4 1/2" grinders

SteelSlaver

SteelSlaver

Joined
Feb 17, 2007
Messages
3,375
I know there has been some discussion and concern about using 4 1/2" grinders to cut steel.

Well, right now I am in charge of a job rebuilding the silencers on the intake ducting on a 75 megawatt combustion turbine (appox 100,000+ horse power)
4 9'x9' pieces of ducting each containing 10 8'x8' baffles. To remove the baffles required 160 2+3/8" cuts of 1/8" steel. Then to disassemble the 40 baffles required cutting out appox 1300 ft of 1/8" fillet weld. After I experiment with scarfing and carbon arc I settled again on 4 1/2" grinders ( I have done this job before) 4 guys using Dewalt 10 amp 4/1/2 grinders went thru approx 375 .045 slitting disks about 125 1/8" disks and maybe 40 1/4" disk in 5 10 hour days to complete disassemble. these were skip welded over 1/3 of their perimeters with 2 4'x8 perforated metal "screens" per baffle. Mostly ground the main part of the weld out with 1/8" then slit the final inside corner with the .045. NO exploded disk, no injuries what so ever. Most people won't go through that many disks (over 500) in a couple life times. Required safety gear. Long sleeve shirts, ear plugs, safety glasses, face shields regular leather gloves.

Cutting with 4 1/2" grinders is fine if you know what your doing and wear your gear.
 
Like most powered tools in the shop, you have to respect there potential for damage. I have 3 of them on my welding bench and can't think of how I would function without them.

Work safe, Fred
 
Incut my blanks out with a 4 1/2" grinder. I've never shattered a disk.
 
I just cut a dozen blanks and used about a quarter of one of the super thin "Pferd" disks- they outlast the Forneys at least five to one.
Face mask, heavy gloves, CLAMP THE WORK PIECE, glasses, CLAMP THE WORK PIECE oh, and did I mention that you need to CLAMP THE WORK PIECE?
...looking at my reattached finger joint...

Yes, I was extremely stupid for one brief moment, one sad little day.
 
When I first got into knife making, I went with a 4 1/2 variable speed angle grinder, instead of a bandsaw. I'm really happy with it. I use nothing but norton wheels, and they last for a long time. They cut steel extremely fast and easy.

I use a sabre saw with a high quality metal cutting blade to make tight cuts. Its not as fast as a bandsaw or the angle grinder, but it gets the job done.
 
All those 4-1/2" inch wheels that were used wore down and were floating in the air that you breathed. I noticed you didn't use a respirator.
 
A grinder disk will cut through stuff that will just strip the teeth off a bandsaw blade and laugh at you. I love my bandsaws, but, grinders have a real place too. I don't, but. I believe I could cut out a decent profile and rough grind the bevels from bar stock to blank faster with a couple grinders, 1 with .045 disks and the other with 1/4 faster than I can with a saw and belts. Plus, the 1/4" would just laugh at the mill scale as it sailed away, where it eats belts. But, then I have used up lots of disks and wore out a lot of 4 1/2", 7" and 9" grinders. But, the thing is I can cut more inches of soft steel with a saw than with disks per $$$.

We used Pferd disks and yes we wore respirators for most of the work. Not only is there grit and metal dust, but fiberglass from the reinforcement in the disks and the frames are filled with insulation material held together with fiberglass cloth. We also wore steel toes boots and during various stages of the work other gear. We removed the ducts bodies from the turbine building with a 180 ton crane (100 ton would have worked) and used body harnesses and lanyards for high work, anything over 10' required this. Where there was a lot of movement we installed a "ratline" a steel cable that ran the length of the work to hook the lanyards too.

I will say that I WOULD NOT buy a Harbor Freight grinder. Although they may be fine for occasional work, for hard use and professional work the only one I really like is the Dewalt like the http://www.dewalt.com/tools/metalworking-grinders-small-angle-grinders-d28402.aspx. (Usually a little less than $100) The paddle switches are the only way to go IMHO and most of my co workers. The Metabos are also very popular and expensive. They also make ones that handle 6" wheels. Another great feature about the Dewalts is they have a simple mechanism for loosening, positioning and securely locking the guard in place at the position you need. This is very important as the ease of adjustment means guys are less apt to try grinding in the wrong position or something because of the way the guard is positioned. With this system in a couple seconds you can more the guard anywhere you need it. PS that same paddle switch is excellent on end grinders too.

