Spoilboard Resurfacing

Basic spoilboard tips. January 28, 2009

I am new to the world of CNC and would like some input on spoilboards. I cut mostly 3/4 melamine and have my throughcut set to .006", I tried .004" but was not satisfied with the quality of cut at the bottom. My spoilboard is 3/4" MDF 5' x 10', my spoilboard program is set at .5 mm I am thinking that this is too much and I am wasting material on my spoilboard. I am thinking that .2 mm should clean it up. The dealer that sold me the machine and supplied the program says that .5 mm is standard and does not want to change it. What are others doing?

Forum Responses
(CNC Forum)
From contributor E:
I think you are correct in your thinking of less is better. I take off only what I need to remove most of the defects and get the surface flat. You didn't say what you’re running but on a 5 X 10 table this should not take too long. I happen to use MFD as my spoilboard and take a light cut off both sides on a new board to open up the pore and get better vac. then only what I need to maintain a good vacuum. My spoilboards last a pretty long time depending on what I'm cutting.

Second - you need to get to a point you are doing the programming and not some salesman or tech guy. It should be an easy thing to go change the z value in the g-code to get to the .2mm you want.

Third - remember who's machine this is. It’s not the salesman's place to be telling you no unless what you are asking is unsafe.

From the original questioner:
I did get into the program and changed the .5mm to .2mm and ran the program. It seemed to get out all my throughcuts and the spoilboard looked great. Yes I did surface both sides of the spoilboard when new. I have a 10 hp vacuum which seems to work fine on a fresh spoilboard but after several nested sheets I have trouble with small parts moving. With a lesser cut on resurfacing I will not be so reluctant to resurface the spoilboard. Is .006" a typical throughcut for melamine board?

From contributor E:

I don't know if there is a "typical" through cut. I have a small vac too so I onion skin and leave a .08 as a last pass, but a good share of that is getting trough the bottom ply of the wood. Look at the bottom cut and look at the vac pressure and balance the two to make yourself happy.

From contributor M:
We also run a 5x10 spoilboard and we also use 3/4" light weight MDF for our spoilboard. We have used regular density MDF but it 'fuzzes' terrible after each thru cut. The LWMDF is a dream to use. We also cut both sides open and we also seal the edges. Edge sealing is a whole other topic. We use 'Bondo' as it seals good, dries quick and by the time we go around the sheet it's ready to install. But to each his own on that subject.

We also cut thru a minimum of .005 on melamine parts for a good edge finish. Depending on how bad the board and cutter tip are we may go through slighty more if we are near re-surfacing time.

From the original questioner:
I have not heard about the Bondo sealing the edges. I am using regular MDF and I painted the edges with a latex paint. I have heard about edgebanding the sheet but getting a 5 x10 through the edgebander is a little difficult for me. I may have to try the lightweight MDF in the future. Thanks for the welcome to the world of CNC. It has sure taken up my spare time on the evenings and weekends and I am only scratching the surface of what this thing can do. I have so much more to learn.

From contributor M:
The program that came with my Thermwood actually asks me how much I want to take off, usually .010 to .015 for us.

From contributor S:
If you want to edgeband your spoilboard, you could always do it the old fashioned way. Buy pre-glued edging and borrow your wife’s iron and do it manually.

From contributor P:
I take off just enough to make the spoilboard flat again. I also "onion peel" the small parts if I think they will move. Of course you must consider cost but with a sharp bit and a flat spoilboard I like to go no more than 1/32 into the spoilboard or I use a compression and barely skim the spoliboard surface.

From contributor T:
We onion skin all cuts and if say we are cutting 18mm MDF we make the first cut -17.5 and the second cut 18.2 Your program should be flexible enough to machine any size board and any thickness. We use this to clean up table tops say 50mm thick with the first cut say 2mm off. We are now using 12mm MDF spoil boards.