PDA

View Full Version : Power Hacksaw Return Stroke



alsinaj
02-10-2004, 11:35 AM
Have been mulling over various home-brew power hacksaw designs. Most have some provision to "lift" the blade on the return stroke.

Is the intent to reduce wear on the blade, or to avoid hardening the work on the return stroke, or both?

Is this feature "nice to have" or "must have"? Do you have to lift the blade off the work, or just relieve the pressure somewhat? How much lift is enough?

hms50
02-10-2004, 12:46 PM
Hi!,
years ago, I had a sears power-hacksaw that used a cam to lift the blade on the back-stroke. If memory serves, the lift was only enough so that the teeth did not contact the metal being cut. As a shop teacher, I've seen many new hand-hacksaw blades ruined in very short order by students who did not release presure on the back stroke. It also is important to not exceed about 60 strokes/second or the blade will over heat. If you are going to build a saw, a lift mechinism will not be that big a deal and will make the blades last much longer. Besides, it's neat to watch the blade lift!
Good luck,
hms50

wierdscience
02-10-2004, 08:49 PM
Yes you do need blade lift on the return stroke,but like mentioned above its not hard to do,it can be made on as part of the eccentric.

PolskiFran
02-10-2004, 09:56 PM
My first power hacksaw did not have any lifting mechanism for the blade and boy did it go through blades. It got a little expensive buying 1"x12" blades. I also had a Robertson Economy power hacksaw. This unit had a hydraulic lift mechanism for the return stroke. My friend's craftsman saw had a cam type arrangement with small fingers that worked their way down a rack to prevent over feed.

Frank

spope14
02-10-2004, 10:08 PM
I think my old Racine is by now a 1988 through 2003 Racine Hacksaw with nothing that is original but the bow and base casting. I have had to make parts for this one forever....I love it....

The cam lifts the blade off the work on the return stroke to keep from stripping the blade and removing the "set". It would seem the "set" might be removed by the kerf walls, but this is not exactly true, if a saw runs back in a cut, the set will rub and try to create cutting action anyway where if it is out, it just rubs the walls it has cut with no "up pressure" on the blade.

I checked this out - believe it or not - to prove why to come back easy on a regular hacksaw, and then saw it again in the same book on machining for the Racine I have - very old book, but my best resource.