Cnc cutting the wrong size..

[Tomnewry]

The belt is a 5mm pitch as for the ballscrew i dont know, any ideas how to find out also can this harm the machine or what problems will it cause.
Thanks

[HankMcSpank]

The belt is a 5mm pitch as for the ballscrew i dont know, any ideas how to find out also can this harm the machine or what problems will it cause.
Thanks

Sounds like you're now sorted (ie 100mm is cutting 100mm), if you're using Mach3 & have access to a dial indicator, here's how to get really granular with accuracy....

[JAZZCNC]

Sounds like you're now sorted (ie 100mm is cutting 100mm), if you're using Mach3 & have access to a dial indicator, here's how to get really granular with accuracy....

Purposefully didn't suggest using the auto feature has it doesn't really help Tom understand whats going off with his machine. Much better if you know the inner workings of the machine, makes fault finding and smooth operation much easier and quicker.

The belt is a 5mm pitch as for the ballscrew i dont know, any ideas how to find out also can this harm the machine or what problems will it cause.
Thanks

Ok well there's a few ways to find screw pitch but easiest way is to simply accurately measure the distance travelled for one full turn of the screw. This will give you pitch then you need to count the teeth on each pulley to find any ratio. (NOTE: 1 Turn of SCREW not MOTOR)

The belt pitch doesn't have any bearing on setting the steps per unit or distance travelled it's just the spacing between teeth.

The other way to find pitch is measure distance between the ball track centres. This technique works ok to give quick eyeball idea but it can catch you out if the screw is multi start.? Multistart screws are common with lead type screws and some of the higher pitch ball screws.
Basicly multistart use 2 or more tracks added together to give affective pitch per rev. IE: 10mm pitch with 2 starts each track will measure 5m centres.
The measuring distance travelled technique is preferred has it's more accurate and less prone to error.

[HankMcSpank]

Purposefully didn't suggest using the auto feature has it doesn't really help Tom understand whats going off with his machine. Much better if you know the inner workings of the machine, makes fault finding and smooth operation much easier and quicker.

....when there are a few unknown variables involved (unknown pitch, pulleys etc), the auto calibrate may not be the most educational metho (from a getting deep down & dirty with steps per unit aspect), but it will likely be the most accurate/painless!

[Tomnewry]

Hi guys thanks for the info. Still not quite sure so im gonna measure between the screw that idea seems the easy one an then ill get back to you with the results, in saying that I cut something today and the size was exact i cut it 640mm by 400mm an it was good so as i say ill keep you informed. Thanks for all the comments.

[Tomnewry]

Oh and sooy about this one but where is the auto calibrate in mach?

[Tomnewry]

Hi guys on another note, I have basically ripped out all the electrics of the old machine and replaced everything but the transformer which runs the 120v porter cable motor but now for some reason the porter cable motor is not running at full speed, I have checked all the wiring and it a ll seems ok, any rough ideas.
Thanks

[Mansour1974]

Thanks Hank
I was looking for this solution since 2 days, mine was 320 steps per unit, I change it to 400
it is perfect and accurate now.

thanks again :)