Alternatives to Biscuit Joint

[CW]

Miller who?

[lwasserm]

There are cabinet shops near Beverly Hills?

Seriously, Lamello biscuits are certainly high quality but there are several other brands that produce equally good results.

[nailshooter41]

And yet, there are those that empirically resist your conclusions, refusing to "get over it". There are those of us living on the edge that believe that the lowly biscuit, tool of the hurried craft/trade person add strength to >certain< joints.

A good discussion brewed here long ago, but not out or my memory:

led to a shopworn article that seemed to me to be well thought out and was actually a controlled experiment:

we can see that the biscuit has it shortcoming... superior to doweling in corner joints, but of almost not value according to this treatise for the corner joint as it pertains to furniture making:

felt like the sum and substance of the above referenced materials satisfied my own curiosity about the biscuit joint controversy long ago. I didn't see any requests for money or blatant advertisements soliciting funds at any of these sites, so I don't think there is much need for conspiracy worries. Sadly, I was unable to find the MIT test that was printed about 5-7 years ago where the compared biscuits, mortise and tenon, dowel, and "loose dowel" joinery. Two or more biscuits carried the day on all but mortise and tenon in solid wood, but the biscuit prevaled in joining baltic birch.

I included the above links because I know this group has many practicing engineers that would be anxious to see actual data, whether they believed in the results, methods, conclusions, etc. or not.

For me, this was my test:

Edge jointed two pieces of 1X12 yellow pine 30" long with biscuits, and did another set the same without biscuits. Ripped and glued the same test materials as above out of 3/4" (nom.) cabinet grade birch ply. Biscuits were set on +/- 6" centers. Glued with TB2, and waited a week. Actually until the next weekend when my fellow scientists could join me.

Put the panels between two sawhorses, resting about 1/2" on each edge. Centered on the joint, I rested a piece of 4X4. the length of the panel so that it would directly stress the joint. Not having the best lab, I settled on cinder blocks (CMU) as weight to stack on the 4X4. Lots were left from a deck job, so they were on hand.

In both cases the plywood and the panels held more weight (if memory serves correctly it was two - three blocks) more with biscuits than without. In fairness, while the glue joint cracked on the yellow pine samples, neither gave way. The 1X12 broke in the field whether it had biscuits or not. So in this case no conclusion was drawn except in the case of the glue joint crack, which could mean that the joint with biscuits which had not perceptible cracking was marginally stronger.

The plywood was the clear winner. It was smoothed over the jointer to ensure a proper edge to join before glueing. The biscuit jointed edge was significantly stronger (3 blocks?) than the edge glued material that received no biscuits.

I am no fan of the biscuit; it has it uses. But to adamantly declare a "truth" saying it is nothing more than an alignment tool is silly.

As always, your mileage may vary.

Robert

[Robatoy]

You keep mentioning epoxy. I have used epoxy in the past when building torsion boxes. Legless tables sticking out from the wall at a donut shop was one such project. I used Gougeon Bros WEST and found it hard to work with... very runny and thin without much gap-filling ability. No matter how accurate I made the lattices, I still didn't get a 'super sandwich'. Vacuum bagging and regular adhesive worked better for me. But... I still like the concept of epoxies. Now, I am somewhat aware of microballoons and newer, more viscous epoxies. Can you give me a jump-off point, supplier, website of some outfit you are familiar and happy with? When I DAGS, I get tons of info, but virtually zero 'hands-on' reports. I do know, that epoxies stick to solid surface materials like dog snot to screen door.

TIA.

r

[Andy Dingley]

So why didn't you fill it? Gougeon recommend this (read their boat building book - it's excellent) and they'll even sell you the varied filler materials to do it with. They rarely recommend their own plain product used unfilled for anything with any sort of gap.

Mind you, I do torsion boxes in a vacuum bag. So long as the skins are stiff enough and the spacing close enough to avoid "starved dog", then I get a good gap-free bond with any adhesive.

[Robatoy]

Gougeon Bros are just up the lake a ways from me here and the WEST stuff is available in a few of my dealers' stores, so I just bought some and didn't really study the application that much. There have been a few requests for kitchen islands with an overhang for stools which go beyond the allowed dimensions for solid surface materials. I do not like the look of brackets, so back to the torsion box idea.

