Glueing acrylic that has polished edges?

[Larry Bratton]

I have read and watched a video from Tap Plastics, that says after an acrylic edge is either flame polished or buff polished it should not be glued with acrylic cement as it will craze. Are you guys that are flame polishing adhering to this practice? What about using the buffing method, same thing? I am trying to make sense of this, if you flame polish an edge and then need to glue it to another piece, what do you do?

[Dan Ashlin]

I've heard of crazing if it comes in contact with alcohol, but not with cement. I've solvent welded flame polished acrylic plenty of times. in fact, it hold up better if it is buffed or polished first.

[Mike Null]

Larry

My supplier advised me to scuff the edge to be glued with fine sandpaper first. I hadn't heard about the flame polished thing.

[Larry Bratton]

Actually I was surprised at this. The comment is made after the demo on flame polishing and buffing. This is in Quicktime format http://www.tapplastics.com/info/video_detail.php?vid=34&format=quicktime& . The problem with crazing is that sometimes it will not occur immediately, it happens after the customer has it and you might not even know about it.

[Dee Gallo]

I'm not an expert at this, but when I made quite a few shallow boxes to hold puzzles, some of them fell apart after a while, and I was using Weldon. For the replacements, I rastered the areas to be glued for some tooth and they stuck together very strongly. So my experience tells me the shinier and smoother edges don't work as well with Weldon, but maybe superglue is a different story.

2 cents worth, dee

[Larry Bratton]

I'm not an expert at this, but when I made quite a few shallow boxes to hold puzzles, some of them fell apart after a while, and I was using Weldon. For the replacements, I rastered the areas to be glued for some tooth and they stuck together very strongly. So my experience tells me the shinier and smoother edges don't work as well with Weldon, but maybe superglue is a different story.

2 cents worth, dee

Dee:
Yes, I have had some issues with Weldon #3 not holding. The surfaces have to be perfectly aligned, absolutely flat or the stuff won't work at all. It is difficult to work with also. If you happen to drop any in the wrong place, you just ruined your work unless you want to work really had to polish it out.
I am working on an acrylic project that has exposed edges. I am trying to figure out, if I polish these before gluing them, are they going to craze as the video said. I have not had much polishing to do, as most of the time, my laser cut edge is acceptable. In this case, it may not be.

[Dee Gallo]

Larry, I was using Weldon #16 - supposedly for acrylic sheet or so it says on the tube... not very impressive, but that's what others recommended so I tried it.

On a related subject, I got some of that TV stuff, "U-Glu" which strangely enough works really well. I wanted to see if I could make a bond between clear pieces that would hold but not show. It is hard to cut into an exact shape, but it does hold without showing if you get it right. It's just like a piece of double faced tape without the tape or a giant stickydot.

Have you used superglue? I've used it on many other plastics such as bakelite, catalin, pyralin and ivorite, but they have been all opaque pieces and not pure plastic. I should do some experiments with cast acrylic...

Thanks for the info on Weldon #3, I won't be trying it! hahaha

cheers, dee

[Mike Null]

Actually Weldon 3 or 4 works very well. I use both and nothing else. I can imagine crazing on extruded acrylic but I've never experienced it with cast acrylic.

Do not press the joint. Doing so starves the joint and you'll get a weak joint.

Here's an example.

[Rodne Gold]

The propensity to craze depends on the glues you use and the type of acrylic , cast is more resistant to crazing than extruded , glues with agressive solvents like acetone and the like are worse than some others. The ideal glue to use is one of the Tensol ranges , don't use a capilliary type glue if you are gluing a T type join , you need a "filler" type glue , not one that "melts" one surface to another, If you use a filler (contains "disolved" acrylic or is a 2 part glue) , you dont even need the polished edges at the join as it fills in saw marks etc. You can try make your own "filler" glue , albeit its not ideal , but disolving a piece of the same acrylic in chloroform till it "thickens" up - you will need to experiment a bit to see what works for you.
Flame polishing is an incredible stressful process for acrylics (as is laser cutting)
You can de stress the material in an oven at about 70-80c for one hour for every mm thickness and you wont get stress cracking at all.

