Extruded Polystyrene Blocks

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These people have a great selection of foam products. One especially for tooling, (CNC and such) The 4500 series sounds like a great option and they will work with you on custom sizing. So I started to request a quote. That page tells you there's a $500 minimum for aerospace and certified foams and a $350 minimum for non-certified foams. That's going out of my affordability range. I have to consider the lack of storage space for bulky items also.

I also have fought the battle with glued-up foam boards. I usually have a hard core (1" dowel) running through the layers. I try to keep the glue on the dowel and the inner couple inches of the foam, avoiding the outside. This tends to leave small gaps on the outside, but they're easier to fill or cover with glass afterwards than to get the hard glue layer sanded evenly.

This is something I haven't tried yet. I thought about it though. I'm sure you had the same issue with glue layers not sanding down smoothly which led me to consider avoiding glue on the outer edges. The whole layering concept would be very nice to avoid altogether. My last effort was not as uniform as it should have been and I admit, I'm pretty new at this.

[/QUOTE]Another (untried!) approach which will probably be cheaper than trying to buy "big" blocks of foam is to make your own. Get a 6" concrete forming tube from Menards, line it with parchment paper, and fill ti with 2-part urethane foam. Then, peel and toss the cardboard. You could even cut centering rings and mount the central wooden dowel before you pour the foam. I think I'll try it on my next nose cone.[/QUOTE]

Why would you need a central dowel on a solid pour? I could see having a solid ply end cap of sorts on the shoulder end to attach to my lathe, and maybe a CR on the other end to make a nice round cylinder shape. This already sounds doable. Now if only I knew what kind of 2 part urethane foam to use. I'm sure there a variety of that to choose from. Particularly for density. Right?
 
Why would you need a central dowel on a solid pour? I could see having a solid ply end cap of sorts on the shoulder end to attach to my lathe, and maybe a CR on the other end to make a nice round cylinder shape. This already sounds doable. Now if only I knew what kind of 2 part urethane foam to use. I'm sure there a variety of that to choose from. Particularly for density. Right?

I use the dowel to mount the foam on the lathe. It's also nice to have a solid tip and something solid for shockcord mounts. I'm usually building larger rockets (12"+).

The lightest foam I've found is 2lb/cf. e.g. Giant Leap's Mega Foam or US Composites: https://www.uscomposites.com/foam.html
 
I use the dowel to mount the foam on the lathe. It's also nice to have a solid tip and something solid for shockcord mounts. I'm usually building larger rockets (12"+).

The lightest foam I've found is 2lb/cf. e.g. Giant Leap's Mega Foam or US Composites: https://www.uscomposites.com/foam.html

OK, I get it on the dowel. That's fine. Now if you can, tell me what kind of mileage I can get from a 4# kit of this foam. Lets say I'm going to fill a 6" wide tube that is aprox 18" in length. Please know that I am totally unfamiliar with the end results on two part foams. A ball park figure on how many finished forms I can make from the 4# kit is what I'm looking for.
 
OK, I get it on the dowel. That's fine. Now if you can, tell me what kind of mileage I can get from a 4# kit of this foam. Lets say I'm going to fill a 6" wide tube that is aprox 18" in length. Please know that I am totally unfamiliar with the end results on two part foams. A ball park figure on how many finished forms I can make from the 4# kit is what I'm looking for.

The manufacturers usually claim a 25x expansion factor --- with perfect mixing and temperature. I usually get less. Maybe 20x. The US Composite site says their quart mix (x2 cans) yields 2 ft^3 = 59.8 quarts, according to google. Your 6x18" example is 508.9 in^3 or 8.8 qts.
 
The manufacturers usually claim a 25x expansion factor --- with perfect mixing and temperature. I usually get less. Maybe 20x. The US Composite site says their quart mix (x2 cans) yields 2 ft^3 = 59.8 quarts, according to google. Your 6x18" example is 508.9 in^3 or 8.8 qts.

Uh......Over my head on that. I get the 20x part though....I think. I suppose, if I can get at least 6-8 finished forms from a kit, it would be pretty cost effective compared to buying manufactured cones from someone else.
 
Look at it this way, a 4# kit of 2#/cubic foot will expand to fill 2 cubic feet if everything goes perfectly. Hint: it won’t.
Now just calculate how long of a cylinder that would be given the diameter you need (if you’re planning to turn it down from a right circular cylinder.)


Steve Shannon
 
Look at it this way, a 4# kit of 2#/cubic foot will expand to fill 2 cubic feet if everything goes perfectly. Hint: it won’t.
Now just calculate how long of a cylinder that would be given the diameter you need (if you’re planning to turn it down from a right circular cylinder.)


Steve Shannon

Well that's just it Steve, I'm not that savvy in this department. That's why I was searching for a ballpark figure on how many finished forms I could get from one of these kits. I already like what I read about the 8lb density kit which is probably what I'd go for.
 
