# Redoing my CNC Bed.... Suggestions?



## honesttjohn (Feb 17, 2015)

The bed wasn't staying level and my spoilboard was skimmed probably 1 too many times, and had to be shimmed to stay level so it's time to do something.

Here's how it looked with the spoilboard.










This is with the spoilboard removed showing the Rockler T-Track I put in the original MDF bed.










This is with the original bed removed.









I added 80/20 T-slot extrusions -- the end pieces are single slot 1.5" wide and the inside pieces are 3" double slot 3" wide - all 3/4" thick. Pretty sturdy stuff.










Now, I can either fill the open areas with another row of the same T-slot, MDF, or just leave it open. It's pretty level but I will still need to have a spoilboard to do text and carving on the material surface without having to skim each piece.

Any suggestions?


----------



## 4DThinker (Feb 16, 2014)

What I'd do in your case is look at the size of signs/plaques you normally make and then make a few MDF blanks close to that size that you can screw into the t-track using nylon screws into nuts that slide into the track. Slide one in and tighten it down. Mill it flat, then faster down your material atop it however you used to. Mill one down to the counterbored nylon screw heads and it is time to make another. If your projects vary greatly in size then make a few MDF blanks in a variety of sizes. 

You'll only have to mill a blank, not the whole bed when you need to be sure it is flat a level to the cutting plane. 

As for filling the area between the track sections with more track I would. It'll reduce the tendency for your blanks to sag between tracks, and give you more options for where you can use t-track clamps to hold down parts.


----------



## 4DThinker (Feb 16, 2014)

What I'd do in your case is look at the size of signs/plaques you normally make and then make a few MDF blanks close to that size that you can screw into the t-track using nylon screws into nuts that slide into the track. Slide one in and tighten it down. Mill it flat, then faster down your material atop it however you used to. Mill one down to the counterbored nylon screw heads and it is time to make another. If your projects vary greatly in size then make a few MDF blanks in a variety of sizes. 

You'll only have to mill a blank, not the whole bed when you need to be sure it is flat a level to the cutting plane. 

As for filling the area between the track sections with more track I would. It'll reduce the tendency for your blanks to sag between tracks, and give you more options for where you can use t-track clamps to hold down parts.


----------



## BalloonEngineer (Mar 27, 2009)

On my DIY CNC I did something a little different and I am happy with how it has been working out. My crossbeams are 40-8080 extrusion (80mm x 80mm, a little over 3" square) spaced 12" apart. Using carriage bolts in the t-track on the sides of the crossbeams I attached 2x4s standing a little proud of the crossbeams. I them surfaced the tops of the 2x4s to be all in the same plane as if it was a spoil board. On top of this I laid a sheet of 3/4" MDF. Since the MDF is very uniform, and it is resting on an already flat base, there was no need to surface the top of the MDF. 

This has several advantages:
1. What I had to surface was real wood, not nasty MDF. There is no danger of the 2x4s warping since they are firmly attached to the much stiffer crossbeams. 

2. The MDF was easy to screw down from the top into the 2x4s instead of trying to hit a nut in a t track that can't be seen. The screws are deeply countersunk 3/8 below the top of the spoilboard, so present no danger to a bit. 

3. I used a keyhole bit to mill t-slots into the MDF. I can add more anytime and anywhere I want. 

My work process is that anytime I am cutting all the way through a board, I raise up the board using some 1/8 hardboard, usually just some small pieces located under my hold down clamps. This means I never cut into my spoilboard so I never have to resurface the MDF. A sheet of 3/4 MDF is very heavy, and surfacing it creates nasty dust. A sheet of 1/8 hardboard is light, costs less than $10, and cut up into little squares, goes a long way. Plus I can just toss it instead of resurfacing it. 










Sent from my iPad using Tapatalk


----------



## Stick486 (Jan 4, 2013)

looks like yur short 3 to 6 cross members (joists???) to start w/ and the rim members could use stiffening........


----------



## MEBCWD (Jan 14, 2012)

John I would add more rails but I would also leave a small section at the front on one side where you can add a angle table like 4D 's design. Also as Stick points out you might want to add some more cross members. 

Like I tell most people, if you are not doing critical work that has to be right on then you don't need to nit-pick your setup to death. I just keep my t-track table as close as possible without nit-picking and use 0.25 MDF spoil boards to fit the job. 

Remember if you are cutting wood different woods cut differently. Softwoods usually have more fuzzies, some woods might need different feeds and speeds to cut correctly. Internal stresses and grain patterns in some woods can also cause cuts to be a little off but the parts can usually still be used without problems. 

Think about running a 3D job that takes 6 to 8 hours to cut and how changes in humidity and temperature during that time can change the freshly cut wood differently than the uncut wood in your project. Will you even be able to tell the cuts are different from beginning to end after sanding and finish is added?

John just get er dun and have fun!


----------



## RainMan 2.0 (May 6, 2014)

BalloonEngineer said:


> On my DIY CNC I did something a little different and I am happy with how it has been working out. My crossbeams are 40-8080 extrusion (80mm x 80mm, a little over 3" square) spaced 12" apart. Using carriage bolts in the t-track on the sides of the crossbeams I attached 2x4s standing a little proud of the crossbeams. I them surfaced the tops of the 2x4s to be all in the same plane as if it was a spoil board. On top of this I laid a sheet of 3/4" MDF. Since the MDF is very uniform, and it is resting on an already flat base, there was no need to surface the top of the MDF.
> 
> This has several advantages:
> 1. What I had to surface was real wood, not nasty MDF. There is no danger of the 2x4s warping since they are firmly attached to the much stiffer crossbeams.
> ...


Richard , that's a really neat ideal secured boards to the sides of the extrusion. Never seen that done before


----------

