Another which should I get Servo or Stepper Question.

[mysterious]

I will be doing a CNC conversion on a Shoptask 3 in 1 machine. I know servos are supposed to be faster and more accurate than steppers, but I am doing this as a hobby and don't need super high speed. Also are servo systems harder to use as far as programming or are they about the same? I haven't heard this discussed too often, so is it not even an issue. I can get servo versus stepper for about $600 more, but is it really worth it? This is a mill lathe conversion and I think steppers would be fast enough, I don't think the machine can keep up with servos top speed anyways. Tell me what you guys think.

[ger21]

Steppers can be every bit or even more accurate than servos. Spend the $600 on other areas and go with the steppers. As long as the steppers can give you enough power.

Gerry

[HuFlungDung]

I would recommend that you use a closed loop system, whichever way you go. That is my main objection to the less expensive stepper systems, is that error can creep in and you will be totally unaware of it until it is too late. This means some kind of encoder feedback, and software that will make use of the information to keep the current commanded position correct.

[ger21]

While Hu raises a valid point, it all depends on your budget and what you're planning on doing. Are you planning on using Geckos to drive the steppers? What size are the steppers? And what software? You can use Geckos, steppers and Mach2 all for typically well under $1000. I'm assuming that since this is a hobby it would be more than adequate. Unless I'm mistaken, the software alone for a system like Hu is talking about can cost more than that. And the hardware even more. Care to elaborate on this Hu?

Gerry

[HuFlungDung]

I can't say that I know much about the detailed workings of the low budget systems. Its up to the buyer to try to find the most performance for the least money. But, part of the equation is knowing what you should be looking for, and knowing the ultimate limitations of the machine that you end up with. Machining without feedback to the controller is like driving blindfolded, IMO

I really don't believe that there is much of a difference between the hobbyist and the professional in wanting the machining job to be carried out successfully. A wide tolerance range is not the same as random errors due to mispositioning.

[Swede]

I tend to agree with Hu in that closing the loop via encoding ensures the accuracy of the program. Importantly, it also provides peace of mind. Consider, you are on machining step 6 of a complex, expensive part. Steps 1 through 5 went great, but during step six, you lose position, the part is scrap.

It is much the same in manual machining. I have had parts that were literally chucked for a week in a dividing head doing numberless operations. The closer I got to finishing the part, the more focused I became in not screwing it up. Scrapping some aluminum round you chucked 10 minutes ago doesn't hurt, but scrapping a radial engine crankcase, or ANY complex part with 3 weeks of work behind it, well let's just say "hurts" is an understatement.

It's all budget, of course, do what you can with what you've got. Best of luck!

[Stevie]

couldn't he use Rutex drivers with servos and then a low cost controler like Mach2 do just as well for him

[mysterious]

I am planning on going with geckos, 500 oz. steppers, and Mach 2. I thought only servos could give feedback and with steppers you just crossed your fingers and hoped that there are no mistakes. I don't hink I will be machining anything too complex, mostly some goped aluminum parts. Back to the feedback thing, so you can have steppers and get feedback on what they are doing? Very interesting. Tell me more on how you set this up. Just when I thought that I was beginning to understand something, I read something else. Also with servos I know you have to be careful with how you wire stuff because you can get cross feed and your coordinates would get lost, how do you guys avoid this?

[mysterious]

Oh also, from what I here geckos with good steppers being run by Mach2 rarely mis any steps. How true is this and if it is would it be more dependable than servos and having to worry about cross feed messing everything up.

[ger21]

With the exception of electrical interference, generally the only reason a stepper will lose steps is if it's not powerful enough for the application. Or, since steppers lose torque as speed increases, because you're going to fast.

[Stevie]

Hey Gerry; your pretty darn close to me; just a hop-skip and a jump over the big river

[ger21]

Actually, I'll be there tomorrow picking my wife up from the airport (she's in Halifax visiting a friend). You wouldn't know off hand which exit the airport is off, would you? I've only been there once before. Thanks.