MDF wasteboard sag

EmilyMaker · September 21, 2015, 6:54am

So, Iv’e been upgrading my 500mm machine a lot, like a makita 1.25 hp spindle, a dust shoe, steel spar, y-skirts and I just finished upgrading to NEMA 23 stepper motors. Holy crap, this x-carve is a beast, absolutely no chatter or sag because of the enhanced rigidity from the spar, mills any material at any depth with the new spindle, and keeps itself and area decently clean thanks to the dust shoe and skirts. Also, through acts of my extreme frugal shopping powers, I’ve managed to keep the upgrade costs lower than the stock machine. (I love you inventables but you sell steppers for way too much)

I also just finished squaring my machine using this guide, and it made a serious difference, the y-rails are now totally square and it moves ever so smoothly with no resistance. I also squared the z axis with a few pieces of paper, and again, helps a lot.

However, after all this time I’m noticing something. I’m noticing that near the middle of the waste board the cuts are coming out almost 0.02 inches too low, and not cutting all the way through the material. It appears that this is caused by the wasteboard ever so slightly sagging where it isn’t supported, since my machine is totally square and calibrated.

What do you think I should do? I know that unsealed mdf will sag over time, I just didn’t expect it so soon. I was thinking about putting a sheet of mdf underneath the wasteboard and bringing the machine up off the table by a mm like a topic I saw on here earlier, and I don’t really want an extruded alum bed as I like the screen printed wasteboard.

IanWatkins · September 21, 2015, 8:43am

Emily,

This? Making 500mm X-Carve more "solid"

Best mod I’ve done on my 500mm X-Carve by far. Just the reduction in chatter while milling aluminium has already paid for the MDF I slid underneath.

Cheers

Ian

sketch42 · September 21, 2015, 8:43am

One of these:

and two of these:

Would probably do the trick, and it is how the 1000mm version handles the issue. You could also use some M5 button head cap screws and a bag of T-Slot pre-insertion nuts, as well as a few M5 button head cap screws. The button heads can go in a few holes that are counter sunk by about 5-6mm in the center line of the waste board.

DanBrown · September 21, 2015, 12:42pm

I’d probably go with Sketch42’s method, myself. Just toss another piece of 20mm extrusion under there for added support, looks like your table is beefy enough already that it’s certainly not the sag source! Alternately, if you have the rest of your wood shop already, just slap down a couple pieces of scrap maple or the like on your planer, and plane it down to 20mm.

EmilyMaker · September 25, 2015, 6:56am

It turns out I found a couple pieces of scrap acrylic laying around that added up to exactly 20.5mm, so I glued them together under the wasteboard and it totally brought the wasteboard back into square with the y-rails. Yay! And oh how wonderfully it cuts. Thanks everyone on the forums who have convinced me to upgrade, and @SamAlaimo who has been a huge help with stepper motors. I’m glad I upgraded everything on my machine, its gone from a hobby mill to futz around with into a reliable and insanely powerful beast that I can use for my business. Without this community the x-carve just wouldn’t be, well the x-carve !