# New Spoil Board for the CNC



## MT Stringer (Aug 15, 2012)

Recently I had become aggravated with the way my spoil board was working for me. It was mdf with T slot grooves cut in it. Although it worked fairly well, sawdust accumulation would hinder the clamp movement when I needed to re-position my clamps. A minor hindrance, but a hindrance all the same.

I started over with the clean bed that came from the factory. I might add a lot of measuring took place before I did anything. Several pieces I have been cutting lately fall on 16, 18, 20, 27, and 30 inches. I wanted to make sure the end of the work pieces would lay on the flat surface and not on an opening for the T track.

Finally, I proceeded to screw several pieces of T track to the factory spoil board. I ran out of the long pieces so I had to splice in two pieces end to end. That works. And I attached a piece across the back to make up for the shorter pieces. Test fitting proved I can set up the clamps and not interfere with the CNC if it gets back to near the rear limits on the y axis travel. Then I started cutting pieces of 3/4 inch MDF to fit in between. Eventually, I had covered the width of the factory bed.

My plan was to bore recessed pockets and 1/4 inch holes for nylon bolts so the boards could be through bolted to the factory bed below. Then it dawned on me...why not let my helper (CNC) do the work. After some careful measuring and making a test hole for the screw in T nuts, I realized the hole in the factory board needed to be 5/16 inch diameter. Since the T tracks were already screwed in place, I used clamps to hold all the boards in place.

I created three different files in VCarve - one each for 3,4 and 5 inch wide boards. The pockets and holes were positioned in the center of each board, four per board.

To accomplish the hole drilling, I set the x,y zero for each of the three size boards and ran the file for each size. Pretty easy. Moving to the next size board was done fairly quickly, just set the xy zero and run the appropriate file.

When that was complete, I put a 5/16 drill bit in a drill and ran it through each hole and the factory board. Then it was time to screw the T slots in from underneath the factory board. The T nuts I have have a shoulder on them and a socket for a metric hex Allen wrench. I cut one of my metric wrenches and chucked it in the drill and commenced to driving the nuts in the holes. Well, shucks, my table frame blocked access to the first four holes on the left end and that almost made it impossible to gt a wrench on the T nut and screw it in. So, I just used regular nuts and washers for those four. ...and on the right side of the machine, I couldn't use the drill but could use an Allen wrench and slowly screw the nut in to place.

With all of the spoil boards firmly bolted in place, I ran a file to surface cut the boards to insure the top is flat. I used a 1 1/2 inch flat bottom router bit and it worked great.

Almost finished. I created a file in VCarve to scribe a line along the x and y axis starting at xy zero. To do that, I used the mdi panel in linuxcnc to move the router 1 inch along both axis. Then I set the x,y axis to zero and ran the file. The router carved a very shallow groove (.010) along both axis. This is exactly what I wanted. As you can see in the pictures, I cut some 1/8th inch plywood into one inch strips and stapled them in place. Now I have a perfect 90 deg jig for my projects.

Note: At some point, I will need to replace the spoil boards and this should be an easy task. Since my xy axis zero is already set, all I would have to do is place a board in the jig, zero the z axis and run the appropriate file. Then unscrew each board and replace with the new ones, surface them and the new boards will be ready to use.

And this job is complete. It is ready to sling some sawdust! :grin:


----------



## 4DThinker (Feb 16, 2014)

Nicely done, and thanks for posting the photos!

My bed went through 3 (maybe 4) iterations before I settled on a solution similar to what you've come up with. The only difference is that my MDF filler pieces have a rabbet on the bottom sides that steps over the short horizontal flat of the t-track to set the gap between them only as wide as the 5/16" bolts I use with my clamps. This keeps the clamps I use from wanting to slip into the gap if aligned with the tracks. 

I also didn't want to lose any Z height clearance, so I trimmed and dropped the factory MDF bed flush into the frame and then added the t-track/mdf atop that. The bottom MDF sits on plywood ledges I've bolted into the frame inner sides.


----------



## rrrun (Jun 17, 2014)

I have mounted a spoil board to my factory spoil board, I started using push clamps to hold pieces in place. I've recently taken to just using screwed holding blocks for my repetitive cuts ... when you're cutting 20+ boards all of the same size, that seemed reasonable to me. The system is not without fault, though, and I don't use hold *downs*, just borders that hold the piece *in place.* 

And when I say the system is not without fault ... guess what that means?

So, is this T-Track method - perhaps with 4DThinker's sunken spoil board to gain some precious Z - the best practice?


----------

