Hello everyone,
I am a new user here coming from a onefinity CNC. With my onefinity I build the torsion box using marine grade baltic birch and added screw inserts to make my waste board replaceable.
Are there any downsides to using marine grase baltic birch over MDF? I will also paint all sides to lessen the chance of moisture affecting the waste bed leveling.
I will upload the pictures once I get home tonight.
Any input would be appreciated!
I can’t imagine there being any down side to plywood, baltic birch or what-have-you. As far as ‘marine’ is concerned … are you planning to use the mill in the shower?
None of these products are prone to large dimensional changes with any (reasonable) change in humidity. Also, the spoil board is skimmed so even if the underlying structure changes slightly, you could just do a skim cut and have a perfect work surface.
@sylthecru Syl: I may be misinterpreting your question. You ask about putting the plywood torsion box OVER the MDF. It should be the other way around. The torsion box is your table bed. The MDF spoil board goes on top of it.
Edit. Oh wait, when you say “over MDF” you mean INSTEAD of MDF, yes. Duh. 
@gwilki I was thinking the same thing. Like why over MDF?? Lol.
Lol.
@sylthecru not sure why you’d want to go the marine-grade route. It likely wouldn’t reduce expansion due to humidity and moisture. Only advantage is in the adhesive and resistance to rot/decay.
Torsion box is a good idea but I’d stick with regular BB ply. I’d probably seal it with a water based poly for a nicer finish that can be wiped clean and reduce slivers at the edges.
@sylthecru Which machine are you getting? The Longmill mk3 I assume. You wouldn’t need a box with the Altmill.
And yes for the inserts for the spoil board slats. That’s what I did.
Let me clarify my previous statement, I was thinking of using marine grade Baltic birch as the base for the MDF slats for my Altmill.
I am trying to replicate the replaceable MDF slats I created on my onefinity CNC.
@jens The marine grade is one option of Baltic Birch that my hardwood store offers.
@gwilki You are correct, I was typing and walking 
@sylthecru Baltic Birch plywood as the base and MDF slats is a common method used by users. I use M4 inserts to attach the MDF but other use wood screws. I also have t-tracks in between the MDF slats.
So your approach is common but I don’t think there’s an advantage to using marine-grade plywood. No harm either for that matter.
