Micro chainsaw anyone?




The blade and the internal reciprocating mechanism in the machine are rigidly connected via the chuck. While the body of the saw vibrates as a result of being connected to this reciprocating combination of parts.
How could one end of this reciprocating combination of parts move, and not the other ?
I haven't snipped or chosen to ignore the remainder of the points which you make to which I'd be happy to return. However to save any further misunderstandings I think it best to proceed one point at a time.
So how could one end of this reciprocating combination of parts - the blade and the mechanism move, and not the other ?
michael adams
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On 18/07/2018 09:02, michael adams wrote:

Agreed

It can't - it must obey the laws of conservation of momentum.
if you simplify it to two connected masses - the saw on one end and the blade on the other. The saw is alternately pushing and pulling on the blade - accelerating and decelerating it. It having a low mass will accelerate quickly. There will be a matched reaction in the movement of the saw body, but it will be at a much reduced velocity due to the substantially greater mass of the saw.
As you add load to the blade, you are increasing its effective mass and inertia. So the velocity of the matched reaction of the saw will increase (i.e. increasing the vibration level).
So if you take this to its ultimate conclusion where you add enough load to the blade to in effect fix its position (say lopping a tree branch that closes on the blade), then you have the mass of blade plus a tree on one side, and only that of the saw on the other. The vast bulk of the movement will now be the saw body itself - causing substantial and very uncomfortable levels of vibration.

Take the example above when cutting a branch. Assuming the blade is still free to move, you get most movement in the blade, and some in the saw. If you now push the saw's rest against the branch you are coupling the mass of the saw to that of the branch. So the momentum equation has blade and friction "mass" on one side, and saw body + tree on the other. So you have massively increased the inertia of the saw body, and thus reduced the velocity of vibration.
(Also for half of the cycle (the "pulling stroke") you now have closed system where the pull on the blade is exactly matched by the push against the saw's rest - eliminating acceleration of the saw body in one direction completely).
--
Cheers,

John.
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.....................................................................................................................

Indeed. This is the normal vibration I've been talking about

In other words where the blade snags or sticks in the work, a possibility you suggested earlier. A situation which is fairly easy to replicate simply by taking hold of the saw, clamping the blade in a bench vice, and squeezing the trigger. Whereby it's the body of the body of the saw which oscillates violently back and forth in the hands of the operator against the blade, which is held firmly in the vice. Causing as you say "substantial and very uncomfortable levels of vibration"
But any and all of which would of course be brought to an immediate halt, by the simple expedient of the operator simply releasing the trigger.
So that, if you're seriously suggesting that vibration from this source represents a very real problem as compared with normal vibration, or any sort of problem at all for that matter, then its necessary for you to come up with some sort of satisfactory explantion as to why, following that initial kick, any operator of that saw would be foolhardy enough not to release the trigger. Which most certainly would be the instinctive reaction I'd have thought.
Or leaving instinct aside, why would they ever think of doing this (not releasing the trigger) a second time ?
As with the blade firmly stuck in the work, the whole weight of the violently oscillating saw, as held in hands of the operator, is now supported at the point where the blade enters the work. Greatly increasing the likelihood that it would snap-off at this point; making the subsequent removal of the broken tip from the work all the more difficult.
Why would anyone ever want to do this ? Why wouldn't they simply release the trigger at the first opportunity ?

Indeed. In such circumstances the combined mass of the saw and the branch/tree would easily dwarf the mass of the oscillating blade and would thereby clearly reduce vibration by a substantial degree. Were it possible that is, to clamp or otherwise securely attach the shoe/guard or any part of the saw body to the work. Although not in this case with the aforementioned bench vice, unfortunately
As it is however, in order to keep the vibrating body of the saw in close contact with the work requires considerable effort on the part of the operator. In fact it amounts almost to a form of torture. Slacken your effort in any way and the vibrations will get a lot worse, an awful lot worse, and we don't want that, do we ? So push!
This is the reason why using such saws for any length of time is so very tiring, and why other means short of clamping the saw to the work - using counterdirectional shafts or damping the shaft at either end of its travel - have been sought in order to lesson the normal vibration which is the real bugbear of such saws.
As I originally said; and to which you took such exception for some unaccountable reason, which is yet to be fully explained.
Or if you don't want to take my word for it, it's safe to assume I'd imagine that all the people who've been using such saws on a regular basis for protracted lengths of time since the 1950's can't have all been mugs. Similarly the competing manufacturers of such saws. And that had there been some simple solution to this problem as might be suggested nowadays on websites, but formerly perhaps in articles in DIY magazines and the like, then this would have become standard practice decades ago.
michael adams
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On 19/07/2018 08:19, michael adams wrote:

ok

Indeed.

You seem to be trying to put words into my mouth... I use the blade jammed illustration simply as an example of one extreme of the various possible scenarios. The other extreme being saw held and braced, with the blade in free space. One will result in the minimum level of vibration likely to be experience, and the other the maximum. Normal use will be somewhere between those two extremes.

