Inventables Community Forum

Modified Millings rates for PCBs

I am working on a Carvey and will be milling FR4 PCB. I have looked up some numbers that seem to have been developed for milling this material but I must make adjustments for the bit types and spindle speed of the Carvey.

Recommended spindle speeds are 20k-60k RPM, I have simply divided the 12k RPM of the Carvey by the suggested spindle rate, then multiplied the result by the suggested linear feed rate. I assume that the depth per pass can remain adjusted (can anyone confirm this?)

The problem I must understand is how to adjust for bit type. The bits that these rates are specified for are for ‘diamond cut 5-flute’ bits (see pic below)
Diamond Cut Bit

*note: These rates are specified for FR4 Fiberglass PCB
These rates are for ‘submicron carbide’ (I assume that means “marketing BS, just solid carbide bits”), however the bits I will be using are from the Inventables guys for PCB drilling
(see below):

Inventables PCB Drill Set

I have the (uneducated) impression they will hold up better than the V-Carve bits in this material. Is this a correct assumption??)
(see below)
Inventables PCB Mill Set

  • I plan to mill 3 ounce copper instead of 1 ounce copper the rates were developed for, I expect that milling thicker copper simply means the bits get to work with more nice soft copper and will last longer, no changed to feed or plunge rates? Can anyone confirm or refute this?

I do understand this glass substrate will be hard on the carbide PCB bits, my main concern at this time is to not break the only bits we have as I need them for current project. With a new machine like this breaking bits will sort of make me look like my opinions are no good so i want to be careful about breaking bits most of all, wearing out bits is ok at this time.

I plan to look up some diamond coated bits as I intend to continue to work FR4 in the Carvey. What is the purpose of the ‘collar’ on some bits but not others, does this tell me how to seat the bit properly for machines that do not self zero z-axis at the start?

EDIT:
is the inventables PCB drill set chisel point or flat end mill? Perhaps I might as well use the milling bits?

I am milling PCBs on the Carvey but using FR1 copper blanks as I thought using FR4 was dangerous with the glass particles.