The internet's first question about any combo axe is the right one: doesn't a hollow handle just break?
A drilled-out solid handle does. You removed the fibre that was carrying shear through the eye and you left a thin wall of wood that splits on the first ugly overstrike. That is why “saw in the handle” has a bad reputation. The reputation is earned.
A tube is a different object
Bending stiffness of a section scales with the fourth power of distance from the centreline (second moment of area). The material in the middle of a solid helve was barely working. A closed tube keeps the material that was doing the work and throws away the material that wasn't.
What a tube can do is dent, oval, and buckle locally under a hard strike. Those are the real load cases. They are also the ones you can design for.
Put the saw back in as structure
HELVE's spine rail slides the full length of the bore and is clamped at both ends — head collar and butt cap — in axial compression. Clamped, it is an internal mandrel. It resists ovalling and raises the local buckling threshold of the wall.
Result, in axe mode: the handle is a tube-plus-core composite, not a hollow tube. Result, in saw mode: the tube is empty, and you are not hitting anything with it. The empty state and the strike load never coincide. That coupling is the invention.
A hand tool comprising a striking head and a hollow handle, wherein an elongate saw spine member is removably received within the handle bore and, when received, is retained in axial compression between the head collar and the butt closure such that it functions as an internal structural core of the handle.
Draft independent claim language. Not filed. See the honesty section.
The curve is in the skin, not the spine
A telescoping rail cannot pass through a bend, so the bore is dead straight. The swept grip — 14 mm drop, fawn's-foot flare — is built in an asymmetric section and a variable-wall overmould. Same geometry a curved wooden helve has always used to index the hand and neutralise the wrist. The invention is untouched.
Two risks could still kill it
- The head joint loosening under sustained impact.
- The tube denting from a glancing overstrike.
Both get answered on the impact rig: 10,000 strike cycles on the joint, published either way. If either fails and cannot be fixed, every pre-order is refunded in full, automatically. We will not ship a compromised tool to clear a deadline.
Why not wood: humidity moves it; it cannot hold the bore tolerance. Why not fibreglass: local dent case at this wall thickness. Why 7075-T6: it can do both, and Type III hard anodising handles abrasion. The cost is shock transmission, mitigated with a 4 mm nitrile isolator and dual-durometer TPE, to be measured against a wooden-helve control.