Newbie needs advice

[TheBulk]

Hi all,

Absolute newbie to DIY CNC'ing and in my haste bought a nema 17 3 axis kit. I'm wanting to build a 3 x 2 ft CNC out of MDF and I'm now thinking that my 17's aren't going to cut it in the power department.

I really don't want to buy larger motors so I'm wondering if there is a way I can make the nema 17's work for me. A couple of ideas I've had are

* Weight saving (Plywood or drilling weight saving holes)
* Program incredibly slow velocity/acceleration into the motors
*Fixed gantry (although I need it to be 3ft of cutting and don't really want it 6 feet long)

Anyway hope you can help either reassuring me the 17's will be adequate or with some other ideas

Thanks in advance
Andrew

[RomanLini]

Lots of people build small machines with Size17 motors, especially if they are the new high-torque ones.

But you will probably be restricted to using threaded rods for leadscrews with lots of turns per inch, so that means slowish speeds.

If this is your first machine then you could just build it and get it cutting (even if a bit slow) then use it to start building your "dream machine". Then a working small machine can always be sold for more than what you paid for the plywood and steppers etc.

[hemsworthlad]

I would use timing belts and gear them 3/1 this will increase the torque and still give you decent speed/resolution. Timing belts pulleys etc are cheap and quite effieceint with good accurecy.

If you want to save weight and still have a moving gantry keeping the foot print small but with decent strength then consider 3 or 4mm Ali plate, 2 piece's per side with spacers in between bolted together, you can drill holes to lighten but will still end up with a very strong but light gantry side.
It will be lighter than MDf last a lot longer and look cool.!! . . . Sell quicker.?

It will be a challenge at this size machine but it can be done, you will just have to sure every thing is lined up perfectly with the least amount of friction possible.

I'm sure you wont do it with threaded rod or even ACME with these motors but with belts and good smooth linear motion you may have a chance.? belts will be the most effiecent and affordable thats for sure.!

I built a belt driven machine for a friend and although it use's extrusion etc it could be modded and made to work with these motors, it works perfect cuts every thing upto Ali. . . . See it here. http://www.cnczone.com/forums/cnc_wo...ee_beasty.html

If you want to know anything about it just ask.

(Obviously the nema 17 will need to be on the larger size and not some weedy 20oz/in)

Good luck.

[awerby]

of those little motors on a machine of that size. Why not scale down the plan a bit, and make one about 6" x 8"? This will give you something you can learn about CNC on without frustrating you too much. If you gear the motors down, feedrates will be agonizingly slow, but it won't seem so bad on a smaller machine. You might also think about using aluminum instead of MDF; the cost of materials won't be as big a factor on a smaller scale, things will be lighter, and you'll have a better machine. It will also help you in making the motor plates and other parts you'll need for the 3-foot machine you want, which you can put larger motors on. You don't say what you're planning to use this for, but wood really needs some speed when it's being cut, or it tends to burn (while plastic melts).

Andrew Werby
ComputerSculpture.com — Home Page for Discount Hardware & Software

Originally Posted by TheBulk Hi all, Absolute newbie to DIY CNC'ing and in my haste bought a nema 17 3 axis kit. I'm wanting to build a 3 x 2 ft CNC out of MDF and I'm now thinking that my 17's aren't going to cut it in the power department. I really don't want to buy larger motors so I'm wondering if there is a way I can make the nema 17's work for me. A couple of ideas I've had are * Weight saving (Plywood or drilling weight saving holes) * Program incredibly slow velocity/acceleration into the motors *Fixed gantry (although I need it to be 3ft of cutting and don't really want it 6 feet long) Anyway hope you can help either reassuring me the 17's will be adequate or with some other ideas Thanks in advance Andrew

[ger21]

I'm guessing that more than likely, they're just too small. What are the voltage, current and torque ratings?

[TheBulk]

Rated Voltage = 2.8 V
Current = 1.68 A
Holding Torque = 4.4kg/cm

As I said I know they are weiney but I'm using a timing belt not a screw thread with a 15 tooth pulley of approximately 13mm or 1/2 inch in diameter so my mechanical advantage should be higher.

[ger21]

61 oz-in is a pretty weak motor. 6 or 7 years ago, a lot of machine used 100 oz motors, but were usually limited to about 30-40 ipm.

[TheBulk]

So it seems that I am going to have to upgrade the motors, anyone have any advice on what I should get?

I'm looking to cut wood and not so very often acrylic, taking out about 1/4inch of material each pass but would like it to be reasonably fast. The machine is now 2ft x 4ft made of mdf and is driven by timing belts.

I'm looking to get a kit off ebay. Can anyone tell me why I shouldn't purchase something like this..... 3 Axis CNC Kit

Thanks for all the help

Andrew

[Hyrum R]

I wouldn't go with any of those China motor/driver kits. They're very poorly matched, and way too easy to fry. Spend your money wisely once and get a G540 kit. Here's a really nice package:
CNCRouterParts

I don't know your setup with the belts, but I can tell you I can get rapids of over 900 ipm with some 269 oz-in motors and a G540. I realize that $519 might seem like a lot, but I can guarantee you'll be very pleased with the performance. Those eBay kits would lead to nothing but frustration.

Maybe someone with a little more electronics knowledge can enlighten me here. Why is it that all these Chinese motors have such a high inductance rating? Is it cheaper to make that way or something? I notice they're almost always high voltage, low current motors. And then they couple them with a driver board that can barely handle 30v, when the motor really could use well over 100v.

Edit:
Ok, I looked at those motors a little closer. They're not as poorly matched as others I've seen, so it might actually work. Those motors would probably work quite nicely with a G540 with a 48v power supply. You've got to realize that a G540 has a lot more built into it than these Chinese drivers. You've got mid-range resonance dampening (which gave me a lot of grief on my previous drives I had), and it's virtually unkillable. Seriously. I did a lot of stupid stuff to my G540, and it's still running great.

[TheBulk]

$550!................... really???????

Do I really need to spend that much to have half decent cnc electronics????

I'm sure all the CNC machines in china don't ship in their electronics from the USA............... So they must work

[hemsworthlad]

Listen to the man he speaks the truth.!

Those chinese kits will cost $837. + wasted time + very poor performance.

But go right ahead if you fancy a taste of the orient.!!

[TheBulk]

ok fair enough.

I see you're a brit, those drivers (cncrouterparts.com) work with our 240V 55HZ mains?

PS: What happened to you guys last test? I thought you were gonna pants us in every match this series

HyrumR - Thank you - I will very heavily consider that package that you have put forward. Probably save me a lot of hair pulling hey so thankyou