I'm not sure what you mean by 'starved dog', but I am guessing that you'll see the ribs if one uses a thin skin. I have been using 3/8" Baltic Birch ply with poplar ribs 3/4"x 3/4" making 4" cavities.

Speaking of vacuum bags, 1/2" acrylic solid surface, such as Corian, Wilsonart Gibraltar, Staron, Meganite vacuum form very nicely. The hard part is getting the temperature 'perfect'.

[Lew Hodgett]

Gougeon is right out your back door and they have good tech service which would make them a good choice for resin.

You want their standard resin and slow hardener.

Since you are buying small quantities, it won't be cheap, but the price won't be too bad.

Fillers, OTOH, are another question.

I use Pacific Coast Chemicals which cover the western US.

Freight should be NBD, since UPS can handle it.

Micro-balloons (Dic-A-Perl, HP500) come in a 30# bag and should be less than $30.

Cab-O-Sil comes in a 10# bag and should be less than $90.

You will be cold and in the ground before you use all of the above.

HTH

Lew

[Lew Hodgett]

Further thoughts:

Gougeon sells hand pumps for resin & hardener to insure proper mix ratio which I'm sure are very handy; however, I've never used them.

I use mixing cups (See below).

If you are going to mess around with epoxy, the following are almost mandatory items.

Boxes of surgical gloves, 2" chip brushes, and plumber's acid brushes.

Strictly single use items.

Watch for the Harbor Freight sales and stock up.

1Oz, 2OZ, 4OZ, 10OZ, 16OZ, 40+OZ cups (No Styrofoam)available at a restaurant supply house.

Popsicle sticks or scraps from the table saw for mixing sticks.

Home Depot furnishes me a lot of paint sticks.

Working with epoxy includes some "black art" which is the type and amount of filler you use for a specific job.

Strictly OJT.

I almost never use just straight epoxy unless I'm laminating some glass which is totally different than gluing wood together.

HTH

Lew

[jcatora]

Micro-balloons and Cab-O-Sil are non-structural fillers generally used for 'fairing' smooth transitions between adjoining surfaces (like fillets between wings and airframes on aircraft). They will thicken the epoxy but provide no real strength advantage (and could actually weaken the joint, since they displace the resin).

For a true *structural* filler (that will also provide some thixotropic (thickening) properties), use chopped fiberglass or kevlar (available from various sources - would have to dig a little, but might could find some) - and, even, cotton flocking. I've got some samples of 1-2mm chopped kevlar 'flocking' that, added to epoxy resin at the rate of

1/2% (i.e. 0.5% --by weight) will *triple* the strength of epoxy. It's that good (this per DuPont lit).

-- john.

(in my 'other life', I do rocketry and trying to find 30,000 feet at Mach 3 will force you to find ways to make epoxy do things most folks are unaware of).

[Lew Hodgett]

Without question, aircraft applications are a different world. I imagine Dick Rutan could provide a lot of info about those types of application.

However, we are talking about wood working here.

The basic strength of epoxy far exceeds the strength of standard wood working adhesives so using some micro-balloons with the epoxy is NBD, IMHO.

If you have an application that requires more strength, add fabrics such as knitted glass, carbon, Kevlar, etc; however, doubt you will need such for wood working.

That's part of the "black art" of epoxy.

Lew

[<marierdj]

The basic strength of epoxy far exceeds the strength of standard wood working adhesives so using some micro-balloons with the epoxy is NBD, IMHO.

I agreed with this statement. However, the structural strength of the bonding is greatly subject to the type wood, lumber or plywood.

In this case, we are talking about maple plywood. I may I missed some posts but I do not know what type of wood is used for the core of this maple plywood. In many instances, the core is made with softwood (not rated as first class) and may have some void. The only hardwood maybe the top surface. Very few manufacturers are making hardwood plywood with a hardwood core without void.

If epoxy is used to bond Harwood plywood made with softwood core and unknown voids mechanical fasteners will be required in order to have a good structural bonding. In some circumstances, a solid wooden carcass/skeleton is necessary.

As for aesthetic look rabbit and dado joinery with carpenter glue and metal screws may well suit the bill for this project A matching wood tape could be used the hide the plywood core.

[J. Clarke]

Don't confuse the bond strength with the bulk strength. Epoxy in bulk is fairlys strong, but when you add microballoons you turn it into something approximating foam--that's the whole purpose of microballoons, to provide a lightweight filler in applications where high strength is not required.

