Quote Originally Posted by purple_rob View Post
Hello all,

I only thought about building a mini cnc last night and have only spent about an hour looking around the net at ideas.

I did'nt really get anywhere but have a few ideas and thought i'd post a few questions to see if what I want to achieve is even possible.

I'm looking at building quite a small CNC to enable me to machine materials such as: hard resin, nylon and possible small quanities of aluminium.

This is hobby only and I want to make it as simple and cost effective as possible for my first build to get good ideas and improve if necessary.

I am happy I am able to build the frame work but need to know about Hardware and Software

OK Questions,

1. If I was looking to purchase some cheap stepper motors from ebay (UK) what would I be looking for?

2. How would I match these motors to the controller and what controller would I be looking for? (how would this connect to my PC)

3. For a novice in software could anyone recommend anything?. Is there any freeware around?

4. Lastly, there are a lot of DIY builds on you tube and i'm quite impressed. I could'nt find any DIY designs on this site, are there any?.

Many thanks to everyone in advance, this site looks pretty amazing and I'm quite excited about starting a project.

Thanks Rob

p.s My apologies if this is in the wrong section of the forums.
Rob,

Welcome to MYCNCUK :)

I'll try and answer your questions, but as I said on CNCZone there is no right answer until you have some idea of the size/shape/performance of the machine you plan to build. For example are you going to use ACME/Trapezoidal screws with a delrin nut or a ballscrew? The difference is friction coefficient is 0.8 to 0.2 roughly - that could make a big difference to the torque required from the stepper motor. Similarly the pitch of the screw and the traverse rate you plan will determine the maximum speed you require from the motor which, depending on the 'knee' of the motor torque curve will determine the voltage you need to run. The torque and therefore the peak current, the voltage and the minimum step size will determine the characteristics of the driver, and whether it microsteps or not which ultimately determines the cost.

As far as motor sizes, anything less than a Nema23 frame motor is likely to be too small. Similarly anything less than a 200 step motor is unlikely to give the resolution required. This rules out most of the very cheap motors on eBay. Something like this would probably do, but that 4.2A rating is going to mean a big, expensive driver. In simple terms a motor up to 2A can be driven with a cheap (£30 - £50 per axis) driver which will give 1/2 and full step capability, above that you need to go to a more sophisticated driver which costs more £££ but will give 1/4, 1/8 and maybe 1/16 step. Somthing like this would also suit, its 1/2 the torque of the bigger motor.

Motion Control (the firm advertising those motor) can supply matching drivers and power supplies. They, like many other suppliers (I am not recommending them specifically) can advise you to some extent but you need to have an idea of your requirement first. Too often we see "I've bought this set of motors, etc., will they do for my mill" only to have to advise they've not got the power, etc. to do the job. Too big can be as bad as too small.. there are resonance effects which come into play and a big motor run below its optimum settings can give as poor results as too small a motor.

The one thing you must have is a good quality breakout board that connects your PC's parallel port to the stepper drivers. An optically isolated board is best as it protects the PC against nasty voltages and resolves any ground loop issues.

Software: The two main products to drive the steppers from the g-code file that describes the motion required are Mach3 for Windows or EMC2 for Linux. Both are good, Mach3 isn't free but the freeware version can handle up to 100 lines of G-Code which is enough for many small jobs. In either case a dedicated PC with the minimum software on it is really essential, especially the Windows approach.

To get g-code you need to generate CAD drawings and process the output files, usually in DXF (autocad) format. I use QCad as my CAD package on Linux as its free if you compile it from source code. There are others. For small requirements freeware such as GDraw can do the CAD and g-code generation in the same package but are fairly limited.

Browse the Open Source Software forum on CNCZone for more ideas.