Glue for finger joints

[Joe Hillmann]

A few months ago I had a person come into my shop we talked for a while and the conversation got around to me having a hard time finding a glue that I could use to glue up my finger jointed boxes that is quick, strong and doesn't make a mess. He told me about some airplane glue he uses that would work great.

He came back today and wanted to see the laser run so I threw in a scrap of wood and made a small box for him. When I was going to glue it together with wood glue he told me not to glue it yet and he ran into town and picked up a bottle of glue at the hobby shop. We did a bit of testing and it works great. It is real thin and runs like water and gets sucked into to joint. After it dried for ten or fifteen minutes the wood broke rather than the glue giving way. It holds stronger and is cleaner than the watered down titebond that I have been using up until now. The problems are, the joint has to be held together very tight for it to hold whereas wood glue would fill small gaps, it dries instantly if you touch it and it isn't something you want to breath.

The glue is Mercury Adhesives M5T I assume it is just a very thin CA type super glue but it works way better than other thin super glues I have used.

[Lee DeRaud]

I use CA of various viscosities for almost everything. The lower the number (5 is the lowest I've seen), the runnier it is. Most generic CA is what I would call 'medium-thick, in the 300-500 range. I've found that 50 is the best all-around, thin enough to wick in between pieces without disappearing into the pores and glue-starving the joint. One strategy that works quite well is to use small amounts of medium-viscosity to get everything together and stable, and then flood the joint with thin, letting it wick it in and seal the areas the medium couldn't get to.

[Joe Hillmann]

Lee, is that what the 5 in M5T stands for? I have tried other superglue that were labeled as thin but they didn't suck into the joint nearly enough.

[Glen Monaghan]

The thinner the CYA glue, the better/tighter the joints have to be. Also, it seriously wicks into endgrain which makes for weak joints. You can get thicker, even gel, forms of the glue that wicks much much less, will fill minor gaps, and won't require such tight clamping, but you're still better off not having large gaps in your joints. As I understand it, moisture on your skin causes it to "go off" when you touch it. You can speed up the set time in your work with a special spray, by sprinkling on a bit of baking powder, or just by breathing heavy on it, but rapid set frequently causes fogging of the normally clear glue. There are also low odor versions of the glue.

[Mike Null]

I believe a visit to the turners forum might prove to be fruitful with respect to using CA glue. I think most of them use it for several turning functions.

[Lee DeRaud]

Lee, is that what the 5 in M5T stands for? I have tried other superglue that were labeled as thin but they didn't suck into the joint nearly enough.

Probably. You usually need to go to a specialty store like Woodcraft or Rockler to get the really thin stuff...places like Home Depot only sell medium (sometimes mislabeled as 'thin') and thick. Or there's starbond.com, which sells five different viscosities from 2 to 2000.

[Chuck Stone]

Probably. You usually need to go to a specialty store like Woodcraft or Rockler to get the really thin stuff...places like Home Depot only sell medium (sometimes mislabeled as 'thin') and thick.

Plus, they've recently changed from 20g bottles to 15g bottles with no price change.
And if you're not REALLY careful, some of the bottles are only 4g! (but for 30% off)

The M5T is very thin cyanoacrylate (super glue)
I use thin CA all the time on finger joints. Depending on the brand,
if it is thin enough to wick into the joint, it works just fine. I don't
have to hold the parts together though.. the joints are tight enough
when the parts come out of the laser.

[Chuck Stone]

I believe a visit to the turners forum might prove to be fruitful with respect to using CA glue. I think most of them use it for several turning functions.

Yep.. it makes a nice glossy acrylic finish on pens, too

[Gary Gardner]

Something to keep in mind is that CA glue does not holdup to shock and deteriorates over time. After the glue really dries it becomes very brittle and if you drop the item it will come apart at the joints.

Gary

[Joe Hillmann]

Gary, How long until it becomes brittle? I know it probably varies but are you talking about months, years or decades?

[Chuck Stone]

Gary, How long until it becomes brittle? I know it probably varies but are you talking about months, years or decades?

I can tell you it isn't months, and I haven't had any problems over the last
10 years. Haven't checked anything beyond that.
(then again, I don't go smashing my things on the ground to find out,
so that might also be a factor..)

[Lee DeRaud]

I can tell you it isn't months, and I haven't had any problems over the last
10 years. Haven't checked anything beyond that.
(then again, I don't go smashing my things on the ground to find out,
so that might also be a factor..)

What he said: in the absence of strong UV, certainly years, probably decades. I've got blobs of it on my workbench dating back to the last century that show no signs of coming off without help from a chisel.

[Joe Hillmann]

Using this thin glue I found that anywhere there are two surfaces touching the glue will work it's way between them no matter how little you put on. That means if you tape your joints like I originally did the glue will work through the joint and then between the face of the wood and the tape which starves the joint of glue and ruins the surface I am working on. Also if you hold the joint and your finger is to close to the joint the glue will get sucked between your finger and the work gluing you to it and causing glue marks on the surface. I found that I can make a jig on the laser that is a friction fit but doesn't touch on any of the corners I can put the glue on so thick that it fills up the joints and begins to puddle in the inside corners of the box but nothing leaks through to the outside and the grain on the outside also doesn't soak it up. With the jig I can now glue up a box that used to take several minutes in less then a minute, which is kind of important because the laser can cut the box in 1minute 19 seconds.

[Mel Fulks]

Sounds like prices on those houses will get even more affordable!

[Chuck Stone]

Using this thin glue I found that anywhere there are two surfaces touching the glue will work it's way between them no matter how little you put on. That means if you tape your joints like I originally did the glue will work through the joint and then between the face of the wood and the tape which starves the joint of glue and ruins the surface I am working on.

With such a thin CA you may not need much.. since it will wick into
(and essentially become part of) the wood itself. In that case I don't
think you would need to tape the joints anyway.. not like you would
with another glue type.