Messages

1141

Show"N"Tell ( What you have made with your CNC machine.) / Re: 6 axis Robot

« on: June 04, 2009, 01:26:11 PM »

Hi Al,

Looks impressive... but a video in needed to understand what's it capable of.

Daniel

1142

Show"N"Tell ( What you have made with your CNC machine.) / Re: Laser Cut Gaskets using a low power laser.

« on: June 04, 2009, 01:22:29 PM »

Tweakie,

Very nice!! I know it's a pain to cut a form from rubber. Now it's rather fun for you. Well done!

What's the material?

Daniel

1143

General Mach Discussion / Re: Inaccurate Cut Dimensions Weirdness

« on: June 01, 2009, 12:58:13 AM »

Hi Terry,

Yes, the error seems to be the same no matter what's the size of the rectangle. Were you thinking it was wrong steps per in motor tuning?

Daniel

1144

General Mach Discussion / Re: Inaccurate Cut Dimensions Weirdness

« on: June 01, 2009, 12:55:44 AM »

Rich,

Wasn't trying to compare machines Wanted to get an idea of what kind of tolerance you can get on your machine with known backlash and gain if you work appropriately, and then work out from there of what can I get if I learn to work correctly with my machine.

So what do you mean by "adjusting steps" and "adding steps"?

Daniel

1145

General Mach Discussion / Re: Inaccurate Cut Dimensions Weirdness

« on: May 31, 2009, 11:44:57 AM »

Hi Rich,

It is true that as the tolerances get tighter more things come into play. But do you really think that 0.05mm can be referred as a tight tolerance in the above sense? I would think that it is 0.01mm and finer tolerances when things get tricky.

What does your gcode look like when you make those adjustments to achieve an accurate circle? I mean, if it's oval then tweaking the radius in the gcode won't do. I would think of using scale factors instead....?

What's your mill's backlash? And what kind of tolerance for the circles can you get?

Daniel

1146

General Mach Discussion / Re: Inaccurate Cut Dimensions Weirdness

« on: May 31, 2009, 08:50:40 AM »

Rich,

OK, thanks! Just was looking for a logical explanation to this I guess...

I will do more testing and try to find any rules, that will allow me to correct the dimensions in the program.

Daniel

1147

General Mach Discussion / Re: Inaccurate Cut Dimensions Weirdness

« on: May 31, 2009, 08:11:25 AM »

OK. I will make that trial cut you suggest anyway, and see what I get.

Daniel

1148

General Mach Discussion / Re: Inaccurate Cut Dimensions Weirdness

« on: May 31, 2009, 08:04:00 AM »

Hood,

I see. So will it mean that the cutter diameter is smaller than nominal or what? Don't think it could be the cutter diameter, since, first, it is Hanita brand cutter, second, I measured the cutter diameter and found no error and third, it happens with any cutter I use.

Daniel

1149

General Mach Discussion / Re: Inaccurate Cut Dimensions Weirdness

« on: May 31, 2009, 07:50:41 AM »

No, I haven't tried this. But may I ask what's the logic behind this? I think that when making a cut like this, when the cutter is loaded from both sides, the width would be slightly bigger than the actual cutter diameter. Is it wrong?

Thanks,
Daniel

1150

General Mach Discussion / Inaccurate Cut Dimensions Weirdness

« on: May 31, 2009, 05:07:17 AM »

Hi,

I have a strange inaccuracy in the parts I cut. If I cut an outside profile, for example a rectangle, I get the dimensions about 0.06mm larger than programmed. If however, I cut an inside profile, for example a rectangular pocket then the dimensions are about 0.05mm smaller than programmed.

My backlash is less than 0.015mm on both X and Y. If it were a backlash issue then, the axes would move less than the programmed distance. But it is not the case when cutting outside profile - if it were backlash, the dimensions would have been 0.015mm less than the programmed, but instead they are 0.05mm bigger. Also in case of backlash, the pocket dimensions would have been 0.015mm smaller, but they are 0.05mm smaller.

I thought it might be a lack of rigidity on my little Emco, but trying to rerun the program to see if it removes more material, it only improved the dimension by 0.01-0.02mm, i.e. from 0.06mm discrepancy to 0.04mm. Subsequent rerunning the program doesn't seem to remove any material.

I was experimenting with aluminum and not cutting too deep, so really seems unlikely to be a rigidity issue...

Any thoughts are appreciated.

Thanks,
Daniel