Why CNC?

[Robin Hewitt]

Are Alibre still doing their $99 offer? That was the bargain of the year. Of course I got referred to a UK dealer who wanted £99, but I knew the Yanks wouldn't turn away my $99 if I pressed on regardless.

My old AutoCAD no longer works now I have to go Windows 7, looked up the replacement and blenched at the price. Searched el webbo for AutoCAD look alikes and ProgeCAD for £220 looks the best bet. Anyone tried it?

CamBam is good, I sent him the money. You have one minor hurdle to leap before you can start stacking cuts down the left hand side of the screen, perhaps not quite as intuitive as the manual thinks. Having to redefine the tool every single blooming time is a pain in the butt and somewhat fraught.

[Smiler]

I make the odd sign or plaque now and then but the real reason was this: (and I saw this quote on a CNC site somewhere but it stuck)

"to make something with my hands that can make something I could never make with my hands"

And that's the real reason, I'd have loved to have been a carpenter but I'm hamfisted where chisels/planes etc are concerned BUT I'm good with CAD and decent at 3d modelling and frigging amazing with a welder. Bish bash bosh, one CNC router and I can now carve wood better than the artist guy who lives in the next valley, faster and better quality too and I don't even own a chisel.

Jeff.

[Robin Hewitt]

I knew I'd arrived with files and saws when my metalwork tutor was asked for someone to copy a security key. With a whole college to choose from he picked me. I cut it out of mild steel on a bench pin, got 40 Bensons and she said it worked better than the original which slightly worried me. I thought it would work the same. Maybe she was just being kind :whistling:

I was taught well for 3 years. I can make most anything by hand (so long as I can find my +4.0 close up glasses for the fiddly bits). OTOH CNC is much easier if you can live within the constraints of 2.5D and radii on internals

[saxonhawthorn]

Gentlemen, you have converted me! I am now gathering the bits and pieces to make a CNC pick-and-place machine for populating PCBs. I couldn't even estimate the number of PCBs I have built by hand over the years, but now I'm looking forward to leaning back in my chair and watching a robot do all the work.

After that will come the various robotics for machining die-cast cases, fitting the PCBs in them, and testing the end product. Time scale to be in production is six months, but for the first time in my life there are no commercial pressures on me so if it takes longer, who cares?

By the way, surveying the CAD scene there seems to be plenty of 2D and 2.5D software around at sensible prices, but there doesn't seem to be so much 3D. How important / useful is 3D? Do people here use it? If you do, could you live without it?

My grateful thanks to all who have responded so magnificently to a stupid newbie's questions! I now understand your enthusiasm for the subject. :)

[Robin Hewitt]

I am now gathering the bits and pieces to make a CNC pick-and-place machine for populating PCBs.

Now that is a subject dear to my heart. Are you doing SMT or conventional? Do tell more

[saxonhawthorn]

Robin,

SMT. It's smaller, neater, and I won't have all those flippin' pig-tails to cut off.

I haven't made up my mind about applying the solder paste yet though because I have never worked with lead-free (sshhhh.....) and I don't know the preferred method: silk screen or a dab from a syringe. Silk screening would be quicker, but probably less controlable for the tiny dots. But I'll have to ask the paste manufacturers.

Otherwise I can't really see any insurmountable problems. I have bought a beautifully machined large worm and wheel for the robot arm major axis, and an equally well made tiny worm and wheel for the component pickup head horizontal rotation. (OK I'm cheating, and I should have machined them; but I'm a beginner, and hobbing those gears is something I'd need to get some practice with).

Ian

[Robin Hewitt]

I haven't made up my mind about applying the solder paste yet though because I have never worked with lead-free (sshhhh.....) and I don't know the preferred method: silk screen or a dab from a syringe.

The paste mask is usually thin brass stretched tight on a wood frame so you can place it slightly above the pcb. The paste dries out to unworkable pdq, at least the cheapies I have tried do. There was some bod lasering paste masks out of Mylar, I forget the details.

Problem with CNC is you either hand feed it or pick from the reel and then square it off while it's on the vacuum head. If you were in no particular rush, squaring might be easiest as a seperate put down.

Have you found plans for this gizmo?

A crummy worm will work because you can go for limited rotation and spring it. An elbow arm is fine if you set the position for every component manually, it's repeatability rather than precision.

[saxonhawthorn]

Plans? What are they? I've never had any plans for anything! In 25 years of writing commercial software I never even once got a specification from a customer. They always wanted me to tell them what they wanted.

I hadn't thought of brass as a screen. Not a bad idea. Not sure if I can afford a laser powerful enough to punch it though. I'd have to etch it.

I envision picking up components from the reel with a vacuum head on a robot arm, then holding them over a camera with some vision recognition software to square them up (that's where the tiny worm & wheel come in) before plonking down on the pasted-up PCB.

I bought the large worm & wheel (£18) because - like Mount Everest - it was there. I didn't have any particular use for it, but I had a hunch I'd find one. When it arrived I was really delighted with the quality, and I'm sure it will be adequate for the job.

As regards Tribbles point about volume: yes, and I can indeed rattle out boards manually at a rate of knots if I have to. But now that I'm liberated from the shackles of somebody else's factory I'm planning new products which I intend will go well, and anyway somebody's got to give the Chinese some competition! Once you've got a production line set up of course, it's easy to switch from one product to another. You just load the appropriate product code, and away you go.

Ian

[Robin Hewitt]

By the way, surveying the CAD scene there seems to be plenty of 2D and 2.5D software around at sensible prices, but there doesn't seem to be so much 3D. How important / useful is 3D? Do people here use it? If you do, could you live without it?

3D requires an extra axis or two and the maths gets complicated once you stray beyond tube cutting.

OTOH you can do a lot of 3D with a 2.5D machine, if you can figure out how to turn the part over without losing position and avoid overhangs.

[tribbles]

I've been doing SMT for quite a while now, but all manually (for three reasons - size, component availability and not having to drill so many damn holes). Not sure if I do the volume for a CNC machine yet though!

I thought that for solder paste you really do have to do a kind of silk screen (at least a mask) - although I suppose it would be possible to use a very small paint brush for some of the pads!