T|Tech Tips - AKA Ron's Rules
Depth of Cut
A common mistake made by experienced and new users alike is setting the milling depth of a tool too deep. This accelerates tool wear even causes premature tool breakage. It’s a good idea when setting your depth of cut to never allow the milling tool to cut any deeper than what’s required to remove all of the copper.
It’s helpful to know how thick the copper layer is before proceeding. For half ounce board material, the thickness is .0007”; one ounce board material is 1.4 mils thick; two ounce board material is 2.8 mils thick. I would suggest using the feeler gage that came with your RF/Microwave protoypes tool kit to correctly set the depth of cut. For half ounce board material, I use the 1.5 mil feeler gage. The 2 mil feeler gage works well when working with one ounce board material. Set the depth of cut to equal one of the above values. Refer to the users manual if you are not clear on how to adjust the depth of cut.
Once you have set the depth of cut to a value that is satisfactory for your particular board material, it would be a good idea to check the setting of the solenoid. The solenoid can be adjusted to increase the downward force or to reduce the force. Generally speaking, larger diameter bits can tolerate the full force of the solenoid. Adjust the solenoid so the e-ring is about 1/16” from the body of the solenoid housing. A word of caution here: if you adjust the solenoid armature too close to the solenoid housing, it will interfere with the downward motion of the z-axis…in fact it will will act as a stop, preventing the z-axis from completing its downward stroke. For smaller diameter bits (i.e. 15 mils or smaller), turn the solenoid adjustment counter clockwise 1 or two turns; this has the effect of reducing the strength of the downward motion and thus reduces the chance you will destroy your bit. Once you understand the relationship between the size of the bit in use, the solenoid adjustment and depth of cut, you will able to mill some fine prototype PC boards will extending tool life.
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