[fokusco]

Ok ladies and gentleman I seem to have run across a huge problem. We have taken on a very large job of cutting 1/4" acrylic... We are making 4" numbers and letters. When we quoted the job and cut a test piece everything went smoothly and the #s and letters came out fantastic! Then we got the job.....


I am having trouble getting the edges from chipping and having a frosting on some of them... Frosting is not that big of a deal but I would like some tips on how to rid of the chiped and exploded edges!

Any tips would be helpful ex: garnet texture and brand, cutting speeds, nozzle height off of material ect,. ANYTHING that will help me get this done!

Thanks all!

[LaserImage]

I wouldn't even consider waterjet cutting acrylic. A laser is a much better choice and will give you almost flame polished edges.

Do you have a laser? Or access to one?

Gary

[fokusco]

hmmm... not the answer I was looking to see.. lol

I do not have a laser but I do have access to one... Don't really feel like sub-contracting an already subbed job! lol

anyone else?!

[DSL PWR]

Are you using cast or extruded acrylic? I don't know what the diff would be on a waterjet, but try which ever one you aren't using.

[jstiltner]

Is it possible that the test piece you cut was actually polycarbonate? AKA lexan? As this would cut much better than acrylic. Sadly I dont have any tips other than thinking that may have been the cause for the difference here. Good luck.

[ImanCarrot]

I know that when I turn or mill cast acrylic it's fine, but extruded is a nightmare. Worth trying as previously mentioned.

[Signmaker]

What grade of Garnet are you using? What size nozzle are you using? What size lead in are you using? How are you setting up your sheets?

Cast and extruded acrylics can both be jetted with ease so it doesn't really matter what type of acrylic you use.

[307startup]

What is your pierce height? What is your cut height? What are your feeds & speeds being used?

[One of Many]

Sometimes it helps to double back tape brittle materials onto a backer board for support like 3/32 HDF.

Chipping may be an indicator that the nozzle is advancing too fast on top of the uncut lower depths.

Have you played with the feed rate to prove any theories?

DC

[mtmcnc]

try to pierce in low pression about 7000 psi and cutting at 30000 psi . hope it work

[Fildain]

So I have been working on our Omax waterjet, and have been working on cutting different thicknesses of acrylic. Not to sure what your machine is but, here is a couple things i learned.

First, put the acrylic on some type of spoilboard, I end up using some scrap luan or something, because where the waterjet splashes back when it hits the slats can cause chipping and damage to the bottom of the piece.

Also i have found that the best way to cut is to pre-drill the pierce points and then line up the jet. This way you dont have the piercing chipping, also i have found that sometimes stress fractures can develop where the waterjet pauses for a second to switch from low to high pressure. To drill the holes I usually print out a to scale pattern that I tape to the top of the work and so i have the pierce points and i can mark a starting location to line up. Oh ya also if you start off the edge of the piece and cut a contour into it, you get rid of the piercing problems.

Again i am not too sure what machine you have, but I know if you are going to be doing alot of this and have an Omax, they have a couple accessories to make this easier. Such as a pull-to-open valve, which opens more controlled then just on/off, so it pierces brittle material better. They also sell a drill head that can attach to the machine, so it drills a pierce point and then starts to cut.

I know we use 80 grit Barton garnet, I am not too sure about the feed speeds because the Omax software works it out on the quality setting.

But I have gotten some good results doing this.

[Fildain]

So I just pulled up the software to find the feed speeds of .25" cast acrylic.

This is at high pressure (46 ksi)

So it seems that Quality 5 on the Omax, which is the highest is about 20 in/min.
Quality 3, medium, is about 35in/min.

But all this will change with your pressure, and how much garnet per min is released. But hopefully this will give you a ballpark

[Maxxheadroom]

So I just pulled up the software to find the feed speeds of .25" cast acrylic.

This is at high pressure (46 ksi)

So it seems that Quality 5 on the Omax, which is the highest is about 20 in/min.
Quality 3, medium, is about 35in/min.

But all this will change with your pressure, and how much garnet per min is released. But hopefully this will give you a ballpark

Thanks for the info, I just started running a Wardjet about 2 months ago, I did some polycarbonate a couple weeks ago with great results, then tried some .5" acrylic today with no so great results. I did all low pressure pierces at 18,000 PSI then cut at high pressure (55,000 PSI) I believe the machine called for 60 IPM for a medium cut which I suspect is WAY to fast. The results weren't horrible BUT I did have some pretty bad cracking and a few edges are blown out. I am going to drop my cutting pressure and run 20 IPM