Bowing Acrylic (theoretical)

[SavannahLion]

I have 1/8" thick scraps, none larger than about 10" square, I'm fooling around with. If I were to have a much larger sheet cut to somewhere in the range of 30"x24" or thereabouts, then sandwich two pieces with art in between, at what point would sagging or bowing of the acrylic become an issue?

Every arcade cab I pulled in with a tinted acrylic overlay exhibited sagging. I assume this has far more to do with excess heat (that's what it looks like to me) rather than the acrylic sagging over time. But I don't know the answer to that. Is my suspicion correct?

I posed this question to the pair of staff working at TAP and I don't think I articulated my question well enough.

Two sheets, flat together, vertical. Like this crappy ASCII representation. ||
When does this (| or () become a problem?

[RandyT]

Acrylic is a very rigid and hard material.  It has internal stresses from the manufacturing process.  Even fresh cut sheets will exhibit some bowing and not be perfectly flat.  It shouldn't sag over time unless there is some amount of heat and pressure on the edges.  But temperature has an effect on it.  The material will expand and contract enough so that mounting holes which are too close to the size of the fastener can actually cause the material to bind and crack when the temperature rises.  So whatever means is used to retain the pieces, must allow for this expansion of the material. 

If I were to guess the cause of the bowing, it would be due to a tight fit in a frame, with no consideration for expansion.  When it gets warm, it expands, causing the material to bow out.  If warm enough, often enough, it stays that way.

[Ken Layton]

The plastic does indeed bow. I have seen it bowed from not only heat from the sun shining through the windows onto the cabinet, but also from internal heat of the cabinet. The light fixture, monitor, power supply, and game board all generate heat which heats up the cabinet including the control panel.

[Vigo]

I'm no expert, but I would go 3/16th for something exposed to heat and other elements. Simply based on that I have seen that acrylic sandwich sign holders are that thickness.

Otherwise, I would say you would be fine if temperature is not a real issue. About 7 years ago, I replaced the shelf panels on my refrigerator with a 1/8th acrylic, probably about 10 x 15 panels. They have been holding up just fine often with multiple full gallon milk jugs consistently on them. I would think a panel twice the size would be able to hold up it's own weight without bowing.

[Howard_Casto]

The plastic does indeed bow. I have seen it bowed from not only heat from the sun shining through the windows onto the cabinet, but also from internal heat of the cabinet. The light fixture, monitor, power supply, and game board all generate heat which heats up the cabinet including the control panel.

This^

You've got to understand though that in an arcade environment the machines might be on all day every day, in some places 24/7.  Unless you love huge power bills your cab will probably never be on long enough for it to be a concern.  What Randy said is also correct though.  Just like you keep expansion gaps in traditional construction, you need to do it with cab construction as well.

[RandyT]

An additional frame of reference is that I have a ~23x20 1/8" piece as the front glass for my cabinet.  It's not on 24x7, but it has been there for the last ~10 years.  No sagging or bowing.

[Vigo]

My company just put up some new signage in our office this morning. I gave them a measure, they are 28" x "22" art posters sandwiched between two sheets of 1/8th acrylic. I figure it is pretty close to what you are looking at. It seems plenty fine, but with the art only being sandwiched together at the 4 corners, they do not hold together as tight as I was thinking at the middle.

I don't know how much care was put into hanging these signs, but I would say that bowing can be an immediate problem if you are only gonna secure the acrylic from the corners and want your art to be sandwiched tightly.

[RandyT]

I don't know how much care was put into hanging these signs, but I would say that bowing can be an immediate problem if you are only gonna secure the acrylic from the corners and want your art to be sandwiched tightly.

If you look at how these are hung, you can see that they are at a downward angle.  The face is sagging under it's own weight.  Over time, the plastic will retain this shape.  A couple of small, unobtrusive clips at the centers of the vertical edges would help this quite a bit.

*edit*

Another thing which could be happening, is the prints inside could be drawing moisture if it is a humid environment, and starting to ripple.  This will have the effect of forcing the plastic apart when there is no support at the sides.

[Vigo]

True, and there is freshly unrolled poster is trying to retain it's shape as well, pushing outward.

[Vigo]

*edit*

Another thing which could be happening, is the prints inside could be drawing moisture if it is a humid environment, and starting to ripple.  This will have the effect of forcing the plastic apart when there is no support at the sides.

Just saw your edit. Yeah, it is not moisture, but the fact the art was rolled up until today, like I mentioned above 

[SavannahLion]

Thanks for the answers.

