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Thread: Foam or other printable materiel for ceiling medallions?

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  1. #1
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    Default Foam or other printable materiel for ceiling medallions?

    I have a large ceiling medallion I want to copy, what is good paintable material to use? I've read suggestions to use "Lowes foam" which I assume means Kingspan Insulation foam. Is that good? Is it better than Home Depot foam?

    I've also heard of "foam coat" but don't know if that's what I should use.

    Also, what bits, feeds and speeds is used with foam?

    Thanks!

    a20190217_215021.jpg

  2. #2
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    most expanded foam cuts well. it needs sealed and then sanded to be smooth. a uncut bit is what you want. the cleanest cost is at 18k if you have a spindle and about 2 ips. the problem with foam is its hard to get the cutter to take the right coil lead. you can cut faster but it will be a tiny bit less clean. you can just spray it with a latex ceiling texture spray too. as long as it is water based and maybe had some elasticity in it it will work.

  3. #3
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    "foam coat" is an acrylic plaster with fiber embedded in the mix. When used right is very easy to work with, cuts well after it dries, sands well and forms a very hard surface on foam. Foam coat takes a bit of practice to use right. Apply it too thick and it cracks. Too thin it is weak and useless. It's hard to apply an even thickness coat and difficult to tell exactly how thick it is and if thick, can take a long time to dry to a workable hardness. The fibers, glass I suspect, can be very irritating and be lodged in your skin by simply picking up your work piece.

    Looking at your ceiling piece, foam coat might not be the best choice. Too much detail. That would get lost smearing it with foam coat. You could cut the foam blank a bit shy of where you want it to be, smear it with foam coat to build up a reasonable layer (1/10th" maybe), then cut it again to a finished size. That would leave a uniform layer of foam coat. It would take a lot of effort to build up enough of that gunk. The best way to apply it is by smearing it with your hand. That causes the fibers to align horizontally which keep them from sticking up and provide the needed reinforcement for strength and to prevent cracking. Be sure to use heavy gloves or spend a lot of time with a bright light and tweezers.

    I suggest you try epoxy which I find is easier to work with and provides an entirely different result. I like the West Systems epoxies myself. Paint it on and in two or three coats, you have a hard surface that will withstand a lot of punishment.

    One real caveat with foam is that it dents extremely easily. You can put a thumb mark in it by picking it up. Foam coat doesn't provide any protection until it is about 1/16" thick. Epoxy, on the other hand, will make it pretty much dent resistant after the second coat. While Epoxy might cost twice as much as foam coat, the results are better and epoxy can be used for many things, unlike foam coat, which is pretty much a one trick pony.

    Good luck!
    Last edited by coryatjohn; 02-18-2019 at 12:01 AM.
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  4. #4
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    You can easily use the pink or blue insulation foam from building supply stores and seal it with a few coats of shellac.
    Cuts like butter and holds detail extremely well. Styrofoam(like used in coolers) does not cut or seal easily. Whole statues have been made this way and last many years.
    You should be able to come up with many posts by doing a forum search. For that part you will be best using a longer tapered ballnose bit like those available from Beckwith Tools.
    5% stepover will reduce sanding, but it sands so easily you can dramatically reduce your cutting time by doing it with a 10% stepover.

  5. #5
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    The blue or pink insulation foam from HD or Lowes is usually very low density and pressure sensitive with 15psi compression strength specification. But they make such XPS foam also in 30, 60 and up to 100 psi (e.g. Owens Corning Foamular1000) which is much more resilient. http://www.foamular.com/assets/0/144...dee5100987.pdf

    Depending on where you live you may find a wholesaler carrying such stuff. Here in the LA area there are some that mainly serve the movie industry for making props. I bought a sheet of 30psi foam there a while ago and got about 3 sheets worth of large cutoffs for free.
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  6. #6
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    Thank you everyone for your help! I will experiment with shellac and epoxy and try those tool settings.

    It hadn't occurred to me there were different PSI strengths of foam. One of the Lowes' boards is 25 PSI, and Home Depot's range from 10/15 to 25, so I'll give 25 PSI a shot if I can't find stronger stuff around here.

    Thanks again!!!

  7. #7
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    For that project, I would suggest using regular MDF and build it up "wedding cake" style. Might end up to be easier, faster and cheaper. Instead of 3D'ing it, you can just buy a couple of roundover bits and carve it directly. The results will be far better than trying to make it with a ballnose.
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  8. #8
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    I'm with John.
    Another material suggestion is Trupan. It's lighter than MDF although there is MDF Light which is about the same weight as Trupan. Both carve well and are much tougher than Foam.

    Joe

  9. #9
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    Quote Originally Posted by coryatjohn View Post
    For that project, I would suggest using regular MDF and build it up "wedding cake" style. Might end up to be easier, faster and cheaper. Instead of 3D'ing it, you can just buy a couple of roundover bits and carve it directly. The results will be far better than trying to make it with a ballnose.
    I'm a little concerned about the weight of a 34" x 34" x 2" MDF sandwich. Solid plaster is probably lighter. Also the last time I tried to CNC a simple molding out of wood it took hours, so I suspect it would also take 30+ hours to cut this medallion out of MDF. I'm guessing foam is closer to 1/100th that time but I need to do the math.

    As for using round over bits, I couldn't even find ones to match a simple piece of backband, carving this accurately seems impossible:

    profile.jpg

    Maybe I'm not understanding something about the router bits, but out of the 20-odd curves, maybe 4 could be close to a 1/4 round.

    When I was trying to carve the backband, there were 3 curves, and of that I could partially match 1. The other 2 were somewhat like an ogee, but it didn't match any of my bits and when I tried to shop for ogee bits it seemed there was no way to see the curve before buying it, so to see if the curve was correct I had to buy them at random and test them. That could get expensive.

    If I'm missing something bit about the router bits I'd love to learn, but I searched for diagrams, formulas, definitions, and found nothing.

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