Hold Downs

Hold down clamp
Knob with rod and foot.

Hold down knob
Knob on slotted board.

This hold down consists of a wooden knob with a tee nut insert that is threaded onto a section of 1/4-20 threaded rod. Rods of 5/16 and 3/8 inch have also served well. The 1/4 inch rod can strip with heavy use.
The hold down clamp is a piece of 3/8 or 1/2 inch stock with a slot cut in it.
The slot is easily made with the CNC machines.

The threaded rod is either screwed into tee nuts that are pressed into the underside of the table bed, or it is attached to a foot that slides in the tee slots.

The foot on the threaded rod is a piece of 1 x 1/8 inch metal flat bar that is drilled and tapped for the rod.
Loctite, epoxy, or solder secure the threads in the foot so the rod will not turn as the knob is tightened.

A locking nut to secure the foot can be used with deep tee slots, but the nut will not fit in the commercially made tee slotted MDF from home centers.

The g-code for the knob is explained on the Knobs page.
Sacrificial Spoil Board
Spoil Board on 10x9
This image is of the 10x9 table with a sacrificial spoil board that is screwed to the original smaller table bed.
This spoil board can be as large as desired as long as it clears the gantry ends.

Clamps can be used around the perimeter of the spoil board, or the stock can be screwed directly onto the board.

Tee nuts for supporting the hold down clamps can be embedded in the bottom of the spoil board as well.
Fender washer hold downs
Fender washers support stock.
Here an odd sized piece of plywood being held to a table bed with drywall screws and fender washers. The bed does not have a hold down system.
The screws work well, but over time they leave a lot of holes in the table bed.

In the photo, a piece of cardboard placed under the stock serves as a spoil board that protects the table bed from the router bit.

Sacrificial Spoil Board
Tile board as a spoil board.
The next image shows a piece of 1/8 inch tempered hardboard (tile board) being used as a spoil board. This material is flat, smooth and inexpensive. It has served well.
It can also be handy to secure this hardboard to the table bed and to use the router bit tracks for aligning other identical parts. This can make setups faster.