I just picked up an old Keller mechanical lift hacksaw. It's a very
handy size for the garage and takes blades a little over a foot long
and it's very heavy for it's size. It looks complete and lifts on the
return stroke using cam, rack and gear and two finger catch. I fingured
everything out except why they use two fingers for the mechanical lift
mechanism.

Thanks.

wrote: (clip) I fingured everything out except why they
use two fingers for the mechanical lift mechanism.
^^^^^^^^^^^^^^^^
You're talking about a pair of pawls running side-by-side on a single
ratchet? If you look closely, I think you'll find that the tips of the
pawls are spaced half a tooth apart. One pawl does the lifting until the
cut sinks by half a tooth, and then the other pawl takes over. This gives
you the same result as having the ratchet twice as fine, but without the
fine teeth. More rugged.

Thanks for explaining that. The one thing that bothers me about this
saw is when it is done cutting it drops very hard and seems like the
pawls and sprocket are getting abused at the time they release.

Thanks.

On 27 Jan 2006 10:18:50 -0800, wrote:

Thanks for explaining that. The one thing that bothers me about this
saw is when it is done cutting it drops very hard and seems like the
pawls and sprocket are getting abused at the time they release.

I don't know about Kellers, but isn't there usually a hydraulic damper ?

In some designs there's a near-vertical cylinder with a short
barrel-shaped piston, hung from a pivot on the hacksaw frame. Oil in the
cylinder is forced through a hole in the piston, slightly damping the
descent of the hacksaw.

There's also a pin mounted in the bottom of the cylinder. When the
hacksaw cuts through and the piston drops, this blocks most of the
piston's oil hole, increasing the damping for the bottom of the fall.