Help with full step 1/2 step 1/4 step

[raceneer]

Hey all.

I have been machining some molds recently that take a fair while, and noticed one or two minor inconsistancies. I did load up the tool once or twice but not enough to loose steps i figure. All in all the finish is great but it made me wonder.

I know very little about steppers and 1/2 1/4 and full step.
I've done some reading, and note that you can pull more torque in full step then 1/2 and it's a significant amount. I would prefer, I think, to go slower, and have more torque, then move fast and potentially miss a step here or there. Is there any way to tell what you running by looking at the board?
Is it true that by adjusting to full or 1/2 step you can pull more torque.
Do you loose noticable resolution?
I think i'm currently running 200 or 300 is steps per in mach3, I will have to double check, but is this worth while, or should I just slow down my feed and slow my accelleration down to avoid missing a step here or there?

Any tips/ hints.
Thanks all.

[elf]

Generally speaking, half and full steps are more accurate than eighth or smaller microsteps, but it will depend on the driver. Once you loose a step, there is no getting it back, so the part will not be the specified size. The setting in Mach must match the setting on your stepper driver. Your documentation will most likely tell you how to set the step size. Programs like GWizard and FSWizard can help you determine the proper feeds and speeds based on the desired chipload recommended by the toolbit manufacturer.

[raceneer]

Generally speaking, half and full steps are more accurate than eighth or smaller microsteps, but it will depend on the driver. Once you loose a step, there is no getting it back, so the part will not be the specified size. The setting in Mach must match the setting on your stepper driver. Your documentation will most likely tell you how to set the step size. Programs like GWizard and FSWizard can help you determine the proper feeds and speeds based on the desired chipload recommended by the toolbit manufacturer.

Thanks for the tips.
I emailed the manufacturer and have read you can measure the thread on the ball screw to help work it out then change pins. I'm not sure what I'm running at the moment but it rapids well and cuts well at 4000mm/min. I'm thinking if I half that and increase torque by changing the steps to full or half I'll still have a fast machine but with more torque and accuracy does that sound right?

[MTNGUN]

I'm thinking if I half that and increase torque by changing the steps to full or half I'll still have a fast machine but with more torque and accuracy does that sound right?

What does the driver manufacturer say?

Gecko generally recommends 10 microsteps for optimal smoothness and resolution. I'm not aware of any decrease in torque with microsteps compared to full steps?

One of the chinese drivers I'm using needed 16 microsteps to produce acceptable smoothness, otherwise I stick with 10.

The disadvantage to microstepping is that it requires more processor speed on the PC (or driver board, if you are using one). That often limits the maximum rapid speed.

[garyhlucas]

Stepper motor torque falls off rapidly with an increase in speed to to increasing back EMF. If your drives can handle a higher voltage than the power supply you have now you could get more torque at higher speeds by raising the voltage.

[raceneer]

Stepper motor torque falls off rapidly with an increase in speed to to increasing back EMF. If your drives can handle a higher voltage than the power supply you have now you could get more torque at higher speeds by raising the voltage.

Hi Gary,
Thanks mate I'm looking into it.
Is there a voltage output pot somewhere on the powersupply or do you need to get a powersupply with a higher output voltage. I can't remember what it is on this but we did inspect everything a little while ago. I noted the voltage feed to the VFD was a pot on the driver board (Adjusted with a screw.) Would this be the same on the power supply?
I'm just asking cause I don't have a clue what I'm doing, but I can use a multitester and a screw driver

[macona]

Or just ditch the steppers and go with small servos. Leadshine and others are making very reasonably priced servo packages now.

[garyhlucas]

The funny part about the servo vs stepper debate is that the stepper guys are not going to give up without a real fight. I see that Primopal, the outfit I got my steppers from, now offers some 4200 in/oz nema 42 steppers with drives that run off 120vac or 220 vac line voltage. That makes a nice retrofit for a Bridgeport I would think. They are also offering closed loop steppers with encoders and drives. The prices on both of these are very reasonable I think. Every year CNC gets easier and cheaper to do!

[raceneer]

Wow maybe i have been living under a rock but servo motors? Since when lol? Where can I read about them and their power output/advantages etc?

Anyway. I'm taking a look at what I have no and will take some photos. I wont be buying anything new till its time to buy a new machine. For now it runs ok but I would like to maybe up the torque in them.

[macona]

Someone asked me to write something about servos and steppers and this was the result:

http://bbs.homeshopmachinist.net/thr...t=servo+macona

Like I say in the post, I avoid steppers like the plague. I tend to get access to drives and motors pretty reasonably priced and they are just so much better. I have them in my little cnc lathe, spindle on my Monarch 10EE, my supermax cnc mill, my laser cutter, my laser welder, and now in my telescope mount I have been building.

[rythmnbls]

Another vote for the servo camp.

I used servos on an X2 mill conversion, some might say that it's putting lipstick on a pig, but I don't regret it.

Steve.

[raceneer]

After reading that entire 5 pages I'm thorougly confused about Servo motors, where to get them cheaply and how to set them up, suffice to say I'm a 'seeing' learner and would probably have to see it all working to understand. They seem awesome, but I wouldn't know where to even begin starting down that journey. For me I think it might be better to put another Stepper motors that matches on each ball screw, making a push/pull mechanism on each end of the ballscrew on the X and Y axis. I can split the same outputs and just run that motor in reverse and run them off a second power supply. Z Axis not sure of yet. I think though, this would provide way more torque at a fraction of the cost of a full servo setup (Please tell me if I'm wrong.)
Is there a company that make setups for servo motors you can buy? Like 3 axis setup with drives??
Thanks.

Found some much higher torque 2.2 and 3.5/4kw spindles that are designed for metal and run at 8000 or 12000 rpm with 6nm of cutting force, 2.2kw 24000rpm spindle standard is 1.8 apparently. :S

Anyway I'm going to research it, but I'm buying a VMC soon anyway.