[Dee Gallo]

Actually Weldon 3 or 4 works very well. I use both and nothing else. I can imagine crazing on extruded acrylic but I've never experienced it with cast acrylic.

Do not press the joint. Doing so starves the joint and you'll get a weak joint.

Here's an example.

AHA! My failure was no doubt from pressing (actually clamping) the pieces together. Thanks, Mike!

[David Fairfield]

Yeah gluing up laser cut panels into display boxes is also a problem due to the fine taper of the cutting beam. I've had good luck flooding the joints with Weldon 3, but its not optimal. Better is to run the panels through an edger for a perfect 90 degree to 90 degree contact.

But this Tensol filler type glue that Rodne mentions is pretty interesting. Anyone have a Domestic USA brand name and supplier?

Dave

[Dan Ashlin]

From my understanding, Tensol is pretty much weld-on here in the states. weldon 16 is a little thicker, but its kind of a mess to handle. gel superglue is great.

[Larry Bratton]

Dee,
Weldon #16 in the red tube is a thicker version of #3. IMO it is more difficult to work with than #3. It is gooey and sets up very fast making it messy. Weldon #3 is water thin. It works via capillary action, when applied to two pieces of acrylic, it flows between the parts and actually "welds" the parts together by dissolving the acrylic and as it evaporates it hardens and creates the bond. I apply it using a very small artist brush or a syringe. One has to be very careful not to let any drip on to the wrong place. It actually requires very little to get a bond, but the parts have to be dead flush to each other. Rodney says don't use for a T joint and he is right. Best way to do a T if possible, is to cut a slot, drop in the piece, then cement it with #3. That works fine.
I have not tried super glue. It is very expensive. A pint can of Weldon #3 will last a long long time,haven't bought any lately but seems like it is about $16.

[Scott Shepherd]

A pint can of Weldon #3 will last a long long time,haven't bought any lately but seems like it is about $16.

I can't get mine to last at all. I keep leaving the lid loose, coming back to find the can bone dry from evaporation :) You'd think I'd learn after the 3rd can :)

[Richard Rumancik]

Over the years I have read a lot of different comments about the potential for crazing of edges. You will get different views and comments because as Rodne indicates it is very material and adhesive dependent. There are many acrylic suppliers and two main types of acrylic, but then there are "alloys" etc etc. So what works and does not work is very dependent on the materials you are using. If you are not careful what supplier you are using (eg buy generic un-branded acrylic) then there is more chance that you will stumble across something that does not work (even if it worked "last time".)

What really worried me about acrylic is the possibility of crazing occuring some time after fabrication (weeks/months). The last thing I want to do is be held liable for product that I shipped and was paid for.

As Rodne suggested, you can stress relieve in an oven but it adds new problems. You need to set up a very well-controlled oven (perhaps an old range could be modified but the temperature control and air circulation would have to be greatly improved). Then you have to suspend/hold your parts so they do not get any marks on them. If they touch a wire rack or even a flat sheet there can be a contact mark. Then you have the problem of shrinkage. The part dimensions can change upon the anneal cycle. Finally, any bends that are done previously (and they should be done before annealing) will try to relax, so if you had a perfect 90 degree bend it may come out at 85 degrees.

If I sound less than enthusiastic it is because there are a lot of traps with fabricating acrylic. Juts know what you are getting into and cover all the bases.

The least risky way of treating a lasered edge is probably to sand off some amount of material and mechanically polishing it to the degree necessary to get a aesthetically pleasing joint. But this is not practicable in all cases.

[Mike Null]

It does evaporate rapidly and is a carcinogenic if I'm not mistaken. In any event, don't breathe the fumes.

I use a syringe for application and if you spill a drop you can clean it quickly with dna on a rag or polish it with Novus.

