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Thread: Foam or other printable materiel for ceiling medallions?

  1. #11
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    Do you have any trouble painting that pink foam Jerry?

  2. #12
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    Quote Originally Posted by EricSchimel View Post
    Do you have any trouble painting that pink foam Jerry?
    No I just use a good latex paint

  3. #13
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    Good to know!

  4. #14
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    Quote Originally Posted by jerry_stanek View Post
    No I just use a good latex paint
    Just don't try spraying it with lacquer or enamel... that could get messy.
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  5. #15
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    I wouldn't use pink/blue insulation foam for that - You'll put a lot of labor and time into it and it will look like something the dog made. Just use MDF - pretty much any variety will be better than foam under 10# density. The pink/blue stuff is around 3#. Polyurethane sign foam is the only foam I would recommend for this.

    Can you finish pink/blue foam? Yes...but it is a LOT of work and you have to put so many coats on it that all the sharp edges will be washed out on it. It has a tendency to 'pimple up' because of the trapped air in it. MDF is cheap and much easier to finish, plus you won't wash away all the detail on it. If you are concerned about weight, just use ultralight MDF. If you want less sanding, use double refined or MRDF, but that isn't something you'll find in a big box store. Strictly from professional sources.

    Pretty much the ONLY use for insulation foam is to either do practice cutting or making very large props where weight is an issue. Because of the larger scale of those kind of parts, washing away details isn't an issue because the thickness of sealer/paint to surface detail is nothing, proportionally speaking.

    The foam ceiling medallions you may have seen in big box stores are cast from either polyurethane foam or polyisocyanurate foam.
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  6. #16
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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.

  7. #17
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    Quote Originally Posted by Brady Watson View Post
    I wouldn't use pink/blue insulation foam for that - You'll put a lot of labor and time into it and it will look like something the dog made. Just use MDF - pretty much any variety will be better than foam under 10# density. The pink/blue stuff is around 3#. Polyurethane sign foam is the only foam I would recommend for this.

    Can you finish pink/blue foam? Yes...but it is a LOT of work and you have to put so many coats on it that all the sharp edges will be washed out on it. It has a tendency to 'pimple up' because of the trapped air in it. MDF is cheap and much easier to finish, plus you won't wash away all the detail on it. If you are concerned about weight, just use ultralight MDF. If you want less sanding, use double refined or MRDF, but that isn't something you'll find in a big box store. Strictly from professional sources.

    Pretty much the ONLY use for insulation foam is to either do practice cutting or making very large props where weight is an issue. Because of the larger scale of those kind of parts, washing away details isn't an issue because the thickness of sealer/paint to surface detail is nothing, proportionally speaking.

    The foam ceiling medallions you may have seen in big box stores are cast from either polyurethane foam or polyisocyanurate foam.
    Super Tuff-R is 25 PSI and says it's density is 2pcf. (So a sheet should weigh 10.66 lbs, but the sheet weighs "12.16lb" according to HD...)

    Formular 250 is 25 PSI, no density given, but the sheet is 7.5lbs according to HD, so I guess less density. I was going to buy this because it's cheaper one but now I'm not sure.

    I will give one of that insulations a shot, and if it doesn't work well the basement can always use more insulation. I'll look into ultra light MDF too. Thanks!

  8. #18
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    Quote Originally Posted by jerry_stanek View Post
    I cut designs in the pink foam from HD. My store carries 2 different densities I use the heavier one.
    Do you have pictures you can share? What bits, feeds and speeds do you use? I think I need to buy a larger ballnose, the 1/8" will take over 6 hours with a profile path. Maybe I need a flute path...

  9. #19
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    >> I'm a little concerned about the weight of a 34" x 34" x 2" MDF sandwich.

    You don't need a solid "cake". The innards would be hollow. That would cut your weight down considerably and allow the inside of the circle of one layer to be used in another layer.

    As for exact matching of profiles, many times a combination of bits can do what's needed. Your image doesn't provide much detail but it looked to me like roundovers on top of roundovers. If you need an exact match for a customer, that could be a problem but if you want to make this for yourself, you can be more creative.
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  10. #20
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    Quote Originally Posted by skintigh View Post
    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....

    ...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.

    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.
    Yes - MDF is 48# (as the crow flies) per cubic foot of volume; cast garden variety plaster is about 52# per cubic foot. This is of course assuming that you would machine the entire medallion out of a solid piece of 2" MDF...

    The material does not have to be solid...you can hollow out inner portions that do not require material for machining. A good example of this would be a carved carousel horse...if the body wasn't hollow it would weigh more than a real horse the same size. How much does the average ceiling fan weigh? Some of them are pretty chunky and many of them suspended by a box with 2 nails holding it in...something to ponder.

    In regards to bits...Forget Ogee and other form cutting tools. Yes, it is possible to do efficient cutting using shaped form cutters, however - there is a lot of time involved to do what some of us call 3D cutting using 2D tools. If you had to make 2 dozen of these, I'd say that the time programming and acquiring custom tooling would be worth it in the long run. However, for one-off work such as this, the accepted 'path of least resistance' is to create some cross sections and sweep that shape to create a 3D relief using Aspire or other program capable of doing that. You would then rough out and do an offset 3D finishing machining toolpath around and around to resolve the shape.

    In regards to machining time...it takes as long as it takes and that's how long it takes. It makes no difference that you think it should machine in 45 minutes...when it comes to 3D work, you can't make shop rate, BUT how else would you be able to produce such a piece on any other machine (or by hand) in the shop? Right. Hammer on the previewer, fiddle with settings until you reach the balance between quality and machining time. Personally, I could care less about machining time if the quickly machined part looks like it belongs on the firewood pile or wall of shame. Quality trumps all. Of course this is not to say every relief should be machined with a 1/32" ball in order to resolve every micro detail - there is a balance that must be found on a case by case basis.

    Only by doing testing with different ball end mills in the previewer (Aspire) can you realize what the largest ball end mill can be used and view the quality of cut you will get using various stepover values for that tool. The time spent 'sneaking up' on an efficient toolpath is worth the time taken in analysis. Keep in mind that when you are new to this type of work, some obvious things are not so obvious. Don't forget this is going to be on the ceiling and painted...nobody except you will know if there is anything wrong with it...(this is called "the builders curse" - and is normal) so if you can't get into every nook and cranny nobody is really going to bat an eye and all that time worrying about it will be for nothing.

    If you want the best material for the job, use 10#/CF HDU 'sign foam' - and if you have shallow pockets on this job, use MDF or ultralight MDF. Bigbox MDF is junk...there is a huge difference in all aspects with professional grade MDF like Plum Creek, Sierra etc. Like anything in life ~ Everything has a price. Buy the right material or put sweat into it. Either way - same price.

    See attached with quick & dirty weight calculations and how it will look using a 1/2" end mill to rough and 1/4" ball end mill to 3D finish machine.

    CeilMedConst.jpgCeilingMedallionCalc.jpg
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