Vertical Striations in Acrylic.

[Tweakie]

Hey Guys,

I wonder if you could help me out here.
I have just laser cut two 50mm diameter discs from 6mm acrylic - one has visible vertical striations one does not. The parameters (power, federate, air assist, material etc.etc.) are the same for both discs, the only difference is the GCode (disc 1 has been cut using a predetermined number of straight lines, whereas disc 2 has been cut using circular interpolation).

Now this might sound like a daft question but “What causes the vertical striations to be made ?”.

Is it the fact that the cutting head stops and starts ?.
Is it the sudden change of direction ?.
Is it acceleration / deceleration of the cutting head ?.
Etc.???

Funny one this, because I know how to create these striations and I know how to prevent them I just don’t know what causes them.

Grateful for any comments or info on this one, thanks,

Tweakie.

[bdring]

They both look pretty good actually.

Could the lines be the edges of "facets". Are you running in CV mode with the lines? Could it be vibration?

[Tweakie]

Bart,

Thanks for the input.

It is certainly facets (not sure if it is the start, middle or end though) but why is it just not smooth flats all round (like a threepenny piece).
Not vibration otherwise both discs would look the same.
I am running in CV but I will try switching to exact stop just to see if that changes the appearance in any way.

Thanks,

Tweakie.

[Tweakie]

For those who follow I think I have now found the answer.
My circle was not round enough (the edge resolution was poor) and the laser was effectively cutting what I had asked it to do. The lesson here is that not all software exports arcs at a high enough resolution for perfect work. Acrylic is difficult stuff to get perfect edges because of remelt, air assist etc etc. but I have had a lot of practice now and I am improving my results as I am developing new techniques.
Here are a couple of 6mm acrylic footprints which are destined to become keyrings.