[4DThinker]

I have a Probotix Meteor CNC, and enjoy their design for it's aluminum extrusion 3060 t-slotted frame with nothing running inside the frame. Over the years I've had it I frequently find a flat hardwood part I've clamped to my MDF t-track bed doesn't cut through evenly all around. Even if I've just milled the bed flat using the CNC. Lately on a mission to tighten up the precision of my Meteor I realize a piece of hardwood with a little warp in it that I clamp flat to cut is warping the MDF bed rather than being pulled flat by the t-track clamps.
A few years back I made some bridges to span between the Meteor side rails to hold an assembled student project inside the frame so I could cut mortise arrays on the bottom for her legs. The bridges are an L shape made from 18mm BB ply and very stiff. They don't flex once bolted to the frame rails. In a moment of inspiration I wondered if 2 or 3 frame bridges, a little fancier than my initial two might be all that is needed for holding flat work down to cut.

So I've made 3 bridges in a T shape that have a single t-track down their middle, a row of holes for pegs to help align projects with, and cam levers on their ends to make it easy to release and move them up or down the frame rails for each project.

Two shown in the attached photo. I use a 3rd when clamping longer boards that might droop or bow up between two.
4D

 

[TimPa]

not sure that i have the total picture, but, i believe that an mdf work table would need substantial (internal) supports to reduce or minimize flex during cutting operations. the more the better. mine are welded steel members, then i have 2 layers of wood/mdf on top of that.

the 2 hold down methods which work for the parts i am cutting are: painters tape/superglue, and screws. sometimes both on smaller parts. i typically use tabs to hold the parts in place.

alternatively, i see no reason that you couldn't use your bridges to support your work. whatever works for you...

 

[4DThinker]

I get so many different furniture part projects to cut that I need flexibility in how my CNC is set up to deal with them all. If I was always just cutting the same flat parts I'd add a few cross members, screw down a new MDF sheet, mill it flat with the CNC, and then jig up the best strategy for holding the parts down. I like the Probotix CNCs for their open frame, and have mine mounted on just 4 cedar posts with nothing under the CNC except a tool chest I can take out if it is in the way for some project cuts. I've gotten in the habit of figuring the best way to clamp a part down/secure before even setting up the job to cut what I need from it. From there I can pick the best place to zero the bit from, the best place to have it home to, my Z clearance to make sure no clamps get cut through, etc.. These bridges can easily be slid up and down the frame, or removed completely if they'll be in the way. I can use my t-track clamps or c-clamps to hold parts down to the bridges. I'm thinking of making two more that will run between front and back rails for the occasions when I have a long part that would be best clamped on the ends. These bridges can also be mounted on the bottom of the frame rails for when I've got thick work that needs more Z axis clearance above it.
4D