Holding down your workpiece on the CNC can be very difficult and clamping from the top is just asking for your bit or dust boot to run into it. I have made a wasteboard with a clamping solution below the surface of your material. This will ensure you never run into anything you didn't mean to.
24”x48” Workholding Wasteboard Files
3 x 1/4-20 T-Nuts- http://amzn.to/2G8JpY8
1/4-20 Hex Bolts - http://amzn.to/2u1GyuV
1/4-20 Washers - http://amzn.to/2GJEpqC
1-3/4 1/4-20 T-Bolts - https://amzn.to/2G1NX21
18 x 1/4-20 Nut - Buy from big box store
2’x4’ sheet of 3/4” MDF
Scraps to make fence
Let’s Get Started
You'll need to purchase the items under the "Items Needed" section before starting. I have included ready to cut Vectric V-Carve or Aspire files depending on the program you use, as well as SVG files if neither of those work for you. All items referenced are included in the files you purchase. Be sure to check all toolpaths and settings before running any of these files to make sure your bits match up and change where necessary.
Before you start on the wasteboard you may want to run the "6x CNC Cam Clamps" included file using your current hold down method (brad nails, screws, double sided tape etc.), if not, you can do it after the wasteboard is complete.
1. Home the machine to the front left corner and run “24x48 Home Positon Groove” to get exact edge of machine limits- x and y zero set to home on machine with a v-bit
2. Place 24x48 piece of MDF on exact home line and use current workholding method to hold it in place (ensure you won’t run into clamps or screws with the toolpath)
3. Set X and Y zero to the home position and z to the top of the MDF
4. Run “T-Nut Through Holes” from the “24x48 Wasteboard Bottom Side” file with 1/4" Endmill (up cut will work best for better chip evacuation)
5. Run “T-Nut Pocket” from the “24x48 Wasteboard Bottom Side” file with 1/2" downcut bit (downcut here will provide the cleanest surface on top and you can switch this to a 1/4” Endmill, I used a 1/2” to save time)
6. Pull off of machine and insert t-nuts on back side
7. Make sure all t-nuts are hammered in below the surface of the MDF
8. Place back on CNC flipped over with the fence side at the same home position line from before
9. Clamp/Screw back down and run the “24x48 Wasteboard - Topside T-Track Holes” file to cut the holes to bolt it down
10. After cut, remove clamps and bolt down wasteboard using 1-3/4" x 1/4-20 t-bolts and 1/4-20 nuts - need 18 total
11. Flatten the wasteboard using the largest flat bit you have, I used the Amana RC-2255 on mine, change the tool used if you are not using that bit (could use 1/4” endmill, it will just take a long time) File -”24x48 Wasteboard - Topside Flatten and Fence” Toolpath - “Topside-Flatten Wasteboard Pocket”
12. Run fence t-nut file for clamping spots under fence using File -”24x48 Wasteboard - Topside Flatten and Fence” Toolpath - “Topside-Under Fence clamp T-Nut Pocket” and “Topside-Under Fence Clamp Through Hole”
13. Insert T-Nuts in holes just cut
14. Clamp/Screw/Nail down 48" x 1" and 23"x1" Fence pieces and run the fence hole file to drill out holes to bolt fence down set Z-zero to the top of the fence. Use File -”24x48 Wasteboard - Topside Flatten and Fence” Toolpath - “Topside-Fence Bolt Head Pocket” and “Topside-Fence Bolt Through Hole”
15. Remove clamps and ensure all holes are free of sawdust
16. Insert a washer and bolt into each hole and tighten the fences down to the wasteboard
17. Run “Topside-Fence-Square Fence” and after that's finished run “Topside-Fence-Clamp Through Holes” to finish off the wasteboard. Be sure to set the through hole depth to the thickness of the fence stock. Make sure you go about .1" deeper on the facing path into the wasteboard to cut a sawdust trap so it won't affect your clamping up against the fence.
18. After that ensure all of the sawdust is out of the holes and your wasteboard is done!
19. If you haven’t already cut out your Cam Clamps and the side holding pieces and enjoy using your new wasteboard!