The Glue Issue
As many of you know the furniture line recently launched by J. Alexander Fine Woodworking is comprised of wood to metal joinery, which is not a regularly used or easy kind of joint . This presented a few issues that needed to be worked out, first of which was figuring out which glues will bond metal and wood.
After some investigation there were three glues readily available that would do the job: Polyurethane Glue (aka. Gorilla Glue), 2-part epoxy, and hot-melt glue. Regular wood glue simply would not work because it is designed to bond wood to wood, and not much else.
Polyurethane Glue
The polyurethane glue did a fabulous job at bonding the aluminum bar to the wood it is inserted into, and allowing plenty of open time to assemble the components, but its drawbacks proved to much.
Here is a view of a .75″ aluminum bar glued into a .75″ hole. The joint is tight enough that no glue was able to expands out of the hole. But, the joint was also so tight that the bar had to be pounded in with a dead blow hammer. This presented issues on very hard woods like the bubinga and the oak, and on the more fragile components like the wishbone stringer on the cocktail table. So we solved this problem by drilling a .781″ hole for the .75″ bar to go into. The ensuing problem is shown below.
Since polyurethane glue foams as it cures, the glue expanded right out of the slack in the hole. All of this extra glue had to be cut away and the metal and wood re-sanded and cleaned up. Also, since the polyurethane foams as it cures, all the bars had to be clamped in place to keep from being pushed out of the hole. This meant that each piece in the furniture line would take 2-3 days to assemble and would need extra labor to clean up the glue that foamed out of each joint.
2-Part Epoxy
The next candidate was an epoxy made up of two parts, a resin and a hardener, which are mixed together in equal parts prior to use.
The epoxy worked great at binding the metal bar and the wood, but the mixing of the two parts can get quite time consuming and monotonous, and it was only available from Home Depot in two 4 ounce bottles, which doesn’t last very long when there are a lot of furniture pieces to build. Also, the working time is quite high, anywhere from 2-6 hours.
The epoxy dried completely clear, and after it was fully cured, removing any excess was a simple task with a sharp chisel.
Hot-Melt Glue System
The next glue we tried was a hot-melt glue system from the makers of the Titebond wood glues. This particular glue system uses a metal glue cartridge that is inserted into a glue gun, which once placed into the electrified base for 15 minutes, melts the glue inside the metal tube allowing you to use the glue. There are two glues made for the gun that bond metal to wood, one cures in 1.5 minutes and the other one has a slightly longer cure time of 5 minutes. We thought this was going to be our saving grace. A glue that bonded metal to wood and cured in 5 minutes? Awesome!
We purchased the system, plugged the base in, inserted the glue cartridge, placed the gun in the base, waited 15 minutes for it to heat up, and then used it. This was pretty much your moms hot glue gun on steroids! The glue easily bonded the metal to the wood and easily cured in the advertised 5 minutes. Once the glue was fully cured it looked and felt like the plastic used to make milk jugs. The gun did exactly what it was advertised to do. It actually cured a bit too fast for us. The downsides we discovered were that the glue was not quite liquid enough to ooze out and around the sides of the bars and out of the hole, which is kind of critical for a strong, long-term hold.
So, after using all three glues and weighing their benefits and drawbacks, we have decided to use the 2-part epoxy system. Not the stuff from Home Depot but rather an even better industrial grade Loctite epoxy we found from Fastenal that uses cartridges and a glue gun with applicator tips that mix the two parts as they are squeezed out. Therefore we threw out the hassle of having to mix and smear the epoxy where we want it, and we still get to enjoy all the benefits.
May 21st, 2009 at 8:38 am
How about model numbers etc for that epoxy cartridge glue gun.
Sounds like what I’ve been looking for to mount rare earth magnets.
May 21st, 2009 at 12:39 pm
The Fastenal part #’s are as follows:
Glue = E20HP DURA #0150496
Gun = 50ML APPLICATR # 0151149
Nozzel = 6mm MixNzLuerTip 10pk #0605223
I am not sure if Fastenal will sell the glue to the consumer or if it has to be sold only to a manufacturer. Good luck. I hope it works.
July 24th, 2009 at 1:04 pm
You made some good points there,I did a search on the topic and found most people will agree with your blog home furnishings needs a lot of patience.
December 2nd, 2009 at 5:59 am
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June 5th, 2010 at 4:18 pm
check out the new lock dowels. Lock dowels join metal to metal, wood to metal and wood to wood. hidden joints that are removable.