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Old 26th February 2013, 01:45 AM   #11
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Default It works basically

Basic principle is fine - the gcode output is all good (although I need to change a few things in the settings) and the cnc router seems to have worked well for the first half of the job.

The second half didn't go so well (I cut the job short in the end) I saw the mill miss a step or two and obviously after that everything was squew-if. I'd have to say though that the software side of all of this seems to be fine though; the issue would exist on the router hardware/electronics side.

Anyway, the top half is fine up to the mounting hole (top right) and then in the bottom half there's lots of errors.

I'll try again, using a .25mm bit and less demanding cuts. I was doing a .5mm depth single pass over the board, so I can see that that is unnecessarily deep.
Attached Images
File Type: jpg PCB Big v1.1.jpg (77.5 KB, 171 views)

Last edited by aspringv; 26th February 2013 at 01:53 AM.
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Old 26th February 2013, 02:29 AM   #12
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So!

Unsuprising news of the day - you can't mill with a .25mm bit. It's just too small.

I also discovered that you don't use a ground plane as such or the code will mill both sides of the trace - that of the trace and that of the polygon that is your ground plane. I'm sure that there must be a way to work around this...
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Old 26th February 2013, 04:50 PM   #13
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Looks as if the technique of routing copper off a clad stock board is working well. Sorry about the stepper motor driver problem. I might look into this, 2 axis lead screw vises come up for <$80 sometimes used. It might have possibly less problems than a used digital stepper control assembly like you may have bought.
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Old 27th February 2013, 04:11 AM   #14
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Default My system

The physical system itself works fine (I've the dual x drive version of the Shapeoko) but I bought some rather odd stepper motors which seem to have a higher resistance and inductance than most nema 17 units. They're getting significantly hotter than I've seen before, and the jobs seem to fail after running for a while - making me suspect that heat is the issue.

That said - the control box is built out of ebay parts, so who knows? I have a G540 control unit and a full set of larger motors so I will give that a spin instead sometime soon.

If you're thinking of making something yourself from what you describe, you'll probably want some beefy motors to overcome the stiction in a cheaper set of leadscrews. A mate and I built a cnc router with a 850mm by 850mm workspace a while back and used proper leadscrews and antibacklash nuts - worth every penny as trying to accommodate the rig not moving when you reverse direction due to <ahem> sloppy nuts is hard to do in software. I'm happy to be contacted if you'd like to discuss - I was hugely inspired by a couple of local cnc builders and the time they took to help saved days.
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Old 28th February 2013, 11:53 PM   #15
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Thanks, I'm the kind of digital idiot they write books for (about). Since intel assembly language and MSAccess basic, everything I've tried has just sat there with a blank screen. I was actually thinking of cranking the vise by hand using the 100% visual feedback control system; so lead screw slop would be less of a problem.
I've been building circuits on Nema LE laminate by drilling a lot of holes and using leaded components and hooking the wires together before soldering (actual insulated wire between components), but they don't always stay soldered. I kicked the board on my latest project in December and broke something, and am struggling this week with wires breaking off a tiny transformer that I can't make hooks out of the leads (too short) on my latest project. A PWB gives better support to your solder connections, even if you have to grind out every line and pad by hand. Thanks for detailing your advanced technology project. Even if I just make pads for particular PWB compatible components out of scraps of copper clad board, this technique could improve reliability.
Oddly, I picked up a lot of tiny stepper motors & drives in scrap obsolete Ishida scale units for food bagging. The aren't big enough to drive a 2 axis vise, but I might try something someday. Maybe a needle valve control for an analog fuel injection system. US fuel is now totally incompatible with carburators, but I refuse to drive a car that won't go 5 miles after the fan belt breaks ( as computer electrical control motor vehicles do). Have fun.
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Last edited by indianajo; 1st March 2013 at 12:06 AM.
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Old 11th April 2013, 12:14 PM   #16
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Default Well I knocked up a prototype

...and it seemed to work fine.

I still need to do a bit more work on the cnc machine in order to get consistent output. I've received some engraving bits which should make the cutting easier, and I'm yet to install the new driver box. So progress here is a few weeks off.

So in the mean time I built a board and power supply to test the design. I matched all the j310's to about 25mA and just bunged a couple of ifr610's in without matching. The power supply was built and worked perfectly using a random fet out of my parts bin - think its a buz71A. First pass was pretty good on the scope, but I decided to change a few things.

First - I ditched the low pass filter on the front end. I'll reconsider should it prove necessary

Secondly - I added a circuit to put a delay on the connection of the outputs after a delay. I'm yet to sim/test this so I'm not confident it's a goer as yet. Advice happily accepted on this...

Where I'm at is detailed visually below.

I'll etch a new version and see how that works...
Attached Images
File Type: png Schematic.png (193.5 KB, 113 views)
File Type: png PCB.png (269.6 KB, 92 views)
File Type: jpg Delay.jpg (28.0 KB, 94 views)
File Type: gif 12v reg.gif (4.9 KB, 90 views)
File Type: gif sstart.gif (14.9 KB, 51 views)
File Type: jpg 20130411_200411.jpg (112.9 KB, 76 views)
File Type: png SStart psu schematic.png (202.4 KB, 62 views)
File Type: png SStart psu.png (230.2 KB, 32 views)

Last edited by aspringv; 11th April 2013 at 12:23 PM.
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Old 11th April 2013, 01:07 PM   #17
rsavas is offline rsavas  Canada
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I came across this site yesterday, he has been working on a CNC pcb router as well.
joebrown.org.uk
Also, have you considered using NXP BF862 as a sub for J310, much lower noise, but only available in SOT-23 pkg.
Your jfet ckt is similar to the Pearl2 MM phono pre-amp from Passdiy, may want to refer to it is as well.
Rick

Last edited by rsavas; 11th April 2013 at 01:10 PM.
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Old 11th April 2013, 10:34 PM   #18
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Cheers for the input rsavas - on his site joebrown references two software packages worth looking at it seems.
Of Itself So - Line Grinder, Gerber to GCode Isolation Milling
Of Itself So - Line Grinder, Gerber to GCode Isolation Milling

I'll give them a look later on.

As for the jfet sub stitution, I'm pretty committed to the j310's now given I bought 100 of em, and then took the time to match them... that was a boring couple of hours! Anywho, it's an option should I revisit the design.

Reading the pass article now - thanks for the steer.

Last edited by aspringv; 11th April 2013 at 10:41 PM. Reason: clarity
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Old 12th April 2013, 12:42 AM   #19
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Default Clarity on the eagle schematic

I used whatever parts in the eagle library that were equivalent in pinout to the Fets and Jfets I'm actually using, as such the parts numbers on the pcb are incorrect. Ditto the parts in the delay circuit.
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Old 12th April 2013, 11:20 PM   #20
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Damn... you got me thinking about how i can alter the pcb design to allow either the NXP BF862 parts, or the j310's...

Guess it'll be another eagle session today!
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