Sharp Acrylic Edge

[Daniel Muller]

Anyone have the problem of a sharp acrylic edge when vector cutting. The face of the acyrlic that is down always gets an edge that is pretty sharp and needs to be filed of sanded off. The setting for 1/4" is 35p 100s.

[Steve Clarkson]

Hi Dan.....welcome to the Creek.

I think if you run a second pass, slightly out of focus, it will give a nice smooth edge to the acrylic.

[Daniel Muller]

Thanks Steve! I have been doing a ton of acrylic medals for skiing lately and I am getting extremely tired of having to ease the edge on a hundred at a time.

[Rodne Gold]

The sharp edge is due to remelt , it means the liquid swarf or melted pex isnt being ejected thru the kerf (cut) , use air assist at higher pressure and try direct it better if you can

[Joe Pelonio]

You must have a lot of power to cut at those settings, I'd suggest higher power and faster speed. I have a 45 watt and cut 1/4" at speed 8 power 100, 25 lb's air assist, and the edges are never sharp.

[Daniel Muller]

Joe,
My bad. That was ecthing. I cut at 8s/100p/500f.
Dan

[Steve Clarkson]

Try changing to 5,000f

[Daniel Muller]

My fingers aren't working today. 8s/100p/5000f. Is there a way to change the pressure on the air assist. My pump doesn't have it and I didn't read anything about it on my machine.

[Frank Corker]

Daniel did you try cutting at a slightly higher speed. Say 9 or 10? The remelt might be because the delay (speed) is too slow.

[Rodne Gold]

I dont know your machine , so cant tell you about pressure or direction adjustments , but if you cutting 1/4" , the beam divergence (albeit pex acts as a wave guide) might be too great , the way to solve this is focus on the top surface but then raise the table about 1/3rd of the thickness of the material , or use a 2.5" or 4" lens with a greater depth of focus than a stock 2"
Alternatively , you can use more power when cutting to "overpower" the cut and ensure clean piercing.
I dont know what you cutting on , but honeycomb tables arent great for pex , we just use pex blocks and elevate the sheet to be cut above the table and use a sheet of black anodised ally over the table to act as a beam stop.

[Curt Stallings]

I get a smooth edge with my Helix 45w at 6s/100p/5000f. I use the standard air pump with no regulator.

Curt

[Joe Pelonio]

I get a smooth edge with my Helix 45w at 6s/100p/5000f. I use the standard air pump with no regulator.

Curt
Same settings I used until the last tube replacement, which allows me to cut it at speed 8. I think there must be some other problem. Is the bottom edge
sharp when a piece is cut anywhere on the table, or just certain areas? Have you cleaned lenses and mirrors, and inspected them? You should be able to cut 3/8" cleanly with that machine.

[Bill Morrison]

Mr Rodne sir, you wrote something the other day about perspex. I think that's what it was, and when I went to my local supplier she didn't know what that was. Is it known by another name?

Bill

[Daniel Muller]

Joe,
Yes the edge that faces the table is getting sharp. I tried a higher speed and seems to work better but still a little edge to it. The top edge on the acrylic is very smooth.

[Scott Shepherd]

Perspex is the name the rest of the world uses for your basic Clear Acrylic if I recall correctly.

[Peck Sidara]

My fingers aren't working today. 8s/100p/5000f. Is there a way to change the pressure on the air assist. My pump doesn't have it and I didn't read anything about it on my machine.


Daniel-As suggested already, try focusing a little bit into the material, 2-3 clicks (raising the table after true focus has been set). As for adjusting the air-pressure, this would be done at the pump, prior to entering the Helix. Our air-assist pump does not offer adjustability to air-flow. A cheap regulator (1/4" plastic input/output w/ adjustable screw/knob for flow) would do the trick.

Another suggestion would be to run the vector w/out air-assist, just be cautious of the flaming that could occur.

[Daniel Muller]

Peck,
Thank you for your input. I will give that a try. It only seems to get sharp edges on clear acrylic and not on colored. I guess I will keep plugging along. Thank you all for your help. Much appreciated.

[James Aldrich]

I to have the same problem with sharp edges on acrylic. I just sand them off. Its a pain. I have never been able to get smooth edges on acrylic, except for 1/4" extruded, it looked polished when cut. Current settings: 1/8" 25s 100p 5000freq - 3/16" 15s 100p 500freq (works best for me) - 1/4" 10s 100p 5000freq. I can get smoother edges if I slow the speed down, but then I get the tic marks from the vector grid. If I run at a faster speed, I get burrs or a sawtooth type affect on the edge. I will try raising the table to see if that helps.

Jim
Epilog Helix 45W

[Joe Pelonio]

I to have the same problem with sharp edges on acrylic. I just sand them off. Its a pain.

Jim
Epilog Helix 45W
This strikes me as odd, 45 watts should give a nice smooth edge all the way down on 1/4" cast acrylic, mine has for 5 years now over 3 tubes. In fact, I can remember people with 35 watts having success cutting it. There's still something going on that needs to be looked into further, I hope one of you can figure it out.

[Marc Myer]

My trouble is a little different. In cutting 1/8" Rowmark metals, I get a raised front edge (the metallic side). Doing a defocused second pass doesn't seem to help.
Suggestions?

[Peck Sidara]

Assuming we're all talking about the same sharp edges, here are some notes in general which may resolve the problem. Ultimately call tech support to trouble-shoot if all else fails and you've come to the conclusion that the fault's within the machine.


