The Sienci-recommended base for the AltMill seems to be MDF, with a second sheet of MDF on top as a spoilboard.
Any reason not to use 3/4” birch plywood for the base layer? It seems like I’d get better screw holding, both to secure the base to the stand, and to secure the spoilboard and t-tracks to the base layer.
Thanks!
Matt
The only thing I can think off is that MDF is more stable then plywood. If you go and buy a sheet of plywood, chances are that it is not flat. MDF is much more likely to be flat.
You might argue that you can use plywood and then surface it to make it flat but you could (at least in theory) have areas where the plywood is floating over top of a section of a stringer. Surfacing is pretty neutral in terms of up or down cut forces. When you install an MDF spoilboard and surface it you might or might not force the plywood onto the stringers …. but now the plywood is no longer flat.
If you use a downcut or upcut bit on your project you will change the forces on the plywood and you might have a surface that is no longer flat.
Note that this is a WAG …..
I tapped my stringers with M5, cut holes into the base board and screwed it down from the top. I then installed metal inserts in the base board to use for screwing down the spoilboard. Screw holding is not an issue at that point.
Thanks for the prompt and thoughtful reply! That makes total sense about the flatness of MDF (as I have yet to find a completely flat sheet of plywood).
Great idea for fastening the base board to the stringers, and the spoilboard to the baseboard.
Cheers,
Matt
I used a sheet of actual Baltic Birch…was it perfectly flat…beats me, but it fit the whole area because the sheet was 5 by 5. I then used MDF for the spoil board. Jen probably knows best. His spoil board looks like it was designed by NASA. It is very impressive.
Baltic Birch is probably flatter than Birch plywood but honestly, I am just throwing out guesses as to why MDF was recommended.
@mrf2004 Another vote for Baltic birch ply. It’s fairly flat and even thickness. MDF spoilboard slats fastened to the plywood base with wide head (flanged) machine screws. Rampa inserts in the plywood for the machine screws will allow replacing the spoilboard without worrying about thread wear.
I wonder if it’s because MDF is more uniform and less likely to warp with humidity changes. Just another WAG but it seems plausible.
Thanks everyone for your input – I appreciate it!
It’s really nice joining a community that’s so helpful and responsive.
M
@mrf2004 wait until @Spamming_Eddie chimes in. He’s a hoot.
@Chucky_ott I’m intrigued, and a little bit frightened.
Oke, someone, I wont mention chuckys name, asked for it so here it is.
Forget about level, flat and straight. Just hotglue something - I mean anything- on, call it “Lookzyhmhmmymack.. magh.. mazzine bet“ and faint. Wake up the next day, all grumpy and akin and out of focus. Get off the floor, find out what you’ve done and give up.
Just as I did.
Like a pro.
That’s what I am using. It is working fine. The mdf spoil board will be flat once it is surfaced.
Thank you — much appreciated. M
You are right. It is LESS likely to warp with humidity changes. I am living in an area with a high level of humidity nine months per year, and in the last months I put two MDF warped panels to the garbage.
Do you think that the solution could be mdf strips separated by t-tracks?
If the environment is that much of an issue, I would suggest you use a material unaffected by the environment. It could be aluminum (even if you put a 1/8” hardboard on top) or some variety of plastic.
Note that if you always zero to the spoilboard you will not cut into the spoilboard unless you have a crash or if you screw up another way.
Just wanted to add - I live within a mile or less of the Pacific Ocean and I do not have an issue with humidity. It rarely goes below 50% but can be as high as 100% outside but in the shop it is relatively steady at all times (don’t know the inside humidity level)
Another thought - humidity is directly related to temperature. If your mill sits inside someplace where the temperature is easily controlled, you could adjust room temperature based on humidity. I don’t know how practical that is in your situation but in my case humidity is under control because of the steady temperature in my basement where the mill is.
Re protecting the spoil board if it is an expensive sheet of Aluminum or plastic - I have heard where people put down a layer of paper (like stuff that is used to protect floors during a reno, available at any major home center) and that will allow you to actually cut right through your stock and not touch the expensive spoil board (is it still a spoil board if you are not spoiling it??)
Great idea. How thick would be the aluminum?
No clue. I would like to add that the Aluminum needs to be cast ‘tooling plate’ aluminum like MIC6 to be sure it is flat.
In retrospect, maybe it wasn’t such a good idea to suggest Aluminum.
Thanks for all the ideas. My setup is in the garage, and while I run an AC/Heater when I’m working and insulated the doors, the environment still swings a lot when I’m not out there—temps from about 30°F to 110°F and humidity anywhere from 30% to 100%. That’s what’s been causing the MDF to warp.
Maybe the best path forward is a combination: an aluminum base to stay stable, and then a replaceable top layer (MDF, hardboard, or even paper like you suggested) to protect it. That way I’d avoid the warping issue, but still have a practical surface I don’t mind cutting into.
Has anyone here tried that kind of setup—aluminum on the bottom with a sacrificial top layer? If so, how did it work out over time?
If humidity is an issue for your MDF spoilboard, take a trick from the model railroaders (who use paperboard homasote for roadbeds, a real moisture wick!) - paint / shellac all 6 sides before installing on your machine.
Even if you cut into the top, the total exposed surface area will be significantly reduced, your MDF will last much longer, and it is cheaper than an aluminun slab 