# Machsupport Forum

## Mach Discussion => General Mach Discussion => Topic started by: Bill_O on September 07, 2010, 07:30:42 PM

Title: size issues
Post by: Bill_O on September 07, 2010, 07:30:42 PM
I am working on a router that has a problem making diamond shapes correct. If a square is cut along just x and y moves the sizes are even. If the same square is rotated 45 deg, 2 sides are long and 2 sides are short. The long sides are on opposite sides of the square and so are the short sides. I need help with this bad.
Thanks,
Bill
Title: Re: size issues
Post by: Tweakie.CNC on September 08, 2010, 02:41:51 AM
Bill,

Are you using 'Local System Rotated' (MDI page) to rotated your square code ?.

Tweakie.
Title: Re: size issues
Post by: RICH on September 08, 2010, 05:58:47 AM
What happens when you try to do a  circle?
Is it egg shaped?
How much difference in the sides?

RICH
Title: Re: size issues
Post by: Bill_O on September 08, 2010, 06:11:48 AM
Tweakie,
I am rotating the file in my g code software. I also plotted the g code points into autocad to ensure they were correct.

Rich,
A circle does the same thing. Small and large on the same sides.

Thanks,
Bill
Title: Re: size issues
Post by: RICH on September 08, 2010, 06:32:33 AM
You don't say how much difference. I am thinking that's it's a mechanical  / steps per unit issue............
The axis system ( ie; say motor, rack or screw may not be linear...can even be different going the opposite direction ) steps per unit may vary
and you have set them based on some distance.
I would set up an indicator, run gcode for around a circle ( four arcs), put a pause in at say the 90 degrees and look at the difference.
You can only do so much to refine the steps per unit and that would be a comprimise of small to large movements.

If things were perfect, like exactly matched axis systems with the same steps per unit, no backlash etc., then the combined movements  would be
produce a perfect square or circle. So there is steps per unit ( lets say software setting ) and the mechanical side ( lets say the axis system  / each axis component contributes  to total ) which one or combination  is not perfect .......only you can explore to find out. Depends on how anal you want to be about it all.......

RICH
Title: Re: size issues
Post by: rcaffin on September 08, 2010, 06:42:13 AM
I am working on a router that has a problem making diamond shapes correct. If a square is cut along just x and y moves the sizes are even. If the same square is rotated 45 deg, 2 sides are long and 2 sides are short. The long sides are on opposite sides of the square and so are the short sides.

Can you post a photo of a good square, a rotated square, and a circle please? This sounds a little bit odd.

Cheers
Title: Re: size issues
Post by: Tweakie.CNC on September 08, 2010, 06:49:25 AM
Bill,

What GCode software are you using ?.

It could be that there is axis scaling built into your software.

Tweakie.
Title: Re: size issues
Post by: RICH on September 08, 2010, 06:50:36 AM
Cheers,
Just do some testing with your machine and see how well it does.
Even an old machine can be tweaked to achieve some fine results for one  particular machine operation.
We live in a computerized machining world and forget that some practical experience goes a long way to achieving the sought after perfection.

RICH
Title: Re: size issues
Post by: Bill_O on September 08, 2010, 09:04:58 AM
rich,
I have been doing some testing and not getting anywhere. very slow cuts and accels make no difference. less than .001 inches of backlash.

Tweakie,
Enroute. i ploted the gcode points in autocad and they are correct.

rcaffin,
you would not see anything in a photo. the differences are about + or - .015 inches.

Thanks,
bill
Title: Re: size issues
Post by: Overloaded on September 08, 2010, 11:39:49 AM
Hi Bill,
What is the actual resolution of the X and Y axis of your machine ?
Steps per.....inch or mm ?
Curious,
Russ
Title: Re: size issues
Post by: Bill_O on September 08, 2010, 12:59:00 PM
Russ,

1000.15 steps per inch

bill
Title: Re: size issues
Post by: Bill_O on September 09, 2010, 06:36:35 AM
Russ,

1000.15 steps/inch

Bill