Hi, I have a 8 by 4 Chinese nesting machine with a pvc table with t slots, 6 vacuum inlets and a machined grid for gasket seal. i ve been told to glue the spoilboard on top of the table but I don’t feel confortable with a glued solution, reading the forum and in some videos I see solutions that screw the spoilboard using nylon screws and it seems to me a more flexible option. my table does not have threaded inserts for this so I’m wondering if I should try to drill and tap them or use the t tracks instead. Also not sure how to locate the t tracks precisely in order to drill the spoilboard. I read about edge finders used in metal milling should I use something like that? Many thanks!!

Forgot to mention that right now I am using the spoilboard with just the vacuum suction which works ok but I’m getting inconsistent results when trying to improve precision when milling pockets, my hunch is that the spoilboard warps slightly in some positions of the working area causing a non square cut most noticeable in pockets and slot based assemblies.

if you have a machined grid for gaskets, you shouldn't need any fasteners. When initially placing the spoilboard, you should machine both faces. Check to see if any of the gasket has not rolled out of position when sliding the board onto the table.

I bet it's not the spoilboard, what type of vac do you have ? Also once milkws it should sit flat no matter what's below it.

So probably an issue elsewhere.

Can you post a photo of your table?
BH Davis

Big difference between theory and reality here.

Don't mess around with half measures - screw it down and not only on the perimeter. We try for no more than 16 or 18 inches between screws.

If you only secure the perimeter the spoilboard will bow up in the centre when surfacing causing varying thickness. This will show up in varying depth pockets as the material is pulled farther down in the centre under vacuum.

If you have a borderline pump you will see pockets depths change when pocketing out one piece MDF shaker doors since the vacuum will vary as material is removed.

Also you need to buy the biggest pump you can afford.

hate to disappoint yall but i have a dekker 40hp vfd & i dont get great vacuum power at 27hg. i really believe my 20hp blower vac system works much better @ 16hg. what i have found is that with a liquid ring vac. is that it will not pull down your parts like a blower will. if the edge of material is raised a blower will pull it down but a liquid ring will just lose the vacuum & not actually pull the material down. sorry for let down. at least on my end.

Just curious, if a spoilboard is screwed down, what are you screwing into?
Not questioning anyone, just not familiar with this .
He mentioned his table has a machined grid, so most are a hard material, phenolic or aluminum.
Personally never had problems with this. Even after many days of no use, never had the board warping or curling on edges.
Is the table flat, machine level, frame twisted? Humidity ?

Thanks for all your responses!! It seems a complex topic with many variables. I believe my table is plastic, probably phenolic and not pvc as I said on my first post, picture attached. My vacuum is a becker pump just 5hp, I know is low but based on my electric setup I cant go for a higher pump so I need to make the most of this using various strategies -for fulll nested sheets with large carcass pieces works well with a good tolerance- for smaller pieces with mortises and tenons joints I am trying to get better accuracy on pockets.

My hunch is that the spoilboard does not lies perfectly flat because pockets tend to be slighty smaller than the program -something between 0.01-0.02 inches smaller than the program- and it is not consistent across the table surface so it shouldnt be a misalignment of the spindle-

Right now I have gasket around three areas such in the picture and the spoilboard feels pretty fix once the vacuum pum is working. CNC manufacturer told me to glue the spoilboard to the table to get a perfect flat and perpendicular base once is surfaced but I am reluctant to glue it, I heard that some people get good results by screwing the spoilboard using nylon screws, I would rather go for something like this if will increase my pockets accuracy.

Thanks again for all the answers!!

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@Dropout, how do you screw the spoilboard to the base using threaded inserts and nylon screws? Could I fix it using just my t-rails? Thanks!!

Nylon screws. Solid carbide spinning at 18000 RPM and moving at 800 IPM hitting a steel screw isn't good :)

T tracks should be fine.

We cover the spoilboard overnight when the heat is on to prevent warping.

Are your pockets having depth issues or dimensional issues?

Thanks, great tip about protecting the spoilboard overnight!

Depth seems accurate enough, I am finding more innaccuracies on the actual width of pockets -between 0.01-0.02 inches, always less than the programmed width- thats why I think is the spoilboard not being completely perpendicular to the spindle and/or warping in certain areas.

Will get some nylon screws, use the ttracks to secure the spoilboard and report back

I have always found that inside pockets are never the proper size and I always end up programming them with a 0.005 to 0.010 offset to get what I want.

Also, if you aren't already, cut the pockets first, then the outside. That way you will be sure the material isn't moving.

Interesting, I need to do more testing then...

Yes, first drillings, then pockets and finally outlines would be my settings.

Thanks!

If you do 2 passes on the final cuts try:

First pass outside
Drill
Pocket
Second pass outside - smallest parts first

You should get better dust collection

Some of the topics covered so far are things I have experienced with a spoilboard that just sits on a plastic grid.A the machine is sited only a hundred yards or so from a river,with weather that goes from quite warm to quite chilly,we have found that covering the spoilboard when not running the machine is a big help.Otherwise the top surface expands or contracts,the sheet bows, and the lack of contact with the table makes it hard to get a seal.The other thing that happens is that the Z datum moves up and down which necessitates establishing it each day if the depths are critical.

When the OP mentions that holding a full sheet isn't a problem,does that indicate that the table doesn't have zones that can be turned off? If so,the old standby of a piece of plastic over the unoccupied area can improve things.

Pockets coming out undersize is something that almost certainly has nothing to do with the spoilboard.In no particular order I would check tool size,wear on the Z axis or wear on the spindle bearings.Tool size is easy,just cut a groove and measure it to see what the tool is actually cutting.For worn components,cut a square of the same size-once with a conventional cut and once with a climb cut and compare the two.

Many thanks Routalot! I will follow your suggestions and make those checks on the machine.