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Power Hack Saw help needed
Looked at all the different ideas on here for making a "Power Hack Saw".
Ended up liking the idea of the one with a frame at the back more than the conventional "Slide" type.
Think there is going to be too much play on the slide and if you set it tight enough to stop the play a lot of power will be used just to overcome the friction.
Has anybody got some dimensions for this type of saw?
Basic givens...
300mm x 25 Starett 14T blade
Stroke 200mm to use maximum of the blade.
That means the crank moving the blade has to be 100mm.
That dictates that the pivot for this crank must be about 120mm above the base plate.
Link from crank to saw blade frame also about 120mm.
Just going to cut this all 1:1 from cardboard and figure out the frame and rear frame dimensions.
Was thinking of using bearing ends as the bearings of the rear frame, setting them up so I can use their tread to fine tune the saw to cut square.
Anything major I am missing?
Google 'straight line machines' to find one that might work for you.
Quote:
Originally Posted by
garage nut
Looked at all the different ideas on here for making a "Power Hack Saw".
Ended up liking the idea of the one with a frame at the back more than the conventional "Slide" type.
Think there is going to be too much play on the slide and if you set it tight enough to stop the play a lot of power will be used just to overcome the friction.
Has anybody got some dimensions for this type of saw?
Basic givens...
300mm x 25 Starett 14T blade
Stroke 200mm to use maximum of the blade.
That means the crank moving the blade has to be 100mm.
That dictates that the pivot for this crank must be about 120mm above the base plate.
Link from crank to saw blade frame also about 120mm.
Just going to cut this all 1:1 from cardboard and figure out the frame and rear frame dimensions.
Was thinking of using bearing ends as the bearings of the rear frame, setting them up so I can use their tread to fine tune the saw to cut square.
Anything major I am missing?
Actually, slide bar machines are most suitable for these machines. Using the slide bar as the reference the crank that drives the connecting rod to extend and return the blade holder shaft center needs to be set so that it is below the location of the point where the connecting rod connects to the moving blade carrier, and the rotation direction is set so the blade is drawn in the cutting direction, pulled, as the crank end of the connecting rod is moving over the the top of its travel, the blade is then moving at a relatively slow speed. As the crank continues its rotation it is pushing the blade away and the connecting rod is angled up to the blade carrier, reducing the down pressure on the blade and reducing wear on the teeth as they back off. In commercial machines, there is a cam and ratchet mechanism that actually lifts the blade off the work on the return stroke so as not to wear down the teeth. without a lift mechanism, the teeth will be worn down quickly. With a hardened steel tooth blade, I would recommend limiting blade cutting speed to 100 surface speed per minute for maximum blade life without coolant, and maybe 150 sfpm if flood coolant is used.
The best source for design information may be the patent office, and since most, if not all relevant patents are no longer enforcable, you are free to copy the devices exactly. In the US, even a still valid patent does not prohibit you from making one for your personal use, you just can't make them to sell. I don't know anything about the patent law elsewhere.
The slide bar free play can be eliminated by using a leaf spring on one side and under the bottom of the slide bar in the moing carrier, and grease on the slide bar.