After a two week hiatus from the MPCNC, I got the itch to get back to making things. I wanted to salvage the spoilboard as much as I could, level it out, and create a few clamps to make workpiece holding a little easier.

Spoilboard Recovery

Last time I worked on the CNC, I ended up with a two part spoilboard where the second part did not match the alignment of holes in the first part. This essentially rendered the two-part assembly useless.

Surfacing Bit

I decided to make the lower part of the board the only part, which meant using a surfacing bit to make the entire work area level and perpendicular to the router.

Countersunk Inserts

I planned a 1mm clearing operation over the entire work are of the board (776x511 mm, or a little over 30x20 inches). To keep from hitting any of the threaded inserts, I drilled them further into the board, leaving a few millimeters of of space between the top of the insert and the spoilboard surface.

A few passes

After a few passes, I could tell this was the right choice. The cut took about 10 minutes to clear the board.

Dusty

I was surprised at how much of the generated dust was not collected by the vacuum. I am using an inexpensive wet/dry vac designed for cleaning cars, which pulls less current than my main shop-vac.

Don’t forget to wear your dust mask

To make sure nothing goes wrong during cuts, I have been staying in the garage with the machine during the entire cutting operation. Don’t forget to wear your dust mask!

The spoilboard came out nice and flat, and I was ready to move on to the other part of the project.

Workholding Clamps

A key part of any CNC router is a workholding system. This can be a simple as double-sided tape, to as complex as hinged clamps that slide on a t-slot system. For my MPCNC, I wanted a set of slotted bars could be bolted into the threaded inserts, resulting in a low profile and easy-to-use clamping system.

First Try

My first try was with 3/4" plywood. If I had put a little more thought into this, I would have realized this was going to be way too tall. It did give me a chance to test out my feeds and speeds on this type of material. A few false starts later, and I had my first clamp.

Stock

I realized I wanted something a little smaller than the plywood. Looking around the shop, I found a few 8x8 inch pieces of 2 mm sheeting I had originally used for laser cutting. This was a little too thin for clamps, so I sandwiched three of them together with some wood glue to make a sturdy 6 mm piece of stock for my clamps. This was left under some cement blocks overnight for the glue to dry.

Making do

The next morning, I planned out a cut of 6 clamps, which should give me enough to work with for the time being. Using a few washers and my thick plywood clamp, I tightened the stock down and set up the operation.

Making more

The clamps were designed to be 4 inches long, which stretched beyond the end of my material. Since the inner slot is still intact, I don’t think this will cause and problems or clamping failures.

Front Side

15 minutes of machining later, and I had my clamps cut out.

Back Side

Since the stock was 6 mm thick, and I set my cut for 6 mm, I ended up with a few spots where it didn’t quite cut through. If i had set the cutting depth just another millimeter thicker, it would have cut clear thought everywhere. All I had to do was bend the board a bit, and the pieces snapped right out.

After some Dremel work

After a few passes with a sanding drum on a rotary tool, the clamps were ready for use. This will make it much easier to set up future cuts without scrambling and scrounging around for washers and makeshift clamps.