Large Scale Central

Basic Acyclic Box

Modeling
#1

I got a chance to inspect Bob’s prototype EBT boxcar at ECLSTS. I was very impressed with how strong the box was. Acrylic seems to be as strong as plywood with less weight and simpler fastening. It’s no surprise that acrylic is fast becoming a favorite base material for cars and buildings.

Eventually I will get started building my EBT cars. I am a bit concerned about my complete lack of experience in working with acrylic. I’d like to get some practice with something smaller and simpler - perhaps a crossing shanty or other small structure.

Would someone who has some acrylic building experience answer the following please ?

  1. What is the source and thickness of the material used for the EBT box car ?

  2. What is the best in-shop method for cutting? I have access to laser for large projects, but can the material be scribed and broken like styrene - or must it be sawed?

  3. Is there a “best practices” procedure for gluing? I’ve heard that the adhesive sets up very fast.

Perhaps a short course in building a cube would be in order.

Thanks :slight_smile:

JR

#2
Jon Radder said:
I got a chance to inspect Bob's prototype EBT boxcar at ECLSTS. I was very impressed with how strong the box was. Acrylic seems to be as strong as plywood with less weight and simpler fastening. It's no surprise that acrylic is fast becoming a favorite base material for cars and buildings.

Eventually I will get started building my EBT cars. I am a bit concerned about my complete lack of experience in working with acrylic. I’d like to get some practice with something smaller and simpler - perhaps a crossing shanty or other small structure.

Would someone who has some acrylic building experience answer the following please ?

  1. What is the source and thickness of the material used for the EBT box car ?

  2. What is the best in-shop method for cutting? I have access to laser for large projects, but can the material be scribed and broken like styrene - or must it be sawed?

  3. Is there a “best practices” procedure for gluing? I’ve heard that the adhesive sets up very fast.

Perhaps a short course in building a cube would be in order.

Thanks :slight_smile:

JR


Hi,

  1. I believe that Bob’s EBT boxcar project is being built with 1/8" “nominal” acrylic sheet. As with the plywood industry, acrylic sheet is invariably thinner than its label - 1/8" sheet is actually around 0.118" or even thinner. Therefore, the actual material you will be using should be measured before attempting to cut/glue any critical parts to avoid mis-alignment! Also realize that different manufacturers may produce differing thicknesses for the same nominal sheet thickness, so don’t mix different labels of sheet on the same project unless the assembly is not critical.

  2. A laser is without question the best way to cut the stuff, though it smells awful. I’ve never had good luck scoring and snapping - it usually shatters; there may be some trick to it of which I am unaware, however. Cutting on a table saw will work, though you need to use a highly specialized blade for it to work well. While such blades are readily available in the larger sizes such as 7" and 10" diameters, they are not cheap and I don’t know if such blades are available in the 4-4.5" diameter blades for the tabletop model saws like the Proxon or Dremel. Additionally, when using a table saw, or even a bandsaw, you have to keep the sheet moving or it will start to melt from the friction! Before cutting a bunch of parts in this way, practice with some scrap on the saw/blade combo you will be using to get the correct feed rate to minimize both chipping and melting - it will take a while, so be patient.

  3. There are several “glues” (actually solvents) available to fusing/welding acrylic parts together. Most are very nasty and should be used outdoors or in a spray booth vented to the outside. While I have not used every single type, most do allow you some time to tweak the fit/position of the parts you’re gluing - much like working with PVC drain pipe. The best practice is to position the parts exactly how you want them, clamp in place, then run a bead of solvent down the joint with a syringe; wait several minutes to hours (depending on the particular solvent) before removing the clamp(s) and moving on to the next joint. For doing large numbers of identical joints/projects (say you wanted to build 30 copies of a boxcar), it usually is a very worthwhile investment of your time to make jigs to hold everything into precise position/alignment.

Brian

#3

Yes, acrylic sheets can readily be scored and broken. There’s a special cutter for scoring, looks like a small hooked carpet knife.

The smoother the edge, the better the solvent will work.

In order to get a smooth, square edge I run the pieces through the router, barely skimming the edge.

#4

I’ve made aquariums from acrylic and score it at least 10 times to snap it. I use weldon no.4 for glue. when making a box place pins between the walls and bottom and apply weldon. Wait 45 sec. and remove the pins and poaition. This make a gap for the solvent to really work on the edges and makes for the strongest waterproof joint. I don’t expect you need that strong of a joint for a car. This site if aquarium based but has great working Ideas. http://www.melevsreef.com/tools.html

#5

Thank everyone -

The link that Mark posted has lots of good information. I’ll spend some time there when I can.

I think for my “practice box” I’ll try to get away with score & snap, then clean up with a router. Like I said, I have access to laser cutting, but its a long ride and it won’t be free.

JR

#6

I finally got 'round to putting the basic “box” together. It went very smoothly and quickly (all of 20 minutes!). I used Plastruct’s solvent cement (the stuff with the orange label) and it seemed to work quite nicely. I have no earthly clue when I’ll get back to working on it, I just got the quick itch to put the box together. Next, cutting the door openings (should have done that prior to construction), building a pseudo-interior (wood floors and paneling half-way up the sides) and the roof joists. With any luck, it’ll be done by the time my Accucraft Mikado gets here. :wink:

Later,

K

#7

Kevin,
I’m not sure how easy it will be to cut now that it’s assembled.

Maybe you should get a second one and cut the doors first? (Bob, do I get my commission now? :wink: )

Anyway, I look forward to your model - it sounds interesting. Actually, it will be neat if we can get pictures of finished models from all.

