Calibration issues, advice needed

[Neale]

Are you talking about being wildly out (e.g. twice or half size) or just a little bit - a few per cent, say?

[JAZZCNC]

Jim.

Your drives main dip switches let you set the Motor Amps and Micro stepping. Motor amps is easy just select the nearist lowest setting to the motors Amp rating.

Micro stepping (MS) is dependant on how you want to run the motors. In general setting the MS to a higher setting gives smoother running motors and to a lesser degree some resolution gain. The trade off is it works the PC and parallel port harder has it needs more pulses to move the same distance has a lower setting. There is also a limit where it's no longer benifical going higher, this around 2000 pulses, but won't get into this now.

What you want or need to know is the relationship between the MS value, ballscrew Pitch and Mach's Step Per setting. . . . It's quite easy really when you get your head around it.!!

Mach Steps per is asking for the number of pulses(steps) to move 1 unit, so if mm's then 1mm.
To calculate this you need to know the Pitch of the Ballscrew, NOT diameter, Pitch is the amount it travels for 1 revolution. Along with the MS the drives are set too.
Then divide the MS by the Pitch. Ie: MS=1600/5mm pitch=320 Pulses(Steps) Per/mm.
If your machine is moving the wrong amount it will be these settings causing it.

The velocity and Acceleration are then adjusted based on your preferances on speed and what the machine is capable of. There are far to many factors which affect this and really nobody can give you any accurate settings for these only guide lines has it's mostly trial and error which is based heavily on the individual machine.

[Kernow Jim]

Hi Neale and Jazz

Thanks for your responses.

Thanks Jazz for your explanation, I think I understand better now.

The problem I had, was after I calibrated and then re-calibrated to check that it was moving the right amount, it would still be out, so I would do it again, and again and after 4 or 5 tries, still not knowing if it was calibrated properly. When I started out, both the x and y were nearly double on the measure. When I thought I was done I did a test cut, just a circle set at 100mm. I ended up with an elipse! The x axis was almost spot on but the y axis was only 38mm.

I have been out with the machine again, the MS drivers are still set to Jazz's settings and after calibration the 'steps per' on all 3 axes are between 1275 and 1286. It seems to cut at a reasonable rate according to the feed rates. I was expecting it to move quicker on rapids and jogging by hand.

Any way I am a lot happier with it now.

Thanks again guys

BTW did you see the picture of my machine on my intro post, I'd like your comments.

Jim

[JAZZCNC]

I have been out with the machine again, the MS drivers are still set to Jazz's settings and after calibration the 'steps per' on all 3 axes are between 1275 and 1286. It seems to cut at a reasonable rate according to the feed rates. I was expecting it to move quicker on rapids and jogging by hand.

That's a very high number of steps per.!! . . . The figures make think you have the Micro stepping set far too high and working on the steps per figures you have given I'd guess you have drives set at 6400 micro steps if using 5mm pitch screws or 3200 if 2.5mm pitch screws. In either case your set too high and should reduce to 2000 at most. Anything above this is just wasting pulses and robbing you of speed. If I'm correct then This will be why you can't get very high rapids.

So Please give details about machine.

#1 Are you using mm's or inch units in Mach3
#2 Micro steps drives set at.
#3 Ballscrew or lead screw pitch.

Edit: I've just been to your Intro and can see you have either 5mm or twin start screws so 10mm pitch so this confims to me you have the Micro stepping set way way to high.
Drop the micro stepping down to 1600 and if 5mm pitch set the steps per to 320. or 160 if 10mm pitch.

Now if the Kernal speed is set to 25Khz you should get in the region of around 4000mm/min velocity with Accel of around 800-1000s/s.

Raising the Kernal speed will allow more pulse rate so a higher velocity can be reached but I wouldn't go any higher than 45khz and even then I don't recommend you change it has every change from 35khz makes the machine potentialy unstable. You'll need a fast PC with good parallel port to higher than 45Khz.