Thread: Cutting metal - angle grinder/ cut off saw or both

Thanks was just a bit concerned with the safety .

Thanks for the concern, as someone whoe works alone in the workshop for extended periods of time I take the traditional pilot's approach - there are old metalworkers, there are bold metal workers, there are no old, bold metalworkers...

Originally Posted by TomH

Good evening all,

I am about to enter the world of welding thanks to the GMC clearance through ebay. I did learn welding at tafe some time ago for a couple of days, and intend to practice solidly to develop my skills.

Whilst I own loads of woodworking tools I do not have many suitable for metal work. In a month or so I need to make the frame for an outdoor chair (my mum has the design), which will involve cutting RHS. I do not own an angle grinder or a cut off saw. It sounds like I definitely need the angle grinder to clean up welds, and was interested as to whether I could use the angle grinder to cut RHS to a sufficient degree of accuracy or do I need to purchase a cut off saw as well?

Cheers,

Tom

Hi Tom

RHS stock can be cut with an angle grinder.But there are provisos that should be followed.

Given that angle grinders are so potentially dangerous and injure many people I will offer some guidelines to follow,if you are inexperienced with them.

1. First there is eye protection / face protection which I will give reasons for later.
   
2. Second is both hands using the tool and always leave the handle fitted.
   
3. Thirdly use a cutting wheel for cutting and a grinding wheel for grinding and use the appropriate wheel flanges. for the depressed center and flat discs. Always check the disc speed rating against that of the angle grinder.

Hold the material to be cut in a vice so it can't twist and jam and break the blade when cutting.

Imagine a jam when cutting and the blade shatters,whats you choice of eye protection then, specs or full face visor ?

Though you will see many do it,angle grinders should not be operated one handed. Bad cuts to the free hand which is usually holding the stock can be a result.

The thin cutting wheels available do a great job and an advantage is when they do grab and shatter in a cut, their mass when propelled towards you is far less than the standard wheel.This is not saying you are totally safe with a thin wheel as they can do damage.

Given you take some sensible precautions and proceed safely you will find that for light cuts in RHS you can get away with an angle grinder. My choice would be one with a dead mans switch, ie turns off itself when released

For bigger jobs ,ie multiple and heavy cuts .the dedicated cut off saws are the go.
hope that helps

Grahame

Thanks for the replies - I appreciate the safety advice. I would agree that a face shield is necessary when using the angle grinder. I work in an industrial environment and eye / face injuries are always concerning, and I am aware of how angle grinder discs can disintegrate.

I was looking for angle grinders and notice there is a massive difference in price in the same size range, even in the same brand, and it's all down to power. So my next question is, given I will be cutting RHS & grinding, how much do I need? I have listed makita prices as I have never been let down by a makita tool.

1400w $324
1020w $267
840w $152
710w $153
710w $97

Any thoughts?

Tom

Personally I'd go for as powerful as you can afford. The trade-off is that generally more powerful is heavier but that is an advantage in some cases as the grinder has more intertia and doesn't buck about as much either.

The problem that you will have with a 5" grinder when cutting RHS is that you won't get much depth of cut as the disk wears so you'll be changing disks frequently. There's not much that can be done about that if you are restricted to the 5" grinder.

You may be better off looking at buying a bandsaw for cutting (and if it's cheap and doesn't cut to within a thou of a right angle it's still going to be better than you'll do free-hand with a grinder anyway) and a cheaper, lower powered, grinder for grinding use only.

If you're going to be doing a lot of grinding, you want at least a 1000w

Originally Posted by Gavin Newman

The problem that you will have with a 5" grinder when cutting RHS is that you won't get much depth of cut as the disk wears so you'll be changing disks frequently. There's not much that can be done about that if you are restricted to the 5" grinder.

Sorry Gavin, I'm going to take issue with this... I understand what you're saying about depth of cut being limited due to the size of the grinding wheel, but since when do you need to cut a new piece of RHS straight through with one cut? RHS has four sides, ranging from 1.6mm to 6mm wall thickness. Mark all four sides with a cut line, and cut one at a time. If you're having dramas cutting through the wall thickness because your blades too worn down, then I think you have bigger issues!


Tom, if you're going to spend $324 on a 1400W angle grinder, then you'd be better off with a 2400W Makita cutt-off saw for not alot more. Then get a cheapie angle grinder for grinding and the portable cuts. If I didn't have my Hitachi and Ryobi Tradeline grinders already before I got my cut-off saw, then I'd just buy 2 $20 grinders. Not only will you then have one for cutting and one for grinding, when one packs it in, you bin it, you've got a back-up grinder to continue the job, while you go out and buy another.

Just a word about the thin cut off wheels. I have probably gone through more than 100 of these since they became available, mostly cutting shs, angle, pipe, bar, galvanized sheet, but also a fair bit of tool steels. I use them on angle grinders and on a small table saw. On the table saw, which also has an overhead blade guard and water cooling, I have made cuts as long as a metre in sheet metal. Despite a number of times where significant sideways forces have been placed on the wheels while operating, none of the wheels have shattered. This of course does not mean that they will never shatter.

The most common problem is starting the feed too quickly on a corner or edge which can take a small chunk out of the wheel which unbalances the wheel. If it is a small nick I generally continue but some nicks can be so big to make the wheel unusable. If the wheel is is newish and the nick is not too big and mounted on a table saw I have use a grinder dressing or devil stone to remove the nick. The advantage of doing this on the table saw is you can feed the devil stone very slowly into the wheel - this is much harder to do the other way around using an angle grinder

The other thing that happens if the wheel has been slipping on the arbor is the wheel breaks off in a neat concentric circle around the arbor. This is a relatively harmless event because the wheel just flops off the arbor and stops turning very quickly. This is more likely to happen on an angle grinder than the table saw.

Yonnee

I understand what you are saying, it's just that after doing that the first 100 times it gets very annoying. If you lash out for either a cutoff-off saw, a 9" grinder or a bandsaw it's so much faster and more convenient especially when you are doing a couple of hundred cuts a day.

I would go with a 5" angle grinder and a 14" netal cut off saw...

Bigger than 5" for general grinding and they just get too heavy for out of position grinding..

Originally Posted by Gavin Newman

Yonnee

I understand what you are saying, it's just that after doing that the first 100 times it gets very annoying. If you lash out for either a cutoff-off saw, a 9" grinder or a bandsaw it's so much faster and more convenient especially when you are doing a couple of hundred cuts a day.

I totally agree. If you were doing those sort of quantities of cuts, you'd be silly not to invest in a cut-off saw. I was asked to build a car trailer for a mate of mine, and factored into the quote was the price of my Makita saw. It does make it so much easier to not only cut large pieces in one go, but to cut them square too.

Yeah can vouch for the Maktex drop saw. Use it every day in the shop, must admit it has surprised me haw long it has lasted, considering the stuff I have cut with it. Can lack a little on power when cutting 4mm plus wall thickness stuff, so I take it slow & or rotate the stuff being cut.

Nothin wrong with starting out with a 4 inch Ozito grinder. Bought mine in late 90's, havent managed it kill it yet. Leave a wire buff on it these days, too lazy to keep taking it off. Sounds a little sick now, but still keeps going. Besides it leaves the five inch for cutting and grinding duties.

Thin blades, yeah have broken a few, am as careful as I can to minimise the flex in em whilst cutting. Definetely less stress on the grinder. Recon they are a must on the cordless grinders, even the good ones.

The 9 inch, hell it spends more time with a masonry disk on it then for metalworking duties. Gets a good blow out & an occasional strip down to remove the conc dust.