|180 forum posts|
I decided to make a LEGO toy model power hacksaw with my kids. Don't worry, they won't be allowed to play with this until they are older! By including a couple of machine screws it was easy enough to mount a standard 12" hacksaw blade and to my surprise it works quite well. In fact, it has now got me wondering about making a small but usable powered hacksaw for those smaller jobs when a high TPI blade is required. Needless to say it won't be made from LEGO (or Meccano, for that matter).
Bearing in mind my model has no blade relief (or rise) on the non-cutting stroke I was not too bothered about blade orientation. However, I stuck with what I was taught a long while ago. Looking online, I see similar working machines of basically the same design and wonder whether there is a preferred blade orientation and the reasoning (if any) why.
I would be interested if you have some knowledge of experience to share.
|Michael Gilligan||12/12/2020 00:12:26|
17641 forum posts
Teeth cutting on the ‘push’ [as per normal hand operated hacksaw] can buckle the blade if the frame is not very stiff.
With teeth cutting on the ‘pull’ [as per fretsaw or piercing saw] the blade stays taut.
|Martin Connelly||12/12/2020 00:15:44|
1690 forum posts
At school the rule for the bent wire junior hacksaw frames used to be cut on the pull stroke as it was safer if the blade caught. The wire frame could spring and release the blade if the blade was the other way and then you drove your hand into the workpiece. Proper frames with tensioning such as the Eclipse ones had the blades in the conventional direction. It is easier when manually sawing to push the blade forward and down to cut than pulling the saw and pushing it down.
I would think about the link that moves the frame. If it was really flimsy then a pull cut would be better as the load on a push cut could end up bending it. You should try to make it strong enough to work in either direction but the tensile force being greater than the compressive force still makes sense. If the bow it at a high position for a large piece of stock the link has to work against gravity as well when pushing the frame up.
4285 forum posts
cutting on the pull is best
1969 forum posts
What a load of rubbish. You always cut on the push. Teeth pointing forward.
The only time i have known for a pull action is when working with the Sikh carpenters who kneel down & cut upwards & towards them. Teeth pointing backwards. Strange to watch.
|129 forum posts|
my rapidor cuts on the push stroke
|Kiwi Bloke||12/12/2020 02:59:31|
|525 forum posts|
Well, of course, that's a 'load of rubbish', unless suitably - and massively - qualified. As MG had previously noted, fretsaws, piercing saws cut on the pull stroke, as do jewellers' saws, many (most?) types of Japanese woodworking saws, chainsaws, bandsaws, etc., etc.
AJAX, I suggest you set the blade in the direction it works best - that's all that matters. Of course, with a suitably rigid frame, a hacksaw pulls the blade...
4285 forum posts
For a human the push stroke is usually best but for a mindless mechanical machine pulling is best and causes the least problems
|Kiwi Bloke||12/12/2020 04:25:39|
|525 forum posts|
Tell the Japanese - and a lot of non-Japanese who understand their advantages - to push their pull-saws then...
Broaches are usually(?) pushed. It may seem strange, because pushing invites buckling, but the reason's clear, after a bit of thought.
|Michael Gilligan||12/12/2020 08:26:31|
17641 forum posts
No, Steve ... it’s not a load of rubbish, and I do not always cut on the push
I suggest you remove the blinkers, and look at the world around you.
|180 forum posts|
I haven't had to use one of those wire framed hacksaws for many years, but the point you make is valid. Thanks.
|Brian Wood||12/12/2020 08:55:24|
|2380 forum posts|
And a good number of broaches work as pull devices, there have to be equally good reasons for that approach as well
|Ian B.||12/12/2020 09:30:20|
|163 forum posts|
Interesting points of view. Which way the blade cuts in both manual and power driven saws is a wider subject.
Consider the work holding device and / or the support for the work. The most efficient and safe way of cutting is to direct the cutting forces against the most rigid surface.
Examples. My power bandsaw cuts basically on the pull stroke. The motor is at the rear and more importantly the fixed jaw of the vice is at the rear. My manual hacksaws all cut on the push stroke, Never use wireframe mini hacksaws, only those that can be tensioned like a full size by the way. Why? Not because of tradition but simple logic. The fixed and most stable jaw of the bench vice is at the rear and I am standing in front of the bench. My piercing saw, fretsaw, power fretsaw et al all cut on the pull stroke. Why? The support table is below the work and the forces need to be transmitted through the most stable part.
I could go on more. But this is demonstrated in very real practical terms. Some years ago I needed a small but decent bench vice. I bought a quite expensive jewellers bench vice of some quality from a very reputable supplier. To my dismay the fixed jaw is at the front!. There is a shoulder below the main casting to set it hard against the bench edge before bolting down. The moving jaw is at the rear. From experience this little very high quality item is far more difficult to use and achieve sensible work in all aspects sawing, cutting, filing. I have observed what is going on and it is directly caused by working against a relatively weak surface, i.e. the moving jaw.
