Power Hacksaw

Hello All,

When recently reading about a home-built power hacksaw in MEW, the question arose--- is the cut supposed to be applied on the pull or push stroke of the saw-blade frame?

I have seen both.

My current Taiwanese machine cuts on the push stroke, but I always felt it should be the other way around on the pull stroke, because of a possible jamb-up buckling all manner of bits.

Best Wishes,

Jim Crawford.

Mine is designed to cut on the push stroke Jim - it's also the way I use the 'Armstrong' version too.

Haven't though too deeply as to why - just the way it I was taught...

Regards,

IanT

Back in the 1950s the apprentices were instructed that the works Rapidor cut on the push stroke ,my Rapidor cuts on the forward stroke . I found by accident when changing motors that they need to have the correct rotation of the crankshaft ,the crank rotates clockwise (viewed from the pulley side)so that the crankpin comes over the top and pushes down on the saw frame. When I attended technical college there was a saw with a brass plate on the saw slide with an arrow and stating direction of cut which was on the pull stroke, don't know if this was original manufacturers plate or whether so genius among the staff thought he knew better and fitted a plate,none of the apprentices from other companies had ever seen a saw cutting backwards and it caused some discussion.Rapidor saws were seen everywhere in all kinds of establishments ,I suppose its another company that just disappeared when manufacturing went the wall in the uk.

It cuts on the push stroke. If you put the blade in back to front, the blade wears out faster as the pull stroke is quicker than the push stroke.

I'm clearly ignorant here but what difference does it make? I have an Axminster hacksaw, which I guess is Chinese, and the cut seems the same regardless of which way the teeth face.

If I remember correctly the last power hacksaw I used cut on the pull. If you let the frame drop on it's own restricted by the dash pot you could see the variation of decent clearly between the push and and pull. More rapid on the pull which showed that there was an appreciable downwards force generated by the crank on the pull stroke which would increase the 'bite' and therefor the cutting speed. Not that power hacksaws ever seemed to cut quickly though.

It's similar geometry too traction engine cranks and slide-bars. If the crankshaft pulls down on the backstroke all the force on the slide-bars is downwards through the mountings and not upwards against the bolts.

regards Martin

Mine lifts the blade and the back stroke so it must cut on the front stroke, my old man told me when he was serving his time in the Army they used to cut pipe with the blade in backwards in order to stop it jamming up.......

All the power hacksaws I have seen are supposed to cut on the backstroke. It is desirable to pull against the fixed vice jaw for rigidity however many machines have some sort of blade lifting on the return stroke which should give a clue. Colin

I can only speak for the Kennedy "Hexacut" hacksaw, instructions for which state the blade cuts on the forward stroke.

It appears that it's simply down to the design intent of the machine ie whether it pulls the blade down into the work on the forward or reverse stroke and there are examples of both. However, for hand tools there seems to be an historical / cultural element.

The Japanese prefer their (wood) saws to cut on the pull, while Westerners like them to cut on the push. They also use water to lubricate their honing stones while we use oil. Both approaches seem to work well enough.

If it's a speed difference/blade lift issue then reversing the motor direction will change the preferred cutting direction.

Neil

I put my blades in forward facing and then turn them when they wear (it's a big old Manchester saw).

Frankly I have no idea which is best - both ways work and I just let the saw run until it finishes.

Cheers - Will

My lash-up hacksaw cuts on the pull, the castoring effect(self steering) creates far less issues

A decent dedicated saw IMO would be fine in both directions

Followed this post you only have four choices clockwise anticlockwise teeth left teeth right.

Built a power hacksaw that cuts best on the pull stroke with the pivot above the centre line of the crank with the blade on the left and the crank turning anti clockwise.

It is hiding at https://www.youtube.com/results?search_query=wobbly+hacksaw

Conclusion is it all depends on the position of the pivot point location in relation to the crank and the overall design of the thousand of variations of a very simple machine

Eric

Beautiful machine Eric - probably not as beautiful as the velo though! Can we see it?

I agree with Neil. The preferred cutting direction will be determined by motor rotation and best performance by the position of the drive axis to the crank. Myfordboy offers what looks to me to be a well sorted design but unlike most info he provides he charges £10 for the plans. Googling myfordboy compact power hacksaw will find it and videos showing it's use.

My initial reaction to this thread was why not buy a horizontal bandsaw instead. When I sorted my saw out they were so cheap that it was really questionable if it was worth making one. Looking on ebay that doesn't seem to be the case now. The only problem with the cheap one I bought is that the cut length stop doesn't work very well, not much of a problem really. I was buying materials to make one and the retailer said are you sure and suggested I bought it instead. The design I was looking at was very compact. The bandsaw type significantly bigger.

John

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My version of the ME Duplex (1950) powered hacksaw cuts on the in-stroke, as per the original design. As the carriage arm pivot is above the crank, this adds load to the cut on the in-stroke and relieves the cut of the out-stroke. The added load depends on the mass being accelerated, and the arm pivot to crank separation distance. While built for the fun of it and learning various machining procedures (I also have a bandsaw) it is in regular use.

All bandsaws seem to work on the pull stroke.

Regards Ian.

Hi, my Rapidor cuts on the forward stroke and relieves on the return stroke, just as described in this advert,

Rodney, nice looking saw, but unusual to see the blade on the left hand side of the vice.

Circlip, not all bandsaws cut with the blade going in the backward direction, the company I used to work for had one where the blade went forward, but technically speaking, bandsaw blades can only work by being pulled, whichever direction they are going.

Regards Nick.

Another nice machine. Perhaps it should really have been called simplex since it cuts one way, but I digress.

Given you have both this and a bandsaw, if you started again, would you just have the bandsaw or are you finding there are advantages with a powered hacksaw for some jobs?.