What's the deal with Bottom Up egraving setting?

[David Fairfield]

Curious as to the potential advantages. When I try bottom up, it doesn't seem any different from top down, just the smoke stains are reversed.
Seems I could do the same thing by rotating the graphic.

So, in what cases would it be a good idea to select bottom up?

Dave

[Dan Hintz]

It's often used on substrates that are not completely vaporized in the lasing process (such as many plastics). Imagine a 2-ply plastic with white as the bottom sheet and black as the cap. As you lase a nice, neat image from the top, the black cap that's blasted away farther down gets pulled into the clean white area by the blower, spoiling the image. By doing it in reverse, there's nothing to spoil in the direction of burnt stuff movement.

[Chuck Stone]

+1 on what Dan said. It helps keep the plastic dust out of the way.

I've been doing a lot of Corian, lasering deep. (2-3mm depth) and it
throws out a LOT of dust.. material that isn't vaporized. THe lasered
surface can be rough and hold this dust. Air assist can't move a lot
of it in the engraved area, but will remove it from the smooth area.

So if I run from bottom to top, the dust doesn't block the beam
because the air can move the dust off of the area I'm about to
engrave. If I've already engraved that line (running top to bottom)
that dust stays there, held by the rough surface. THe beam might
not get through the dust.

this is especially true on multiple passes

[Belinda Barfield]

+1 Dan, +1 Chuck. I engrave everything bottom to top.

[Steve Clarkson]

+1 Dan, +1 Chuck. I engrave everything bottom to top.

+1 Dan, +1 Chuck, +1 Belinda. I engrave everything bottom to top too.

[David Fairfield]

Ok thanks for the information everyone. I will keep it in mind if I work with a more dust prone material.

Dave

[Roy Brewer]

I will keep it in mind if I work with a more dust prone material.

Dave,

Additionally, I like bottom up because I get a good look at how I'm doing sooner.

[Mark Ross]

I just set my air assist to 60 psi...no dust issues...but it can cause the part to move.

Seriously tho, that is the reason.

[Jakob Franz]

I just set my air assist to 60 psi...no dust issues...but it can cause the part to move.

Seriously tho, that is the reason.

60 PSI? On my VLS i was told to set it at 15. What are the benefits of higher PSI and what materials do you use such an amount on?

[Mike Null]

Jakob

I do not use air asist when raster engraving. I do not find it to be helpful.

[Dan Hintz]

Jakob,

Various pressures have varying effects on different materials, and higher pressure is not always a benefit. I can't say I've ever used 60 psi on anything yet...

[David Fairfield]

I've tried air assist on rastering to reduce smoke stains, but I find it only worsens the problem by spreading the charred material everywhere.

Now, if it were possible to reverse the air assist and make it into a mini vacuum, maybe with an extention tube to put it right behind the beam, that might work better than bottom up. All my other shop tools have a vacuum attachment, so why not?