Thread: using M8 SS wood inserts..

If the work pieces are splitting at the recommended and slightly oversize pilot sizes then I would suggest that they are highly likely to split at some time in the future if the anchor is coaxed into the wood at installation using a clamped caul or similar compression.

So much depends upon the wood species, the application and the loads applied to the anchor joint, especially racking force loads, and the direction of the applied forces relative to wood grain direction. Shear or uplift / down force loads may be ok in some directions.

Wood also moves seasonally, even daily in response to the environmental moisture content of its surroundings. If the anchors are an attempt to restrict wood movement (expansion, cupping or bowing) of a table top like surface then those forces created by EMC expansion & contraction alone may be sufficient to split the material surrounding the anchor over time i.e. failure. Again so much depends upon design and construction details.

Thanks for your insight.

The join is a pretty basic mortise tenon with a drawbore so I suppose there's a load vertically and horizontally so to speak.

do you think using inserts of a 'softer' material eg zinc instead of stainless steel would be less prone to split the wood.

the 'split' is lifting a surface layer/s around the hole - rather than splittingor cracking from top to bottom.

Thanks again.

Softer insert material won't make any difference. Clamping might work but I would experiment first.

Here's a trick I have used for that surface type splitting and it involves turning one of your inserts into a 'tap".

Take one of your inserts and insert it onto the a short length (50mm) of spare hex key. You can epoxy it in if you like.
Place the key into a metal lathe and turn a light/shallow taper onto the outside of the insert
The outboard end of the insert will need support by a live tailstock.
The shallowest part of the taper will need to be towards the outside section of the insert
Use a Dremel with thin metal cutting disc to cut slots right across all the inset threads.
Then use the slotted insert as a sort of a threading tap to partially thread the hole.
You will have to repeatedly tap a little and then remove the tap and clear the dust in the slots.
Using it at slow speed in a portable drill works.

If you don't have a metal lath a rough approximation can be obtained by putting the hex key into a power drill or wood lathe with a chuck, and grind or file the taper.
The taper does not have to be accurate it just has to be able to par form the threads near the top of the hole to reduce the likelihood of splitting.