How Strong are Biscuit Joints? Test Tuesday! [148]

Have you ever wondered what difference it makes using biscuits in a woodworking joint? Do they actually make the joint any stronger? How strong are biscuit joints? Today I’m having a look at edge-grain to face-grain biscuit joints in MDF to see how strong joints are with and without biscuits.

Watch the full test video here:

Tools & products used

  • DeWalt DW682K Biscuit Jointer (UK / US)
  • Festool Quick Lever Clamps (UK / US)
  • No. 20 Biscuits (UK / US)
  • Titebond II Wood Glue (UK / US)

Please note that I used UJK Technology biscuits from Axminster Tools.

Introduction

A while ago, Keith from the Rag n’ Bone Brown YouTube channel did a very interesting test on end-grain to end-grain biscuit joints and actually found the joint was weaker in MDF! Here’s a link to Keith’s original video and awesome test. Today I want to know how strong biscuit joints are in and end-grain to face-grain test – a really common joint in cabinet making and shelving.

Test specifications

If you want to play along at home (or at work if you have fancier test equipment than me!) you should be able to re-create this test from the information below:

  • MDF used: Trupan 18mm non-MR
  • Biscuits used: UJK No. 20 biscuits
  • Glue used: Titebond II (clamped for 24hrs)
  • Size of back test piece: 142mm x 190mm
  • Size of front test load piece: 142mm x 50mm
  • Distance of base to start of joint: 50mm
  • Metal L-bracket location: Central to underside of test load piece
  • Biscuit location: Biscuits are located with 2mm gap to edge and approx. 2mm gap in middle

How strong are biscuit joints?

The loading was applied as evenly as possible directly above the pull-point on the test piece of MDF using my very unscientific load measuring jig. Results below:

  • WITH BISCUIT: 45.3kg
  • WITHOUT BISCUIT: 44.5kg

VERY close results and I suspect if I repeated this test a few times the results would get even closer. Kind of good news that the joint wasn’t weaker as a result of the biscuits, in this case… but still, VERY close.

So what happens if you don’t bother using clamps??