like that?
Thank you!
Yes, it’s been done. Go to “Shapeoko and Nomad Users Group (Unofficial)” group on facebook and type “8020” in a search bar. Should bring plenty of projects like that.
A lot of people remove the feet and lay the steel cross members directly on their flat work table/bench (think torsion box) to more evenly distribute forces too.
removing feet make a lot of sense - my double-3/4" ply table would be a great surface. I’ll try that.
You can also mount a flat base material, like the supplied mdf baseboard, underneath the steel straps. You’d just need to add back the thickness in supplementary wasteboards.
Yup, but you would be better off rotating the tubing 90 degrees to maximize stiffness, spacing, and/or reduce tubing wall thickness to save money. You can then use a flat melamine spoil board or flatten a MDF one to save even more money. You probably don’t need fancy/expensive extrusions or a thick aluminum bed and would probably be better off without them 
I just installed the PWNCNC kit and its FANTASTIC! Very rigid, adds a lot of hold down points, (fairly) easy to install, and makes the XXL look so much more industrial.
Could we get some eye candy?
Im actively debating between the PWCNC extrusion kit and the Saunders aluminum base. Both seem really nice (https://saundersmachineworks.com/collections/smw-fixture-plates/products/carbide-3d-shapeoko-3-aluminum-fixture-tooling-plate)
edit: I guess the Saunders base is only for the standard and XL
The Saunders base is two pieces for an SO3 and four pieces for SO3 XL.
Have you considered the Ohio Diesel Parts aluminum baseboard? Their SO3 XXL setup includes two plates, but SO3 and SO3 XL are single plates, I believe. https://www.ohiodieselparts.com/product-page/shapeoko-xxl-fixture-table-custom-metal-aluminum-plates-600-mounting-points
Or you could order your own ATP 5 sheet of aluminum and DIY.
Oh nice, I thought the Ohio diesel plate was comparable in price the the SMW but its quite a bit cheaper! I like the idea of 1/4" mounting holes for my zoo of C3D clamps though. I’ll have to see how much they’d charge to do that instead of the 5/16" threaded holes.
Yes - it’s only a couple hundred more than the price of the extrusions so seems worth it.
I am not sold on alum sheet bed… Wouldn’t want my bits getting near it, and if the base isn’t solid, it will still bend…
Yup, aluminum sheet/plate, like Melamine and MDF, will bend under its own weight if not properly supported.
Question for those who’ve taken the feet off and bolted their Shapeoko straight down to a flat base, were the bottom edges of the shapeoko support rails straight and flat enough to just clamp down to the bed or did they need spacing / shimming?
This is the only photo I have which was during the assembly process. Unfortunately, the machine is disassembled due to an issue with my HDZ (had to send it back to get inspected), but once everything is back in order ill take some better photos.
I have an XXL alumunim bed from Ohio Diesel Parts, and they only charged me a $50 setup fee to have 1/4"-20 threaded holes instead of the 5/16" holes.
I apologize, I’m having a hard time understanding your question, are you referencing the rails that connect the Y-axis extrusions to be the support rails or the three cross members that are oriented north/south? And, when you mentioned clamping down to the bed, are you referring to clamping down to your work table/surface?
I took the feet off, and I currently have the whole machine sitting on my work bench with a yoga mat in-between. I know some people have used Harbor Freight fatigue mats too. This dampens the vibration as well as conforms to more surface area underneath the frame. I also sized the depth of my counter-bores that secure my baseboard into the metal frame of the SO so that the screws are flush as @Griff importantly notes not to have them sticking out for obvious but forgettable reasons. Hope some of that helps.
Great thx,
Yep, the three north / south underneath that link the main front and back angled steel plates.
Yep, I have a ply torsion box which is nice and flat.
Excellent, thanks, that does help.
Hadn’t thought of the absorbtive layer, I can see some neoprene rubber heading toward the shed…