Please explain

[bearwen]

I am ready to start building my First cnc and well I have to figure out the electronics. I have looked around and read a few things and well I just dont know what to use I want to keep the cost down but I will pay extra for reliability and quality performance. I am unsure as to what motors and drivers to use could some one explain bipolar motor vs unipolar and what about boards. From reading and asking a few questions most people tell me to get 200 oz/in motors the cnc I plan to build is basiclly a modified and beefed up JGRO ( to start). Here are the motors I was thinking about the small nema 23 http://www.homeshopcnc.com/page3.html I was thinking about building the ss3977 board on pminmo website as the controllers and the 4 axis pc interface board for the BOB but I dont know if bipolar or unipolar is better what about Opto Isolation do I need this? Also I noticed that the current rating for the as3977 is only 2.5a @35v and the motors I posted are 2.8a does it matter or should I use the Picstep by alan on pminmo website and I still need a BOB the more I look the more I get confussed .

Thank You to all who contribute.

[pminmo]

You might want to look into these motors if your on a budget:

new 250oz-in steppers for $24? although at 3.3A your driver price goes up.

The 2.8A motors work very well at 2.5A. Unipolar vs bipolar, unipolar drivers are usually cheaper. Bipolar motors are stronger everything else being equal. Give me some insite on your electonics capability...soldering, troubleshooting.

[bearwen]

Pminmo,

Well I am a component level electronics repair tech for the goverment and I am 2m micro certified in soldering for ISO 9000 facility. I understand electronics but cant design stuff repair or build with schematic no problem.
My budget is not the problem I just want to quality machine to start and then make it bigger and better as I learn so what do you recomend for controlers, BOB and motors?

Thanks

[pminmo]

The stepper in your original post is a pretty good value, there are also pretty good values at automationdirect.com:
http://web1.automationdirect.com/adc...ors_-z-_Cables
The 3977, picstep, l297/l298 will run the 2.8A motor. Also the Xylotex (3977 based). The picstep will give the best performance when utilizing the full power supply voltage of the LMD drivers, but they (LMD) are a touch pricey at $20/axis (2/board $10ea).

[bearwen]

Which do you recommend the picstep is pricy but affordable also the steppers what would you recommend nothing under 200oz/in? thanks for the input so far. The steppers is where I have a hard time I understand how to calculate there torque etc.. when you up the voltage and what not however I dont really know how to calculate and figure just how much force/torque I need I know there is a lot to figure such as bearings bearing size frame material blah blah blah but any help in rough figuring would be great.

Thanks again

[H500]

I'm using 120 oz-in on a small milling machine and a 6" rotary table. It's underpowered, but acceptable. The nema23 250+ oz motors listed above are probably a good fit for your machine. That's as big as you can go without spending a lot more for drivers.

[pminmo]

If it fits the budget, Picsteps, the homeshop cnc motors (262oz) double shaft, use the other shaft for a handwheel. A 45V DC supply at 11+ amps.

[bearwen]

Pminmo,
Thanks for the input thats what I was thinking but wanted reassurance from people out there that have built and use these things it is always cheaper and less stressful to learn from people who have been there and done that. Which of the 2 BOB boards on your site do you recommend with the above mentioned setup? I would like to add axises in the future but we can add a second lpt port to do that. So how exactlly does the torque curves play into this thing I have ballpark 400 lbs of force rough guess at rest (it will drop as the stepper spins ) the question is how much does it drop and what does this number mean does it mean that lets say at full rpm etc... the force is dropped to 125lbs does this mean that I can move 125lbs of mass or pressure on lets say the y axis? What is the formula for figureing the torque in lbs/in I have seen a few different ones posted? I will be using a 1/2 - 10 lead screw unless you have a suggestion that is better I have read that this gives me a .1"/rev lead to make figuring feed rates easier?

Almost ready to build starting to come to gether in my head.

Thank you for the help!