Knobs


Overview and G-Codes

It can be handy to move the axes by hand rather than by jogging, especially during job preparation. A variety of knobs on the axes make this easier.

Control knobs work well with some steppers. Knobs with a 1/4 inch bore and a set screw are easily attached to the stepper's shaft.

Knobs similar to this old style volume knob are available from Mouser.

Control knob on stepper.
Control knob on stepper.
 
Knob cut with round bit.
Knob pressed on pulley hub.

Knob cut with straight bit.
Knob with clamping screw.

A disk that is cut with a hole saw makes a serviceable knob; simple CNC cut knobs also work well.

The g-codes for the knobs are linked at the bottom of this page.
As shown in the photos the center hole of a knob can be drilled larger so it will fit tightly over the hub of a pulley.

A slot cut in the knob can be clamped shut with a screw and nut as shown next. The screw head and nut can be recessed in the knob.

These two "cookie" knobs use the same g-code. The top one was cut with a 1/4 inch round end bit, and the lower one was cut with a 1/4 inch a straight bit.

The center hole that is bored with the CNC work is slightly over 1/4 inch in diameter. It can be enlarged to the desired size with a drill.

These knobs are ~5/8 inch thick, but the g-code is for 3/4 inch stock. An initial roughing pass removes excess stock.

The final CNC pass leaves tabs that connect the knobs to the stock. The tabs can be cut with a knife or chisel after the job is completed.

Z zero is the top of the 3/4 inch stock. X zero, Y zero is the lower left hand corner. The bottom of the cut is −0.8 inch (negative 0.8 inch). A spoil board under the stock protects the table top.
 
Knob 2D.
Simple 2D knob.
This 2D knob is cut with nine identical passes. A tenth pass leaves tabs that connect the knob to the stock. A center hole is marked but not bored.

The g-code is for 3/4 inch stock with Z zero at the top of the stock. X zero, Y zero is the lower left hand corner.

Thinner stock can be used, and the first few passes will cut air. Take care that Z zero is 3/4 inch above the table bed or the bit will cut deeply into the bed. The bottom of the cut is −0.8 inch.
 
Knob with tee nut.
Hold down knob with tee nut.

This is the knob that is used with the hold downs as described on the Hold Downs page.

The knob was designed to be cut quickly with horizontal roughing cuts, no parallel passes. Because of this, it is not highly finished, but it only takes a few minutes to carve.

The knob is approximately 2.5 inches in diameter.

The code is for 3/4 inch stock. The cut is less than 3/4 inch deep.
MDF works well with this cut. There is no grain to split other than the laminations, and they make removal of the knob from the stock easy. Simply "peel" the finished knob from the stock.

The code was made for a 1/4 inch round tipped bit. A flat end will also work, but the knob's edges will be stepped rather than smooth.

X zero and Y zero are just inside the lower left hand corner of the knob.
The clearance plane is at 0.81 inch.
Z at 0.6300 should lightly cut into the top of the stock. This will leave some material at the bottom of the stock.
Z at 0 is the bottom of the cut.

For setup, the Z axis is lowered until the bit rests on the top of the stock. Then the Z axis' DRO is set to 0.63.

In Mach the DRO is set by clicking the DRO box and entering the desired value, and then hitting Enter.
 
The codes have been simplified to only use G01 moves. All arc and circular motion is broken into short line segments. This is done so the codes can be used with basic controller software.

These short segments will cut more smoothly with constant contour activated. (G64 in Mach)
The first few lines of the code may need to be deleted with TurboCNC.

Disclaimer: These codes have been tested on my CNC systems and have worked well.

You assume all risk and responsibility when using them.
 
G-Codes           Cookie Knob      2D Knob         Hold Down Knob