PCB Mill from spare parts

[Rhodan]

Before I start on a MechMate I figured I'd make myself a little machine for PCB making. Right now I have to change spindles and add a tabletop (which has to be surfaced since more than a couple 'thou deviation can blow a board). Of course PCB's need enclosures and enclosures need routing so I have to swap spindles a few times while I get the PCB and Enclosure to actually work together! In other words, I really need two seperate machines.

I have a few odds and ends laying around as well as the old gantry rails and linear bearings (3/4") that I replaced with supported rails recently so I decided to make a light duty router for engraving only. Its very light duty so I can cheap out on a lot of the components. I also decided to use a fixed gantry and sliding table. This is so I can use drawer slides (ball bearing type).

I buy copper clad boards that are 12x12 so thats what I need for a work area. I figure I'll shoot for 14x14 travel just for some breathing room and a Z travel around 4" (more to fit my hand under the spindle and pull out bits than anything about the work itself).

I'm going to try plain old 3/8th-16 allthread with two nuts arranged like I saw on a build here. Two pieces of HDPE with a (tight) slot routed out for the nuts. On fixed to the Z and the other screwed into the first. The slots face one another so tightening the screws will compress nuts against the leadscrew threads.

The Z linear bearings are skate bearings on round rod. The abnormal thing is I'm not tilting them. I'm using drill rod and the pre-load will be quite light. As for work loading... Well, cutting 0.006" deep into copper with a V-Engraver isn't exactly a high resistance task. About the worst it'll see is cutting 1/16th FR4 with a 0.063" rasp router bit at 10" minute.

I've been working all day on designing the Z itself. I have some aluminium bits and pieces around here from .25" to .75" and I'm going to use a little of it. Mostly where I need both thin and stiff - like the router mounting plate.

Anyway, here's some pics of the design and the Rhino file. Not quite finished yet as I haven't decided what I'm going to use to mount the Z-Stepper or how to get the home switch situated. I'm also half expecting to have to enclose the sides with 1/4 MDF as I'm not sure the 3/4 MDF top and bottom won't end up flapping around.

MDF doesn't thread very well at all so I'm using cross dowels and bolts. These are used for MDF furniture and are very good connectors that allow butt joints which would normally be suicidal.

[epineh]

I will be following this thread to see how you go, looks like you are off to a good start.

Have you thought of using a permanent marker instead of a cutter ? I did a board today as a matter of fact, and as I had a little unused room around the board so I drew a happy face with a permanent marker to test as I had heard it works as a resist, and the result was pretty impressive, the edge definition is perfect.

You can get drafting pens down to 0.2mm (0.0079in)that you can fill with whatever ink you want to, easily small enough to do even most of the surface mount stuff. It is something I want to try eventually, as you said with a dedicated machine.

A second hand plotter would probably save a little time as well.

I took a pic so you can see what I mean.

Russell.

[Rhodan]

I've already done surface mount (soic) with both photolithography and my router. The first one I did with the router used a 30 degree V-Bit from think and tinker to make a breadboard adapter for an SOIC-8 Fram. It doesn't come in DIPs and it's real hard to plug those SOIC legs into breadboards 8)

I found the cuts too narrow with the 30 degree bit and had a very hard time not bridging to the unused copper (don't want to wipe-out, takes too long). So I switched to a 45 degree. I find that as long as I surface the table and use lots of screws around the board it lays quite flat so depth of cut is quite consistant.

I posted a couple of (blurry) pics of circuits cut in this thread Wolfgang Engineering TB-350 spindle review

The focus makes it look like there was uncut portions but they were actually complete. I'll have to cut something else and film it with my new camera. Its way better! Here's a sign I made a little while ago.

http://www.youtube.com/watch?v=M9fG8trDLxQ
http://www.youtube.com/watch?v=xtmUbquYuuI

[epineh]

Originally Posted by Rhodan I've already done surface mount (soic) with both photolithography and my router. The first one I did with the router used a 30 degree V-Bit from think and tinker to make a breadboard adapter for an SOIC-8 Fram. It doesn't come in DIPs and it's real hard to plug those SOIC legs into breadboards 8)

Yeah and using a hammer kinda doesn't help, wish it did

Nice work on the routed circuits, I did a TSSOP board with my printer once and while it came out perfect soldering it on still gives me nightmares ! I have mainly stuck to DIP's since then but I may venture back to the dark side (of smt chips) one day

Russell.

[Rhodan]

Actually, I had a thought this morning. The Z leadscrew doesn't need to be fixed at both ends. I can move the lower bearing and sandwidth the top plate between two bearings using nyloc nuts making preload easier. Whipping shouldn't be a problem since I only need about 5-6" of screw below the lower bearing and the lead nut should constrain it quite well.

This would let me use a slightly shorter bottom plate to give more clearance to the spindle mount which is pretty darned close at the moment.

I'm also humming and hawing over whether to drop down to 1/4-20 instead of 3/8-16. The motors are 1.8 degree and with a 16 pitch that gives 0.0003125 inch per step. The 1/4-20 would be .00025 which multiplies nicely to 0.001 which is the target resolution. Of course, 1/2-10 would work too but that means going ACME which adds more expense etc. Might upgrade later when I have everything set up and know exactly what dimensions I need before getting any machined.

The steppers I have are 6V 2.4A 80 oz-in and round: quite anemic but this is a pretty small setup. The power supply is switching type, 24V@15A x 2 (can you say overkill?) but it cost me something like $30 surplus. With only 4 x motor voltage rating these things aren't going to be screaming.

I have a DeskCNC board with three Zylotex drivers but I decided against using DeskCNC for the moment as I've really come to love Mach3. I'll have to make a breakout board for it and figure out how to work in an E-Stop. Its probably just going to connect to the ENA# pins on each driver.

[Rhodan]

Well I took video of making a 4-20MA transmitter board on the K2 router which I still have to edit into a decent little video. In the meantime I uploaded the runout check portion (raw) to youtube for folks to see. I'm using a Wolfgang Engineering TB-350 spindle which is just awesome and the video shows the zero runout proven by dial micrometer. The needle doesn't move at all!

http://www.youtube.com/watch?v=nzSjIV9tr3E

And the routing vid just finished processing (takes longer than making the board!)

http://www.youtube.com/watch?v=VUDW5pQbxAY

Once I edit together something decent I'll post the whole thing as a primer for those wanting to route PCBs.