Help! Plasma cutting undersize on X axis

[Normsthename]

I built my Plasma machine over a year ago, and it has performed really well in that time.
Today I got a rush job to do on it, and the parts were a lot bigger than I normally cut (500mm square approx.)
I have a problem where the machine is cutting small on the X Axis by about 2mm
E.G
Part should be 505mm and the part was 503mm
The Y axis measurement was spot-on
I cut a couple of parts rotated 90° and it again cut short on the X Axis.
At first I thought it was the Kerf set wrong, but after correcting that the machine still cut short on the X axis.
The machine uses 5mm leadscrews on the X & Y Axis and a 3mm on the Z Axis.
It is set to 320 steps on the X & y and 266.66 steps on the Z Axis
I have not touched the Mach3 settings since I got the machine up and running so I am at a loss why it is cutting short on the X axis.
Is it possible to compensate on Mach3 to get around the problem?
Any ideas?

Andy

[DanOSB]

what is your step/reveloution?

if u change 1 number it would make a huge difference.. so if you could give me ur numbers and i can probably give u correct numbers to fix that problem..

[Normsthename]

what is your step/reveloution?

The machine uses 5mm leadscrews on the X & Y Axis and a 3mm on the Z Axis.
It is set to 320 steps on the X & y and 266.66 steps on the Z Axis
Is that what you require?
It's such a long time since I set up the machine I have forgotten the formulas!

Andy

[DanOSB]

ur step/rev should be 321.2724

[Normsthename]

Hi Dan
What is the formula for that?
Is that just for the X Axis?
Do you have any idea why the X Axis is out???
The machine uses commercial ballscrews and ballnuts so I would not expect them to worn out yet with the little use the machine has had.........


Thanks

Andy

[DanOSB]

my guess the 360 was a wrong number.. i used a software that calculate the step/rev.. putting in desired movement wanted and the acutual movement and old step/rev and it will show the correct numbers..

best way to use this software try measure the max legnth your machine can do then it will give u the best numbers..

i cant find where to download that software..

[Normsthename]

No problem Dan, I worked out how you came up with that figure

505mm divided by 503mm (Actual) = 1.0039761

320 (Original Steps) x 1.0039761 = 321.27235

I will cut a longer test part to get the accuracy better
But I would still like to know why I need to tweak the numbers.........


Andy

[DanOSB]

tweak the numbers to get perfect amount of travel..

for my machine.. i tweaked the number and then checked every couple months and havent had problem since..

maybe the numbers 360 wasnt the right number at the first time..

hope it will work..

Cheers
Dan

[Normsthename]

I cut a test piece today that was 900mm long.
It actually came out 896.5mm on the X axis
So I did the above formula and adjusted the Steps/Rev
When I ran the part again it came out 900mm
It was as close as I could get it with my trusty tape measure
Thanks

Andy

[Bigtoy302]

I would check your backlash. Check the ballscrew and also all the mounting points. I bet something loosened up.