I am getting my table ready and I have seen various opinions on what spoilboard material to use. Some say 3/4 mdf. Others say a 1 inch foam board would be fine. Others say plywood because mdf can dull a bit. I am leaning mdf since I am using a ping pong table and could use the weight give it a little extra help in leveling. I have put table aligners and locks under the table, but it is off just a tiny bit in the middle. What is everyones opinion? Thanks!
I am curious to hear what everyone else says. But I was going to build my next machine with thick particle board (sub flooring) as the table top. Then I will add a thin 3/8 or 1/4 inch MDF as the spoil board. Particle board worked fine for me before on my previous machine builds. Good quality Plywood as a spoil board seems like a waste to me.
However I am worried about the particle board in Missouri. I am not used to living in a humid area. So I don’t know if it will cause problems or not.
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I don’t think it makes much difference. I like it a little on the thick side, so I can put screws in it as hold downs. But I would be happy with mdf, chip board, or cheap plywood.
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I’m using 5/8" MDF.
My reasons for choosing this:
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MDF is inexpensive, about 40% less than the same thickness in most plywood.
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MDF doesn’t splinter, sands easily making for a consistent surface even after it’s been chewed into a few times.
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I won’t feel bad “spoiling” it.
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I chose 5/8" as being thick enough to handle most mistakes I might make in cut depth, as well as hold T nuts, but thin enough to manage cost per sheet and not weigh a freaking ton.
There are downsides.
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MDF makes for nasty sawdust. Don’t breathe that stuff. Cutting into the spoilboard then makes MDF sawdust no matter what the actual material you’re cutting.
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MDF conforms (eventually) to whatever surface it’s on top of, so if your machine base under the spoilboard isn’t flat, your spoilboard won’t be flat either. You can’t use an MDF plate to force a non-flat machine to become flat. (Though it can be easily surfaced afterwards, which you can’t do with plywood nearly as easy.)
For things that need a very flat spoilboard for accurate Z depth, I do have 1/2" insulation foam, which I can surface quickly and easily. You have to be somewhat careful putting the material down on it, because it dents easily, but is reasonably strong to pressure spread across the surface. I’d screw the foam down to the actual spoilboard before surfacing (Make sure the screws won’t get surfaced!) This also makes a terrible mess and fills the shop vac quickly.
To me, the importan things for a spoilboard are that it protects the machine itself, won’t ruin your bits, won’t damage your work, and is replaceable, as it’s definitely a “wear part.”
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I’m using half inch (I think) mdf. Like everyone else says, it surfaces nice when you really screw it up, but is strong enough to actually hold a screw. I have holes cut in mine to roughly match the holes that are in my table top for clamps.
I’m new to this type of machine so I can’t offer anything in that respect but I worked for over 20 years in the lumber and plywood industry. I can say authoritatively that particleboard is not a good product. It will not hold screws for very long but, more importantly, it is very susceptible to moisture and breaks down quickly. It just crumbles. Two very good alternatives to plywood, which is now very expensive, is OSB (Oriented Strand Board) or Waferboard . Both are very strong and hold up very well in heavy humidity and they are a little cheaper than plywood.
Hope this helps… 
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I’d use mdf over particle board any day.
I had a strong itch over MDF for a long time. Today I cut some MDF and used the 1/8" single flute, with 4mmDOC and only 10mm/s. It actually cut quite nicely! Not much of that super fine dust that clings everywhere. I guess you have to find some good speeds and numbers when working with MDF, to avoid the worst dust-disaster.
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I also use the 5/8 MDF. The one thing that helps a lot is to not cut too deep when you are cutting out parts. The best way that I found is to zero to your work surface and not work from the top of the material. This way you don’t cut into the spoilboard.
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I have 3/4" mdf on mine. My recommendation however would be to try different things until you find what works for you in your situation. The spoil board is ment to be replaceable and cheap. But if you don’t do through cuts then maybe you want somthing nicer and flatter than mdf. On the other hand if you use your machine alot and cut the spiilboard to shreds every week than somthing cheaper and less durable (like particle board) would be better. I think MDF is a good starting point to get the machine dirty. But I don’t think there is or ever will be a “best” spoilboard material.
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I have only done woodworking in colorado. So moisture isn’t usually my concern (unless it is a product that will sit in the snow).
It is a spoil board afterall. It will get spoiled, so take a risk and try something. Worst case, it needs to be replaced a few months earlier, and you’ve learned something.
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One more in the MDF club, but I would have rather used HDPE to be mist proof. I have t track and use mdf slats screwed down between them, faced with a mill. Then if I am cutting through a part, I stack an MDF spoilboard on top to preserve the table boards.
Mdf is pretty dimensionally stable for a wood, which is good for Cnc. Mdf dust is nasty and it is abrasive on bits, but it is the price I pay to not get grained woods that warp more with temperature and humidity.
Now there is an idea I haven’t thought of before(why not plastic?). I wonder if I could make a mold thay I could melt all my 3d printer scripts into and pop out a spoil board? That would be cool and it would reduce waste.
Edit: on second thought wouldn’t HDPE and other thermo plastics melt and clog up the bit on through cuts?
The way I imagine it, HDPE for the table top and slats between t tracks, and some mdf scraps cut into convenient spoiboard sizes on the side (for through cuts).
My primo right now has the original mdf slats installed, but I baby the heck out of them. With an HDPE setup, when I am using my vice to cut alum, or other ops that don’t require a spoil board, I can crank up the mist more without worry other than getting the garage messy. Even with my mdf slats, when I need a spoil board, I just use mdf scrap. It will survive several jobs with mist anyways, and longer if I carefully meter the mist. The bigger deal, is that I don’t have to worry about mist affecting the table long term. Spoilboards are easy, tables are not.
All of this sounds nice, but I won’t replace my mdf slats until they need replacement. My problem is the way I baby them, it could be a while before I get to play with HDPE.
(Edit
Just thought of another con. HDPE is a slippery surface to clamp to.)
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HDPE cuts really nice. The side panels of my 3d printer are cut from 1/4" 4X8 sheets of MDF from Menards.
Has anyone tried using rigid foam? I’ve seen a few people using it to rip plywood sheets on the ground and it made me think that I could use it for a spoilboard.
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@vicious1 used to use the purple foam as a waste board (I think). The only downside I see is that it can be tough to get your work secured.
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Yeah I I have been using the purple foam also for a while. It has been hard to hold down for sure. I ended up using painters tape and wrapping it around the foam and my table. The other thing that I didn’t like was that I ended up with the pink dust everywhere and it stuck to the lube on my z axis when I surfaced it. It may not matter for people who have a good dust collection system. It inspired me to get my dust collection working though.
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I’ve seen rigid foam used as a base for cutting foam board with a needle cutter. I’ve also seen it made into a vacuum hold-down also for cutting foam board with a needle cutter. I don’t think it would work well for cutting wood. Unless you used inserts in the backing board, you’d be limited to double sided tape for holding stock. I imagine it deforms easily meaning it would be difficult to keep the stock surface parallel to the router. It would work well for contour cutting where precise Z cutting is not required.
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On my MPCNC I use MDF
On my LowRider I use 1/4" lauan (comes in 2’ x 4’ sheets)