Angle grinder for cutting wood



Same as me probably
Stuart
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Midlands Midsummer Mug show, for all things RISC OS, July 10th 2010.
Stuart Winsor
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wrote:

Fuckwit.
A diamond disc will not cut wood due to the mimimal depth of the cutting surfaces, it will instead burn through whilst spinning at circa 10,000 RPM.
A diamond disc with sintered tabs, several long teeth interspersed by gaps, will snag on the wood fibres - flinging unsecured wood at some function of the 80m/sec disc speed, kicking back off sufficiently immovable wood or shredding wood into a fibrous pulp rather than efficiently cutting. With sintered tab on wood there is some risk of ejecting a tab or a limited risk of catastrophic disc fracturing from a tab gap (most discs have the tab slot ending at a circular hole to reduce crack propogation across the disc causing separation which at circa 10,000rpm would be unpleasant).
A diamond disc that is continuous (does not have a tabbed perimeter) will just bounce off the surface or burn through.
This is exactly how someone killed themselves with a diamond disc in an angle grinder, it kicked back off a tree stump and embedded itself in their neck severing an artery. Most likely a tabbed diamond disc where the slots snagged on a particularly resilient group of wood fibres so launching the grinder up into the victim's neck.
Any blade for wood cutting at angle-grinder RPM will need to have a very robust disc construction, very robust teeth to resist the peak shear forces along with an appropriate tip cutting angle, and large inter teeth gap to handle the extremely high material ejection levels at such high RPM. That is to say teeth gaps of several millimetres compared to the sub-milimetre gap for diamond cutting brick particle ejection.


Alligator saw has double blades, demolition saw has single blade. An alligator saw is a lot more useful to a DIYer.
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js.b1 wrote:

Potty mouth.

Don't use many angle grinders do you? Regardless of the 10,000 RPM, it still does not approach the speed of a simple circular saw or a sawzall.

It's clear you don't use an angle grinder much. Any wheel in an angle grinder is capable of kick back. All you have to do is contact the leading edge of the rotating wheel. To my point - it's not a matter of the wheel in use, it's a matter of where you contact it.
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My simple circular saw RPM is less than half that. Peripheral speed unknown though
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On 16/05/2010 14:48, stuart noble wrote:

Multiply by the blade circumference... so for a 190mm blade at 4500 rpm that is 4500 x 0.19 x pi = 2686 m/sec
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Cheers,

John.

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John Rumm wrote:

I knew I could count on you :-)
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Heh-heh, blade tip travelling at beyond even rail gun projectile hypersonic speed would be fun.

RPS = 4500rpm / 60 = 75 Circumference is 2*Pi*R = 2 * 3.14 * 0.19/2 = 0.59m Circumferential speed = 75 * 0.49 = 44m/sec.
At 4,500rpm you have almost 100 miles per hour. At 10,000rpm you have 200 miles per hour. Quite a few angle grinders run 12,000rpm, still far below the sound barrier.
Due to the way an angle grinder is mechanically driven, stopping one in motion as with a tree root will hurl the saw at speed. A chainsaw will not do this hence eminently less dangeous than a freakin angle grinder.
Alligator saw is expensive but handles both demolition & general precise wood cutting, a jigsaw with a wood ripping blade is cheaper.
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On 16/05/2010 17:09, js.b1 wrote:

Well what's a factor of 60 between friends ;-)
Yup, my bad - sorry!
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John.

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John Rumm wrote:

What an old boss of mine would term a "slip-up" rather than a mistake :-)
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On 17/05/2010 09:35, stuart noble wrote:

The daft thing was having done the sum the result felt intuitively wrong - for starters I expected the rim speed to be lower than that of the AG.
(and hit send before looking at the actual number and realising that the edge would be going supersonic several times over!!)
Still in hindsight - the answer was actually ok, just had the wrong units. It should have been a linear speed of 2686 m/min ;-)
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John.

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wrote:

Heh-heh, blade tip travelling at beyond even rail gun projectile hypersonic speed would be fun.

