New Machine Build- PCB mill Stepper & Controller choise

[knutselman]

Hello,

I'm planning on building an PCB milling machine. It has a working space of about 200mm * 150mm. The linear guides will be built out of stainless steel rods (12mm thick), and the movement out of a threaded rod of M6. I will use a piece of Delrin with M6 in it (to minimise backlash).

I'm thinking of an accuracy of about 0.05mm

Which stepper motors are the best for my purpose? Which torque should they have? I think NEMA17 is big enough.

I would like to buy these, because it's all-in-one, and not too expensive:
http://cgi.benl.ebay.be/150661185642

Or should I go for these?
3 Axis Schrittmotor Steuerkarte CNC Kit NEMA23 24V PSU | eBay

Are these steppers strong enough? Does the driver work well?

Thank you!
Knutselman

[knutselman]

Could some moderator please move this topic? I didn't saw that it was in the woodworking-forum....

[hub]

Originally Posted by knutselman Hello, I'm planning on building an PCB milling machine. It has a working space of about 200mm * 150mm. The linear guides will be built out of stainless steel rods (12mm thick), and the movement out of a threaded rod of M6. I will use a piece of Delrin with M6 in it (to minimise backlash). I'm thinking of an accuracy of about 0.05mm Which stepper motors are the best for my purpose? Which torque should they have? I think NEMA17 is big enough. I would like to buy these, because it's all-in-one, and not too expensive: CNC Kit 3 Axis Stepper Motor Driver Nema17 12V10A 220V | eBay Or should I go for these? 3 Axis Schrittmotor Steuerkarte CNC Kit NEMA23 24V PSU | eBay Are these steppers strong enough? Does the driver work well? Thank you! Knutselman

- Threaded rod will not have 0.05mm accuracy
- The steppers should be fine, not much torque needed for PCB.
- "Nema" size is only outer/mounting dimension. Alone, it does not tell motor force etc..

[knutselman]

Which accuracy should I expect when using an M6 rod and a threaded nut 50mm long in Delrin? So, the steppers should be good enough. I'd like to mill PCB's with pretty small SMD components (of about 0,4mm pitch)

Thank you!

[doorknob]

Originally Posted by knutselman I would like to buy these, because it's all-in-one, and not too expensive: CNC Kit 3 Axis Stepper Motor Driver Nema17 12V10A 220V | eBay Or should I go for these? 3 Axis Schrittmotor Steuerkarte CNC Kit NEMA23 24V PSU | eBay Are these steppers strong enough? Does the driver work well?

Some people have reported success with those Chinese TB6560-based driver boards, while others have reported problems.

There is an informative (but long) thread about them at http://www.cnczone.com/forums/genera...y_chinese.html

You will probably find that a 24-volt power supply will be better matched to the motors than a 12-volt power supply.

[hub]

Originally Posted by knutselman Which accuracy should I expect when using an M6 rod and a threaded nut 50mm long in Delrin? So, the steppers should be good enough. I'd like to mill PCB's with pretty small SMD components (of about 0,4mm pitch) Thank you!

The "problem" with threaded rod is that it's manufactured as a fastener not as a lead screw. So the tolerances are low. And it varies over the lenght of the screw. Mach3 has a function called "screw mapping" to fix that, but I haven't tried it.

But, with a 50mm long nut I think you could get decent accuracy. Try to make your delrin nut with adjustable anti-backlash.
I have used M10&M12 threaded rod on my machine, it worked actually surprisingly well. I haven't measured the precision, but it's probably around +-0.2mm.

And remember, there can be very big differences between threaded rods. Some are good, some are very bad. When selecting one, visually inspect it first. Then run a nut on it from start to end, it should rotate smoothly & not get stuck on any point.

Also, a threaded rod's threads are sharp, it will wear out a plastic nut pretty fast.

[aarggh]

For pcb and most light work NEMA 17 will be more than adeqate, usually the motors will ideally be rated at the higher end of 50-60oz/in roughly, and would be more than suitable for pcb without breaking a sweat. This rating will also be more than suitable for wood carving, shaping, and engraving, cuttings plastics, engraving most metals, without any issues.

The problem you have though is for smd work, I will be very dificult to get a high enough and repeatable resolution to get the traces okay. I do a large amount of pcb work, and on my little machine which uses trapaziodal thread but good quality anti-backlash nust and bearings, I can do very fine work, but struggle to approach 0.3mm probably. On a good day I can generally route up to 3 very fine tracks inbetween IC dip holes using a 0.1mm engraving bit. I use isolation routing for this, as if you do it the normal way, you double the tracks. Isolation routing means just one cut to seperate tracks.

This is a link to the type of machine i'm talking about:

Panther-210 CNC Router PCB Engraver mill Machine | eBay

If your budget extends to it, I'd seriously consider buying one of these units for starters, as I think initially you may struggle to get a good enough resolution, and the costs of the parts to build yourself will add up considerably? I think you'd need to weigh up how much will the parts to build, how long will it take, etc.

Also, having a machine ready to go is fantastic for the learning process. :-)

cheers,
Ian