Hacksaw blade orientation – your opinion please

[Roger BestParticipant @rogerbest89007]

This is an interesting thread as reciprocating mechanical saws are museum pieces now.

As well as lifting the blade on the return stoke some machines have the crank offset to give a quicker return stroke and more power on the cut. I don't know why I think that but I am sure I have noticed it on a real machine somewhere. (Real as opposed to my collection of toy saws.)

It might be fun to experiment with Lego and see how it works.

[blowlampParticipant @blowlamp]

Any blade that is under tension must surely be cutting on the pull, no matter from which end of the blade a person or machine drives it

Martin.

[peak4Participant @peak4]

Just a quick addendum to bench vices on my previous post.
There is an older British make which uses a fixed front jaw, though I can't remember the make.

Both Leinen from Germany and Orcan from India still make vices with a dovetail sliding jaw; I assume the latter is a copy of the former.

https://www.hhw.de/en/Shop/Clamping%20equipment/Vices/53600105/Bench_vice_fixed_jaw_width_150
http://www.orcan.com/rear-jaw-sliding-bench-vice.htm

See also Futuro
https://www.brw.ch/en/workbench-vice-futuro-413970

There seem to be a few other designs around, such as this one,
https://www.dreamstime.com/royalty-free-stock-photo-vice-block-metal-image24101345
but I can't seem to find the old British one that I saw for sale a little while ago on our local market.

Bill

Edited By peak4 on 12/12/2020 14:40:41

[blowlampParticipant @blowlamp]

I'm interested in the Femi claim that reversing the direction of blade travel makes their saw cut ~ 60% faster – how does that work, I wonder?

Martin.

[peak4Participant @peak4]

Posted by blowlamp on 12/12/2020 14:39:16:

Any blade that is under tension must surely be cutting on the pull, no matter from which end of the blade a person or machine drives it

Martin.

Indeed, but it's down to which end of the frame is most rigid, compared to where the force is applied.
Consider a power hacksaw; if the blade cuts on the stroke towards the con rod, the con rod itself and that end of the blade is under most tension.
If it cuts towards the other end of the blade, i.e. the con rod is under compression, then the force must be transferred to the far end of the frame. The frame itself is already under stress due to tensioning the blade, and the cutting force adds to that.
I've seen a couple of photos, and also a friends saw, where the frame has broken. In a couple of cases, I think it was because the workpiece moved, jamming the blade.
The frame broke before the blade did.

It's a bit like junior hacksaw blades jumping out of the frame at the rear, when used cutting on the push stroke, except the frame distorts, rather than cracking.

Bill

[Robert Atkinson 2Participant @robertatkinson2]

Posted by Roger Best on 12/12/2020 14:30:12:

This is an interesting thread as reciprocating mechanical saws are museum pieces now.

As well as lifting the blade on the return stoke some machines have the crank offset to give a quicker return stroke and more power on the cut. I don't know why I think that but I am sure I have noticed it on a real machine somewhere. (Real as opposed to my collection of toy saws.)

It might be fun to experiment with Lego and see how it works.

For museum pieces there are lot of people still selling new ones!

http://www.knighton-tools.co.uk/acatalog/POWER_HACKSAWS.html

https://www.warco.co.uk/metal-bandsaws-metalworking-saws/303280-industrial-hydraulic-power-hacksaw.html

Not just hobby either at £7400
https://www.cromwell.co.uk/shop/power-tools/power-hacksaws/hydraulic-power-hacksaws/f/3937

[AJAXParticipant @ajax]

For museum pieces there are lot of people still selling new ones!

http://www.knighton-tools.co.uk/acatalog/POWER_HACKSAWS.html

https://www.warco.co.uk/metal-bandsaws-metalworking-saws/303280-industrial-hydraulic-power-hacksaw.html

Not just hobby either at £7400
https://www.cromwell.co.uk/shop/power-tools/power-hacksaws/hydraulic-power-hacksaws/f/3937

The thing about power hacksaws is they are clean, relatively quiet and reliable. Safety somewhat depends on the user, but I I rank them as less dangerous than many other cutting machines too.

