15lbs versus 18lbs sign board foam (Precision Board)

[dlcw]

I did a search and didn't find anything on the subject so I wanted to run it by the sign experts here.

I have a sign project for Fedex (about 84" wide by 42" tall by 2" thick when carved and cut out) and was wondering what the difference between 15lbs and 18lbs is except the $100 per sheet price increase for 18lbs over 15lbs.

- Is there a difference in carving quality
- Do they both take the sign board foam primer equally
- How it accepts paint
- Maintains it's shape (interior sign, not exterior)
- Suggestions for mounting (I was thinking of an aluminum french cleat system)
- Should the sign be backed with another material that the french cleat can mount to (i.e. MDO, MDF, etc. - remember interior sign)

Thanks in advance. All my previous sign work has been done with wood or MDO. Sign foam is a new adventure for me.

[bleeth]

Heavier board carves much better detail. I know guys that only use 30 lb as it is much harder to dent and also prime/paint. I've never used less than 20 and they figure the extra cost is worth the savings in labor and quality of the sign, but 20 is very common.

Aluminum cleat is fine. You can epoxy a wood "nailer" into a pocket in the back to screw your cleat to or have a rear applied border in the back (depends on your design) to hide the hanging system. Lot's of signs are layered up by cutting logo's and lettering as seperate pieces and slightly pocketing the firld for them so you can finish the parts seperatly and get good fine detail.

The lighter the weight the more priming/sanding you will need to do.

It takes paint great-Many use all acrylic exterior paints from someone like sherwin williams and many use sign paints like one-shot.

It will hold shape forever-unless there is an earthquake, building fire, or steroid happy jerk who punches it.

There are some great blogs/how-to's on precision boards site.
If you want to email me your art I'll be glad to g ive you tech input.

[phil_o]

I recently ordered 18# signfoam. This was my first experience with this material. The driver told me that just about all of the sign guys on his route order 15#. They claim the additional expense is not justified.

Obviously Dave has a different opinion. I'd bet he's correct in his evaluation of the heavier products. However, the question is " is the added cost worth it?"

Phil

[bleeth]

There's a couple ways to look at it. If you hold a piece of 15lb in your hand and compare it to 20 and 30 the difference in both hardness (resistance to scratching and dents) and closeness of the pores (ease of finishing) is apparent. When machined the detail of finer work is also apparent.

Another consideration is the overall quantity you are using. If I were doing a small one-off and didn't use the product regularly it would be hard to justify the difference as profit would be tough. On a larger project where I'm getting good usage of the material I buy it is easy to put the additional cost into the pricing, particularly when put against the lower amount of sanding and filling and primer.

Your own sense of quality comes into play as well. I'm not saying that a sign made of lower density is low quality. All this stuff is pricey. Depending on the sign design, I may even suggest using pvc and not sign foam at all.

It's actually a very large subject and has been gone into in much depth in other forums more dedicated to this type of work. If I had a nearby distributor, there is much, for example, to be said of using the Duna brand. A couple sign carvers I have great respect for swear that pound for pound it is the best one to use when comparing foam of the same density.

I go through the same considerations when selecting the material I use in my cabinetry and furniture. For one project I may just order what I need from the yard(s) and for another go there in person to pick out precisely the boards or veneer sheets I want, or even select specific flitches of raw veneer to splice and set our own.

If, for example, I were doing a large rectangular sign with a fairly linear raised Logo and/or wording I likely wouldn't use sign foam at all. I might do it in pvc with pocketed letters or even aluminum with letters cut from acrylic. If this same sign had an area with high detail carving on it I may choose to do the carving area in HD foam and the rest in PVC.

I may even decide it makes perfect sense to do the whole thing in MDF.

[GlenP]

I use 15lb mostly but 20 on bigger stuff. I think a 20 lb would be minimum for this size of sign IMHO. How are you mounting it Don? HDU isn't strong enough on its own to mount unless attaching it to a flat wall and even then I usually pocket mdo into the backside. A buddy of mine that I cut signs for has a mount made up to insert into the sign. He usually has glues 2 pieces of HDU together with the metal mount inside and it sticks out the ends to bolt the sign to the posts. To me that is the only downside of HDU is the no very strong by itself.
When gluing HDU to other materials take consideration to their expanding and how they behave with humidity. I have seen a post on here before about a sign failing due to the humidity and different expansion factors. Look forward to seeing your sign, please post some pics.

[dlcw]

Thank you all for the great info!!!

My local supplier has only 15lbs and 18lbs Precision Board. I called Coastal Enterprises and talked with them about what I want to do and they indicated 18lbs would work and that I should create a pocket in the back and epoxy MDO into it using West Systems and attach the french cleat to that. They also indicated I could spray the primer using a HVLP sprayer with a 3.0 tip and thinned 20%. A 180 grit flap sander will do a great job sanding the primer and they said the process should go pretty quick.

Based on the manufacturers info, would you sign experts agree with their conclusions for my application?

Dave, if I can get your email, I will send over a preview of the artwork.

Thanks!

[dlcw]

One other question for the HDU cutting guru's.

Got a sheet of 2" thick 18lbs Precision Board.

I normally cut plywood at 5-6ips (11k rpm) and hardwoods at 4-5ips (11k rpm). I'm thinking HDU at 6-7ips (14k rpm). 2.2hp spindle, 14k rpm?

Does that sound reasonable?

[phil_o]

The signfoam web site has a short section on machining. This is their recommendation: SIGN·FOAM is friendly to your router and you will find that a spindle rate between 18,000-20,000 rpm's and a feed rate of 250 to 350 inches per minute will cut SIGN·FOAM cleanly and efficiently.
http://www.signfoam.com/routing.html

I also have a 2.2 HP spindle. I experimented with the recommended speed and feed rates. I settled on 150"/minute at 18K (max on my spindle)
250 seemed too fast. I have a Shopbot Benchtop with a 4g board.

Phil

[bleeth]

DaveR at professionalmillwork dot com