I had this nice long response but I'll save it for the project announcement.

The short response is, I need to take a break.

Working with the scraps made me realize a couple of design mistakes I didn't think about. Fortunately, the changes are easy. Unfortunately, I would have to purchase additional tools to pull it off. A CNC would be perfect but slightly out of my budget. Despite not wanting to learn anything from my dad (another long story) I did pick up some of his jig building skills and, more importantly, discovered that my wife has been holding out. She owns a smallish drill press brand new in the box. Just what I needed!  Now I don't have to rebuild my own larger, and much older than I am, drill press.

But at this point, my incentive has run out. I have the software component to work on. I have the wiring harness and the plastics to assemble. Circuit boards to fabricate and solder together. And it's still not recognizable as anything yet, just parts all over the bench and files in the computer. In the past week, I have had this severe pain in the finger joints of my left hand. For the past week, every morning and on occasion in the afternoons, the pain rears its ugly head. It's like fire. At times, the pain is so severe that just trying to button my kids clothing in the mornings or tie my own shoes is blinding. Medication helps, but is a pathetically short term solution. Warmth seems to help more, but I detest the warmth. I'm a winter kind of guy.

Two days ago, I was soldering SMD components (1206, 0805 and 0603 and small IC packages). I'm right handed, that's where my solder iron always is. I'm not sure what the  ---fudgesicle--- I was thinking. I guess I forgot I switched it on. Or maybe I was too tired as it was only about 10ish and I was up until 1AMish the previous two nights. I reached over with my left hand while looking through the magnifier and, dumb of dumb, grabbed the "stalk" portion with my left hand. I wasn't doing anything with the right....

I don't need to explain what happened next. The burn across my index prevents me from bending it properly and thankfully the callouses on my thumb afforded some protection. Joint pain and burns make it tough to manipulate SMD parts.

This is just the latest in a string of injuries and mishaps over the past two or three weeks. Even my wife commented on the unusual situation. Enough is enough. I need a break.

[RandyT]

Two days ago, I was soldering SMD components (1206, 0805 and 0603 and small IC packages). I'm right handed, that's where my solder iron always is. I'm not sure what the  ---fudgesicle--- I was thinking. I guess I forgot I switched it on. Or maybe I was too tired as it was only about 10ish and I was up until 1AMish the previous two nights. I reached over with my left hand while looking through the magnifier and, dumb of dumb, grabbed the "stalk" portion with my left hand. I wasn't doing anything with the right....

Ouch....Have done something like this a couple of times myself.  I use the type which has the tip, shaft and heating element as a 1pc "plug-in" .  When you want to change to a different tip, you pull the whole thing out and replace it with a different one.  I'll bet you can guess what happens when you forget it's on and try to change the tip.  I learned the hard way to use pliers, hot or cold.  Serious burns get infected really easily, so keep it clean and dry.

Sorry to hear about your issues and hope it feels better soon.   

[Howard_Casto]

I feel for ya man.  I've been dealing with my own medical issues.... nothing life threatening, but as you are explaining it makes day to day stuff hard sometimes.  Family issues as well, but I don't like to get into that stuff on a public forum. 

I'm not sure why I'm responding, I'm not the touchy feely type, but I guess I'm just read this at an odd time. 

You all know that Saint's been having a hard time and that bothers me.  I've never met the man and yet I still consider him a friend.  I get the feeling he thinks that we don't care about his problems and that's not really the case.  I want him to rely on us more, even if all we can offer is emotional support.  I don't know how many of you remember Planetjay, but he's been having a hard time as well.  He all but left the forums for years, and yet we still talk regularly.  So I worry about him as well. 

And then I've got my own stuff to deal with. 

I think it's starting to bother me because as it's probably no surprise to anyone, these forums and this community has always been a thankful distraction for me.  Lots of faceless names on a screen that I can have fun with and occasionally vent on without the consequences of the real world.  The funny thing is, as the years have rolled on my affection for you guys has grown to the point to where you are all important to me.  It's a funny time we live in.  I never thought I would get attached to words on a screen. 

Now that we've all gotten older together it seems like things such as age, and fatigue and what-not are creeping into the hobby and the community in general.  That depresses me a bit sometimes and I guess that's what all this hot mess I wrote is about. 

So sorry, I'll be back to my old self in the morning hopefully and sorry for derailing into a strange tangent. 

What I meant to say was just take care of yourself and don't worry about the projects so much... they are just an excuse to stick around anyway and we don't want you going anywhere regardless.