Foam or other printable materiel for ceiling medallions?

[skintigh]

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!

a32518

[knight_toolworks]

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.

[coryatjohn]

"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!

[bleeth]

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.

[Burkhardt]

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/0/144/172/174/bf64ec70-16f1-4748-abc7-c9dee5100987.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.

[skintigh]

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!!!

[coryatjohn]

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.

[joe]

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

[EricSchimel]

I'd take a look at Medex. I've never liked the surface quality on MDF until I started using that stuff.

http://www.roseburg.com/Product/medex/

[jerry_stanek]

I cut designs in the pink foam from HD. My store carries 2 different densities I use the heavier one.

[EricSchimel]

Do you have any trouble painting that pink foam Jerry?

[jerry_stanek]

Do you have any trouble painting that pink foam Jerry?

No I just use a good latex paint

[EricSchimel]

Good to know!

[coryatjohn]

No I just use a good latex paint

Just don't try spraying it with lacquer or enamel... that could get messy.

[Brady Watson]

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.

[skintigh]

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:

32539

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.

[skintigh]

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!

[skintigh]

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...

[coryatjohn]

>> 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.

[Brady Watson]

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.

3254032541

[bleeth]

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?"

[skintigh]

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 :rolleyes: ), trace it onto metal, cut that metal into a knife and spin it around a pile of plaster.

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[Kyle Stapleton]

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.

[jerry_stanek]

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.

[bob_dodd]

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

[coryatjohn]

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.

[garyb]

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.
http://www.talkshopbot.com/forum/attachment.php?attachmentid=32598&stc=1
http://www.talkshopbot.com/forum/attachment.php?attachmentid=32599&stc=1
Gary

[joe]

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