I see that in sienci’s guide and what other folks have done is leave the bed of the machine short when they put down their first layer of MDF. I’m think because of the size of the bed the mdf at 4 by 8, does not cover it all. Either way, I have baltic birch available locally at 5 by 5 and was thinking that I would put a sheet of that down and then put down a 48 by 48 mdf spoilboard on top. Has anyone used baltic as a bed? Just curious how it has worked out. Maybe you guys could post some pics of your 4 by 4 Altmill beds.
That’s an expensive, but great way to go. Around here, 3/4” Baltic Burch runs nearly $200 for a 4x8 sheet. I went the cheap way with MDF and added a piece of cheap plywood to fill in the back section. There is no chance of damaging this back section, but there is a possibility of drilling through the front portion. I recently had a couple “bad program setting” that went through the Spoilboards and into the base layer.
Although I could have used a full 5x5 sheet to cover the entire bed, I actually have it in two sections. The first section covers the first 3 spans between the first four cross beams. The last section covers the span between the 4th and 5th cross beam. I did it that way so that the rear section can be removed in the event I want to surface the sides of lumber. For example, I plan to do some items with 4" x 12" stock and need to surface the 4" side. I’d mount it in such a way that the 12" side extends below the table. I opted to do this at the rear of the machine since it’s not something I’d do often and I have space on all four sides of my Altmill. Otherwise I’d have done it at the front. And no, I don’t have a jointer, which would be the better tool for this.
My t-tracks are attached to the BB base with Rampa insert nuts and 4mm machine screws. The MDF spoil board is also attached to the BB base with Rampa insert nuts and large head machine screws. I think machine screws are better than wood screws since they can be removed and replaced many times without having to worry about screws holes.
I used Baltic Birch as the base and MDF as the spoil board. I ran the birch 49" X 60". But I also set it up so I had multiple size secondary spoil boards that screw into the spoil board. That way, I can have projects I do all the time have dedicated spoil boards. Plus, I never cut into the main spoil board.