Certain acrylic cuts better than others. I always get the two mixed up. Extruded vs. cast. One cuts better than the other, someone please confirm which is which. If possible, use the best acrylic for the job.
If you're getting what I considered "ridges" which in my view is sharp edges and looks like the side of a coin then it's possible you're not using enough power or frequency or have the speed set too high. Slow it down in 1% decrements and if "tick" marks appear from the vector grid, use something to raise the entire peice of acrylic in the corners and somewhere in the middle.
Taking the beam slightly further "in" focus, closer into the material keeps the laser beam in focus for a longer distance. It'll be a little bit bigger as it enters the acrylic but will stay in focus all the way thru. A longer focal length lens would help as it keeps the laser beam the same diameter for a longer distance by design.
Air-assist helps as it keeps the flaming down. Adjusting the air-pressure may provide better or worse quality.
James-use the 6%S, 100%P & 5K Freq and raise the acrylic off the bed a little. This will give you the flame polished edge you're looking for an will remove an ticks from the laser flashback.

Daniel-Your comment "It only seems to get sharp edges on clear acrylic and not on colored." leads me to beleive that 1) you're using two different types of acrylic 2) the thickness is slightly different. All things being equal, you should get the same results.

Try going at a slower rate of speed, down to 7 then 6 if needed and also try the other suggestions (variable air, re-focus etc.).

I also wanted to mention that not all lasers with the same rating will output the same. Some are hotter than others. If there's a difference in model but same wattage, speed settings will be different. If we're talking about the same model, same firmware and same wattage and there's a huge gap in settings when compared, something else is wrong like faulty/dirty optics, alignment or laser tube.

HTH guys.:)

[Daniel Muller]

You guys are the best. So much help and so little time. I am giving them all a go and will leave feedback on what seems to work.
THANK YOU THANK YOU THANK YOU

[Rodne Gold]

Extruded , which is a short polymer chain acrylic cuts better and is a lot better in terms of tolerances thickness wise than cast - it however does not engrave well and , worst of all , is the worst to use for laser processing as the laser induces a huge amount of stress in the material and WILL lead to stress cracking , especially if you use a solvent on or near it...beware of this as the stress cracks can appear instantly or months ahead.

The best way to remove burrs or sharp edges or striations on acrylic is to scrape it with a hard steel flat edge , a scissor blade works well , or a duburring tool for irregular contours
This serves to actually remove a lot of the heat affected zone.
Edge striations (coin effect) is all to do with air assist and remelt ... this can be minimised by using the correct speed and power and air assist pressure and direction.
You need enough speed , power and freq(ppi) to melt the stuff to get the polished effect , but have to reduce the air assist to the point of where it still ejects swarf thru the cut but does not "supercool" the melt which leads to a slightly frosty edge
Ideally the air assist should be directed in a thin stream just after the beam , not co incident with it. You can probably buy an adjustable nozzle at tool supply houses. You will never get a totally striation free edge. There are other issues with straitions in terms of that the perspex or acrylic expands when heated , a lot in fact and the continued expansion and contraction and the micro movement of the pex on the cutting surface (due to machine motions etc) will also contribute. The beam itself "wanders" cos of slight mirror motion and in fact as the beam path gets longer , smaller movements of the mirrors actually translate to much bigger movements. Think of photography , you cannot use low shutter speeds with telephoto lenses , but can with wide angle or normal , as the motion blur in tele's is vastly magnified.
If you do 2 pass cuts into pex , you will never get good results as the melt is never ejected thru the cut on the first pass.
I repeat , honeycomb cutting tables suck with pex as you almost ALWAYS get the tick marks from flashback.
We cut 3-5mm DIRECTLY on the table and thicker on elevated blocks.
PS note to Laser mnfgrs ...I have NEVER seen a decent mirror mounting fixture or one that is easily adjustable. On most , just removing and replacing the mirrors can give a slightly different beam alignment EVERY time.
Another suggestion is to check your beam alignment. This is pretty easy to do.
Cut a square of 5-6mm pex at all corners and the centre of the table ...use a setting that JUST cuts thru at lets say , top left , if any others dont cut thru , you out of alignement. A further test to this is to stand each square on edge , all 4 of their edges , if the square tilts in any direction...you are out of alignment. Obviously use a vernier to see if the acrylic (pex or perspex) itself isnt varying in thickness when you do this
Alignment is fiddly , however pays huge dividends , think about it , any beam divergence off the perpendicular leads to an oval spot and a far smaller spot power density , any time the beam doesnt hit the final focussing optic dead centre , it leads to power density loss as well. Translates to less then ideal engraving and cutting and up to an effective 25% "loss" of power. So you lose 25% in terms of time re cutting , and you have paid for a machine that delivers 75% of the power you thought you were getting.
It's often WELL worth the hr or 2 it takes to align.
PS note to laser mnfgrs -- is there NO way an "autoalign" feature can be included??

[James Aldrich]

Peck and Rodne

The "ridges" or coin effect is something I get on all acrylic (extruded and cast) when cutting. Except for 1/4" Extruded, this comes out smooth and polish look. I have ran at different combination of speed, power and freq. with same results. I just figured that was natural. To my supprise 3/16" cast cuts better for ma at a freq of 500, 5000 makes the ridges worse. The 1/4" extruded acrylic that gives me a nice clean smooth edge is cheap stuff from a local hardware store. I use it to make templates, it cuts great but does not etch very well. I will try your recomendations and see what happens. I will also try to take some pictures to post of current process.

Thanks for the information.
Jim