[balsaman]

Hey guys,

I am currently working on my second cnc machine. This one will have a 24"x36"x5" cutting volume.

Here are the plans. They make use of 80/20 extruded aluminum channel and THK linear rail and bearings.

Base is purple, gantry is black/white, rail is red, bearings are blue.

Eric

[balsaman]

closeup of gantry

[balsaman]

Sides of gantry will be 1/2" aluminum plate. I started cutting the aluminum channel for the hardware on my other cnc. (pockets)

[balsaman]

Here are the first few parts. The four standoffs between the bases. I had my machine cut the pockets then cut the part off the longer lenght.

I have hardware that fits into the pockets to fix two 80/20 parts together at right angles.

[paulried]

Man that looks sweet! I sure wish I was 2% as good at cad as you guys are. I am currently fighting the uphill learning battle.

I love that you are using generation #1 to build #2.

[balsaman]

Paul,

I took two courses at a local college. Best thing I ever did. Trying to self learn is frustrating. I am trying to teach myself 3d...very frustrating....

Eric

[chuckknigh]

Where can I find extrusion like this? I don't have the slightest idea where, even, to look!

Although, knowing this crowd, it's probably available at McMaster/Carr.

-- Chuck Knight

[balsaman]

www.8020.net

www.tslot.com

[Max]

80/20 sent me a cd along with their catalog that has useful files and drawings.
Only problem is that the Auto Quoter program relies on AutoCAD R12 to work.
I wish it would work with any generic cad program that I could afford.
If anything, just having their catalog is a useful reference.

[Zephrant]

Very cool- What kind of drive are you going to use? Single ball/screw for the X?

Zeph

[HomeCNC]

Have you purchased the THK rails and bearings yet? That should set you back some. Or are you the guy that gets these rails and things for free from your company???

[balsaman]

I don't have the rails/bearings yet. I keep a look out at work for some being tossed or as machines become obsolete/replaced. There is a posibility I can get some from an obsolete die in the next week or two.

I am planning to use 3/4"-6 of 7/8"-5 acme rod and delrin nuts driven by Geckos and dc servo motors. I have the three brushed motors so far.... They are 1.1 amp 110 VDC motors. I know I can only run the Geckos at 80 volts.

Eric

[HomeCNC]

I wish I knew more about electronics. It is interesting that your motors are higher on voltage but lower on amps than my servo motors. My motors are only 36 volts but are 5 amps. I wonder what is better, more voltage or more amps?

[ToyMaker]

Which is better, volts or amps?

It depends , One way to look at it is by power.

Here's some arithmetic;
Eric's motor: 110Vdc @ 1.1A, R=E/I, Ohms = 110/1.1 = 100 Ohms
Current at 80V, I=E/R, Amps = 80/100 = 0.8 Amps
Power P=E*I, Watts = 80 * 0.8 = 64 Watts
Horsepower 1 hp = 746W, 64W = 0.08 hp

Jeff's motor: 36Vdc @ 5A
Power P=E*I, Watts = 36 & 5 = 180 Watts
Horsepower 1 hp = 746W, 180W = 0.24 hp

So... under full rated load Jeff's motor is going to put more "rubber on the road" so to speak. I think that Eric's motors will deliver a higher no-load speed because of the higher drive voltage (the motor has to turn faster to build up the counter emf).

robotic regards,

Tom

[balsaman]

Tom, correct me if I am wrong. The motor will draw something less than the rated current when not loaded. Loading the motor will make it draw more current. If that is true, i will be able to make it draw 1.1 amps at 80 volts (the gecko's have a max current trim pot), so watts is 88, and the HP is .117 in, something less out, as the motor isn't 100% efficient.

I think both motors will work fine (I hope). Probably Jeff's are better.

Eric

[ToyMaker]

Eric:
You are right. Your motor will draw a lot less than rated amps when not loaded. In fact it will draw just enough power to overcome the friction in the bearings.
But that is not the whole story. I think the Gecko drives are choppers. That means there is the frequency of the chop signal and the inductance of the motor coils to take into account too (it's a never ending story ).

robotic regards,

Tom

[balsaman]

I will find out I guess. I know those motors will have lots more torque and speed than the steppers!

I managed an hour or two in the shop today. I got the base of the machine done. I am glad I won't have to paint this one. I hate paint!

This thing is rather large. How come it always looks smaller on my computer screen?

Eric

[paulried]

Because you need to get a bigger computer screen!

I want one that has a sticker on it that says "Images shown on this screen may be larger than real life" like the mirror on my car!

[HomeCNC]

Well knowing you, your motors were most likely FREE!!!! And free always beats most anything.

[balsaman]

Hi everyone.

Today I cut the gantry sides out of 6061 aluminum plate. I cut it 1/8" oversize on a bandsaw then used my wood router to clean up the sides and cut the pockets in for the extruded aluminum. My wood router doesn't like the aluminum too much but it's fine if the feed rate is kept down. This was all done at 3" per minute up to 9" for some lighter cuts. Turned out pretty good.

here is a pic of the router cutting aluminum...lots of chips. The dust collector was going but most of the chips stayed behind.