In this article, we will be exploring the strength of different joints - biscuit joints, dowel joints, and domino joints. This experiment follows a previous strength test video where the strength of glue was compared with and without biscuits. The results of that experiment were surprising, so let’s dive into this follow-up experiment and see what we discover.
The Experiment
For this experiment, the creator used 18 millimeter hardwood plywood as the test material. Solid wood side grain joints are known to be stronger than plywood end grain joints due to the alternating grain direction in each layer of ply. The goal of this experiment was to test the strength that biscuits, dowels, and dominoes add to a glue joint, rather than the strength of the glue itself.
Test Scenarios
The creator used six different test scenarios to compare the strength of the joints:
- Wood glue only
- Wood glue with size 20 biscuits (two biscuits in the test piece)
- 8 millimeter by 40 millimeter dowels (three dowels in the test piece)
- 10 millimeter by 40 millimeter dowels (three dowels in the test piece)
- 5 millimeter by 40 millimeter dominoes (two dominoes in the test piece)
- 8 millimeter by 50 millimeter dominoes
Each test piece was clamped up in the same way, applying approximately the same clamping pressure. The glue was allowed to dry for 24 hours in a warm room to ensure full curing. To check the strength of the joints, a pair of bathroom scales and clamps were used, along with a camera to monitor the clamping pressure applied to each joint at the point of failure.
Test Results
Glue Only
The test with glue only showed that PVA wood glue on its own is incredibly strong. It managed to withstand 66 kilograms of clamping force before breaking. This test also reinforced the finding from the previous experiment that glue without biscuits is slightly stronger than glue with biscuits.
Dowel Joints
The dowel tests showed that dowels do add strength to a joint. Three 8 millimeter by 40 millimeter dowels reached a peak clamping force of 71 kilograms before the glue joint failed. Even when the glue joint failed, the dowels remained intact. Similarly, the test with three 10 millimeter by 40 millimeter dowels showed a peak force of 74 kilograms.
Domino Joints
The test with 5 millimeter by 40 millimeter dominoes was surprising. The dominoes only reached a peak force of 56 kilograms, which was lower than expected. Both the glue-only and glue-with-biscuits tests performed better than the domino test. However, it is worth noting that the dominoes themselves remained intact even after the joint broke.
The test with 8 millimeter by 50 millimeter dominoes reached a peak force of 67 kilograms. While this was slightly stronger than the glue-only and glue-with-biscuits tests, the domino joint still failed sooner than the dowel joints.
Analysis and Conclusion
Based on these tests, it can be concluded that PVA wood glue is incredibly strong on its own. Biscuits, on the other hand, are primarily used for alignment rather than adding strength to a joint. Dowels and dominoes seem to offer similar levels of strength, especially considering they are both made of solid beech.
However, it is important to note that this experiment was not scientific and the results may vary. Factors such as inconsistencies in the glue-ups or plywood could have influenced the clamping force results. Additionally, solid wood side grain joints may perform differently than plywood end grain joints.
In terms of practicality, dowel joints take more time and effort to produce and align correctly, even with a good quality doweling jig. On the other hand, the domino jointer offers speed and efficiency in creating perfect floating tenon joints.
Overall, the choice between dowels and dominoes depends on the specific project’s requirements and the woodworker’s preferences. The strength provided by both types of joints is likely sufficient for most applications.
In conclusion, this experiment provided valuable insights into the strength of biscuit joints, dowel joints, and domino joints. While dowels and dominoes seem to offer similar levels of strength, other factors such as speed and ease of use may influence the choice between them. For those seeking optimal strength, solid wood side grain joints may offer the strongest results. However, it is important to conduct further tests and experiments to fully understand the capabilities and limitations of each joint type.
If you found this experiment interesting or entertaining, consider subscribing to the creator’s Youtube channel for more weekly woodworking videos. Support for the channel is also available on Patreon, with benefits such as early access to videos, exclusive content, project plans, and name credits in videos. Happy woodworking!
