Hand-Held Radio-Frequency Gluing Devices

      Several companies make portable RF glue-curing guns. Here's advice on choosing and using one. April 20, 2007

I recently received some advice by a representative of Veneer Systems. He described to me a portable radio frequency gluing device (gun/wand?). I cannot find any information on any such device, and haven't heard back from the rep. Was this person pulling my leg? The price of this tool was around 3-4000 dollars.

Forum Responses
(Adhesives Forum)
From contributor P:
Such devices do exist! There are at least two manufacturers in the UK, so there must be some in the USA, too. (Try looking for dielelectric glue curing.) One of the UK companies is called Gibbs and I believe that they do sell their products in the US of A. The actual product you want is one they bought a year or two back called the Tregarne Wood Welder.

I have a Tregarne in the shop and as it is valve-based (yes, valve, not solid state). It is hardly portable; rather it sits on a bench by the assembly area and the hand gun is taken to the job at the end of a 12 foot long coaxial cable. The danger of moving these units is that valves can be very temperamental if bumped - so mine stays put and we bring the work to it. The advantages for us are that we can spot-weld a dowelled carcass together in 3 to 5 minutes, thus freeing the cramps up for the next unit, so we need a lot less cramps. The carcass still needs to be left for 24 hours for the rest of the joints to cure, but the saving in cost of cramps and improvement in productivity have been well worth it. My only qualms are about using what is, in effect, a microwave oven on a trigger handle - if you aren't careful using it, it is possible to burn yourself.

By the way, there is one other manufacturer who does a solid-state machine (truly portable, but even more expensive), but I can't locate the details right now.

From the original questioner:
So for veneering curved stair stringers... I am able to achieve perfect butt splices (using book and butt matched veneer). I've been using the iron-on hobbyist product called HeatLock. When I iron the joint, though, it is no longer perfect. I am looking for a way to do this besides vacuum bagging these 4-500 lb monsters.

Thanks for the advice. These wood welders are described to work as a magic wand. How well do they actually perform? And could you zap the glued area again in order to release the bond if you had to reposition (due to a mistake)?

The HeatLock is actually bonding pretty darned well. The joints aren't horrible; it is just too bad to create a perfect taped up splice, and then obtain less than professional results (after the ironing).

Oh, and the ironing process! Two men with irons in each hand takes over an hour to do the actual ironing of one side of one of these stringers (about 35 square feet). The stringers themselves were bent around frame wall jigs (just like we normally do), but laminated with 1/4" plywood/troweled on construction adhesive (Liquid Nails/PL type) and thousands of screws, at the direction of the client who has tried to reinvent many tried and true processes throughout this project.

The final skin was masonite and a great deal of Duraglass (tigerhair/bondoglass strand type filler), lots of bondo, and glazing putty. It was treated like an automotive paint prep except for wet sanding, of course. The laminating process just described yielded very poor results. The primer used for the scratch coat was shellac based, which is what was recommended to me to be a superior primer for hiding all the bondo-work and bonding to both bondo and masonite. And this heavy primer coat was sanded to 100g and then the HeatLock was rolled on with adhesive style paint rollers.

This is our seventh curved staircase. We would never have made something like this; it is a real mess, and at this point we're trying to make the proverbial silk purse out of a sow's ear. (We caul and clamp Italian bending poplar with Titebond 2 to make ours, and they don't require anything but a half day's sanding to prepare for veneer, which we also caul and clamp in our shop, rather than onsite.)

Back to my nightmare... The bond on our test piece at 74 degrees F and ironed on linen temperature (as hot as the irons will go) at approximately 2 minutes per square foot yielded a bond that actually couldn't be broken.

I hope our $68,000 + staircase bonds hold up so well! I can't even imagine how difficult it would be to veneer one in place. But I'm soon to find out, since this stair is double-stacked over another identically shaped curved stair below it. The one at hand is freestanding, the next (down below) is framed in.