Effectively if you're using epoxy and microballoons to fill a gap you're bonding two pieces of wood together with a piece of styrofoam in the middle (yeah, chemists, I know that's not precisely correct) and no matter how strong the bond between the styrofoam and the wood, it remains styrofoam without a whole lot of strength of its own.

Lot of stuff out there made with plywood and glue of various kinds with no mechanical fasteners that has been holding up very well for decades. While there are voids I think you are exaggerating their importance--the typical voids in commercial plywood are going to degrade the joint a good deal less than the microballoons.

[Andy Dingley]

Aren't they also one-shot items? I remember they were for polyester resins and kayak making.

I measure my hardener by eyeball, or with a S/H digital lab scale if I'm mixing a lot or want to be accurate. Instant tareing is a wonderful thing.

Mine are a soft "waxy" plastic - polypropylene ? Originally sold as packaging for screws. If I leave the epoxy a day and then flex the tub, it flakes clean off.

My ubiquitous bamboo chopsticks. I only eat icecream in the Summer, but I can go out for noodles all year round. I never leave our local noodle bar without pocketing the chopsticks. They turn up in everything afterwards - drive them through a dowel plate and they're great for pegging tenons.

I'd add that microballoons are also usable as a structural filler. They don't add strength per se, but they certainly lighten a large fillet and improve the strength to weight ratio. Model rockets was where I first used them.

As for Kevlar, I use this a lot as a filler material. I start with offcuts of sheet material (I sew my own Kevlar clothing and luggage) and then cut 1/2" diagonal strips. As it's a loose weave, these easily tease apart into loose fibres and then get thrown in a bag in the epoxy crate. Excellent stuff for strong fillets, or for repairing loose tool handles.

[jcatora]

If the strength far exceeds , then it doesn't really make a lot of sense to use it -- all that 'extra strength' is, fundamentally, wasted. Just use Elmer's or Gorilla, etc. (I would be inclined to agree this may be overkill - but, then, to answer that question intelligently would require a little more info into the application)

My point in responding was that one poster commented about the West Systems being too thin - and then the followups about using fillers. If one is going out to buy a filler, might as well go ahead and get/use a structural one (assuming the cost is roughly the same). Cotton flocking is amazingly inexpensive (not shown in below link) - but is a pretty decent structural filler.

According to Fiberglast (see link), using Kevlar would be very little cost differential than any of the non-structural fillers. But, again, this may be moot (as you note) -- just use a more conventional adhesive.

Several fillers here....

john.

[Lew Hodgett]

You must have missed the start of the thread.

Basic reason to use epoxy in wood working applications is "open time".

The fact that epoxy will stick to damn near anything and provides increased strength are side benefits, not the primary reason to use them.

As far as fillers are concerned, Cab-O-Sil adds some strength, but does absolutely nothing for vertical hang time and is a absolute bitch to sand.

OTOH, micro-balloons, extend open time, provide vertical hang time as long as you don't exceed about 1/2" per pass, without sagging.

None of the above means anything to anybody except a boat builder.

Some basic resin thickened as required for the application with micro-balloons, which usually means hang time, will satisfy 90% of all wood working applications, the basic exception being white oak.

White oak and epoxy are not compatible, need the purple stuff, resorcinol for that.

As far as other fillers are concerned, don't see any application in wood working or even building boats.

SFWIW, got a 10 lb box of 1/8" chopped glass when I started building the boat. Must have at least 8 lbs left.

If I need added strength, I use the appropriate cloth and wet it out.

May not be a good approach for space ships, but I'm not building them.

Lew

[Robatoy]

Lew Hodgett wrote: lots of good stuff about epoxies.

I appreciate the discussion on epoxy quite a lot. I find myself in situations like that the odd time where I need to glue aluminum, solid surface material, wood, glass.. like a jeweller's display case recently. Composites are fun. I used to experiment with a lot of different materials in the creation of woofer cones.

I have to ask: what's up with white oak and epoxy?

Again, thanks for the input.

r

[Lew Hodgett]

NBD, just keep your 24 grit, right angle sander handy to rough up all those funny surfaces before you epoxy them together.

Have nothing to offer.

Don't know for sure, suspect it has something to do with the tannic acid.

Lew

[imp2aca]

Otherwise, with 3/4" ply, it's going to sag in the middle.