CNC spoil board

Hi my team has a cnc router and since we got it our spoil board was a wood plate that we had to switch every 3 months because it absorbed too many liquid do you have other options for cheap material that we can use for long times

We used 10 mm thick pollycarbonate, it worked fine throughout the season but we haven’t tested since.

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Honestly, I think getting plywood (or MDF) and just swapping it out every few months is a solid solution, especially if you have excess spoil boards you’ve made ahead of time and a system that makes swapping boards super easy it hits that cheap requirement you have while also giving you an easy spoil solution long-term.


Define “wood plate” a little bit more? Do you use a vacuum system to hold your parts down? Tabs? Clamps? Screws? What do you cut that is requiring liquids? (I am assuming aluminum, but just verifying)

MDF is cheap, readily available, and will cost you a fraction of what you would spend on other materials. I recommend having a dedicated one for use with cutting fluids and a few that you can use dry. Swapping out every 3 months isn’t too bad. We routinely swap out our spoil board at least once a month if not more frequently, unless it’s dedicated to a specific product, in which case we put a lot of effort into making one that will last for months or more.

We use an exterior grade MDF. In Canada it’s sold as Xtiraboard and sold by Rona and other places. I buy it in 3/4 x 49 x 97” sheets for about $135 and get them to cut it as it’s very dense. I use my CNC router to engrave 12x 24 plaques for the local historical society and go through a fair amount of it. I’ve soaked a piece in a bucket of water for 2 weeks and it didn’t swell. Extira Exterior Panels | MiraTEC Trim and Extira Panels


We just finished our 3rd season using the same MDF spoilboard on our router. We cut wood, plastic, and aluminum on the router and when we cut aluminum, we use a lubricant mister. We cut or drill hole patterns in pretty much all of the aluminum on our robot(s). It’s not like we cut aluminum every day, but we cut a decent amount every season.

You may want to look into how much lubricant you are applying to the aluminum you cut. A little pointed right at the cutting zone goes a long way. You should have to clean the lubricant off the top surface of your parts, but if there is a bunch of lubricant running off the part edges and soaking the spoilboard, you are probably using too much. Regulating your lubricant flow might save you a lot of effort in changing out spoilboards.

You should also be able to resurface your spoilboard. If you get something like a 1.5-2 inch fly cutter, you can knock a few hundredths off your spoilboard every so often and freshen it up. Our piece of 3/4" MDF is probably down to 1/2" or so after 3 seasons. We’ll probably replace it in the fall, but only because it’s cheap and easy to do. It could still be used a while longer if needed.

We use isopropyl alcohol as a lubricant for aluminum cuttinh, it doesn’t affect MDF.
Must have an exhaust fan to carry away the fumes though.


Want to second IPA as cutting fluid. I usually run anywhere from 50-70% IPA. 50% is definitely more messy (doesn’t evaporate as quickly).

I always run a big fan near the job with an open window or door to keep fumes from building up.

Even if the IPA soaks into the MDF it will dry out without ruining the board. The board will stay flatter for longer and allow you to resurface it multiple times before replacing.

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We use 2 PVC sheets, half inch thick, glued together with PVC cement.

Every season we take a fly cutter and take off the top 1/16” or so, gives us a pretty flat surface, we’re on the same board for 3 seasons I think. Doesn’t absorb anything.


I think we are a bit unique. We use 2x12s planed flat (using the router) then mount that on the table, 4x 4ft long pieces total. Or workholding process is based on wood screws so we actually have two 2x12s stacked on top of each other to give some length for the screws. Then every year or so the top piece gets thin enough then we replace it. It usually doesn’t have much issue from coolant even though we really overdo it, but over the COVID break it started to warp. We usually go .02-.05 below zero on our cuts so we have to remachine the boards somewhat often.

I’ve looked into plastic, but for the way we use it I think it’d get really expensive. And MDF swells up way too much when it gets wet.

We use 1" thick HDPE sheets and counter bore the mounting bolts, then we can face the sheet several times when/ if we need to due to profiles etc. being cut out.

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This is what we used when we first got our CNC, but we moved away from it because we weren’t happy with our ability to fixture plates to it. We switched to MDF, which definitely expands from the coolant but it’s manageable with frequent facing. That allows us to use regular wood screws to hold plates down, which was much more difficult using HDPE. How do you fixture plates with HDPE?

We have cut dry on our router so that the MDF lasts, I believe we use a couple layers of construction grade plywood as a spoil board of our CNC that we use for aluminum, that doesn’t give any issues with mist coolant.

On our Tormach we would just use drywall screws with an impact, process was this:
1- Bolt spoil board to table with t-nuts
2- Drill out stock with matching hole locations (across multiple pieces) by hand drill or drill press
3- Screw stock down
4- Drill ALL holes first
5- Add screws to all drilled holes
6- Remove all stock screws to allow for pieces of scrap to fall off
7- Finish machining

We are upgrading to a Haas VF2SS this summer, with more power and torque I will be paying careful attention to how this fixturing method works.

One of our sponsors uses very strong double sided tape to hold aluminum to Polycarb, but you have to watch the heat in the workpiece, make sure its going into the chip.

We don’t use HDPE for a spoilboard, but one method for holding plates on HDPE that would probably work is double-sided tape. We use this. A little goes a long way. HDPE is pretty slippery, but I bet you could hold aluminum sheets to it for CNC routing with that tape.

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