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Thread: Foam or other printable materiel for ceiling medallions?

  1. #21
    Join Date
    Mar 2004
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    Delray Beach, FL
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    3,708

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    Seth:
    I must say it has been fun watching all the hairsplitting on this. I have great respect for all the helpful commentators here, but there is a vast experience gap.
    These medallions are old hat to me. I have bought, sold, and installed them for years and have had to duplicate existing several times due to original suppliers specific designs being no longer available.
    I would hope that you have checked at least some of the many suppliers of pre-manufactured ones to see if the one needed is more readily available.
    If you HAVE to make it solid or layered foam is the way to go for a couple reasons. One of the main ones is since it is light it is also very easy to install. Good quality construction adhesive and caulk for the edges and a prop while it dries does the trick. It machines easy and can be easily smoothed and painted. Yes, as Brady points out, HDU sign foam is superior (more dense) than the "denser" and much cheaper insulation foam, but they both machine just fine for this type of project. I liked a 1/2" ball nose with 10% stepover. My first shot at it was based on the experience of a really great signmaker and she used tons of the pink stuff for large installations. It worked like a charm so I became a believer. Worst part, like mdf, is cleaning up the cutting dust. light scraping/sanding took care of anything that needed it and sealing with shellac, as I mentioned before, or KILS gave a fine base coat for final paint. If you don't want to come back and remove the temp prop after install and the customer chokes you can also use a couple large flathead screws into a joist and immediately spackle them. There are several easy ways to skin this cat and when you actually do it you'll end up going "Why did I worry about it so much?"

  2. #22
    Join Date
    Jun 2018
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    Update:

    I bought the "blue Lowes" foam, which I assume is Dow Tuff-R because that's the only blue foam board they sell, and the results were disappointing.

    I cut 1/16th of a medallion.
    1/4" clear pass was estimated at 10:59, actual was 30:32 And I need to slow it waaaay down because it was ripping the foam.
    1/8" tapered ball nose at 10% step over at 20,000 RPM and 6 IPS was estimated at 17:28, actual: 1:09:33.

    So 1 hour 40 minutes for 1/16th of a circle, and the result was fuzzy and hairy from fiberglass strands and easily damaged. Perhaps the pink board is better, but if it has fiberglass in it I wouldn't even bother. Besides, it sounds like sign foam or good MDF is the way to go.

    Now, it seemed like for every 1 second of cutting, the machine spent 3 seconds moving the head at 0.0001IPS and that was with aggressive settings. (I had to lie about the length of the tool, otherwise the Shopbot would lift it up 1.5" and lower it 1.5" at both ends of every pass!) So perhaps that means the total time would "only" be T*1/4 * 16 + T*3/4 = 7:55:00. But maybe twice that or longer with a tougher foam or MDF and slower clear pass. And I'd have to sit next to the machine the entire time per Makerspace rules.

    Anyway, it now seems like the fastest and easiest way to do this is to learn how (I assume) they did it in the old days. I'll print out the profile (in software that supports printing ), trace it onto metal, cut that metal into a knife and spin it around a pile of plaster.

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    20190315_142254.jpg

  3. #23
    Join Date
    Feb 2013
    Location
    River Fall WI
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    Just a few pointers:
    1) The is no need to run a clearing pass for foam.
    2) The x,y, and z must be set at the same speed or the you will be cutting at the slowest of them all. So while you think you are cutting at 6ips your are not even close if your z is set at .8ips. Move all 3 to 3ips (maybe higher)
    3) Just because you cut a 1/16 of your does not mean that it will take 16 times as long to cut the whole part. (As you stated "Shopbot would lift it up 1.5" and lower it 1.5" at both ends of every pass!") so if you raster the whole thing that is not as many starts and stops as you may think.
    4) The fussy you are talking about can only be seen ZOOMED in and I beleive this is going a ceiling.
    Kyle Stapleton
    River Falls Renaissance Academy
    Math/Technology Education Teacher


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  4. #24
    Join Date
    Dec 2007
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    I haven't had much luck with the blue foam. My home Depot carries 2 density pink foam I like the higher one I think it is either 150 and 250 or 30 and 40 but I get the higher number.

  5. #25
    Join Date
    Aug 2004
    Location
    Northern , new jersey
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    During the restoration of Ellis Island I had the opportunity to watch the Plaster's make ceiling cove molding , and they would place a pile of plaster (did not harden fast ) on a table and used a comb to shape it , I would think you make your comb / knife one half the dia. and pin it with something the size of the pipe holding the light fixture , They made 8 foot lengths , They did it in 2 or 3 steps and got great results. Hope this helps
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  6. #26
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    Mar 2013
    Location
    Memphis TN
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    The pink foam at HD has slices cut into it about every 14". They do this so it's easy to cut it into chunks that can be inserted between joists for insulation. These cuts can screw up anything that's intricate.

    I suggest skipping the foam and go directly to the wedding cake method with light weight MDF.
    ShopBot Details:
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  7. #27
    Join Date
    Mar 2005
    Location
    Beckwith Decor Products, Derby/Wichita KS
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    612

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    As Dave noted, and interesting read but I have to say Brady summed it up back on page 2 post 15, xps foam usually used just in large models and does take a lot of finishing.
    then secondly its all about feed/speed and tooling when it comes to machining it.


    Gary
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    Beckwith Decor Products
    Caveco Distributor, USA
    Custom CNC Tooling/Onsrud Distributor


  8. #28
    Join Date
    Jan 2004
    Location
    Norman, Ok
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    3,251

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    Wondering why anyone would make a ceiling molding since Amazon has a tone of them for almost nothing.

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