Best Practices for HDU foamboard?

[Jim Underwood]

I'm wondering if you could help me and a friend who are wondering what are the best practices for making signs out of HDU foamboard. We'll be using a CNC router to cut this out. I think the sign is roughly 48" tall by 70-80" wide, and 2" thick.


1) When cutting the background between letters and the border, do you use a large diameter bit to remove as much waste as quickly as possible? What bit do you use? Feeds and speeds?
2) If you don't use the 2D area clear method described above, why do you use a carving method?
3) When removing that background, how deep do you go? Or in other words, how high off the background are your letters?
4) What's the smallest section on the letters? In other words, what kind of cross section height/width ratio do you use? (What will the HDU material stand?)
I'm concerned that I'll make the letters too skinny and too tall.
5) How do you typically fasten HDU foamboard to support posts or masonry?
If you can help me with any or all of these questions, I'd appreciate it.
Thanks,
Jim

[Tom Klass]

Hello Jim, I'm sure Keith will chime in to your question but here are 3 guy's that are top notch in sign making and the use of HDU
www.trmacsigns.com
mm@mezalick.com
www.mcgrewwoodwork.com

I've seen first hand work of all 3 and if I had to have a sign made I would be really hard pressed to try and choose which I would have do it!! You can see some of their work on the camheads forum
good luck with your project show some pics when your done
Tom K.

[Ken Gentry]

I am a CNC mill newbie so I can't comment on all your questions. I saw a sign like you are describing in front of a housing development. I couldn't quite figure out the exact material but it had a cellulose like cross section about 1 inch thick. A thin metal plate was attached to the back of the sign and I'm not sure how it was attached to the posts. It's possible the metal plate was screwed into the posts and then the foamboard sign was glued on to the metal plate.

The background was surprising shallow at about 1/8". The sign has three ducks on it and are colored/painted somehow. I didn't look to see if the ducks where part of the foam board or if they were glued onto the sign. If I think about it I will take some photos of the sign and attach them here in a day or two.

My question for this thread would be where to buy this material as a hobbyist who would want one sheet at a time. I called a couple of companies in my area about it and they did not sell to the public.

[Paul Phillips]

I'm wondering if you could help me and a friend who are wondering what are the best practices for making signs out of HDU foamboard. We'll be using a CNC router to cut this out. I think the sign is roughly 48" tall by 70-80" wide, and 2" thick.

Hi Jim, I've cut quite a bit of HDU so I'll try to answer as best I can. The first question you need to answer is what density do you need? There is a wide range available (anywhere from 4 lb-75 lb) that significantly affects pricing, strength, durability and detail, first you must determine what your budget is and then buy the highest density that you can afford and still make a profit. For example, if you are just doing a large raised letter panel and or if weight is an issue, then a lower density (10 lb-15 lb) should be enough, but if you want to do a textured background and you want to make sure that it doesn't get damaged in any way, then a higher density (20 lb-30 lb) might be a better fit. The higher the density the stronger the material and the more detail it will take (think basswood or mahogany), also the easier it is to prime and paint, the lower densities are very porous and take a lot of special high build primer to seal properly. The only drawback to higher density is that the price goes up significantly, where a sheet of 2" thick 15 lb might go for $380 per sheet, 2" thick 30 lb might be $880 per sheet, more than double the price, but once you have worked with both you will see a huge difference in quality and workabilty, I always use as high of a density as I can afford.

1) When cutting the background between letters and the border, do you use a large diameter bit to remove as much waste as quickly as possible? What bit do you use? Feeds and speeds?

Yes, I typically use a .5" diameter but you can certainly use larger. Feed rates are fantastic, you can go pretty fast in this stuff, even in the higher densities, 300-600 ipm .25" deep with a .25" End mill is a place to start of course each machine will vary, that's on my MultiCam.

2) If you don't use the 2D area clear method described above, why do you use a carving method?

I Assume you mean carving method to be some sort of texture, I've done a lot of signs with a hand carved/gouged texture using a .5" ball nose bit or a sandblasted texture using a 90deg conic bit.

3) When removing that background, how deep do you go? Or in other words, how high off the background are your letters?

Depends on design/size of the sign and desired effects, on a smaller sign .25" depth on smaller letters might look fine but i would probably go deeper, .375"-.5" deep on a large sign with big letters for nice contrast, the question is a bit subjective but hopefully that gives you a place to start.

4) What's the smallest section on the letters? In other words, what kind of cross section height/width ratio do you use? (What will the HDU material stand? I'm concerned that I'll make the letters too skinny and too tall.)

This kind of goes back to the density issue, the higher the density the greater the detail it will hold, I've done some very fine detail in 30 lb which is my favorite to use when I can get it. Think of it as working like a dense wood but without any chipping.

5) How do you typically fasten HDU foamboard to support posts or masonry?
If you can help me with any or all of these questions, I'd appreciate it.
Thanks,
Jim

You can cut it and work it just like you would plywood or 2'x4"s, wood screws and silicone work fine, typical wood fasteners on the higher densities, on 15 lb or less you might try doing an inlay on the back side with some aluminum or steel epoxied in for fixturing/mounting with extra strength, you can drill and tap into the metal (additionally, you can tap straight into the 30 lb and it will hold a stud, it's about the same density as Acrylic!)
There are many brands out there, i prefer to use http://precisionboard.com/ they have lots of good help and support online and also sell the glues and primers that work well with it.
For some inspiration on what can be done with it check out this blog. http://precisionboard.com/dan-sawatzky/
Here is a sign we did for the San Diego Zoo using 30 lb and a hand carved texture with the Ball nose bit.
SD Zoo1.jpg

HDU is also excellent for doing 3d work on the CNC, here is one we did recently for the Discovery Science museum in Santa Ana.
first.jpg
step4.jpg
Hope this helps, feel free to PM me if you have any questions.

[Jim Underwood]

Thanks Paul. That was very helpful.
I also spoke with Mr. MacMunn from Ottawa the other day on the phone. He was a veritable font of information...

[Rob Mulcare]

Found it...