Just a few thoughts.
Edited By Ian B. on 12/12/2020 09:32:39
|Mike Poole||12/12/2020 09:40:45|
2936 forum posts
Martin makes a good point about the wire junior hacksaw and they work fine in pull mode, a normal manual hacksaw would be more tiring to use in pull mode as only arm power would be used,in push mode you can get your weight behind it. I know the saw should do the work but you do need to apply enough weight to make the teeth cut rather than skid and of course you do need to apply the effort required to cut. I think the expression is for those who think you can force the saw to cut faster by applying excessive weight to it. With the Lego saw the frame has limited rigidity and strength so pull may be best in this application. For a reasonably fit person sawing should be an activity that can be maintained without tiring or breaking too much of a sweat, a good technique should result in accurate sawing and minimal filing. Sawing a three inch bar by hand is a daunting prospect but can be done with a bit of effort and patience. The fact that so many of us use machine saws would tend to indicate that sawing is not a popular activity or maybe time is better used in other more interesting activity.
|not done it yet||12/12/2020 11:00:31|
|5776 forum posts|
As most of us on the forum are likely close to (or beyond) the ‘normal’ retirement age, manual sawing is best reserved as a gentle exercise - not like 50 years ago (for me).
Thinner blades are better for sawing but that needs to be tempered with rigidity. Most conventional hand timber saws cut a wider kerf than our metal cutting examples but have much wider blades to keep them sufficiently rigid to enable a push-cut.
This has all been mentioned, sort of, above - where pull saws are considered. With a band saw the tension will always be there when cutting, whatever the motor position. The differences likely arise with the rigidity of the band saw frame. Lightweight has its disadvantages, particularly when built down to a cost rather than up to a quality.
The mass of the motor on a ‘pull’ machine will have less effect as cutting proceeds, compared to the motor at the top end of the frame. Note the springs added as a modification by the chappie in the video on the other thread. In fact, it will be positioned at the optimum balance point on the well-designed machines
|Peter G. Shaw||12/12/2020 11:07:38|
1256 forum posts
I must admit that I have never thought about reversing the blade in a junior hacksaw, but then I haven't had many problems in the conventional direction. But, food for thought.
I also have a Stanley Mini-Hack Saw, part no. 20-807 which I use in awkward situations. On checking, I find that I do indeed have the teeth the "wrong" way round, and furthermore, the illustration by Stanley clearly shows the blade inserted in a pull direction.
Interesting, and thanks to Ajax for raising this subject. Yet again I've learned something.
Peter G. Shaw
|roy entwistle||12/12/2020 11:12:58|
|1336 forum posts|
I much prefer the old style hacksaw where the handle is in line with the blade like a file.
|524 forum posts|
I was always told to insert a hacksaw blade with teeth facing forward, same for junior hacksaw so you push to cut, but fretsaw etc the other way round so you pull to cut. Kennedy style hacksaw machines I believe are best set up to cut on the pull stroke, but it is entirely up to you, whatever you feel more comfortable with.
|Nicholas Farr||12/12/2020 11:31:04|
2682 forum posts
Hi, as far as power saws, that is reciprocating or band, it is really down to the manufacturers design, as to which way the blade is moved and it doesn't matter if it's towards the fixed jaw or the moving jaw, I've used both types in both directions and towards both jaws. (but not all those ways at the same time or on the same machine) At one time in my old job, we had a band saw that "pushed" the blade towards the moving jaw, one time when the blade needed changing, a guy who thought he knew best, put the blade on the other way round thinking that it should be pulled, guess what, the blade jammed up on the very first cut and ripped a couple of teeth out of the blade. I told him to have a look at the fitting instructions, which were hanging on the back of the machine, that clearly stated that the blade should be cutting forwards toward the moving vice and must not be fitted the other way. Like Gary's Rapidor my one cuts by "pushing" towards the fixed jaw and the oil dashpot lifts the blade away from the cut on the backward stroke and the reciprocating action pushes it down on the cut in the forward stroke. However, when in a ridged frame on power saws, the blade is in effect pulling the teeth which ever way round it is, it's just the design of the machine that makes the difference.
As far as hacksaws are concerned, pushing on the blade is normal, but at times when there are space restraints, put the blade the other way round so you pull, works much better, horses for courses and all that.
Edited By Nicholas Farr on 12/12/2020 11:42:27
|Martin Kyte||12/12/2020 12:00:42|
2309 forum posts
I don't think you can 'push' a blade in a frame. You can push and pull the frame but the blade will always be pulled by the end of the frame leading the cut. I think Nicholas said that above. Weather the blade cuts on the forward or reverse stroke is another matter. The saw geometry will determine if more force is exerted downwards on the forward or reverse stroke. (or indeed if it's symetrical). Basically is the crank offset above or below.
Bandsaws allways cut towards the driven wheel for obvious reasons.
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