#8

I’m thinking miniature table saw. I’ve cut styrene on it in the past without much trouble. Probably I’ll clamp the car to the deck and raise the blade into the side to make the cut. This way I can cut just the opening and maintain the rigidity of the side as best as possible. I may have to finish the corners with a razor saw, but that’s not a big deal, either. (And if it totally goes to pieces, then I’ll just build new sides from styrene or whatever I have lying around.

Later,

K

#9

I cut all of my acrylic on a 10" table saw. Use a sharp 60 to 80 tooth carbide blade on a saw with a good, accurate fence. I raise the blade slightly higher than I would normally for wood of the same thickness. The only critical thing is to hold the material firmly down on the table. If it is allowed to raise it will chip out at the cut. I cut 1/8", 3/16" and 1/4" (nominal sizes) regularly.

I also have cut foamed PVC the same way. TAP Plastics also has a blade especially for this purpose I believe. I haven’t used it myself but you could ask Russ Miller at TAP, San Leandro, Ca. store about it.

#10

Richard -

Thanks for the table saw advice. I have one but just couldn’t see buying the $80 blade recommended on that aquarium website. I think I could rig a finger board or two to keep the acrylic down tight to the table.

I think I’ll see if Homely Depot has suitable acrylic in-stock for a test project this weekend - it’s going to be rainy and cold here.

JR

#11

I get my acrylic at Home Depote, I also found a blade at an Ace Hardware for $20. The teeth can’t be off set, just straight behind each other. I’ll get the name here in a bit.

#12
Marc Bergmueller said:
I get my acrylic at Home Depote, I also found a blade at an Ace Hardware for $20. The teeth can't be off set, just straight behind each other. I'll get the name here in a bit.
Probably a veneer blade. Lots of small teeth, not terribly expensive. I have one, but it's been burned in the circular saw - will look for another.

Thanks Mark -

JR

#13

I have built several building out of acrylic. I use 1/4" think which really is closer to 3/16" It is very rigid and strong. I use my 10" table saw with a Freud Diablo 7 1/4" 40 tooth thinkerf blade. I belive you can get the blade for $14 or $15 at HD. It is important to have a zero clearance insert to reduce chipping. You need to hold the acrylic down as mentioned previously. I use GOOP to adhere the parts. They make a marine type but I use the standard houehold stuff which says its waterproof. I make the side cut on door openings on the table saw and then use the band saw for the top cut. Windows are just glued to the acrylic. Once I have the basic structure it forms a great base to start from. David Cozzens

#14

Thanks Dave -

Good advice on the Zero Clearance throat plate. I have one, but probably wouldn’t have thought to use it. I’ll check HD for that blade. My veneer blade is only 7" pretty badly burned - probably best off with a new blade.

I picked up a small sheet of 1/4" “Hobby” grade acrylic from Home Depot. As far as I can tell, the difference in grades is clarity - so if you are going to paint, the cloudy hobby grade is just fine. The crystal clear Polycarbonate is very expensive by comparison. Anyone know if there is there also a strength difference?

For adhesives, I think I’ll go with the acrylic cement (welder) rather than Goop. I might try multi-purpose PVC/ABS stuff just 'cause I have some. I think it is MEK based and it’s much thicker than the special TAP Plastics acrylic cement.

Jon

#15

I prefer using the acrylic cements over something like Goop or epoxy. They just stick the pieces together, however sturidly, whereas the acrylic cements dissove the acrylics and weld them together… it is, allegedly, much stronger. Your mileage may vary.

#16

I’m going to start out small. Found this and thought it an appropriate beginner project…

I estimate based on a door height of 6’6" that this structure is 5’ wide X 6-7’ deep with 7’ walls. The peak is about 11’ or whatever it works out to with a 1-in-1 pitch roof. Add another 2’6" for the stack. Now the question I’m asking myself is do I build in in 1:24 to make the math super simple, or try and get close to 1:20 without having a scale rule in stock. Wait Kevin don’t say it - I know - use 1 Foot = 15mm :slight_smile: JR

#17

Jon Radder said:
I’m going to start out small. Found this and thought it an appropriate beginner project…

I estimate based on a door height of 6’6" that this structure is 5’ wide X 6-7’ deep with 7’ walls. The peak is about 11’ or whatever it works out to with a 1-in-1 pitch roof. Add another 2’6" for the stack. Now the question I’m asking myself is do I build in in 1:24 to make the math super simple, or try and get close to 1:20 without having a scale rule in stock. Wait Kevin don’t say it - I know - use 1 Foot = 15mm :slight_smile: JR

Is that what it is! Cool!

#18
Steve Featherkile said:
[b]Is that what it is! Cool![/b]
Not exactly, but close enough for Gummint work. [I think]

If 45MM track = 3 Feet 15MM = 1 Foot.

Problem is, how do you divide 15 by 4 to get accuracy to 3 or 6" ? I suppose you can use thirds and just go with accuracy to 4" (5MM = 4 In.)

JR

#19

I just resurrected this project last night. Spring got in the way in April and it got shelved. Now I’m looking for stuff to do inside. I did my best to transpose the photo to a scale drawing last night. According to the night crew on Chat, I still need to work some things out. The door and the whole front is probably wider. I drew the door at 24" x 6’ and the front 6’ wide. The roof pitch is also too steep. You can see where I erased a 1 in 1 pitch and drew it as 4 in 3. I’m going back to 1 in 1 (45 degrees). BTW, this mini graph paper works out to be quite close to 2 inches per square in 1:20.3. At least close enough for a structure, perhaps not for a car.

Jon

#20

Nice… the peak looks a little steep on the drawing, but the rest of the proportions look good…