need help with knowing the strength of two part epoxy

[roy_shimp]

Does anyone know of technical papers that document the strength of screws in 2 part epoxy? I'll need the data for a sign permit. The intent is to attach 72" z-clip rails ( the rails have screw holes) to 18lb hdu by drilling slightly oversized pilot holes for the screws into the hdu, filling the holes with the 2-pt epoxy and inserting the screw thru the z-clip screw hole into the 2-pt epoxy. I sent an email requesting the info to West Systems. Waiting their response.
Thanks , Roy Shimp

[dlcw]

I would suggest contacting the manufacturer of the epoxy you will be using. They should have that data.

[joe]

Roy,

You might consider contacting one of the HDU manufacturers since all of them recommend this kind of technique. Precision Board and SignFoam and Duna HDU would be some to contact.
With HDU one of the considerations is it's density. Also, when we use this technique a burr is used to enlarge the bottom of the hole. That makes for extra holding power.

Joe

[roy_shimp]

Thank you. how do you usually make a burr?

[roy_shimp]

thank you, i'm waiting their replys

[a.werby]

It might be stronger if you used threaded inserts into the HDU, instead of expecting the glue to hold the screw threads. You can glue in the inserts: https://www.ezlok.com/

[Precision Board HDU]

Not sure if this information is too late, but we had West System test our material to destruction using their Six10 Epoxy. The results are here: http://precisionboard.com/precision-board-test-report/.

We also have a page with tips for mounting HDU signs that you might find useful here: http://precisionboard.com/sign-making/tips-mounting-precision-board-hdu-signs/.

If you have more questions, you can always call our tech support team at 800-845-0745. Thanks!

[joe]

A critical look at this question begs the point. The person asking that question wouldn't know what the proper answer is. I've been making application for sign permits in six cities and this must be the most weird question of all. But, the permit person has the control.

Few, if any, of the city officials I deal with know anything or are knowledgeable about stress loads on HDU. Not to mention about Epoxy. I would have to ask them what stress load they are looking for. It's a question posed by a slow thinker who is exercising their authority.

Joe

[willnewton]

A critical look at this question begs the point. The person asking that question wouldn't know what the proper answer is. I've been making application for sign permits in six cities and this must be the most weird question of all. But, the permit person has the control.

Few, if any, of the city officials I deal with know anything or are knowledgeable about stress loads on HDU. Not to mention about Epoxy. I would have to ask them what stress load they are looking for. It's a question posed by a slow thinker who is exercising their authority.

Joe

THIS RIGHT HERE! Guy does not know the answer to his own question, rather than find out, they make the permitee do the leg work, come back with an answer of X, and THEN they look at their book and say, “That is not the right spec. You need to start over.”

“Well, what should it be?”

“I’ll let you know when you bring in the correct numbers.”

50% of the city employees work and the other half are just waiting for their pensions to kick in.

Sorry for the rant, but I have been dealing with city permitting lately and this is exactly how these guys work in my town. They don’t even bother with actual specifications, they just say “No.” when anything new appears so they won’t have to do any work. Then you spend all your time researching and finding out that things are within the rules. You go back with the info and then they are really upset because you proved them wrong and so they put more obstacles in your way.

[steve_g]

Roy…

“Thank you. how do you usually make a burr?”

Here’s a cross section of a hole that’s been undercut with a “burr” its purpose is to add mechanical strength to the plug of epoxy by making the bottom of the hole larger than the top. Typically a file type rotary bit, referred to as a burr, is chucked in a drill or Dremel type tool and hand wallowed around to create the undercut profile.
SG

http://www.talkshopbot.com/forum/attachment.php?attachmentid=31611&stc=1http://www.talkshopbot.com/forum/attachment.php?attachmentid=31612&stc=1

[joe]

Good for you fellows!

Thanks Roy for the illustration. It's spot on.
I'm not using HDU any longer but the best I've found is Duna (Corafoam) and Sign Foam. Both are superior to Precision Board. That stuff is so gritty I won't let in my shop.

Joe

[jim shula]

My response is almost two months after your original question, so you've probably found the answer by now. Anyways, I asked the the West System rep at the boat show one year this very same question since I both build boats and carve signs. He sent me to this study in the West System Advisor:

https://epoxyworks.com/index.php/bonding-fasteners-in-high-density-urethane-foam/

Also if you need technical data, this is also from West Systems. Other manufacturers publish similar data about their products:

https://www.westsystem.com/wp-content/uploads/105-205-Epoxy-Resin.pdf