It's interesting to see the Knighton machine weighs only 140 kg but has a sizeable cutting capacity. I have a Q&S 6H that weighs well over twice that but with a slightly smaller capacity. I wonder whether any compromises have been made.

[AJAXParticipant @ajax]

Posted by blowlamp on 12/12/2020 14:50:26:

I'm interested in the Femi claim that reversing the direction of blade travel makes their saw cut ~ 60% faster – how does that work, I wonder?

Martin.

I can't answer that question but I did notice the saw at work has the blade installed the wrong way and it still cuts fine.

[AJAXParticipant @ajax]

Posted by Roger Best on 12/12/2020 14:30:12:

This is an interesting thread as reciprocating mechanical saws are museum pieces now.

As well as lifting the blade on the return stoke some machines have the crank offset to give a quicker return stroke and more power on the cut. I don't know why I think that but I am sure I have noticed it on a real machine somewhere. (Real as opposed to my collection of toy saws.)

It might be fun to experiment with Lego and see how it works.

Maybe I should post part 2 of the video when the LEGO model decides to self destruct. 😐

[Roger BestParticipant @rogerbest89007]

You must be right Robert, I guess there is a market.

Interesting that the Warco and Ajax are obviously by the same manufacturer.

My experience was that power hacksaws were being replaced by bandsaws as bandsaws are at least twice as fast for most sections. Even my previous employer, 17 years ago, had moved to bandsaws.

Looking at the Cromwell site bandsaws are a lot cheaper for a similar capacity, but I wonder if they last as long?

[AJAXParticipant @ajax]

Posted by peak4 on 12/12/2020 14:17:14:

Finally the mid sized Manchester Rapidor Minor (9" blade) isn't immediately obvious. On closer inspection, the angle of the blade isn't parallel to the motion of the frame in which it sits. It is lower at the rear, so when it cuts on the forward stroke, the dashpot provides pressure relief on the return stroke.
I understand the same is true of the larger Rapidors as well, It you look at the drawings on Tony's site, one of them even has a badge on the top of the frame showing the teeth set forwards.
Oddly in all cases they cut towards the moving jaw of the vice.

I've seen several larger power hacksaws which cut on the pull stroke, where the dashpot provides both relief and also pumps the frame back up under no sawing lead.

Edited By peak4 on 12/12/2020 14:41:22

I sold a Rapidor Manchester today that had a modified vice with the fixed jaw at the front and movable at the rear (closest to the driving linkage). That actually made sense especially as the blade was set to cut on the forward stroke.

On the other hand, my Q&S 6H cuts on the pull stroke and has the fixed jaw at the rear. The hydraulic relief gives a very slight lift (or reduction of weight) on the forward stroke.

[Roger BestParticipant @rogerbest89007]

Posted by AJAX on 12/12/2020 17:40:24:

Posted by Roger Best on 12/12/2020 14:30:12:

This is an interesting thread as reciprocating mechanical saws are museum pieces now.

As well as lifting the blade on the return stoke some machines have the crank offset to give a quicker return stroke and more power on the cut. I don't know why I think that but I am sure I have noticed it on a real machine somewhere. (Real as opposed to my collection of toy saws.)

It might be fun to experiment with Lego and see how it works.

Maybe I should post part 2 of the video when the LEGO model decides to self destruct. 😐

Yes, do so. Its always fun.

[Michael BriggsParticipant @michaelbriggs82422]

Posted by blowlamp on 12/12/2020 14:50:26:

I'm interested in the Femi claim that reversing the direction of blade travel makes their saw cut ~ 60% faster – how does that work, I wonder?

I saw (no pun intended) a Femi video some time ago showing the "NG" reverse blade saw cutting faster than the standard version. The demo used the same fixed weight hung from the handle to load each type of saw.

I don't think the cut is faster per se, just faster for a given force applied by the operator.

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