mikejohn
02-22-2006, 12:35 PM
Having discovered (as mentioned in another thread) that I could offset from .eps files in PW, I entrusted a 6 meter long plexiglass sign to its care.
It was to cut a 3mm 'rabbet' around the edge of the letters, 1.5mm deep, then cut out the letters.
I was cutting with a 6mm two flute with no problems.
In order to assist the final cut off, I offset the rabbet cut outwards by 3mm, cutting in fact a 9mm 'slot'
The using the same 6mm bit, along the offset rabbet toolpath, I cut down the remaining 1.5mm to cut out the letter
All straight lines were perfectly set at 3mm offset but the curves had some sort of different arc!
I checked the shopbot file, taking the start x,y points along the curve sectors for the original and the offset, and it appears they are good curves
In places I had a cut of just 6mm, the bit width, in others as much as 12mm (i was expecting 9mm).
I cut and re-cut the rabbet part of the same file, and each time these air cuts, just brushing the material , followed identical paths.
Each and every time for 5 consecutive attempts it cut no new material, just brushed along the original cut.
So we can rule out intermittent interference or bad earthing, we can rule out bit flex (3mm would be a bit steep anyway,) we can rule out a loose shopbot, it would hardly be identically loose cutting over an area of 1 meter by 2 meters.
I solved the problem to an extent by using the original (non-offset) as the cutting path, and using the same path with a12mm bit to create the 3mm rabbet.
The letters lost 3mm around there edge, but they are a meter tall , and going 10 meters up on the side of a building, so my client accepted it OK.
And when I cut these two paths with different bits, they cut perfectly.
Does anyone have the faintest idea whats going on?
speeds were perfect for the plexiglass. no melting, nice chips, smooth edges. It was just problems on the arcs.
It was as if the shopbot was accepting what appears to be a good file, and interpreting it badly, or PW did something odd.
Arc/mm by the way.
..........Mike
It was to cut a 3mm 'rabbet' around the edge of the letters, 1.5mm deep, then cut out the letters.
I was cutting with a 6mm two flute with no problems.
In order to assist the final cut off, I offset the rabbet cut outwards by 3mm, cutting in fact a 9mm 'slot'
The using the same 6mm bit, along the offset rabbet toolpath, I cut down the remaining 1.5mm to cut out the letter
All straight lines were perfectly set at 3mm offset but the curves had some sort of different arc!
I checked the shopbot file, taking the start x,y points along the curve sectors for the original and the offset, and it appears they are good curves
In places I had a cut of just 6mm, the bit width, in others as much as 12mm (i was expecting 9mm).
I cut and re-cut the rabbet part of the same file, and each time these air cuts, just brushing the material , followed identical paths.
Each and every time for 5 consecutive attempts it cut no new material, just brushed along the original cut.
So we can rule out intermittent interference or bad earthing, we can rule out bit flex (3mm would be a bit steep anyway,) we can rule out a loose shopbot, it would hardly be identically loose cutting over an area of 1 meter by 2 meters.
I solved the problem to an extent by using the original (non-offset) as the cutting path, and using the same path with a12mm bit to create the 3mm rabbet.
The letters lost 3mm around there edge, but they are a meter tall , and going 10 meters up on the side of a building, so my client accepted it OK.
And when I cut these two paths with different bits, they cut perfectly.
Does anyone have the faintest idea whats going on?
speeds were perfect for the plexiglass. no melting, nice chips, smooth edges. It was just problems on the arcs.
It was as if the shopbot was accepting what appears to be a good file, and interpreting it badly, or PW did something odd.
Arc/mm by the way.
..........Mike