[Dee Gallo]

Dee,
Weldon #16 in the red tube is a thicker version of #3. IMO it is more difficult to work with than #3. It is gooey and sets up very fast making it messy. Weldon #3 is water thin. It works via capillary action, when applied to two pieces of acrylic, it flows between the parts and actually "welds" the parts together by dissolving the acrylic and as it evaporates it hardens and creates the bond. I apply it using a very small artist brush or a syringe. One has to be very careful not to let any drip on to the wrong place. It actually requires very little to get a bond, but the parts have to be dead flush to each other. Rodney says don't use for a T joint and he is right. Best way to do a T if possible, is to cut a slot, drop in the piece, then cement it with #3. That works fine.
I have not tried super glue. It is very expensive. A pint can of Weldon #3 will last a long long time,haven't bought any lately but seems like it is about $16.

Thanks for that explanation, Larry. It explains a lot of my problems and what I can do to make things go smoother in the future. I was under the impression that #16 would help with any tiny imperfect fit issues, but apparently I didn't know that pressing them would negate that. I love it when I learn something new!

So when making a shallow tray shape, what do you guys recommend? I can't make a slot and still have the sides flush. I've been making the bottom sit inside the sides so there is less pressure on the sides and the joint doesn't show as much, but then the bottom takes all the weight. Perhaps I should try some kind of lap joint?

thanks, dee

[Rodne Gold]

Annealing is really only an option if you HAVE to do it , like for military or construction type acrylics - worst of all if you do anneal after machining is that the material "relaxes" and dimensions can be out - so it might have to be re-machined and then annealed again , eventually you might end up with a 20" x 20" item becoming a grain of sand :)
Crazing many months after manufacturing is normally caused by the user of the item , lets say you have bent a tent shape for a desk name plate etc which requires NO glueing , the bend is really stressed and retains that stress , maybe someone cleans it with something that has a solvent or some other chemical the streesed pex doesnt like , or even perhaps cleans something NEAR it with a solvent , the solvent fumes etc can make it crack at the bend. The problem is that cast acrylic , which is the most stress crack resistant , is more expensive than extruded , which in itself isnt a huge problem , BUT the issue with cast is that a sheet can vary up to + and - 10-20% thickness due to the way it's made (is worse with big sheets cos the glass pieces its cast between tend to either bow or bulge in the centre) so in terms of precise fabrication , the extruded is much better to work with as its pretty much the same flatness - and of course cheaper - and of course more prone to stress cracking.. it's a kinda lose - lose situation.
The thick tensol we work with for uberstrong bonds takes a long time to set - you need to make holding jigs and leave items there for an hour or 2 before handling it - it's irritating. We use methylene chloride for capilliary type bonds. I Also use superglue for "unseen" bonds (hidden so you dont have issues with superglue "whitening" etc - PS the secret of using superglue is that it reacts with moisture - so when doing a superglue bond , you get a much quicker set and stronger bond if you breathe on the 2 pieces before sticking em together)

[Larry Bratton]

"you get a much quicker set and stronger bond if you breathe on the 2 pieces before sticking em together"
What happens if I have ALCOHOL on my breath?????:D

[Robert Walters]

It does evaporate rapidly and is a carcinogenic if I'm not mistaken.

Mike, you are correct.
IPS Weld-on #3 is a carcinogenic (cancer causing).

It contains METHYLENE CHLORIDE (aka Dichloromethane)
CAS: 75-09-2
MSDS: http://www.jtbaker.com/msds/englishhtml/m4420.htm

I've used MEK in the past, it's available at the hardware store by the pint/gallon, and is not a carcinogenic.
METHYL ETHYL KETONE (aka MEK, Butanone)
CAS: 78-93-3
MSDS: http://www.jtbaker.com/msds/englishhtml/m4628.htm



If you over-apply the solvent, don't touch/rub it. Just let it evaporate is usually what I do.


FWIW...
In the US, almost all chemicals *MUST* have a MSDS (Material Safety Data Sheet) available.
The MSDS will usually list the primary active ingredients and have the CAS numbers listed.

The CAS number is a registry of compounds, so even if it goes by different names, you can easily look up the CAS number and get any details.

[Larry Bratton]

Will MEK work as well as the Weldon?