Guide rails and other questions

Finaly got time to order parts and odered a smoothie and megatronics. So my next step was guide rails and then motors. After looking I see everyone using 8mm rails. I'm planning on using this as double duty, a 3d printer and a cnc machine. The 8mm rods are very small. If I go up to 12mm do you think the mass would be too high to move with nema 17 motors?

I'm also going with a bowden design too whitch will remove some mass.

I should have researched more but didn't have time. I should have got a controller board capable of handling nema 23 steppers instead of nema 17 but too late now.

It depends on what you are expecting from the machine, but I have been extremely disapointed every time I use unsupported linear shafts for milling.

Milling and 3d printing are mostly incompatible processes in a single machine. If you use belts you won't have enough rigidity for milling. If you use screws you won't have enough acceleration for printing. Nema17 stepper motors are unlikely to be a limiting component in either case.

Laser and 3d printing are better aligned from a dynamics standpoint, although the working volumes are different.

Here is a small router I've built. It looks pretty, but 12mm shafts ruin the machine and flop around like jello.

[imgur.com]


If you really want a hybrid machine you basically need to build a mill (supported rail, ballscrews). A slow 3d printer is just slow, whereas a sloppy milling machine is trash.

I'm planning on milling only small acrylic and pcb boards, not metal.

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I'm planning on using this as double duty, a 3d printer and a cnc machine.
If I go up to 12mm do you think the mass would be too high to move with nema 17 motors?

There's no think, engineering a machine is all about calculation. If you don't know the formulas, don't design a machine. If you realy want to desing a machine, get some skills. CNC mills and 3D printer are ways different. A mill is a bodybuilder while the 3D printer is fitness. The mill needs mass while 3D printer do not. It can't be good on both application, and compromises will make the machine clumsy for both jobs. They don't work at the same speed. To make a good mill, it will cost you about $1000, and a correct home made 3D printer starts around $300. Building a dual function machine will also cost you much more than two separate machines. No economy here, or you'll get a bad tool. A pure CNC mill will need strong motors, if you add a 3D printer head, you'll need them to be also fast and agile, so it will be more expensive. The sames principle apply on many components. Don't waste that money on a clumsy machine. Otherhand, a CNC Mill produce a lot of dust and chips while a 3D printer needs to stay dust free. To me, one function equals one machine. Maybe start with a proper 3D printer, then save money to build a good CNC mill.

Edited 1 time(s). Last edit at 02/27/2015 03:41AM by Zavashier.

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Collective intelligence emerges when a group of people work together effectively. Prusa i3 Folger (A lot of the parts are wrong, boring !)

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I'm planning on milling only small acrylic and pcb boards, not metal.

The thing about CNC is that even really shitty machines can look okay at first glance. You don't realize just how frustrating they are until you actually use one.

I'd consider a machine like this to be pretty trashy and it uses 16mm rods with very small travels.

[www.ebay.com]

In addition, Nema 17 and Nema 23 are just motor frame sizes. They don't specify the torque or anything else about the motor. Drivers usually are specified by the amount of current they can deliver to the motors. There are quite a few threads on the internet about creating multi-use machines, but I don't think I've seen any that were a resounding success. My CNC router uses 25mm unsupported shafts with a build area of 50cmX50cm and I would say that they are barely adequate.

You're kind of building your machine backwards.

Normally you decide what the machine should do, then you figure out the mechanical stuff required to make it do that, finally you select the electronics. I'm not sure why you think you need NEMA-23 motors (why not NEMA-34?) or why you think that a smoothieboard can't drive a NEMA-23 motor (it will drive any size stepper up to 2A).

You have a lot of research to do and a lot to learn. If you don't have time to do it, maybe you should take up some other hobby that doesn't require so much time, effort, or knowledge.