Quick and Dirty mdf cnc machine

[mark]

This is a crappy video of my co-worker messing around with a cnc machine he just built from plans on instructables.com. Now that we've got the basic jist of the thing, we're working on a larger, better version.

enjoy.

[macdadmorgan]

damm, can you play pitfall on that as well. seriously, coolest thing i have seen made in a long time. looking in some of my shop tool mags, some things are way beyond me, and you made one, damm.

[mark]

damm, can you play pitfall on that as well.

No, but you can set a knife in it and play that game where you stick it between your fingers realy fast!

I just lent a hand building the machine in the video. My co-worker Eric, the guy in the video, is the one who built it.

[collin]

Was it this one?

http://www.instructables.com/id/How-to- ... aply-and-/

Did you guys buy the stepper motors or scavenge them?

[G-man]

Hi collin,

I thought I'd chime in here cause I've done a ton of research over the past 9 months on homemade CNC machines. Stepper motors are rated on their holding torque in oz./inch ratings. A machine like the one in mark's post above (uses a Dremel type unit as a spindle) could get by with 70 to 100 oz./in. motors. A CNC machine that uses an actual router unit as a spindle would need steppers in the range of 200 oz. or more. Steppers that are available for scavenge from printers (even bigger printers) are only in the range of 30 oz. Retired copy machines may have a larger stepper or two, but the motor specs are often difficult to ascertain. I love to tear apart old machines for all their little goodies, but quite honestly, new components are often so inexpensive, I'd be better of to just go and buy a new part. Still, I enjoy the hunt. New stepper motors are really affordable. 200 to 300 oz./in. motors are about $35 to $45 each. I got 205's for my CNC machine, but I'm betting that I'll upgrade to 3 or 400's before too long. Bigger steppers just mean that the machine can move a little faster because, as a machine gets bigger and heavier, it takes a lot of torque to quickly change cutting direction. Smaller steppers can handle slower speeds better because there's lower inertia to overcome. Inertia increases as velocity and mass increase. Inertia sucks up torque.

I've gotten way more nit-picky with my machine than I had originally intended, but it's a real beauty. I'll post pics (and maybe a video if I can figure out how to do it) when it's finished. My y-axis and z-axis are finished, but it'll take another month to get the x-axis complete.

Sure was fun to see mark and his friend's machine running. The DIY CNC bug is so addicting.

G-man

[mark]

Was it this one?

http://www.instructables.com/id/How-to- ... aply-and-/

Did you guys buy the stepper motors or scavenge them?

Yes, that's it. All parts were bought new. I'm not aware of all the details on the motors and such. I'll see if I can get Eric on here to answer any questions. This machine is pretty neat but I think some significant improvements can be made to it without a tremendous effort.

[Head Monkey]

G-man, I’d like to suggest that you use larger motors. I used steppers with 680 oz-in of holding force for my X and Y axes, and 228 oz-in for the Z axis. A stepper motor has its greatest holding force when motionless, and I can overcome the holding force on either axis without too much effort by pushing on the gantry when the machine is idle. It’s even easier to stop it when it’s moving. Unless you have a closed-loop system and can tolerate lost steps, then I think with 205 oz-in motors you’ll either need to run very, very slow (10-20 in/sec) or take very shallow cuts with many passes, which works out to the same thing.

I posted a bunch of info on making your own CNC machine on grafsnowboards.com in the past. Here are some links:
http://www.grafsnowboards.com/phpBB2/vi ... highlight=
http://www.grafsnowboards.com/phpBB2/vi ... highlight=

There’s more information on my machine here:
http://www.happymonkeysnowboards.com/mike/CNC/index.htm

Good luck!

[hydrant71]

damn that is too cool, what a sweet machine.

jason

[G-man]

Hi Mike,

Thanks much for the suggestion regarding the larger steppers. It's good to get feedback from a real world user who actually uses a machine for the same purpose that I will be. I had pretty much figured that I'd need to run at a relatively slow speed with the smaller motors, but really, I'm not too concerned about a fast cutting speed at this point (I know, everybody says that initially... then they develop the need for faster and faster cutting speed). If my whimpy machine can mill out a totally new core shape/length, with very accurate insert holes and edge relief groove, and with a matching base in an hour or two, that's way ahead of the 3 days that it now takes me to create a whole set of templates for a new design. My real problem is that I just love to build stuff, just for the shear joy of building and learning. Which is one of the reasons for the limitations associated with my motor size. I built my stepper drivers from a HobbyCNC kit. It has been a really good experience for me and has led to me being a bit hooked on building other PCB based goodies. The HCNC driver board, however, is limited to 3 amps and 42 VDC, and I've not found a stepper motor bigger than a 305 (yet) that the HCNC board can handle. From viewing the pictures on your site, it looks like you're using Ghecko's. I may have to eventually move in that direction, but I'd sure like to find a bare PCB design (that I can build up myself) that would allow the use of a motor with a bigger amperage appetite. Also, (and somewhat embarrassing after seeing pics of your machine again) my machine is MDF based. I think it might be happier with the slower speeds that the smaller motors will limit it to. I know, metal would have been a better choice for such a large machine, but I kinda wanted to challenge myself to see if I could build a functional 97 inch machine... ACME driven, no less.

I had viewed the links that you posted a few months ago, but I sure enjoyed taking another look at them today. Great technical writing with an occasional chuckle thrown in...

I started by using a 14gal shop vac from Sears on my CNC machine. I had many problems: one, the hose wasn't long enough, so the gantry would drag the shop vac back and forth across the shop floor. (Okay, so that was fun to watch.)

Thanks again,

G-man

[Head Monkey]

You’re right that you’ll be limited in motor size by the current your drivers can support. I did use Gecko Drives, G201’s I think. They work very, very well… I highly recommend them. I admire your drive to build these yourself… very cool. I can’t wait to see your machine go!

And I forgot about the poor ShopVac following the CNC gantry back and forth like a little puppy…

[kohlrabi]

Here's something that you guys might find interesting.

For the past 6 weeks or so I've been helping to assemble, set up and commission a fairly large 5-axis CNC machine.

it has 45' of travel in the X axis, 20 in the Y and 8' in the Z. It's got an aerospace grade controller which is awesome.

You have no idea how painstaking it was to get two 45 foot steel rails 20 feet apart to be perfectly level straight and true. There .015" runout over the 45' x axis. That took over a week to achieve.

The size of the servo motors is also really something else.

I'll get some pictures and video to post as well