We could have used fewer disk by using less pressure on them, but, disk cost was not as big a factor as man power cost and the timeline. Today the blasted and repainted frames should be back to start reassembly. I know I am supposed to be retired, but this was the perfect little 3 week job, that will help my projects fund and end in plenty of time for me to get everything ready for elk camp.
 
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I use a Dewalt at the office and a B/D Firehawk at home. both have paddle switches and easily adjusted guards. I also use a variable speed Makita, but it does not have a paddle switch. I remember many accidents that would not have happened if the grinder had been equipped with a paddle switch.
size the job, don't use a 4 1/2 when a 2" will do ok. don't use a grinding disc if a wire wheel would do.
at the office we are stuck with whatever cutting or grinding disc F*st*n*l has in stock this week
how do you control heat at the cut? it won't matter too much if you go blue on the handle, it changes the whole HT scheme if it is part of the blade.
Scott
 
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Wish you had some pictures Jim--- sounds like quite a job!!! :eek:

I totally agree with 'ya, they are an amazing tool.

I think the issues that have come up mostly boil down to the number of guys tinkering in their garage that simply don't seem to have much common sense when it comes to working with tools. ***Anybody here remember the guy that was saying you could profile a blade with a carbide router bit... holding the steel in one hand and the router in the other!!! :eek: :eek: :eek: :rolleyes:***


I actually hurt myself this summer using a 4.5" grinder with slitting disc.... :o :foot: LOL. I needed to take apart a couple press dies. They're pretty beefy--- there's a piece of 1" thick X 4" wide X 8" long flat bar welded to them. Had the die shoe held in the big vise, and I was scoring the welds with the slitting disc so I could separate them.... Accidentally cut all the way through the welds and the flat bar fell off and right onto my ankle. Of course I was wearing shorts and tennis shoes... the standard gear for a fab shop ;) LOL

INSTANTLY had a goose-egg, looked like I had a golf-ball under the skin!

Now, I could go on and on about how the angle grinder hurt me... or I could nut up and admit that I should have put a clamp on the bar just in case, shouldn't have cut all the way through the weld, and should have had more protective clothing on.

But this is the interwebz and the world of immediate gratification, so surely it was the evil angle grinder's fault!!! :grumpy:



;) :D


Great post Jim. :)
 
I really hate angle grinders, not because of injuries I have sustained or blown up disks. They are just so loud and they spray sparks in all directions that can start fires later and have burned through some of my shirts. I only use it outside. However there are many tasks in knife making that it is simply the best tool for the job, so I still use it all the time, begrudgingly.
 
As already said, this is a cool job. Last summer my family got a private tour of the Cold Lake Air Force Base, where my cousin headed up the maintenance of the F-18s. We got an up close look at the jet engines that power these fighters and it was way beyond cool. He is now in Germany doing his Masters Degree in Engineering specializing in jet propulsion. He got married this year to a girl from Germany who has a Masters Degree in Engineering. She specializes in corrosion prevention in orthotic appliances. I made them a W2 bowie as a wedding present. They thought my hobby is pretty cool. Go figure.
 
I teach week-long metal fab classes now and then, and though the potential for serious injury may be greater with other tools, the hand held 4-5" grinders are the ones that send people to the doctor (not in class so far) way more than any other tool. If it's not sparks and debris in the eye, it's a fire, or work piece catching and twisting, falling as Nick said, disk grabs and cuts through a glove. Goes on and on. It's the only tool that's sent me to the doctor, and I'm up to three times now. Two of those times it was clearly operator error.
They say buffers are worse, but there are simple guards and catchers that minimize that if you take a minute and install them.

And given all that, they're still an incredibly useful, if not irreplaceable tool in almost every shop.
I've got a bit of hardened D2 that needs to be annealed, but it's too big to go in my forge- the cutoff makes short work of that, I'm going out to the shop now to do that...but you can bet I'll have my gear on and clamp it down good. :)
 
Clamping it down right is going to save you a lot of heartache.

I have a vise set horizontally at thigh height. So I can just stick the bar stock in and its ready to cut. I prefer cutting with the work piece a little bit lower, so I have more control, and I can see over it much better.
 
I always cut on a flat surface and use a sacrificial backup board- just a piece of scrap plywood about a foot square- so the disk can't go too deep and grab, on a platen table you just slam a dog down on it and go.
 
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