Which pneumatic grinder for grinding welds? 12000 or 20000 rpms?

[Spooled-up]

I'm in the market for a grinder to do some finish work after welding. There are basically two kinds of pneumatic grinders I've found, but they are significantly different. Having no experience with them, could someone recommend which one to get to finish off a piece after welding?



Here's the first type:

3102 Super Duty



This type has 1/3 hp and a 20000 rpm free speed and you can use various tools such as grinding stones and sanding pads on it - kind of like a Dremel on steroids.



Here's the second type:

3445 Super Duty



This is a larger tool at . 8 hp and only spins at 12000 rpm. It looks like it only takes 4. 5" grinding wheels.



I'll be grinding on 12 ga sheet metal and up to 1/4" mild steel for now. My compressor is a 60 gallon vertical IR with 15. 8cfm @90psi output. I haven't even fired it up yet and have to wire it up in the garage as it's 230 volt. I've got to put a sub-panel out in the garage to run the welder and compressor. (Sears had a red tag on the compressor one day and I stole it from them for $500 -couldn't pass it up)



I had been hesitating to do this because we were thinking of moving, but I could end up waiting for months to start using all these tools! The next guy will appreciate the sub panel out there if he spends any significant amount of time out in the garage.

 

[nickleinonen]

for grinding welds, go with the angle grinder. . the die grinder is good for carbides and the 3" roloc sanding/surfacing disks, but if you are taking off metal [grinding a weld down or veeing your metal for welding] a course disk on the grinder will work best. . and for finish work, you can use the flap wheels. .


at work i have a 4" CP angle grinder in my toolbox. it gets used often for prep work and some finish grinding after i bubblegum stuff together. i had a die grinder until my toolbox was raped and emptied of all the good stuff [auto dimming welding mask, flashlights, various hand tools, air tools... ] and it only really got used for making small holes bigger or slotted, veeing out cracks before welding, and for deburring engine parts [crankshaft counter weights, internal webs, gears... ]

 

[MA2LA]

definatly go with the angle grinder. you will have a larger selection of wheels to choose from and it will remove more material faster. I have never realy liked air powered grinders for heavy grinding though. My weapon of choise id a Milwaukee 4. 5in 13 amp grinder. its a little bigger than most grinders but it has the power of the big boys but is very useable. and add a 6" cutoff wheel and it cuts like crazy.

 

[Spooled-up]

I never really considered the electric ones. I guess I just assumed that with a compressor I should be getting air tools. I guess they have more horsepower? Any other advantages to electric?

 

[JFaulkner]

If you do end up getting an air grinder make sure you get wheels rated for that RPM. A friend had one explode and he spent the night in the hospital getting grinding disk removed from his legs.



I've also found that a flap wheel on an angle grinder works great for smoothing out welds because they don't cut deep groves a regular disk will.

 

[MA2LA]

well there are a few advantages, whee every you have power you can use it, a good electric will have adjustable speeds witch helps with cirtian grinding wheels.

 

[GHarman]

I would get both! I have used both kinds, Angle and die, pneumatic and electric. Finish work can involve flushing an over bead or touchup of the toe of a weld with the overbead intact. Prep for a root weld, tack weld tapers and high spot removal between passes.

Radial flap wheels remove metal better than a hard disc for flushing and leave a nicer finish. Match your wheels with the max RPM of the grinder. GregH

 

[DCreed]

anouther question would be ,where are you using it? An electric is NOT the tool of choice in the rain. And under hard/ continuous use electrics get HOT. Also most air tools are lighter and less bulky to work with in tight quarters. That said I use my 4 1/2 electric near every day and it works fine, it's also got ALOT of options for abrasives. Whichever you choose ALWAYS wear eye protection! A brand new wheel can shatter on its first rev! You'll only go blind once so save that for shine! LOL!

 

[Rebel Ram]

I've been working with steel for 25 years. I've used pnumatic and electric grinders both. In order to have enough air to run a good grinder you will need a BIG compresor. A good quality electric grinder will be much easier to use and use much less energy. If you need to remove lots of metal, get a 9" electric. For most jobs a 4" will be more than enough.

Also to get an air powered grinder that will perform like an electric it will cost 6 times as much. Just my observations.

BTW, 20K RPM is more than any wheel can take over 1" round.

 

[GHarman]

anouther question would be ,where are you using it? An electric is NOT the tool of choice in the rain. And under hard/ continuous use electrics get HOT. Also most air tools are lighter and less bulky to work with in tight quarters. That said I use my 4 1/2 electric near every day and it works fine, it's also got ALOT of options for abrasives. Whichever you choose ALWAYS wear eye protection! A brand new wheel can shatter on its first rev! You'll only go blind once so save that for shine! LOL!

Good Stuff! One other thing! Very important. You will thank me when you get to hug yer Grandchildren! Wear a RESPIRATOR when you are grinding. Lots of Weldors and Fitters I know have Respiratory diseases because they were to "TUFF" to wear a nosebag. Your lungs are not designed to filter abrasive dust, binders and metallic dusts. If you ignore anything else I have written about, do yourself and yer family a big favor and wear the proper PPE. GregH

 

[Spooled-up]

Thanks for all the stuff to think about guys.



GHarman,

I never would have thought to wear that kind of protection. Is a simple disposable mask enough, or is there a specific kind of respirator to wear?

 

[nickleinonen]

Thanks for all the stuff to think about guys.



GHarman,

I never would have thought to wear that kind of protection. Is a simple disposable mask enough, or is there a specific kind of respirator to wear?

at minimum, an N95 rated paper dust mask that seals well to your face. . there are many good N95 dust masks but all they do stop is dust, not fumes.



safety glasses at minimum. . goggles are better [i normally use a face shield/welding mask at work as i have prescription safety glasses]

 

[GHarman]

For occasional light grinding the neoprene fitted edged dust masks will work, With SAFETY GLASSES, another important piece of PPE. NIOSH has specifications for respritory protection. A good act to follow. If you blow your nose after using a dust mask and the results are dirty. The mask doesnt work! I have used MSA half mask and Full face respirators as well as PAPR's. None of these supply oxygen. THEY ARE NOT USEABLE IN A POISONOUS ATMOSPHERE. YOU MUST HAVE AN OUTSIDE OXYGEN SOURCE in the case of LOW OXYGEN, NO OXYGEN or POISONOUS GAS ATMOSPHERE. I had to say this! I hope you understand. Heavy Grinding on rusted metal, Metal edge preparation in a production mode is a heads up for best quality respiratory protection. Its your health and longevity we are discussing. Binders in grinding wheels include fiberglass, and fuming resins that are N. G. , Dusts from Iron Oxide and Dusts from disintigrating Silica* grinding wheels is like breathing microscopic glass knives*. Foreign made grinding discs and abrasives may include ASBESTOS in the binders. KNOW WHAT YOU ARE GRINDING ON AND WITH! I am telling you these things based on more than 35 years in Welding & Fabrication, Maintainence Pipefitter. Dont Be Scared, BE ADVISED and PREPARED! Use earplugs or ear muffs to protect your hearing. Take CARE of YOUR most important PRECISION TOOL, YOU! Have a GREAT EXPERIENCE! Oo. GregH