Of course. (lets ignore the trigger lock "on" situation for the moment).

Well having got the blade snagged, you now need to free it. Most I would expect will do as I do, adjust the position of the blade in the cut (if possible) and re-apply power.

They are IME quite difficult to break - certainly for wood blades anyway. It does depend a bit on how long the blade is and where along its length its snagged.

You said that above.

Well you *could* do that in the vice example, although the saw is going to be might unhappy!

I have not found this to be the case. Remember we are dealing with "normal" operation here - not a jammed blade. Applying similar levels of force against the rest as you are applying in the direction of cut is often adequate (in fact you can play one off against the other).
This is exactly the same situation as using a jigsaw - you get much less vibration if you keep the sole plate firmly in contact with what you are cutting. The moment you lift it away from the surface and try to cut with the body of the machine unsupported, you get a significant increase in vibration transmitted to the operator.

As with any tool, there are some use techniques that get better results than others. Personally I don't find it difficult to use in such a way as to control the vibration to a reasonable extent.
Now don't read into this that I am suggesting that these are particularly sophisticated or smooth cutting tools. I would not want to use one all day and every day.

I am a little confused by this... my initial comment on the subject was simply:
"The trick to controlling vibration on a recip saw is to make sure you push the blade guard firmly against the thing being cut"
That (to my internal voice at least) does not in any way amount to "such exception".

Whoa horse! You are now romping off at a tangent having your own argument. By all means do, but don't pretend its with me.
I have at no point suggested you don't get vibration from this kind of tool. I am also fully aware that vibration is harmful, especially with prolonged exposure. (read the power tools faq which I wrote many years ago - its a topic I pick up on frequently). I have spent many years here encouraging people to select better quality power tools, even if for occasional use, because you usually get a better quality result and more comfortable operation.
I gave a simple tip that helps reduce the impact on the user. I mention it because it does not appear to be self evident to some users IME.
For example, some years ago when de-tialing a roof. I passed a mains powered recip saw to my friend to cut down a row of tile battens nailed to the rafters. A good application for such a saw since its fairly blade hostile environment, and you want a cut flush to the side of a rafter - a recip saw will do it quickly and easily - and if you kill a blade in the process then who cares?
However he (an experienced builder) was struggling - the saw would snag quite often as not all the tile battens were well fixed - they could flex and pinch the blade. He was frequently getting the lions share of the reciprocation through him and not the wood. He passed it back to be and said "I have never been able to use those things". So I took over, and did the job with no drama simply by the expedient of doing what I suggested - engaging the rest against the top of the batten and applying some forward pressure, and cutting with the bit of the blade closest to the tool, rather than trying to use the end of the blade as he had done. This resulted in no snagging, and way less vibration for me.

Well this *is* standard practice and advice. You can read it in the handbook that comes with the saws, but then who reads those eh?
I am also not disputing that the more refined saws can better help control vibration than the cheap ones (especially that which results from the translation of rotational work to longitudinal, and balancing a somewhat variable blade mass). Floating and spring loading the mechanism also helps, as do vibration dampening grips.
However, the operator can still do a huge amount to influence the experience with any recip saw by their choice of technique.
--
Cheers,

John.
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The previous version included a graphic element inadvertently pasted from the Makita website which might lead to its rejection on some NewsServers.
</quote>
There are two different things being discussed here.
To keep things simple assume inside the saw is a rod (attached to the free moving blade via the chuck) which moves forwards 1 inch, stops, and then moves backwards 1 inch, and then stops at say 2,000 times a minute. In simple terms this causes the body of the saw to vibrate; while in holding on to the saw, rather than allow it to move around on the bench the operator will absorb some of that vibration. That is the normal vibration (A) associated with reciprocating saws where the operator absorbs some of the vibration.
In addition if the blade is trapped, the entire body of the saw will move forward 1 inch, stop, and then move backwards 1 inch, and then stop say 2,000 times a minute. Which is (B). In this case its impossible for the operator to absorb any of this movement or more technically vibration. All that will happen should this be attempted is that the weakest link in the chain will malfunction or break, be it the saw blade, the chuck, the internal linkage, the motor, or the operator him, or her self

So the trigger is pressed rather than released.
However on the basis of your claim that (B) is such a common occurrence "the problem many seem to have with recip saws", I'd imagined there might have been a reluctance on their part to lock the trigger. Even if at the cost of losing the odd millisecond here or there,

What I meant was if they didn't stop the saw, and thus subjected themselves to a good dose of (B) the first time around, once having experienced (B) why would they do this a second time ?

In other words you stop the saw.
Previously you claimed if you remember that B) vibrations, those resulting from the entire body of the saw moving forward 1 inch, stopping, and then moving backwards 1 inch, and then stopping say 2,000 times a minute was a major problem. Whereas if you've immediately stopped the saw in such circumstances then clearly it isn't.