Well that's just it Steve, I'm not that savvy in this department. That's why I was searching for a ballpark figure on how many finished forms I could get from one of these kits. I already like what I read about the 8lb density kit which is probably what I'd go for.

I’d be happy to help you with the calculations.
Here’s something to keep in mind. Two pounds of the mixture from the 2 lb. density kit will fill a block one foot square (12x12x12 inches) on all sides and when done will still weigh two lbs.
Two lbs. of mixture from the 8lb. density kit will only fill a quarter of that same volume, so it would fill 12x12x3 inches.
 
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I’d be happy to help you with the calculations.
Here’s something to keep in mind. Two pounds of the mixture from the 2 lb. density kit will fill a block one foot square (12x12x12 inches) on all sides and when done will still weigh two lbs.
Two lbs. of mixture from the 8lb. density kit will only fill a quarter of that same volume, so it would fill 12x12x3 inches.

So basically, I could get about 3 round forms in the 6x18" concrete tubes if I use the 2# density foam, right? And the heavier density foam requires more product because it doesn't expand as much, right? Hmmmmm, This doesn't sound as cost effective as I had hoped. I'm prolly better off honing my skills on thick as I can get wall boards. I did find some XPS 4" thick in my search earlier. Thanks for your help Steve. I've never used two part foam before so I needed some edumuhkashun.
 
2cf = 2 x 12 x 12 x 12 cu in = 3456 cu in.

A 6" cylinder has volume pi * r^2 * h = 28.3 * h.

So, 3456 = 28.3 * h means that h = 122.1.

In a perfect world you would get 6.7 of your 6x18" cylinders from a single batch of 2# foam.

Assume you get only get 5 of your cylinders, ignoring shipping, that's only $4.50 per slug using the US Composites price.
 
2cf = 2 x 12 x 12 x 12 cu in = 3456 cu in.

A 6" cylinder has volume pi * r^2 * h = 28.3 * h.

So, 3456 = 28.3 * h means that h = 122.1.

In a perfect world you would get 6.7 of your 6x18" cylinders from a single batch of 2# foam.

Assume you get only get 5 of your cylinders, ignoring shipping, that's only $4.50 per slug using the US Composites price.

And in a not so perfect world, there's always some degree of waste somewhere, so lets just say I can get 5 of these "slugs" from the 2# kit as per your math (which btw is indecipherable to me) I know not of these equations. That's better than the three I was guessing, based on what Steve was saying.

In a nutshell, I can't afford to experiment on filling the molds to see how much I'll need to top one off. It's part of the reason for all of my questions here. SO if I can make at least 5 slugs from one kit (with shipping and cost of a tube, if I can even find one short enough) and come out around 6-7 bucks a slug, that's within a reasonable cost factor. I could live with that.
 
