Milling through frame base for spoilboard

I’m new at this, so perhaps this is obvious, but working on a spoilboard for an SO3 XL.

I plan on milling an MDF spoilboard and adding threaded inserts into the backside, but how do I mill the SO3 base itself? I found this doc online ( but it doesn’t explain how to mill the holes into baseboard and not hit the center frame support strap. I can leave an onion skin there, but being new at this, that seems like a dicey first project to get right.

Any suggestions? Do I just span the center area with no wasteboard hold-downs? Do you just use self-tapping screws to anchor the wasteboard to the machine base and not worry about CNCing any thing other than the center points?


I think that guide is suggesting drilling the Spoilboard (the user added extra chunk of MDF that brings the surface up to the level of the front steel rail) and not the underlying machine baseboard, however…

If I were to be drilling the baseboard I might either;
a) Use the method in the guide to set the maximum plunge reach of the bit to just above the height of the steel (and cross everything)
b) Deliberately mill the holes a few mm short, take the baseboard off the machine and drill the remainder by hand with a drill once the machine has made an accurate hole grid for me to follow


That’s a little confusing… the written guide is machining the base board and the video preview image (I didn’t watch it) shows a wasteboard, and has wasteboard in the title.

You mentioned that you’re going to make a spoilboard/wasteboard, but are wondering how to machine the base board or are you wondering how to attach the spoil board to baseboard to make it?

When I made my first wasteboard, I created a file with mounting holes with counterbores to eventually hold my wasteboard to baseboard with 1/4-20 screws. I cut my wasteboard by holding it down with brad nails, and set my toolpaths as Liam suggested, not cutting all the way through except the holes that were going to mount the WB to BB - those can spot drill marks to go back and drill out later for threaded inserts (I installed the ones in the BB the wrong way - taper side up). Having the inserts/holes in my BB allowed me to make new WBs to swap out A little easier. I make new WBs using the painters tape and CA glue work holding method on top of my current WB.

I know some people prefer to screw their WBs into the BB, creating new holes each time, and they’re keen to replacing their BBs more often.


I used the Myers Woodshop spoil board plan for my XXL. I had bought a new sheet of MDF so I cut out 3 spoil boards and used the 3/16 long 1/4-20 inch Tee nuts. Since I had 3 spoil boards I just serially cut each one since I had the set up all made.

After I got the 3 spoil boards milled I put the first one on the base mdf and drilled a 1/4 inch hole about 3 inches away from the corners. Then I took the first spoil board off and stacked all 3 of the spoil boards together and drilled the second and third spoil boards using the first SB as a guide. I then had a reference on the base mdf and drilled and put 1/4-20 brass inserts in. I placed the first spoil board on and with a manual countersink I cut the mdf by hand so a flat head 1/4-20 bolt would sit about a 1/4 inch below the surface.

After resurfacing my original spoil board I replaced with the second spoil board. I knocked out off of the Tee nuts and installed on the 2nd spoil board. Then I repeated the countersinking of the 4 holes so the flat head bolt would sit about 1/4 inch below the surface. This countersinking gives me room to resurface a few times.

One consequence of surfacing my spoil board I had to replace my bolts that are used in my cam clamps because the original 1.5 inch 1/4-20 bolts would bottom out on the base mdf and push my spoil board up. So I replaced the 1.5 inch bolts with 1.25 inch bolts and that worked until I replaced the spoil board.

@RoughDraft40 I’m following a similar vein. Planning to add a spoilboard on top of the baseboard and wanted to put threaded inserts into the baseboard to allow for swappable spoilboards without damaging the baseboard. It sounds like you put the threaded inserts into the baseboard from the top even though that goes against the taper? If so, milling them shouldn’t be too much of a problem as I don’t have to punch through.

To be clear, I’d mill holes fore threaded inserts in the top of the baseboard, install the threaded inserts from the top, trusting to tight hole tolerances and the fact that pull-up forces aren’t too significant, and then mill counterbores in the spoilboard in the same location for through holes into the baseboard. The rest of spoilboard would be milled with holes for threaded inserts that were then installed from the backside to keep the metal below any accidental run-ins with the end mill. For future spoilboards, all I have to do is duplicate the threaded inserts and counterbore locations, and bolt the board down in the same spot.

Sound about right? Any issues with using the threaded inserts on the wrong side of the MDF baseboard? Any pullout problems? Fine if you make sure the holes are on the tight side?


You don’t need or want very many holes to hold down a spoilboard. Just mill holes where you know you’re clear.

No, just make sure to set them below the surface.

Not necessarily. The MDF will bulge if they’re too tight. I’d recommend using a scrap and test a few sizes (milled by the SO3).

That’s how I have mine done.

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My threaded 1/4-20 brass inserts have no top or bottom. You drill a hole that is slightly smaller than the lowest part of the thread and screw them in. There are other types of inserts that have tabs or fins that are directional but mine are not directional. You do have to screw them in from one direction or the other but once installed the 1/4-20 bolt will tighten from either direction without pulling the insert out.


Adam - you are correct. That’s what I did and no issues. The main thing, and looks like you understand already, is that the inserts in the spoilboard are installed from the bottom. I didn’t have any issues with the MDF base and I don’t have any issues with inserts from the top on my Delrin base board either (that I’m aware of).

Neil replied with very good points in regards to setting below the surface, test cuts, and bulging.

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@neilferreri Thanks Neil. Your method sounds about right.

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