Invisible Babies

[EEtwidget]

I had my heart set on building a CNC router. I did my homework and narrowed the list down to three possible choices. If you're considering a CNC build, these three are solid:

 

Brian Oltrogge Grunblau Platform

Kronos Robotics KRMx02

Openbuild OX CNC

 

I even considered a Chinese 6040 and upgrading the electronics.

 

Unfortunately though my wife has baby fever. Her biological clock is ticking and we have been unsuccessful in our many attempts.

 

Went to the baby making Doctor today. $400 conversation turned into $1200 'peek under the hood'.

 

Although we have great insurance, these fertility visits aren't covered. So it looks like no CNC build in my near future. 

 

Damn invisible baby is already a pain in my ass.

[KnarlyCarl]

You have some pretty slick stuff going on with your robotic work man, I've been checking in on your progress, very cool to watch the different projects come to life! But that really sucks about your wife's situation. Its just the opposite with us... hope things work put for you two!

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[Stercorarius]

Sorry about that whole deal. Unrelated, back in freshman year I was working on a design for a CNC plasma cutting table I was going to build for the HS shop, still dicking around with a bunch of cad drawings for it. The one I'm designing now is more industrial vs a lightweight extruded aluminum one that I was going to build. I'm assuming on the router builds you use all-thread for all the axis because it is slow speed and a lot of resistance. I was planning on using drive chains for the x and y axis and all thread for z. Can you get away with using chain for routers?

[EEtwidget]

You wouldn't want to use chain, although I have seen it doen. Chain stretches too much. Belts are the way to go if speed is desired. The wider the belt the better. But if the axis is long, ~60" belts might not work. Just depends on the design.

 

Threaded-rod is used on DIY builds but it's not accurate. Lots of backlash. ACME rod, ball screws, or rack & pinion is more common, but more $$$.

 

ACME rod isn't too bad but ball screws & racks are $$$. It's what the pros use. eBay has deals though. Belts can be used but when milling hard wood or aluminum, feeds and speeds are a big deal.

 

Take a look at the Shapeoko 3 for an example of a low cost, belt drive CNC. 

 

Besides backlash & rigidity, the electronics make a big impact on accuracy. This is also an area people tend to cheap out, ... at first. 

 

 

 

[Stercorarius]

Yeah, I was thinking about stepper motors for cost's Saks and decided that I'd better just pay the extra and use servos. I forgot about backlash on all thread, been a while since I did my research. I think with the stretch issue on a 12' run it would get off somewhere under a tenth of an inch. I think my original plan was for rack and pinion. I want to say Helical cut is more money but also more precise. I've never actually heard of a belt drive. 

[EEtwidget]

No need to buy servos, although if you have the cash they are the best, steppers will work just fine.

 

gecko 540 controller with NEMA 23 steppers. Configured in micro-step mode, these things will be really fast. Pair the kit with some quality shielded wire, eliminate noise (electronic interference, not audible) Also a good power supply is key. You want nice clean power.

 

The nice thing about a plasma cutter, like a laser, there is no mechanical resistance with the work so the machine doesn't have to be as rigid as a CNC milling steel.

 

I would recommend using extruded aluminum reinforced with steel. It's lightweight and easy to work with. Your main obstacle will be keeping the Z-axis light. The heavier the gantry, the slower it is. Also takes more to get moving & stopped.