RPS = 4500rpm / 60 = 75 Circumference is 2*Pi*R = 2 * 3.14 * 0.19/2 = 0.59m Circumferential speed = 75 * 0.49 = 44m/sec.
At 4,500rpm you have almost 100 miles per hour. At 10,000rpm you have 200 miles per hour. Quite a few angle grinders run 12,000rpm, still far below the sound barrier.
Due to the way an angle grinder is mechanically driven, stopping one in motion as with a tree root will hurl the saw at speed. A chainsaw will not do this hence eminently less dangeous than a freakin angle grinder. --------------------------------------------------------------------------
A chain saw Can kick back. Hence the use of face shield and helmet when using one.
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Lobby Dosser wrote:

Chain saws will most certainly kick back - as Lobby says. Very violently in fact. The face shield and helmet are of no value if they do kidk back that hard - they'll just disappear in the blood splatter. Face shields and helmets are useful for lesser flying debris but they sure as hell won't stop a chain coming at your head. Regardless - not only will chainsaws kick back - they are very well known for this capability. Evidence that the previous poster knows nothing at all about using chainsaws - and all the reason to ignore his comments.
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wrote:

Didn't mean to imply that the face shield or helmet would stop a chain. They might gain enough time for the chain brake to engage.
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And you would not want your nice sharp chainsaw blade to be anywhere near grit, earth, and any bit of wood with a nasty nail therein;!...
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Tony Sayer



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tony sayer wrote:

. That's why you sharpen them regularly.
Oh and as far as kickbacks go, thats why you tend NOT to out your face over the blade: Always you cut soo the swaw will kick over your shoulder.
As pointed out, the mask is not there to stop a saw blade. Flying chips only.
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I /knew/ someone that happened to :-(
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Your mind is made up so I know this is a waste of time. Your wild ass statement about a diamond blade kicking back and cutting a man's neck is pure hyperbola, fiction, and prevarication. A diamond blade would be very hard pressed to cut your hand if you ran it into your hand at full speed. They do an excellent job cutting really hard things like glass and tile, they really suck on anything else.
I have no idea what an alligator saw is. I've been in the commercial contracting business for over 50 years so please enlighten me as I may need one some day.
You may not be strong enough to hang onto a grinder when the blade hits something, be it a tree root or whatever, but I sure as hell am and have done so, though that is NOT the object when using the tool.
The reason most us have said to not use the grinder with a blade has much more to do with the OP's opening line which said that he was not experienced. Let it alone.
I really hate it when people babble and pontificate about things of which they have no experience. If you have information or experience to share, have at: otherwise, sit back and listen (read).
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DanG wrote:

It wasn't a diamond blade http://www.metro.co.uk/news/627085-man-killed-by-improvised-power-tool
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Dave - The Medway Handyman
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On 17/05/2010 02:15, DanG wrote:

Hardly - a quick google will show that angle grinder fatalities are not uncommon. In fact a builder died at a junior school local to me a few years ago as a result of copping a diamond blade to the neck. He bled to death on the scene in front of his son before medical help could get there.
Granted not all of these are the direct results of kickback as such - but some form of loss of control of the tool or falling onto is typically the cause.

There is good Makita safety video that quite nicely demonstrates the common lower leg injuries that occur when a grinder with diamond blade hits a typical bit of meat under clothing.

Just because something is sub optimal for cutting flesh, does not mean it won't.

Its a reciprocating saw with twin counter moving blades.
http://www.dewalt.co.uk/powertools/productdetails/catno/DW390 /

Rather than continuing the willy waving, perhaps we can agree that an angle grinder is not the tool for this job and leave it at that?

Perhaps you might care to review some of these: (Warning, some of these are graphic)
http://www.head-face-med.com/content/4/1/1 http://www.sswahs.nsw.gov.au/liverpool/trauma/45m.html http://www.news.com.au/breaking-news/man-near-death-after-angle-grinder-accident/story-e6frfku0-1225820724743 http://www.citizen.co.za/index/article.aspx?pDesc 2382,1,22
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Cheers,

John.

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-snip-
Cool tool. I don't think they are available in the US. all I get when I search for Alligator saw is those chainsaw/loppers with the scissor action- http://www.buzzillions.com/reviews/black-decker-electric-alligator-saw-lp1000-reviews
The downside of a reciprocating saw is their tendency to pull light material back and forth if it isn't secured.
Can you, for instance, cut a small branch off a tree and keep both hands on the saw without it shaking the bejeebers out of the tree?
Jim
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