Making PCB's

[Galoot]

This project has been a long time in the making. I recently built a GRBL CNC controller and last week got a Sherline 5410 mill. This evening I made my very first isolation routed PCB. This first attempt is for an SMD RF pre-amplifier so is only 40mm X 50mm. I'm 90% happy with it and it will only get better from here. I don't have the right collett yet for the cutter and am waiting for a high speed air driven spindle. Think dentist drill. This attempt was cut using a Chinese cutter in a 1/4" Jacobs chuck at 2800 RPM; definitely not an ideal speed for this operation. I have a high grade carbide cutter and with that mounted in a collett and run at 30K RPM or so will make for a cleaner finish and of course I can then up the feed rate. Other improvements - reduce the depth of cut by almost half and make it smaller. Maybe microstep more - currently running 400.
The next project is to migrate to LinuxCNC. I have a vintage PC that I just got loaded and working. I went through 4 duds before I got one with a low enough latency to software step.
All that is required for it is a breakout board and hookup to the steppers to make it go. I'm new at this so for now GRBL works fine for me.
Anyway, that's what I've been doing..

 

[PeterT]

Wow, not thats that's a Tech-ey looking shop there. I don't have any CNC experience so will just have to watch from the sidelines lol
I'm curious about the HS air spindle you have coming. Do you have a link? What will drive the rpm control (like pressure or flow valve) then or will you just manually set it for the job at hand?

 

[Galoot]

It's this one: https://www.sherline.com/product/8900-high-speed-engraving-spindle/
It's made to fit the Sherline and I liked the runout spec. It is backordered but hope to have it in a month.
There is a knurled knob on it to adjust speed and I don't think I'll ever use it's max 54K RPM without thinking about getting a tooth filled! I have tried one before on wood and whatever you apply the cutter to just vanishes. A good feature with copper which has a tendency to gall. My thought is I can up the feed rate considerably doing it this way. As far as actually setting a speed goes, I'll just go by sound. One CNC made for PCB's has a spindle speed of 20K so I imagine something that sounds like 20-30K should be fine and the poor little bearings may enjoy a longer life.

 

[Johnwa]

I can’t see why you aren’t 100% satisfied! That looks really good.
What software are you using to create your gcode?
And more details on the air spindle.

 

[Galoot]

I can’t see why you aren’t 100% satisfied! That looks really good.
What software are you using to create your gcode?
And more details on the air spindle.

Thanks! Well, couple of reasons: I overcut the depth: -0.22mm instead of -0.05mm. That's huge!! There was a tiny bit of copper galling due to the 2800RPM speed and with 160mm feed rate the process took longer than I expected. The galling was a biggie to me and only visible under a microscope. It was not much, but still... Also I wanted to engrave the silk screen on it and didn't think it was possible & just found out after making it that it was possible. And no matter how small I make it, it could always be smaller so there is room for improvement there for sure. Finally, not being 100% happy = reasons for new tool acquisitions.
As far as software goes, lots. I start with a circuit simulator LTspice. When I'm happy that it works I use KiCad to layout the PCB. Then take the gerbers from KiCad to FlatCam which outputs the G-Code for trace routing and hole drilling. I take that G-Code into bCNC and perform a height map since when cutting to a fraction of a mm, any variation in flatness is a bad thing; some copper is cut too deep and areas may not cut at all. This essentially modifies the G-Code and allows Z axis cut depth to vary based on the map during cutting. bCNC then just sends everything to the Arduino.
I'll post air driven spindle results when it eventually gets here. Everything is slowed down these days due to you-know-what.

 

[PeterT]

I cant offer much for practical advice other than machining copper can be a bugger at the best of times. Its malleable & tends to stick to cutting tools, plug or constrain chip flow & adversely affect the cutting edge. The universal solution is some kind of cutting lubrication, WD-40 works amazingly well. I've also had to cut G10 for other projects & that material is challenging for different reasons. I know there are specific burrs used on G10 that look nothing like what the metal industry uses. I think circuit board stock is kind of a sandwich of those two? Anyways I'm sure you have the right cutters but maybe there is some experimenting you could try on that front too. I occasionally use some carbides like this (peck drilling not milling), typical Ebay specials. I can believe how cheap they are. But who knows, maybe they are clocked out vs. brand new & that's why.

 

[PeterT]

This place was mentioned on another forum, Not sure if its showing anything new you haven't seen. (No affiliation pr purchaser experience)
https://www.precisebits.com/applications/pcbtools.htm
https://www.precisebits.com/

 

[Galoot]

Thanks! I came across that site a while ago and they are great bits. It was the prices that worried me. I already crashed one of the Chinese bits.