Another update on this machine... I've got a couple more things to do:
- Find a way of accurately locating the PCBs on the bed, so I don't have to arse about aligning them every time (anyone who's set up a job on a milling machine will know what I mean...)
- Setup the Z-probe so I can do tool-changes mid-program.
Taking the second one first, I've identified that the tip of the tool is, conveniently, electrically connected to the body of the motor, which isn't connected to either positive or negative terminals. So I need to find a way of attaching the motor body to one side of the probe pin. For the bed, I can either use the copper surface of the PCB being drilled, or I could make a standard "puck" to do the job.
Anyway, having proved the probe actually works, I decided to do the first item instead.
So, the way this will work is: At a specific machine position on the bed, I'll mount a couple of fences, to which the PCB is aligned, before being stuck down with double-sided sticky tape. The first photo will make it clear (and if not, some of the other ones will put it beyond doubt!
)
First job, therefore, was to mill a couple of slots in that bed plate. To ensure they're dead straight and aligned with each other and the machine... I chose to do them on the machine itself
Remember how I said I didn't intend to do any engraving (let alone milling!) on this machine due to it's rigidity issues?
More of that in a moment...
So. Recently I bought a 2mm end mill for another part of this project. Seemed ideal! Plus it fits in the only ER11 collet I have, which is a bit of a Brucie Bonus. Mount it up in the machine, knock together a nice simple bit of G-code, Billy's your aunt, Fanny's your uncle, and everyone's very confused
I decided on 0.25mm cut depth, nice slow feed rate of about 100mm/min, as I'm really not convinced this machine's stable enough for heavy cuts, even in plastic. More about that in a moment...
So, off it went! I videoed the whole thing, and once I get time to edit it & do the timewarp thing (who wants to watch a noisy machine vibrate it's way around an "L" shape for 15 minutes?), I'll upload it into a post below. Thus, no photos of the process. However, it seemed to go OK. Noisy, like I said, and lots of vibration. This really isn't any cop as a milling machine... but it got there. I suddenly realised (3mm into the slot, which I'd planned to be 5mm deep) that my cutter was looking awfully close to the tapered section. A quick scan of Arc Euro's website for the bit showed - yep, the one I've got has only got 3mm depth of cut! As it was already onto the 3.25mm cut, I let it finish that, and stopped it. Result is the first photo, after a bit of a clean up.
Next, time to get the real milling machine out, and make an aluminium fence. First, I cut a piece of 6mm ali down to 2mm, 0.100" DOC (like NASA, I like to mix up my units. Keeps everyone on their toes
). Figured I'd better test it in the slot before I went much futher and... what's this?! Wibble-wobble! Break out the digital calipers and - crumbs! The slot is 2.3mm wide! Not good! That's where the lack of rigidity/vibration, or maybe it's backlash, shows up. So, if anyone was wondering, no: This is not suitable as a desktop milling machine...
Anyhow, this was no disaster for my purposes; I simply hacked off the 2mm bit & did a 2.3mm bit instead (I even got the old digital micrometer out for a bit of exercise!). After hacking it off the parent metal with the Deadly Dangerous Circular Saw From Beyond The Grave, and a bit of clean up, cut to length, repeat (the piece of metal wasn't long enough to do both), you end up with 2 tidy looking aluminium fences, per photo 2. These, gratifyingly, are a nice tight press fit into the slots, resulting in photo 3.
Happy days! Now I can simply line a PCB up to the two fences, stick it down, and I'll know it's exactly (to within the tolerances I need) where it should be! Plus, as it's only 2 sides, I can put different sized boards on without any hassle. As they're just push-fit, if I ever replace the bed, or need to drill a bigger board than I've left space for, I can pop them out, and either cut new slots on a new bed, or replace them once I'm done with the big board. (photos 4, 5)
All in all, a happy couple of hours machining
PS: Sometimes, the Chinese aren't too sharp with the PCB cutting tools... see photo 6 - this board's a bit wonky! When it comes to making the real thing, I'll probably use UK-sourced board, which I hope will be rather squarer cut! In fairness to the Chinese though, that's the only one that I've found that's out of kilter.
Next episode should be Z-probing, and possibly drilling an actual board!
