Bearing fit into aluminium tube, and tube into wood.

Can't you simply countersink a bearing into the wood an either friction fit or a small amount of adhesive to hold it?

Does the alu tube do anything other than hold the bearings?

Proper bearing bore press fits at the size of bearing you're using are around 10 microns under the nominal size of the bearing (which is usually 0\-8um ish).  You won't hit the correct spec without a lathe.

However, thin wall tube will distort a fair bit, so get the hammer out.  Easier solution would be to buy a loose bearing headset as the cups are a bit more tolerant than normal bearings.

My concern with that was the bearing working loose in the wood over time, whereas the aluminium tube would spread the load within the wood and hopefully stop it working loose. May be totally wrong though!

I think I've used H6 tolerance in the past for press fit bearings, using heat/freezer/press to fit. For 22mm that works out as 19.987-20.000, so 19.9935 nominal. If you go for bang on 20.000 use 638 bearing retainer, although not ideal if under side loads.

Slap it in with epoxy and it should be fine for a decade. I glued my sisters dol to the patio and you could still see bits of the doll there when they dug up the patio

Gluing  - Aerolite 306 Or Polyproof totally waterproof glue. Either will survive anything, even leaving the bike out in the rain

Rough up the alloy tube before applying glue to it.

As you want a tight fit, I'd make the tube overly long, so you can hammer the end in and not care about damaging it. Then saw that off flush and file smooth.

I'm pretty sure Aerolite 306 won't stick to aluminium ???

I'd use epoxy - maybe even epoxy the bearings directly into the wood (carefully), without the need for an alloy tube.

I’d use epoxy – maybe even epoxy the bearings directly into the wood (carefully), without the need for an alloy tube.

This, but I'd make a few nicks in the outer face of the bearing with a grinder to give the epoxy something mechanical to hold onto.

Would it be easier to do away with the bearings and run a bolt / shaft through a wooden tube that is bonded in? I think that, or similar, is what Easy Rider do on their wooden bikes.

Thanks all - frogstomp I did think about that but was also worried there would be a bit of slop or you'd have to do bolt up tight to get rid of slop and there'd be loads of friction) - or over time the bolt wears away at the wood

Not sure how well the alloy tube will stand up if it's soft enough to drive the bearings into? Maybe just set the bearings into the headstock using JB Weld - but either way, add a length of tube between the bearings (same OD as the inner race) so you can tighten up the yoke bolt properly.

(Apologies if this old news/granny sucking eggs etc).

I reckon if you've got a decent block of wood for the headstock, sandwiched between the outer layers of ply and you drill for the bearings with a nice sharp Forstner bit and glue them in appropriately it'll be plenty strong enough to cinch down on.

It's a balance bike for a kid that'll grow out of it after all, not Gee Atherton's Rampage bike 😊

The frame I made / Lidl fork just ran on a long bolt. Can't remember if I put a tube in the frame. There is no front brake so headset slop isn't noticeable. Will go have a look.

Bolts are stuck as last touched 18 years ago.... From memory I think it is a pair of short top hat bushes in the frame. Still steers fine and no play.

I have also once made a wooden frame but that would be overkill - bonded on stainless spreader brackets with 20mm stub tubes for a normal headset.