He makes it clear that his application was the error but he wrongly diagnoses the error. The error is that hardwood or its equivalent are needed to support the use of the horn.

The equivalent would be to drill the hole and then saturate the wood on both sides and into the hole with thin CA. This would require using an L-bend awl in the hole and lifting the covering away from the wood and flowing thin CA around the area, doing so on both sides.

A good ARF will provide a hardwood insert but sometimes the builder chooses another area for the horn. If the arf does not have the hardwood insert, then the equivalent must be provided as outlined.