Indeed. Whereas in fact they don't. As you've just explained they stop the saw so (B) isn't as big a problem as you previously suggested it was.

Quite possibly but not enough to compensate for the fact that a reciprocating saw vibrates four times as far/much/whatever - 22 m/sec? when cutting chipboard as does a chainsaw 3.9 m/sec? Rear Grip 5.2 m/sec? Front Grip (task unspecified) . All Hitachi figures
http://www.makitauk.com/products/saws/reciprocating-saws/all-reciprocating-saws/jr3050t-reciprocating-saw.html
http://www.makitauk.com/products/garden-machinery/chainsaws/electric-chainsaws/uc3551a-electric-chainsaw-35cm.html
This is the original point from Theo which I was responding to
"Out of interest, what would be a suitable alternative for cutting trees? Having a similar portable, relatively safe, battery-powered form factor - where a full chainsaw is not appropriate "
All I was seeking to point out, was that while with a chainsaw its possible to let the saw do the work some of the time, given the weight of the bar and the chain. IOW that it's not always necessary to apply maximum force, even if this is inefficient and will prolong the job to some degree. (here we go!) Whereas with a reciprocating saw which is usually suggested as the closest alternative, this simply isn't possible. Not only is it necessary to apply constant force on the blade but as I suspected and confirmed by the figures above, the level of vibration is considerably higher even in the most capable hands. So one must assume at least. Making reciprocating saws correspondingly that more tiring to use over extended periods
michael adams
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On 20/07/2018 14:15, michael adams wrote:

God I am glad we are finally in agreement, let's move on.
--
Cheers,

John.
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On 21/07/18 03:03, John Rumm wrote:

:)
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Indeed.
Taking into due consideration all those facts having any bearing on the matter in hand, the position you currently find yourself in, and the almost inevitable result should you choose to continue, were I called upon to do so, this is exactly the advice I would have given myself.
Try and move on, and put it all behind you; and in a while you'll most likely have forgotten all about it.
michael adams
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On 23/07/18 08:40, michael adams wrote:

FYPFY
YVW
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I have a B&D alligator chain saw bought from a boot sale for ?10 its ideal tool for pruning woody shrubs but never seen one that runs on a battery as yet
-
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If it is only relatively small stuff do you really need a power tool? The speed and simplicity of use of such things as bowsaws provided they have a good quality blade is something that seems to have been forgotten in recent times, its got that almost no task can be done unless a power tool is involved.
GH
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On 16 Jul 2018 21:37:33 GMT, Marland wrote:

For a lot of small, perhaps fairly dense, growth I prefer a garden saw of the comact sort. I bought a Spear and Jackson Garden Predator a few years ago and it's been very useful. Looks as if it's been rebadged: https://www.toolstation.com/shop/Landscaping/d130/Garden+Saws/sd3265/Razorsharp+Garden+Saw/p52906
--
Peter.
The gods will stay away
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+1
Those saws were mentioned here a couple of years ago, and I immediately bought one. I use it for smaller stuff including small logs and it so easy, not worth digging out a power tool.
--
Graeme

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writes

I prefer a bow saw, bigger teeth and so it cuts quicker and no chance of the saw bending. https://www.walmart.com/ip/Fiskars-Bow-Saw-21/1112519
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On 17/07/2018 19:40, Rod Speed wrote:

Ah, many years ago the only time in my life when I've attended accident and emergency at the local hospital. Using it to cut logs and on the first cut the saw bounced out and cut into the back of two of my fingers. I can vouch for the fact that the blade is sharp - there was a lot of blood.
--
mailto : news admac myzen co uk

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Yeah, they can certainly bite you.
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There's sometimes quite a lot of relatively small stuff, such that the human battery gets depleted, and recharging it is a bit trickier than plugging into a car charger.
The Ryobi One style of saw looks interesting, thanks. I was also a bit dubious by the batteries on some of the other tools like the Bosch - 10.8V 1.5Ah, which surely can't last for very long.
Theo
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On 17/07/2018 09:35, Theo wrote:

I have a small recip saw which I mainly use for plumbing and some building work:
https://www.lawson-his.co.uk/makita-jr100dzw-body-only-white-10-8v-li-ion-cordless-reciprocating-saw-tool-less-blade-change
Its good at getting into tight corners where a hacksaw is the only option, and its very quick for lopping off things like 40mm wast pipe and even trimming 110mm soil pipe. It also shares batteries with my small drill driver / ID combo.
If I stick a "green wood" blade on that its not bad for a quick bit of pruning - you only get 10 mins or so of work out of a battery, but the batteries are small enough to have a spare in your pocket.
--
Cheers,

John.
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Pretty fucked ad given the cooking shit in the middle.
Slower cutting that I expected tho.
Very convenient blade swap.
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