Here I am going to show you how to upgrade the steps per inch from 1909.86 to 2123.7

This is done by changing the CNCRouterParts 20 tooth timing pulley to an 18 tooth timing pulley.


First, let me start off by saying:

This upgrade will gain you about 11.5% in resolution.  If all you cut on your KRMx02 is wood products, you probably don't need the added resolution.  So the cost of the three pulleys ($60) wont be worth it to you.  I do a lot of aluminum milling and feel any increase in resolution and torque is worth it.

Second, if you did not install the stock 1/4" shaft motors the book calls for, you can not do this upgrade. 

You will need three 18 tooth x 9mm wide timing pulleys.


SDP/SI 18tooth Timing Pulley

Note that these are better quality pulleys. They use a clamping operation to hold the pinion instead of the grub screw. I have found this system of holding pulleys or collars much more efficiant, and it does not damage the motor shaft.


Y Axis Conversion

Start by loosening the turnbuckle on the Y axis drive.

Carffuly disenguage the turnbuckle from the spring.  Be sure to support the drive so that it does not slam down against the steel angle.

With the power removed from the KRMx02 disconnect the 9 pin conncector from the cable.

Using a 6mm allen wrench remove the drive assembly.  Be carfull not to loose the small thin spacer that sits between the mounting bolt and the carriage.

Remove the 4 screws holding the motor in-place.

Using a 2mm allen wrench, loosen the two grub screws holding the 20 tooth pulley in place.

Slide the pulley off the shaft.  If the pulley i too tight, you can slip a flat head screw driver between the pulley base and the motor and pry it off.

Loosen the 7/64 hex head screw on the 18 tooth pulley. and slip it onto the shaft.

The bottom of the grooves should sit .518" above the motor.

Tighten the screw.

Reinstall the motor and add the timing belt.

Using this picture as a reference, snug the bottom screw. Then, while prying with a flat head screw driver against the nut tighten the top screw.

You want the belt very tight.

Tighten the other two screws.

Re-install the drive assembly and attach the 9 pin connector to the cable.


A Axis Conversion

The A axis drive is identical, but you must pull the 9 pin connector through the opening before removing it.


X Axis Conversion

The X axis conversion procedure is pretty much the same as the Y axis.

You may have to shuffle the cables a bit in in order to gain access to the turn buckle and connector.


Mach3 Configuration

The original "Steps Per" setting for the 20 tooth pulley is 1909.86 for the 

X, Y, and A axis.

Change each of them to 2123.7. Make sure to hit the "Save Axis Settings" button before going to the next axis.


Update 5/5/2018

Calculating Steps Using the Long Method

While the original 2128.93 setting worked for me, I found that I was running long when milling over large distances.  I came up with a better system for setting up your steps.

Here is how I came up with my new setting of 21.23.7.

Step 1

I started by marking a very thin line on the left side of my machine.

I then marked on 15" over towards the right side.  Notice how I use the 1" mark for the starting point.  Then mark it at the 16" point.


Step 2

Place the edge of your bit in the center of the line, then zero the X axis.



Step 3

Move the machine exactly 15" to the right. You can use the manual Gcode entry from the MDI pane.

Into the Input field, type:

G0 X15

and hit Enter.

In my case you can see that it was visibly off. If the bit edge ends up further than the line there are too many steps and you need to reduce them.

If the edge sits shy, you will need to add a couple steps.


Step 4

To adjust and retest, first move back to your x zero position:

G0 X0

now open up the motor tuning form and change the x axis.  Start by adding or removing 2 steps.

Once entered you zero point will be off slightly.  Zero the X axis again.


Repeat as Needed

Go back to Step three and move the bit 15" to the right.

Continue adjusting as needed.


That's it.  You now have an extra 213 steps per inch and a little more torque.