Clamping // Spoilboard

I need a little advice to spark my interests in using my CNC. I have it all built, and then ran into a snag - I built my table different than suggested, and needed to build a spoilboard after the fact, and bolt it to the top of my table (see attached photos). It has T-nuts hammered into the bottom so I can thread a clamp into the spoilboard at any interval I choose. My build is 4’ x 4’, so I’m aware that opens doors to inaccuracies, etc. But so far, I’m happy with the results, and will work around those.

Problem is, my surface is nowhere near level, and that’s been evident in some of the cuts I’ve made. What are some methods to creating a flat surface to secure my material to?

Also, I need to create/buy clamp(s) that would function for my build. Does anyone have a recommendation?

Get a 3/4" to 1" end mill or fly cutter and run a large pocket on the entire spoil board only 1-2mm deep. Repeat the process until you’ve cut the entire board level.

I did a 1mm depth of cut and had to run the program twice to fully level the spoil board.


I am hoping shows up for Christmas.



I am totally new myself, but it seems like people run this bit over the entire surface to make it level. Going down a tiny bit each time until the surface it flat.

1 Like

I had a feeling it would involve cutting down the spoilboard. Makes sense for sure.
I want to add 4 more bolts in the center of the board to secure it more to the table - I think that’ll reduce a gradual center bow that’s occuring (it’s only secured from the outside edges).

New myself as well - thank you for including a link to this bit. I’ll have to do a little research, as I’m on a tight budget at the moment.

Im planning on doing the exact same thing on my spoilboard as well to be sure along with the t nuts too.


Im wondering if the white side bit will be suitable for cleaning up surfaces before carving as well…

Depending on which router you’re using, that whiteside bit might not be a good choice. Looks like the packaging recommends running under 18,000 RPM:

The package indicates 3/4 to 1 1/2 inch Cutting Diameter 18000 Max RPM. 6210 is a 1 inch cut dia.
I used this one:


my first one I did with a regular 1/4 end mill took a while but no extra expense but I now uses the Whiteside linked above you also don't have to do the whole table to start just a area bigger that your project

I’m not sure how I quoted myself but the second router bit will work great also

I did not notice that at all. Thanks for pointing that out. I will have to do a little more research I guess…


Noted from another thread, I plan on picking up one of these to control the speed on my 660:

I purchased the Whiteside bit - Can anyone recommend a travel speed to cut with when resurfacing the spoilboard? I have a 48x48 table, and really don’t want this to take all day :frowning:

Do it right, or do it twice. If this but goes too fast, bad things will happen. Keep in mind that if you set Z=0 at a low spot, you could be cutting more than 1mm.

1 Like

First thing: it’s likely that nothing is flat in part because of your threaded inserts. You should have milled a little recess so that the heads wouldn’t protrude off the board. I suggest you to fix this, it will not only help with flatness, but also with vibrations and noise.

You’ll have to use some surfacing bit, as you already guessed it. As the others suggested already, you have to respect the maximum rpm your bit is designed for, otherwise it will be likely to explode in your face because of the centrifugal forces. It’s unlikely, to happen, but if it does it will be nasty.
As for which one to use, I can’t really say, it depends of what kind of power your router has, I’m not familiar with those dewalts, so I’ll let the experts tell you. :wink:

To surface the board, I suggest you to find some kind of pencil, randomly write all around the board. Then try to find the highest spot on the whole surface and do a 0.5mm pass first. don’t go deeper the first time because you cannot really trust that you actually found the real high spot, and you don’t want to suddenly dig 2mm of material with such high diameter bits.
After the first pass, you’ll still be able to see the low spots where the pencil marks remain. Do another pass, this time 1mm, you’ll be guaranteed that the cutter won’t ever face anything more than this now.
Repeat the operation as long as you still can see pencils marks on the surface.

Before all that, you’ll need to make sure your router is dead square to the surface, which will not be a piece of cake if your surface is crooked to begin with. So I suggest you to check for perpendicularity between each pass and adjust. That is, if you want a really perfect, spot on result.

Yes, it will probably take you a good part of your day. No magic here, unfortunately, but it will pay back later.


I’m likely going to run trials several mm above the board for this very instance. I have a feeling the center is bowed upwards, since the outer edge is bolted to the table.
I wanted to bolt it down in the center, but that’ll have to be something I consider on my next spoilboard, once this one is warn down.
At this point, I just need to get the thing functioning, so I can begin the process of making my investment back on it.

You can do a lot of work without having a perfectly flat spoil board. I have never flattened mine. Carving is the toughest. Through cutting and pocketing is no big deal.

I use the whiteside bit linked and never noticed its rpm rating (whoops). Definitely making a mental note of that!

I do two passes, perpendicular to each other at the same depth. Imperfect tram will leave ridges, the second pass gets rid of them (for me). Then I throw on the tram gauge and work on that if I feel its worth the trouble. Pretty sure I do 1016mm/min on speed with 1mm or less DOC. No clue where/how I landed on that number but its what I see in my last gcode file. Seems fast looking at it, careful with that if you just plug it in lol. It’s possible I saved some value to the project that I didn’t end up using somehow.

Someone else pointed out the inserts bowing your spoilboard up. I switched to something like to avoid that, also so I could install them from the top as needed because I’m lazy and didn’t want to screw in a million of the things at once. One of my machines was also 4x4 so that was a lot of holes. You have to be careful with those though, if you screw them down too far and hit the table under the spoilboard (if there is one), you’re bowing yourself again. They’re also zinc, the few times I’ve accidentally gone too deep the bit just goes through them like they don’t exist (for me).

Oh another note if you surface the spoilboard. However much dust you think it’s going to create, it’s worse than that. Have your vacuum/dust collector/dust masks/broom all prepared to do their jobs lol

1 Like

That’s more or less what my motivation was to pull the trigger finally. I shaved down the spoilboard yesterday and was pleasantly surprised that it was much more flat than originally anticipated. I’m not looking for perfection, so having a few mm off from one end to the other isn’t going to make or break at this point.
Luckily, I’ve kept busy from the design perspective, and I have a few projects that I can jump right into and begin, as all the necessary files are already setup and ready to go.

1 Like

I’m going a different path than the inserts, using C channel and smaller pieces of MDF between. I can get 1x4’ pieces of MDF in the building supply and just cut in half for my 24x24" build area. The other advantage is I can replace just 1/2 of the spoilboard if it gets messed up.

Painter’s Tape and Super glue…

1 Like