Smallest jog with cursor key?

[gerald_d]

What is the shortest x,y move that folk can typically do by tapping a cursor key quickly?

Ours is about 0.2mm (0.008") - how much is yours?

[harold_weber]

You can adjust the smallest distance MOVED (not JOGGED)in the Windows software (Ver 3.4.23)

In the VD or Display Values menu, set "Keypad Fixed Distance" to the value you want (I have set mine to 0.005 inches and it can be set smaller.

Then when you press SK or K to bring up the Keypad window, you need to press the "FIXED" button there to access this small movement.

Then with single taps to the arrow keys I get 0.005 inch movements for precise setups.

Not sure how (or if) this can be done in DOS version of the software - I have not used DOD software for about 2 years now.

[rhfurniture]

I can do .028mm
r

[dingwall]

We could probably do .2 or less, but I've got it set for .5 mm

[gerald_d]

I mean a quick tap of the key while the SB is in "continuous" mode at your typical move speed. ie. if you didn't tap, but held the key down, it would carry on running. (I shouldn't have used the word jog in the thread title).

I am trying to establish the "sensitivity" of the typical cursor key. Our own DIY machine is a bit wild in this respect.

Thanks for the replies so far.

[richards]

Mine is totally random. Sometimes I get about 0.25-inch, but usually it's closer to 0.5-inch. I usually set the other mode at 0.025-inch, depending on what I'm trying to do.

[oddcoach]

You can adjust the sensitivity by lowering the move speed first. The slower you go the smaller the move of just a tap

[patricktoomey]

Mine is random just like Mike's. At 1.5ips move speed, I get as low as .25" but usually more like .5" It's a little annoying and I wish it was more predictable. I'm assuming the main problem is that Windows is terrible at very fine timing/repeatability especially when it comes to registering keyboard inputs.

[gerald_d]

Patrick, you have just reminded me of another reason why we are still in DOS. This must be the reason why we think our Win machine is wild compared to the DOS machine. But we do get a fairly predictable 1.2mm to 2mm (.05 to .08") from it (Win) - not as bad as the 6 to 12mm (.25 to .5") being mentioned here.

[stevem]

I tried this today just for this thread. .005" to .008" indicated on the DRO with jog speed set to 600 IPM.

[patricktoomey]

Gerald,

That's true, I have often wondered if DOS would be better for this application. I am running on a fairly old and slow computer, maybe that's why mine has such a large movement. I'm about ready to upgrade to a much faster machine, we'll see if that helps matters any.

[richards]

To me, the minimum distance isn't a problem. I normally use a J2,x,y command to get close to where I want to be. If everything is messed up to the point that the DRO is useless, I do a Z2 command, use a tape measure to find the distance to the destination point and then use a J2 or M2 command to get close. If I don't want to hassle with a tape measure, I use the keyboard jog in normal mode. When I'm about where I want to be, I switch to Keyboard fixed-distance mode and tap away until I'm as close as my eyes allow. It only takes a few seconds.

[gerald_d]

Remember that I have Van in the workshop. It was pretty easy to show him press "K" and then the arrows to center the cutter over a pencil mark....

[odulfst]

my favorite way to line stuff up is to kill the machine and move it manually. moves real easy with the power off, and i have real e-stops that cut both feed lines and the return, so no need to unplug. i used to try to move w/ the fixed setting. always bumped into material :-(.

[richards]

Tony,
Moving an axis, even with the power off, can destroy the drivers. You need to turn off the power, wait for the power supplies to discharage and then disconnect the steppers from the drivers before moving an axis.

[odulfst]

Mike
so, you're saying the motors build up a charge and back feed to the drivers? ya, that's no good. but i really like moving it by hand...any suggestions on how to do it safely without opening control box?

thanks

[richards]

Tony,
No way that I know of. A stepper motor turns into a generator (as do most motors) when it is moved by hand. Unfortunately, the drivers that supply stepper pulses normally aren't designed to work with a generator. The only safe way to move the motor is to turn off the power, disconnect the motor and then move the axis.

[gerald_d]

Mike, a stepper driver should be able to sink the energy of a decelerating mass, and it can only do this if connected. No?

[richards]

Gerald,
You ask hard questions. The short answer is yes, the driver should be able to sink the energy of a decelerating mass. But, as they say, the devil is in the details. A 'properly' designed driver has some kind of 'steering/shunt diodes' that keep 'generated' current from harming the driver, which means that if the driver has those 'steering/shunt diodes', the attached stepper could be turned by hand without fear of damaging anything making the question moot. The safe answer is that in a 'properly' designed system , the stepper motor(s) would be under control at all times. Acceleration ramps and deceleration ramps would keep the motor under control so that the user would never have to worry about harming the electronics and there would never be a time when the motor sourced current because it would always be using or sinking current. The easiest way to tell if the system is under control is to check whether the steppers lose steps when accelerating or gain steps when decelerating. If either condition occurs, the system is NOT under control.

(It's probably important to know that there are stepper drivers that are designed to handle back-voltage; however, because of the cautions that Shopbot has issued about moving an axis by hand, I would have to believe that those types of drivers are not used by Shopbot.)

[odulfst]

i don't think i got that warning, although I didn't exactly read every page of the bible they sent me (most of it though, really!). maybe it's worth giving them a call about.

thanks for the info.

[richards]

The warning about connecting/disconnecting the steppers and moving the steppers manually can be found in the Shopbot Assembly Manual, August 2004, PRTAlpha - 10.