Kalsow did a good job on those calculations. His first line is simply a calculation of how many cubic inches are in two cubic feet. One cubic foot is a cube that is 12 inches by 12 inches x 12 inches. 12” x 12” x 12” = 1728 inches cubed (which is expressed as inches to the third power or in.^3)
So, two cubic feet would be twice that or 3456 inches cubed.
Next, he demonstrated how to calculate the volume of a cylinder. A cylinder is just a circle that has a depth or thickness. Volume of a cylinder is calculated by finding the area of the circle and multiplying it by the length of the cylinder. Or, since you’re looking for how many of these cylindrical slugs you can get out of a kit that makes two cubic feet the inverse relationship can be used to get that answer. A six inch diameter circle has an area A of πr^2 (pronounced pie are squared)
pi = 3.141528… (no units)
The radius is 3 inches (half the diameter). Radius squared then is 9 square inches; thus the area is 9 in^2 x 3.141528 or 28.274 square inches.
Dividing that area into 3456 cubic inches tells you how long of a cylinder you could cast.
3456 in^3 / 28.274 = 122 inches, just a tad longer that ten feet.
You could cut that into 6 full 6” diameter x 18” long cylinders and have one 14 inch cylinder left over.
 
~~~~~122 inches, just a tad longer that ten feet.
You could cut that into 6 full 6” diameter x 18” long cylinders and have one 14 inch cylinder left over.

Thank you for the math lesson Steve. Those little symbols he was using...^ & these configs, 2cf pi * r^2 * h = 28.3 * h. So, 3456 = 28.3 * h means that h = 122.1......had my head spinning. I really don't know that kind of math, but it does make a little more sense now.

So in the long run, I'd have 6 slugs for the maximum fit in my lathe and a shortie leftover? Cool! That might come in handy if BELDAR bites the dust. (that's in another build thread I have on standby.) I'll have to see if my landlord/construction company man can get me some 6" Sonotube, or reasonable facsimile. You guys have been a big help. Even if some of it read like hieroglyphics.
 
Thank you for the math lesson Steve. Those little symbols he was using...^ & these configs, 2cf pi * r^2 * h = 28.3 * h. So, 3456 = 28.3 * h means that h = 122.1......had my head spinning. I really don't know that kind of math, but it does make a little more sense now.

So in the long run, I'd have 6 slugs for the maximum fit in my lathe and a shortie leftover? Cool! That might come in handy if BELDAR bites the dust. (that's in another build thread I have on standby.) I'll have to see if my landlord/construction company man can get me some 6" Sonotube, or reasonable facsimile. You guys have been a big help. Even if some of it read like hieroglyphics.

The caret symbol (^) is used to show that something’s being raised to a power, such as being squared, or cubed.
Something is squared when it is multiplied by itself, so 3 squared is the same as 3^2, which just means 3 x 3. Also, sometimes instead of an x meaning multiplication, we’ll use an asterisk (*).
Something is cubed when it’s multiplied by itself another time, so 3 cubed would be 3 x 3 x 3, which equals 27. If you work construction you know that one “yard” of concrete, which really means one cubic yard, contains 27 cubic feet (cf).
Math is full of those hieroglyphs; otherwise it would take so much space to write a formula.


Steve Shannon
 
I've used this foam with great success before. It's not cheap but you can get it up to 4" thick. I use 3M spray glue to hold blocks together while shaping. You can also use Epoxy by only use in the center of the blocks where you know it won't be exposed when shaping. A combination of both glues works perfect as well. This white beaded foam is very dense and leaves a very smooth surface after sanding.

https://woodlandscenics.woodlandscenics.com/show/item/FOAMSH/page/1


John Boren
 
I've used this foam with great success before. It's not cheap but you can get it up to 4" thick. I use 3M spray glue to hold blocks together while shaping. You can also use Epoxy by only use in the center of the blocks where you know it won't be exposed when shaping. A combination of both glues works perfect as well. This white beaded foam is very dense and leaves a very smooth surface after sanding.

https://woodlandscenics.woodlandscenics.com/show/item/FOAMSH/page/1John Boren

Oh I already found an adhesive of choice. Takes a few days to set up, but it's worth it. Glidden Gripper primer is what the prop masters use in Hollywood and a lot of the major Halloween displays are using.

That beaded, aka EPS "expanded polyurethane" has been problematic for me in the past and I have worked with various densities. Maybe not the brand you are suggesting, and really, you are the first person to suggest EPS. The closed cell, aka XPS "extruded polyurethane, is much more user friendly. In all honesty, I didn't know about using adhesives in a manner like you mentioned until recently. I had been coating the entire surface and was plagued with thin wafers of glue between layers that seem impossible to deal with. If I EVER work with glued layers again, I will certainly remember this tip. And just patch any gaps after turning. I think I want to try making foam slugs in tubes just to see how that goes. I will, of course, post my results.
 
Disclaimer: I've never actually done this; what follows is just the result of these ideas jangling around in the hollow space in my head.

In all honesty, I didn't know about using adhesives in a manner like you mentioned until recently. I had been coating the entire surface and was plagued with thin wafers of glue between layers that seem impossible to deal with. If I EVER work with glued layers again, I will certainly remember this tip. And just patch any gaps after turning.
I presume that the gluing strategy would be to keep the glue inside the bounds of the finished cone... not just inside the edges of the block you'll be turning.... That would mean a fair bit of figuring before you glue the sheets together. It could be even better to simply leave a gap in the glue where the perimeter of the finished cone would be, just to hold everything together more solidly while you're turning it. Again, this requires you to have a pretty precise idea of the shape of the cone before you glue together the sheets.

Dunno if I'm stating this clearly but hopefully the idea gets through.
 
Disclaimer: I've never actually done this; what follows is just the result of these ideas jangling around in the hollow space in my head.


I presume that the gluing strategy would be to keep the glue inside the bounds of the finished cone... not just inside the edges of the block you'll be turning.... That would mean a fair bit of figuring before you glue the sheets together. It could be even better to simply leave a gap in the glue where the perimeter of the finished cone would be, just to hold everything together more solidly while you're turning it. Again, this requires you to have a pretty precise idea of the shape of the cone before you glue together the sheets.

Dunno if I'm stating this clearly but hopefully the idea gets through.
Seeing how I make templates of these nose cones, the same template can be used to draw on all the layers to be used as a gluing guide. Then, turn as usual based on the same template. Pretty easy really.
 
Hey conehead!

have you checked out the standard stuff from any craft stores...here's 3 pages. Find even a 6in by 24in cone for a conehead...lol blocks..sheets..etc & don't forget the 40% off coupon!

https://www.michaels.com/floral-supplies/styrofoam/915464174

Yeah, I know about that stuff. It too porous. I suppose if you were going to cover it with paper machete, it might be an option. But I'm pretty certain it's too fragile and delicate to spin on a lathe. Plus, if you've ever worked with that stuff, it get's everywhere. And much worse that the expanded bead kind.
 
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