Official Luthiers Forum!

Slowly but surely, in part due to threads like Steve Sporadyk's on CNCzone.com, and in part because I realized the multi-purpose routing jig/setup I'd drawn out would take up as much or more space than a tabletop CNC system, I'm increasingly tempted to take the plunge and build a system very much like Steve's (The fact I've been told in no uncertain terms that I don't have space for more wood, and I do have a few thousand bucks I could spend).

I don't really see myself using it for stuff like carving (electric) tops, or necks, or bodies (mostly because I like the woodworking too much), but repetitive inlay stuff like logos, radiussing fingerboards, and all sorts of jig and template-making donkey-work (which, unlike many, I do because I have to, not because I enjoy making jigs) could be made more accurate, and less tedious. I'm also pretty sure there are folks around locally I could help out with the thing.

I'm still not quite clear on how much I'd need to spend, other than 'more than I think'. I'm also trying to work out how much metal cutting (I'm thinking mostly of using aluminum for some jigging) I could get done with an aluminum gantry-type setup with a PC 690 as the spindle...

If he's still poking his head in here, I'm pretty sure John Watkins has built one and might be able to give some insight.

_________________
Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

I'm planning the same thing Mattia. Fortunately, I know Steve pretty well, and live only an hour away, so I can get some pointers from him as I get started.

Do you have a link to his thread?

_________________
"I want to know what kind of pickups Vince Gill uses in his Tele, because if I had those, as good of a player as I am, I'm sure I could make it sound like that.
Only badly."

Don, here you go:

http://www.cnczone.com/forums/showthread.php?t=27527

I've just found a local place that'll do a full set of steppers/drivers/wiring (big, hefty ones) for a decent price (they have a basic set for 300-ish, and a really hefty set for 600), no shipping/importing needed. The linear bearings and ballscrews are a bit horribly expensive there, so I'm going to start watching the 'bay carefully...

Seems like you're on the right track, Mattia. The machine I built served me well for 3 years. It just couldn't keep up as my business grew. I wouldn't have hesitated to build it's replacement from scratch either, I just didn't have the time.

The only advice I would give is to take your time with it and to buy the motors and drives last. That way you can put all of your remaining budget into them. Go servo if you can.

Here's a pic of my first machine and the current beast.

_________________
John Watkins
CNC Guitar Parts

John: nice looking machines! How did you find the rigidity/stability of the linear rails (as opposed to, say, THK slides)?

Also, I'm still not entirely clear on the advantages of Servo motors over a good, high-powered microstepper. Is it simply the 'closed loop' thing (if I understand it correctly, the machine can tell the computer where it is, rather than simply how far its moved from the home position)? Do they draw less power for the same performance? More? They're less common on eBay and the like, and pretty pricey.

Mattia, the ground rails and pillow blocks are built to have some play in them so that the rails don't have to be dead parallel for them to function without binding. I would recommend the linear guides every time, but the surfaces they attach to and the mounting holes have to be very accurate, flat, square, etc.

Countless discussions on the differences between steppers and servos can be found all over the internet with input from folks much more knowledgeable than I.

That being said, the basic difference is that steppers will never be completely predictable no matter what you do. Servos, when setup correctly, will never make a mistake.....ever. I can crash my machine (oops) into it's end of travel at top speed (1200 ipm) and the e-stop will shut everything down and throw up lots of red text up on the screen and you'll feel it in your shoes, but when you back it up and re-enable everything, it goes back to zero and it's within .001" of where it was before. Amazing really.

I will tell you that the torque curve on servos is the polar opposite of steppers. Steppers have the most power when standing still and lose power as speed increases. Servos are more like your car. More RPMs equals more torque. This makes much more sense because the faster you go, the more material you're cutting and the more power you need. My first machine was 48v, 4.6a stepper. My current machine is 90v, 5a servo. The latter easily has 5 times the power. I ran it into a vise once with a 1/2" carbide cutter chucked in. It broke the cutter clear in half and maintained position.

This is mostly just rambling, but hopefully it'll give you an idea. I never understood it myself until I saw the a/b comparison.

_________________
John Watkins
CNC Guitar Parts

Maxnc
And then you have stepper motors with encoders which is kind of a third category. They do call it a "servo drive" I believe.
Just noticed this new Maxnc today with built in computer, a new wrinkle for them. Wondering how expensive it would be to replace the computer?
Nelson

Mattia, a DIY CNC can be a fun project. Very satisfying and managable given the large amount of information out there. I was looking for a different project that would also help me in my day to day work - and it fit the bill. It's a great way to learn about the different technologies and options out there.

If you watch eBay and the CNCzone classifieds you can do pretty well on parts. I definitely recommend THK style rails and rolled ballscrews. I like the 8020, and am happy with that choice. Lots of sources for aluminum and structural materials. I spent less than $2k to get everything together (maybe closer to $1500), not including software.

My motor choice was purely economics. 425oz/in steppers and the Xylotex kit were a few hundred bucks - total. An entry level servo/gecko setup would be $1000-1500 minimum. I just didn't have the spare cash. Running the steppers at the fat part of the torque curve has given me good speed and reliability. As John describes, as you push the RPMs you lose torque and eventually steps.

Of course, as soon as it's "done" you start dreaming about what you would want to do next time! My machine does everything I need it to, and it works accurately and reliably. If I was roughing out lots of larger parts (necks, etc), more speed would be nice, but most of the time I'm running smaller bits (inlay, etc) which really limit how fast I can push things.

What I really want now is a giant vacuum system...

Steve