Acrylic fabrication questions? I can help!

[karimwassef]

Here's how it works in the application

<a href="http://s1062.photobucket.com/user/karimwassef/media/0_zpstupuba7s.png.html" target="_blank"><img src="http://i1062.photobucket.com/albums/t496/karimwassef/0_zpstupuba7s.png" border="0" alt=" photo 0_zpstupuba7s.png"/></a>

 

[Floyd R Turbo]

I would say run a bead of weldon #40.

 

[karimwassef]

I used the thin stuff last time and got it to wet the gap with the needle. Why did that not work?

 

[Gorgok]

Was the edge polished or something? That looks like it exploded basically when the solvent hit it...

 

[Floyd R Turbo]

liquid-thin solvent is not a gap filler, it dries to a thin profile, so while it appears to "fill" it does not when it dries (evaporates)

 

[karimwassef]

?? Confused.

I thought the parts should be flush and smooth, then put against each other and the liquid is applied with a needle against the seam. It flows in by capillary motion and liquifies both ends and fuses them.

I usually use the thick stuff, but this is 1/4" so I thought it would be easier with the liquid solvent.

 

[Floyd R Turbo]

Maybe I'm confused about what you are asking:

For an initial weld, you are correct, you can wick the solvent into the gap, and as long as the joint is firmed up so that the pieces are touching while it cures, you will have a sealed joint.

What appears to have happened is that you did not have a tight fit on this joint, so air intruded into the joint. What I do is set up the horizontal panel on a surface that is covered with compressible foam so take out the irregularities in the thickness, add the solvent, then add weight to the top of the assembly to make sure air doesn't intrude.

I thought what you were asking was related to adding solvent AFTER this was done - meaning, to the existing piece, after it was found to be leaking. If this is indeed what you are referring to, the issue is that once you have a bonded joint that is leaking, you can't "un bond" the joint just by adding solvent - there is not enough time for the solvent to dissolve the joint, because all you need for a joint to not hold water is one tiny pathway. You can seal off this pathway with repeated treatments of liquid thin solvent, think of it like painting on layers. Each application dissolves and liquifies a bit of material, so repeated applications should eventually seal up the gap well enough. The gel type solvent - weld on 16 - does this a bit better. #40 is a gap filler and one bead on each inside joint will seal it for sure.

 

[karimwassef]

yes. I can fix it with the fix stuff, but I wanted to understand the reason for the failure first.

So - not enough pressure during the drying.

 

[H20ENG]

Did you use the "pins method" when solvent welding? Was the acrylic rough cut or routered smooth on the edges? If there is not enough soak time for the solvent to work, it will be a dry joint.
Floyd's advice is sound. Before gluing a joint, there must be no gaps or the solvent will evaporate out and create a dry joint. Edge prep could be a culprit as well.
Another thought, how fresh is your solvent? The MC will evaporate out of the solution in the can and give bad results. I've learned that the hard way.

 

[karimwassef]

My can was over a year old. I use clamps, but maybe I didn't push hard enough.

 

[H20ENG]

Clamping should be light pressure at best. It will squeeze all the solvent right out of the joint. Then when whatever is left evaporates, you'll a be left with a dry joint. By gluing on a base of foam, you can prop up the piece with a 90 degree jig, then look along the joint. Anywhere there is a gap, you can put a small shim underneath between the foam and base acrylic to close the gap. I use a feeler gauge to get it tight all the way down the hoint. Shims can be as simple as folded paper or razor blades.
Do you practice the pins method? This allows more soak time for the solvent to work on the acrylic before joining the pieces. Just the capillary method with no pins has never worked for me. Unfortunately this is how most literature tells you how to bond. It's the same in application, just with a slight uniform gap to allow the solvent to work longer. When you pull the pins and the joint oozes clear goo, you then know it will be a good bond. Lots of tricks in practice to make bullet proof joints.

 

[karimwassef]

The difficulty is that this seam is 96" long and 1/4" thick lining up to the edge. By the time I get to the end, the start has dried (with solvent only).

 

[H20ENG]

Another way the pins will help you- it gives you more working time. Trying to glue a joint directly at the edge invites air in the joint. Most joints are set back 1/8" then flush routed afterward.

 

[H20ENG]

Btw, love your renderings!

 

[karimwassef]

Thanks. Drawing is easier (and cheaper) than real life. Mistakes are a whole lot easier to undo

So I create everything in 3D first, then make it real.

 

[Floyd R Turbo]

My can was over a year old. I use clamps, but maybe I didn't push hard enough.

If you had ever opened the can, it's possible that enough evaporated out to make it a poor solvent. I got to the bottom of one can after it had been open for a month and it literally did nothing adn wiped clean off the acrylic. There are a lot of fillers in the name-brand solvent welding products

The difficulty is that this seam is 96" long and 1/4" thick lining up to the edge. By the time I get to the end, the start has dried (with solvent only).

If doing it via capillary action, yes. But if you use the pins method, then you can run the whole joint and when you pull the pins, then add weight, you will have a good joint. Especially for one for your type of use.

After reading your comments and H2O's response though I think he's right, clamping the joints tight immediately after doing a capillary joint might have resulted in a dry joint.

I didn't really think of that as a possibility, I guess I should have asked more question. The key to getting each side of the joint to dissolve and then re-form as a single piece is allowing enough time for the solvent to bite into each piece. That's what the pins method is all about - allowing soak time.

Capillary joints bond almost immediately and there's no time for the solvent to act. As H2O mentioned, there are a lot of videos out the showing this and they are all dead wrong.

 

[karimwassef]

I clamped first, then applied the solvent at the seam and watched to make sure the thickness of the joint was fully wetted with solvent.

At this point, I'm going to take the easy road and use the Weldon #16 gel (don't have the 40 handy).

 

[BeanMachine]

I have a piece of 3/4 in 70x21 1/2 for sale if any one whants it text me at 7252447065

This is a different number then what you gave me when I bought the light that I never received.

Ripping people off during the holidays is beyond low.

**Sorry for the derail, just don't want anyone here get taken advantage of by this person.

 

[sinisterreef]

So I was wondering if someone could help me with the pins method. I have seen different information posted elsewhere and I would like some feedback here.

1. What gauge wire should I use?
2. How long before I pull the pins? I'm guessing this will vary depending on temperature/humidity
3. How much working time do I have to straighten the panels after I pull the pins?
4. Is clamping necessary?

I would also love to see people's camper insulation strips and where to place them under the bottom panel. Thank you!

 

[Floyd R Turbo]

1. I use 28 gauge picture hanging wire from Home Depot. You can use garbage bag twist ties, stripped (leave a bit for a "handle")

2. 15-30 seconds. Mainly this depends on the solvent, Weld on #3 evaps faster, #4 longer. I use straight MC with 5% AA and I go 15 seconds minimum. You want enough soak time to "bite" into each side. I've gone longer than 30s but then you have to be sure to add a little weight right away to get the squish out and fillet

3. depends on #2, usually 10 seconds, after that you can "force" if you need to but it's obviously not ideal. It will slide right after you pull the last pin so that's when you gotta watch close, get it in position and hold it there for at least 10 seconds.

4. No, and not advised either. Clamping will push out the solvent and can leave a dry joint. You can and in most cases should add weight, but weight that is evenly distributed. Like for a 30g size build for instance I will set 3 or 4 12 packs of pop on top (on each corner). Or I'll put a couple 2x4s across the top and set a few 10lb weights on the 2x4s