Chris152":3q7lieqz said:
sunnybob":3q7lieqz said:
But.... a disc cutter with a wood carving blade has a bad reputation. Stumpy nubs (a skilled woodworker on you tube) had a very narrow escape (but blood and gore was involved) and now hates the things with a vengeance.
That's that off my list of things to do then. I was seduced by short videos of people removing wood swiftly, I guess they omitted to show the fails...
I borrowed an angle grinder once, to dismantle the kids' climbing frame and it was pretty dodgy - the off switch was sticky and I had one catch which put the heeby jeebies up me. But I can see we need to learn to work with one at some point - the lad's starting a welding course in September so hopefully they'll show him how to use it then, I'm certainly not the person to do it after my brief encounter.
Don't be totally put off the angle grinder, so long as you use it safely with
proper cutting accessories you'll be fine. It's a very versatile tool (Disc cutting, grinding, flap-wheeling, wire-wheeling, polycarbide wheels, etc....) and a
must-have if you're doing any kind of work in steel.
As Bob says, Stumpy Nubs did have an accident with one, if you haven't seen the video it is here:
[youtubessl]IIQu1e8DGUw[/youtubessl]
In a sort of impromptu case study, let's dissect what happened maturely without tarring all cutting equipment with the same brush, as there are a number of factors at play in Stumpy's accident that almost made him his namesake. The first factor is it is the chainsaw-type of cutting wheel, which has recently been effectively banned (token gesture) from being sold/marketed as an angle grinder attachment in the UK due to the high risk of injury:
https://www.gov.uk/government/news/uk-safety-alert-issued-for-angle-grinder-chainsaw-disc-attachment
The risk of injury comes from the fact that these cutters are poorly designed with little to no chip limitation, with any rotating cutter that is hand-held or manually fed by a human should be designed with chip limitation in mind. Chip limitation is where you have a piece of material in front of the cutting part of the cutter that limits the amount of material that can be removed in a single revolution, without it a cutter is free to take a full depth of cut in a single revolution, you may have seen this on "anti-kickback" circular saw blades in the past, like this:
The nodule in front of the carbide tooth is raised from the saw plate to be about 1mm or so below the cutting arc of the tooth, which means the saw blade can only ever remove 1mm of material in a single revolution thereby helping to prevent a serious kickback. The chainsaw angle grinder attachments do have a depth gauge as with a regular chainsaw chain, but this only limits the depth of cut on a plunging cut rather than a scraping cut on the side of the wheel which is used most of the time with these attachments as shown in Stumpy's video.
The second factor is that Stumpy was effectively climb-cutting with the grinder. If you watch the video when he is carving out the workpiece you can actually see that he is struggling to control the grinder as it's bouncing about in his hands a bit, that was an early warning sign that the machine was liable to kickback and cause injury. This was happening because he was (possibly inadvertantly) using the wrong side of the cutting disc for his positioning, I'll show you in this little diagram below:
So as with any piece of woodcutting equipment with rotating cutters, be it a router, spindle moulder, planer, or saw there is a general rule that you work
against the rotation of the cutter (there are some rare exceptions to the rule where climb cutting is preferable but 99% of the time you will be working against the rotation). I've marked on the image where the cut should be taking place in green to keep control of the grinder as you will be working against the cutter rotation in his particular position on the workpiece, but as shown in the video most of his cutting appears to be happening in the spot marked blue which means Stumpy is cutting
with the rotation of the cutting wheel, climb cutting is the term used for this. Now, as you can see from the video Stumpy appears to be struggling to control the grinder as it digs into the material with the rotation of the cutter until it eventually digs enough that it "climbs" the material towards him, where a chip-limited tool may be controlled the unlimited cutter bites deep with each revolution, My Makita 4 1/2" grinder spins at 11,000RPM, which means in one-tenth of a second it will rotate
18 times, with the possibility of taking such large bites so quickly it uses the full power of the motor to fling itself back towards Stumpy as though it was a pinion gear meshed to a gear rack.
The same is true with cutting metal with the grinder also, if you are cutting a steel sheet with the cutting wheel in a vertical plane (the grinder nut would be facing to the left horizontally) you would want to cut with a pull cut as this would be working against the rotation of the cutter resulting in a safe and stable cut. Trying to cut with a push-cut in this position would make the grinder climb up the cut and try to shoot across the piece of metal.
The third factor in the seriousness of Stumpy's injury (This is my opinion, it is a bit of a contested subject) was glove entanglement. Now, using these attachments isn't a totally pleasant experience as you do get pelted with wood chips so one may be tempted to wear gloves to help prevent being sand-blasted by the chips, but this is a very dangerous practice with rotating machinery. Stumpy was going to get a pretty nasty injury, gloves or not, but I believe it may have been made more severe because of the cutter biting and pulling itself into the glove. You should never use gloves around rotating machinery for this very reason, where a solid piece of flesh would simply be cut, a loose glove with catch on the spinning cutter and the injury made worse. In theory, gloves should be fine on a grinder because you should have both hands on the grinder at all times (one on the body and the other on the handle) but I think with this type of tooling the risks outweigh the gains.
A fourth factor that may have been a contributor to the accident is that Stumpy Nubs has a neurological tremor in his hands that causes them to shake, I believe this generally isn't an issue with stationary machines, but when trying to manhandle a grinder I would imagine this doesn't help.
Now, if you're cutting wood like the above example and the chainsaw attachment isn't the one to use, which one is? You should buy from reputable companies such as Arbortech or Saburrtooth who have had years of research and development go into their tools (Arbortech started out because the owner thought the chainsaw wheel was way too dangerous!), Yes, they are more expensive than the cheap Chinese alternatives but can you really put a price on your own wellbeing? A hand or any bodily injury is debilitating and can put you out of work for a very long time if not on a permanent basis if the injury is severe enough.
https://www.arbortech-tools.com/
https://www.saburrtooth.com/
Both companies make excellent and safe-to-use products, there is still an element of danger to the cutters but they are far safer than any alternatives. The Saburrtooth cutters in particular are a very good one to purchase for a beginner for shaping wood with an angle grinder as they are more of an abrader than a cutter, with chip-limitation built into the tool by having the teeth only protrude so far away from the body of the tool.
In all, use the grinder with safe cutting techniques, use safe cutting equipment, avoid wearing gloves, and always wear safety glasses if not a full-face visor. If you follow those you will be as safe as you can possibly be!