This is why we chose the HeatLock iron-on adhesive in the first place. Is there a better choice? Is the WoodWelder the right tool for the job? The WoodWelder is a Workrite Industries product, right? Are these others you told me about better quality units? If one of these machines works as well as they are purported, one might be worth using back in our shop for future jobs (we'll never work for a DIY owner/builder again, like this). What adhesive would we use with the WoodWelder for our stair laminating and veneering operations?

From contributor D:
We have used one in our plant making office furniture. We were bonding solid wood edges on desk tops. We used a PVA adhesive for this. We never tried using it for veneer applications.

From contributor P:
Our Tregarne performs reasonably well on carcasses, but we aren't expecting the RF to penetrate more than a couple of inches (our dowels or biscuits are never deeper than that). Doesn't make much difference whether it is pine, oak, or MDF. When I was looking around to buy one a few years back, I did talk to one joinery shop (window maker) who reckoned that theirs would penetrate 4 inches in from the surface, but that was all.

Maybe I'm wrong, but I don't think that these devices will work on your HeatLock product, as that sounds like a heat (re-)activated PUR adhesive which contains no water. My understanding is that RF units work on the basis that the short wave radiation generated excites the water molecules within the glue (i.e. literally boils it), thus causing the glue to set on a localized basis. Once set, urea formaldehyde (plastic resin, Aerolite) or cross-linked PVAs (Titebond III?) simply don't reverse. Works well for us with these glues, but then we're looking for a permanent bond. The Tregarne machine has certainly sold well into certain sectors of the joinery trade here in the UK (notably window frame and coffin makers, both of whom are looking for a quick turn-around), so I reckon it would speed up your spiral staircase fabrication, too.

The WorkRite Industries WoodWelder is a different product to the Tregarne, although I believe technically very similar. WorkRites were available here at one time, but we haven't seen them in the UK for a long time now.

From Jeff Pitcher, forum technical advisor:
You can find all the information you need at workriteinc.com. I'd recommend using a urea resin for use with the Woodwelder and without it. It's strong and gives you a long open time. Plus, it's thermosetting, so you get no creep.

From contributor A:
I am not familiar with urea glue. Could someone explain to me what it is? I have been using West System epoxy for fifteen years and have never had a problem with it.

From contributor P:
UF or urea formaldehyde glue is commonly referred to as plastic resin glue in the USA, I believe. They were used, most famously, in the construction of the Mosquito fighter/bomber (or "wooden wonder") in WWII. Most UF glues I've used are one-part, although some, like Aerolite 306, are 2-part with a separate hardener. Aerolite 306 is commonly used in wooden aircraft/glider construction and also boat building. The main advantage to us of UF is that it is considerably cheaper than epoxy.

From contributor P:
The solid state RF Wood Welder machine is the Electrobond by Coaxial Power Systems in Eastbourne, Sussex.

From contributor R:
We recently purchased a Workrite Woodwelder. We have used it on D4 glue and recently on PUR with very little success. Based on the manufacturer's claim, the welded items can be worked on right after welding; not so in our case. We have conducted evaluations on strength after 24 hours curing, one using Woodwelder and the other using traditional method (clamping), and so far we have not achieved the joint strength that we normally get with the traditional curing. We find that it works well, though, for edgebanding.

From Jeff Pitcher, forum technical advisor:
If it isn't giving you an immediate bond, you are doing something wrong. First, I'd suggest using a UF resin. PUR won't work, as there is no water in it. Next, make sure the platens are going across the glue line and not perpendicular to it. You should see a small puff of steam after a second or two, indicating that the glue is cooked at that point. If none of the above works, contact Bob Meyers at WorkRite and he can fix whatever the issue might be.

From contributor P:
Contributor R, I think you're using an inappropriate glue. D4 (or polyurethane) has no water content, so RF won't work with it at all. The best results I've had have been with D3 (PVAc or exterior grade/cross-linking PVA) and UF/RF type glues.

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