Thread: Advice on biscuit usage

I am a fan of biscuits with a small proviso; I don't touch Australian made biscuits except when they are used for alignment purposes only. Biccies were invented in Europe and were quickly adopted by the US soon afterwards; the biscuits from both continents are made from compressed beech which has excellent strength. Unfortunately an Australian company decided that hoop pine would be a good substitute; presumably this decision was based on... actually I can't imagine what particular lunacy influenced that decision. The result was a glut of slightly cheaper biscuits flooding the market with all the inherent strength of Weetbix. When professional furniture makers state that in their (usually considerable) experience they have found biscuit joints to be as weak as wee-wee, my first question is "were the biscuits you used made in Australia?"

The Big Green Shed sells "Haron" branded biccies; these are from the US and are made from beech as they should be.

However; no biccy will be any good if it is fitted incorrectly or subjected to tension loads. In the case of a cabinet door with mitred joints the joint is only weak if the frame is subjected to racking; providing you desist from using the door handle as a swing all will be good. The hinges should fail well before the frame comes apart! Your design will be able to resist all racking loads providing you cut the slots properly...

When fitting biccies make sure the slot isn't cut too wide; the biscuit should be tight in the slot when fitted dry. The more expensive cutters achieve this quite easily but cheaper units like Aldi often have a lot of slop in the mechanism allowing the blade to wobble in use; making the slot wider than it should be. It doesn't mean the cheaper ones are useless; it just means that you really need to practice using the machine on lots and lots of scrap timber to perfect the way you hold the machine while plunging. At the same time use this opportunity to correct the plunge depth; the blade should plunge just a bee's winky deeper than half the depth of a biscuit. I tune mine by cutting a slot and fitting a biscuit into it, then drawing a pencil line across the join. Pull biccy out and reverse; the pencil line should have just vanished into the slot. Draw a second line across the join then pull it out. The two lines should be no more than 1mm apart.

When applying glue I use a thin stiff bristled brush to paint the entire inside surfaces of the slots and also paint the biscuit surfaces. This is time consuming so you need a glue with a good working time; Selley's External Aquadhere and Titebond III have given me good results for PVA. Polyurethane or epoxies will give you more open time but are more expensive, messy and harder to clean up.

Proper cabinet joints such as mortice and tenon are of course considerably stronger.