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  1. #1
    garage nut's Avatar
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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?
    Attached Thumbnails Attached Thumbnails Power Hack Saw help needed-saw-scetch.jpg  

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  3. #2
    ncollar's Avatar
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    Garage Nut
    Send me a PM and I'll send you several sets of plans ofor a power hacksaw.
    Nelson


    ncollar1957 (AT) gmail (DOT) com

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  5. #3
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    I have tried to build a power hacksaw, bought the motor and 24" Bahco hacksaw blades and every thing. was planning to use I beam to make the base and 4"x 2"box for the bow, then realised a bandsaw is a greater beast. at a 300mm stroke you will be able to cut a maximum of 6" wide at best, if you want to cut at 45 degrees then that's a whole new challenge. If you go down the route of a bandsaw then technically you can make it as big as you want - i was looking to cut I beam and 12" pipe so making a saw for a 18" throat wouldn't be such a big issue. There are standard blade lengths off the shelf, ok they can cost between $20 upwards but far cheaper than the beefy hacksaw blades, which incidentally always wear in the same place - the middle. The idea is still burning a hole in my head and not being burnt out of steel yet. I'm limited for space, there are 66 million people living in the UK in a country a quarter of the size of Kansas - it gets a bit cramped when you need a bigger home shop. I'm thinking a Ranch would be about the smallest piece of real-estate that could house all my ideas and projects.
    Ill be interested in seeing how you get on and following your progress.
    Smoke makes electronics work, if it escapes the equipment breaks.
    Got to keep the smoke in.

  6. #4
    ncollar's Avatar
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    I seen a young man shop there in Aust. and was supprized the space he is utilizing and the quality of work preforms.

  7. #5
    Toolmaker51's Avatar
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    The most important feature in hacksawing, physical or mechanized, is to lift the blade on the return stroke and preserve the cutting edges from rolling in or chipping out. Like a file, they only cut in one direction. Usually the lift is coupled to the crank and con-rod action as an over-centering motion and deflect the frame upward. The feed rate is controlled easily by pawl(s) and ratchet teeth. Feed pressure can be adjusted by a sliding weight. Power hacksaws are compact and even the little versions with 12" hand hack blades work nicely. Size wise, they cover an incredible range of capacity. Power Hack Saw help needed-hacksaws.jpg
    I've edited the jpeg with a crude sketch of a slide bar that will regulate your concerns with friction. It depicts inside of the slide relieved of full contact with bar, brass, nylon or other non-galling 'gibs' and setcrews to take up eventual wear. Though sketch is from overhead, the same arrangement is suitable for the closure, or top plate. This could easily be assembled, if you haven't access to a mill, from flat bar. The bar itself deserves a good flat stoning on sides subject to motion.
    Other mechanical considerations; cutting speed, many run 60 <> strokes per minute with 12" blades, too fast with a longer blade. Elsewhere a recommendation of 100' feet per minute with coolant is right on. Designing a little bit of range wouldn't hurt a bit. Hacksaws excel at heavier sections if you can locate blades of proper pitch (teeth per inch or mm).
    A swiveling vise jaw, at least on the moving side.
    A gap below the bed to 'park' the blade, and where it reciprocates before shut off.
    A work stop for repetitive cuts.
    Build height on a cart to match height of a table you could use it with, or benchtop with cribbing to keep longer stock level. If a cart is chosen, put two wheels on back legs to aid transportation.
    Infeed table proportions seem to run 2 or 3 times the jaw capacity. That will help positioning stock for better square cutting in the vertical plane.
    Last edited by Toolmaker51; 10-04-2017 at 11:02 AM. Reason: photo comparision, other additions
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    Toolmaker51
    ...we'll learn more by wandering than searching...

  8. #6
    whome
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    Google 'straight line machines' to find one that might work for you.

    Quote Originally Posted by garage nut View Post
    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.
    Last edited by whome; 10-03-2017 at 09:13 PM.

  9. #7
    olderdan's Avatar
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    Take a look at myfordboy blog and online resources: Compact Power Hacksaw
    He sells plans for £10 for a super compact machine and just watching the video may help in your quest.
    Good luck.

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  11. #8
    Frank S's Avatar
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    Here is my power hacksaw made around 38 years ago patterned off of the ones I made and showed guys how to make nearly 50 years ago I probably copied plans for it from an article found in an old Popular Science or Popular Mechanics magazine
    Power Hack Saw help needed-dscf7150c.jpg
    click on the link for more pics. An old power hack saw turns up
    Hard to see in the pictures but the motor was salvaged from an old swamp cooler
    Last edited by Frank S; 10-04-2017 at 02:21 AM.
    Never try to tell me it can't be done
    When I have to paint I use http://kbs.justoldtrucks.com/

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  13. #9
    garage nut's Avatar
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    Only need this machine to cut slugs off bar stock to use in my lathe. It is a very small lathe and the chuck throat is only 20mm.

    So anything bigger than that I have to cut to roughly the correct length before starting the job. very seldom anything bigger than 100mm.

    Tubing, angle iron d cutting at angles is left to my abrasion wheel cut off machine. also made it myself and have served me for about 30 years and the only thing I will change is to fit a proper vice to it. Will post a pic..

    Also building a ring roller to do 60mm pipe for an excosceletal (how ever you spell that ??)car I am building, but caught in a bit of chicken egg situation as I need one machine to build the other

  14. #10
    Frank S's Avatar
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    Ha,ha needing to build 1 machine to build another often leads to having to make a tool to make a tool to make a lot of parts to build a machine to make more tools so you can use them to make parts to build the next machine. Welcome to the world of DIY innovative progression.
    Never try to tell me it can't be done
    When I have to paint I use http://kbs.justoldtrucks.com/

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