Engraving deeper at same temp.

[ncamacho2000]

Hi All

Im getting a couple of different results when i engrave this is most noticeable of Glass & Acrylic, I am engraving all at the same speed & temp (power 10, speed 150, Scan gap 0.05), i seem to be getting deeper engraves at different points mainly where the beam flashes quickly over a small piece continuously. If the laser travels some distance and then back it seems a bit of a lighter engrave.

However, if there is a repeated large area then i can get a dark line appear almost like a water mark (you can see this through the top of the S & E in the full photo). I have enclosed a couple of photos. As im writing this im starting to think it maybe something to do with the scan gap. I thought it could be the glass/acrylic but it seems to be the same on each batch.

Any ideas guys??

Cheers Nigel (6040)

[richardofswansea]

Hmmm, the experts have been quiet today so maybe I should chip in!

I've not had this problem, but from my experience your scan gap looks very small. With those settings engraving the plaque pictured must take days! I think you may be going over the same area of hot acrylic again and again as the scan gap isn't enough to move the beam into a fresh piece of acrylic on each pass. I tend to use 0.2, or 0.15 if I'm feeling finickety (and patient!).

Richard

[ncamacho2000]

Hi Richard

Your right it takes ages! But i was originally finding a step/jagged edges when i had increased the scan gap (but this was always on wood). i think you maybe right so will have ago at increasing it. Can i ask what speed power you would normally engrave acrylic or glass on?

Ill see if anyone else has any recommendations too.

Thanks for your advice.

Nige

[Daven]

I think banding has also to do with a mis-match between scap gap and the resolution of the artwork - will see if I can find where I read it

Best

Dave

[ncamacho2000]

Thanks dave

Any info is greatly appreciated, the artwork was all vector form (the text created in corel ) dropped into corel draw converted to dxf format and then imported to laserscript. I was under the impression that this would mean resolution would be all the same as there were no bitmap images etc, does this sound right?

Cheers Nige

[Daven]

Yeah I would not expect to see that issue with vector. Is it reverse engraving acrylic?

Cheers

Dave

[ncamacho2000]

Hi Dave

No its not a reverse engraving or reverse engraving acrylic, i was thinking the same as Richard too hot with a small scan gap, but havn't tried anything else yet, its just a bit strange that it happens on some parts where there is more engraving to be done or where there is a small amount of engraving so the head is flashing quick over it. Weirdly i also get patches on glass too.

Could it be something to do with whatever fires the tube or the tube itself?

Cheers Nige

[Daven]

I've seen posts elsewere about power spikes causing banding but remain sceptical in the UK unless you have a dodgy supply. How old is the tube?

The other thing going through my mind is water temp. Do you use a cooler and is the pump ok? Just wondering if it's heating up and then cooling down again for some reason. Machanical reasons such as the belt tension is a possibilty. Guess you could try a rastor version next to a vector and see if the band appears on both.

Cheers

Dave

[ncamacho2000]

Hi Dave

Thanks ill go through the process of looking at the various things you have pointed out to see if i can eliminate anything, if its ok ill message you about it and let you know where i am with it.

Thanks Dave and Richard

Cheers Nige

[Spooky]

Hi Nige,

Try reducing the air assist pressure as well,I've seen banding like that caused by heat as they guys said but also by redeposition on the job due to too much air.

0.15 is a good scangap as Richard said, too small will simply heat the item up and going smaller than the spot size by more than 25% actually achieves very little (apart from increasing run times)

I'd try power 12 to 15%, speed 325 and a scan gap of 0.15 and see how it goes.Bidirectional as well

best wishes

Dave