Cutting steel with an angle grinder

[Quandary]

I am considering modifying a boat cradle to make it more transportable. The longest (rear) cross frame is a rectangle 3.5 x0.6m. of 80x80x 3mm RHS and the idea is to cut both the long sections and insert internal sleeves of 70x 70 when reassembling. The cuts woulld be staggered so that each half would have a section about 2.1m max length. The inserts would be secured with bolts through the walls.
If I buy a good quality 125mm diamond cutting blade (recommendations sought) for my small angle grinder should it cope with that?
I also have a 9" Makita used for cutting paving slabs etc. more powerful but quite heavy and unweildy.

 

[Norman_E]

For cutting steel don't bother with diamond blades. Buy ordinary metal cutting disks. You will find that a small angle grinder will work as the steel is quite thin, but I would use the 9 inch grinder and something like these. Metal Metal Cutting Disc 9

 

[harvey38]

Mark the steel properly and I'd use a 4 1/2" angle grinder with a few decent cutting discs, easier to use than a 9" jobbie, particularly if using to cut horizontally and less flex in the actual disc.

 

[BobnLesley]

I'm with Harvey38 - the 4.5" blades are easier to cut accurately - and as Norman_E notes, there's no gain whatsoever from diamond blades; my usual/go to blade are the s/steel ones from Screwfix, Angle Grinder Discs | Power Tool Accessories | Screwfix.com I'm pretty sure that I'm using their Erbauer discs at the moment, but the DeWalts look cheap this week; any brand you've heard of will be fine.

 

[Wing Mark]

Buy a couple of decent hacksaw blades and some biscuits and just get on with it.
The biscuits are because you'll need a tea break.

 

[RobbieW]

...my usual/go to blade are the s/steel ones from Screwfix...

This would also be my suggestion, [edit] often referred to as Inox disks

 

[Daydream believer]

Use the 9 inch angle grinder. They are not heavy at all. I have a 9 inch Makita a Bosch & a Hitachi one. P..cing around with a toy is for girls. Get hold of the thing & use it. You will be through the steel before you know it. By the time you have changed blades loads of times on a 4.5 inch grinder the job will be done. Do not bother with diamond blades. Adjust the guard so you get a comfortable position.
DO NOT FORGET THE GOGGLES for eye protection. Stand to one side so the sparks do not burn the embarrassing bit out of your trousers, Do not do it next to the wife's car & do not drop it on your foot with the blade running
Place the steel so the cut opens up, not closes so it jams the blade.

 

[steadyeddy]

Use the 9 inch angle grinder. They are not heavy at all. I have a 9 inch Makita a Bosch & a Hitachi one. P..cing around with a toy is for girls. Get hold of the thing & use it. You will be through the steel before you know it. By the time you have changed blades loads of times on a 4.5 inch grinder the job will be done. Do not bother with diamond blades. Adjust the guard so you get a comfortable position.
DO NOT FORGET THE GOGGLES for eye protection. Stand to one side so the sparks do not burn the embarrassing bit out of your trousers, Do not do it next to the wife's car & do not drop it on your foot with the blade running
Place the steel so the cut opens up, not closes so it jams the blade.

 

[steadyeddy]

Be very careful when using a 9 inch grinder as they are heavy and can fly back when using one a guy in kent was using one when it jumped back and cut the archery on his neck ,just saying.

 

[snowbird30ds]

An archery on his neck? You mean a bow tie?

 

[pandos]

Be very careful when using a 9 inch grinder as they are heavy and can fly back when using one a guy in kent was using one when it jumped back and cut the archery on his neck ,just saying.

Second this... Dangerous noisey yokes.
Much better with a 4 and 1/2 grinder with those thin discs for stainless steel.

I did a lot of steel work in the past and have both sizes and a battery worked one from Aldi.

I was getting structural steel fitted a few weeks ago and the contractor whom I have known from way back, but have not used for 20 years produced a 4.5inch hilty rechargable to cut a 6x6 column, marked it like a carpenter with a pencil and square and cut it perfectly. No fuss no great racket or danger and a near perfect flat accurate cut.

 

[Rappey]

I've cut more large bolts, shackles and chain than I care to remember. Nearly always with a 125mm as access is often a problem for a larger grinder.
The company usually supplies me erbauer as that's what screwfix sell.
Recently I had some packs of bosch inox, fast cut rapid. Claimed 30% longer life. They are noticeably faster cutting and last well !

 

[DownWest]

Second this... Dangerous noisey yokes.
Much better with a 4 and 1/2 grinder with those thin discs for stainless steel.

I did a lot of steel work in the past and have both sizes and a battery worked one from Aldi.

I was getting structural steel fitted a few weeks ago and the contractor whom I have known from way back, but have not used for 20 years produced a 4.5inch hilty rechargable to cut a 6x6 column, marked it like a carpenter with a pencil and square and cut it perfectly. No fuss no great racket or danger and a near perfect flat accurate cut.

Wot he said. Mark it out and go with a small grinder. I do a LOT of this and only use the big grinder when depth of cut is a problem. Just make really sure that the later cuts do not try to close up on the disc. Thin 125mm discs prefered. 1 or 1.5mm. Used carefully, you might do it with one.

To add: 'Diamond blades' are used for stone, not steel. Toothed tipped blades are good for steel, but I really wouldn't use one in an angle grinder, only in a cut off rig.

 

[earlybird]

I'm late to the party, but I too wouldn't use my 9" grinder to cut up a trailer. The risk of the disc grabbing and resultant nasty injury is always there. It would happen in an instant. 4 1/2" grinder is adequate and much less risky.

 

[cherod]

If you are familiar / competent with grinders ( then you would not have to ask ?) then use the 9 “ , if not then the smaller one , One point not mentioned , use as a cutting , ie front of the disc , small contact area , not as in a grinding manner , larger contact area

 

[mickywillis]

Or if you can get one, far safer to use a Plasma cutter if you can get your hands on one?

 

[cherod]

Or if you can get one, far safer to use a Plasma cutter if you can get your hands on one?

Yes , and get someone to show you how to use it !!??

 

[Bouba]

I have a plasma cutter and a chop saw for metal. But the tools you use all the time, in order, first the angle grinder, next the electric drill and third the stick welder.

 

[DownWest]

I too, have a plasma, but it would not be my first choice for this job.

 

[waynes world]

4.5" Gary the Grinder is best way to go. I have done so much with them. Once tried a 9 inch but as folk have said, nah .

besides things like work benches and tables this i have made with the 4.5" grinder with the 1mm thick type of discs and so quick and easy.

Although now i have a band saw to do this much quieter and accurate.