First Machine, Questions

[wallyh]

I'm about to build my first CNC machine which will be based on the JGRO and Joe's CNC machines. I'm planning to use 3/4" Baltic plywood instead of MDF for all the wood parts except for the adjustable blocks which will be 3/4" HDPE.
I will be using 5/16" lead screws and will pretty much follow the plans for the above machines. The bed will be 22” X 36”, overall dimension will be 32.5” X 36”.
I think, with help from you, I can build the machine but I want to make sure I understand how it’s supposed to work. So I would really appreciate if you could add and correct my ideas where needed. I have read many posts on this forum and would not be this far in my thinking without your comments and work.
As I understand it, you need:
1. A CAD program to design with – AutoCad, TurboCad, etc.
2. A CAM program that converts the design into machine code – BobCadCam, DeskCNC, etc.
3. A computer to run the machine code.( question, what specs would you need for the computer? ie, CPU speed, hard drive size, memory size.) The computer uses the code from the CAM program and converts it into step signals which are outputted through the parallel port of the computer. – Mach, EMC, DeskCNC, etc.
4. A breakout board that interfaces to the parallel port of the computer – Xylotex, HobbyCNC, DeskCNC, etc.
5. Drivers that take the step signals and convert them into pulses that drive the stepper motors. A power supply is needed for the drivers.
As said above, any and all comments, corrections, additions , etc will be welcome.
Wally
Planning on starting on the adjustment blocks this weekend so I have plenty of time to revise my plans.

[joecnc2006]

Depending on your driver #4 and #5 are combined into one board as is my HobbyCNC Boards, I have had two of them so far with no problems, One running 100oz motors and the other running 200oz motors.

as far as a computer to run the contollor software (Mach 2/3 or EMC or TurboCNC and so on) I would go for atleast a 1g machine, you really do not need a large hard drive, and it needs to be a bare bone type of system with not much running in the background to mess up the pulses.

[spalm]

Hey Wally, Welcome to the Zone.

I agree with Joe. HobbyCNC hardware is the best bang for the buck, unless you want to try to build PC boards from scratch and try to save some money; in which case we can point you to sites to do this. You might find motors cheaper on eBay. The PC should be dedicated to running the motors. 1 GHz or so, hard drive size does not matter, running XP or W2K.

You have the right idea on the flow. You state 5 steps, but it is really a three (major) step process (although some software bundles will hide this). It can be compared to printing a document. You create the source file with something like Word or PhotoShop or Excel (this is the CAD) then you send it through a Print Driver (this is the CAM) and send it to the printer (this is the Controller). Just like printing, the CAD will let you create, the CAM will let you change parameters (paper size for printing, bit size for CAM), and the Controller will turn the motors and spray the ink or control the router.

You seem to be leaning towards a JGRO or Joe’s first machine. These are easy to build, but not the most accurate, so I take it that there is a budget involved. So for software I would recommend using one of the free CAD programs, then use SheetCam (free demo) or CncZone’s free CamBam for CAM, and Mach3 for the controller.

Steve

[wallyh]

Thank you for your replies. I have a budget but also want something that wil work for model airplane cutting. I have 3 - 80 oz steppermotors that I have from a long time ago, I've never used them. I can build a computer to suit the requirements, I have a 40 GB hard drive to use and a cpu that's ok. What about memory? Also no special video card requirements I guess.
I have AutoCad 2002 and TurboCad 9.2 to use and I don't think I want to build boards from scratch, so thanks for the suggestions.
If JGRO and Joe's machines are not too accurate, what do you suggest that I can build? I chose those because I thought I could build one from their plans. Is there a kit or other plans that I should be looking at?
Wally

[ger21]

80 oz motors are on the small side. If your going to use Mach3, youshould have about 512 MB memory. You can probably get by with 256, but 512 would be better. Mach 3 can be picky about built in video on some older systems, but any cheap videocard should work fine.

I wrote a macro for AutoCAD that will create G-code from within AutoCAD, so you can use that and you won't need a CAM program. It's free, here: AutoCAD 2 G-Code macro


It's not that those designs are not accurate. If your just cutting balsa, they should be fine. But for heavier cutting, they are not the most rigid machines, and can flex a lot.

[wallyh]

I thought the 80 oz motors were on the small side, now I know. These were given to me some time ago. Thanks Gerry for the G-code download info, I'll be using it when the time comes.
The y axis is planned to be shorter, maybe this will help on the rigidity.
Is there another plan that I should be looking at?
Wally

[ger21]

Is there another plan that I should be looking at?
Wally

I think you'd probably be better off to build the JGRO, then you can get a better understnding of it's strengths and weaknesses, then use it to build a better one. You could probably use all the components onthe next one, if you plan carefully. I'd build this one out of MDF, and save the Baltic Birch for the next one.

Few people are completely satisfied with the first machine they build, and the first one can teach valuable lessons.

[wallyh]

I think that's a good idea-building the JGRO. I got a great deal on the Baltic Birch, $30 for enough to build the JGRO, so think I'll use that instead of MDF. I'm not doing the torsion box, using Joe's design with angle iron.
Will start on the plastic parts first. Thanks for all the info.
Wally