Altmill Base: Plywood vs MDF

[Headshop]

I too used a sheet of 5x5 Baltic birch that had been stored unused for the last 7 or 8 years!

[gwilki]

@yappy You can search on the forum and find installations using very pricey aluminum plates for the underlay. The thing to keep in mind is that, if you then put MDF on top of it so that you don’t start cutting into the aluminum, you will have spent hundreds on aluminum and still have an MDF warping/swelling problem. My spoilboard is made up of MDF slats and t=tracks. The MDF slats don’t warp, in part, because they are adequatley held down to the bed. Just MHO.

[_Michael]

@yappy

Do you think that the solution could be mdf strips separated by t-tracks?

Having strips instead of one large piece might help some. I use strips and I’ve had them warp some but I think it’s probably the plywood table top under the spoil board that causes it for me. In general I think strips have more room to expand before deforming.

Alternative materials is one way to go but it’ll cost more. Way more for aluminum, most places I’ve found don’t even list a price. Whether that’s because the price of aluminum is always changing or they don’t want to give people heart attacks, I’m not sure. I’m guessing that a 4’x4’ aluminum tool plate would cost about as much as my LongMill Mk1!

HDPE (High-density polyethylene) might be an option. Online I’ve seen 1/2" sheets for roughly double the price of 3/4 MDF. Interestingly Wikipedia lists plastic lumber as one of the uses for HDPE. That might be a more cost effective way to purchase it and save some cutting to boot.

Zero’ing to the spoil board surface does take some getting used too but it will prevent damage like @Jens suggested.

[Spamming_Eddie]

Hey mrf,

I didn’t want to barge in this thread for the origional question was this or that and what I have is a third option that I thought would not add to the discussion, but on the other hand, my solution might help mitigate your warping problem.

It’s not fancy, nor estatic, but it gets the job done and it’s the most cost effective way I could think of to have a “spoil board“ level to my machine despite a warping slab of mdf being the base of tne machine.

Small pine strips, that can be leveled individual, saving time on surfacing.

Here’s a topic on these for more info.

Cheap ass tiling jig

Hi folks, A week or so ago, someone requested a sign that needed to be around 70 inch long (7,5inch wide). When I constructed my mill table, I figured I would need to be able to slide through longer material so I kept the back and front of my mill open and threw a few casters onder the legs of the table to be able to create distancve between the walls and the table if needed. I made a design the client approved wich included a dedicated cutout to custom shape the sign. Nothing fancy, just a ki…

[beerbarrel]

You could always get that black MDF…I think that it comes in other colors too but the last time I checked it was a couple hundred dollars a sheet. It is moisture resistant too.

BLACK-DIAMOND-MDF-WEBPAGE-2016.pdf

[Chucky_ott]

@Spamming_Eddie That’s a good idea and who doesn’t have a bunch of scraps lying around, waiting for a purpose?

[mrf2004]

I appreciate everyone’s suggestions.

In the spirit of not ‘letting perfect be the enemy of good’, I went ahead and used plywood under MDF for now. I’m in the Northeast US and it shouldn’t get too humid again for the next six months or so. I’ll keep an eye out for any warping and report back.

Ultimately, I may just have to fill my garage with AltMills and run a more controlled experiment…