[sbaker56]

Something I've always noticed is despite the fact I probably do more grinding than welding, and so do most repair/field welders and those working with hot rolled steel there really isn't nearly as much info and good comparisons online as there are for different welders, electrodes/filler and processes.

I finally bought a 7 inch 12 pound makita after doing all my grinding including heavy stock removal with a 4 1/2-5 inch Dewalt and its night and day different, the weight is actually an advantage because I can use little to no down force and still just chew through steel faster than I can putting what feels like half my weight on a smaller grinder.

I've found the brands of cut off wheel makes a major difference in cut speed and longevity, I've found in the 4 1/2 size a good 40 grit flap disc to be much faster at heavy material removal than a hard disc, but nearly worthless for heavy plate mill scale.

I can post my preferences and such, but I'm curious what you guys have to share, Are one brand of discs really faster cutting than other premium brands in your experience, do you prefer resin fiber discs or flap discs? Etc

[Oscar]

On finished weld beads, If you need to remove metal fast= 3M fiber discs with Cubitron II abrasive, coarse grit 24-36. 2nd best = 3M Cubitron II Flap disc, 24-36 grit.

If you need to remove metal fast before welding, I prefer the 3M Cubitron II hard grinding discs, but it's tougher to keep the level surface because it really gouges it out.

[Simclardy]

I just purchased the metabo 7" about 6 months ago and i don't know why i waited so long. For straight cuts or grinding work it just kills it compared to my 4.5 dewalt.
The metabo is 15amps and the dewalt is around 5a i think. So my point is a grinding disk on my dewalt is different than a grinding disk on the metabo.
Cheers

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[sbaker56]

On finished weld beads, If you need to remove metal fast= 3M fiber discs with Cubitron II abrasive, coarse grit 24-36. 2nd best = 3M Cubitron II Flap disc, 24-36 grit.

If you need to remove metal fast before welding, I prefer the 3M Cubitron II hard grinding discs, but it's tougher to keep the level surface because it really gouges it out.

I've heard a lot about 3M's Cubitron line, especially the resin discs, After seeing the video below I'm convinced if they're half as fast as they seem they're worth picking up a few. The downside is they seem to be packaged in commercial sizes, I don't need a whole 200$ box worth of discs

[youtube]https://www.youtube.com/watch?v=pDTln6BnIX0[/youtube]

The gouging problem is why I dislike removing mill scale with a hard rock in most applications. The larger grinder is much better in removing scale from a reasonably large area in a timely manner without grooving and gouging the plate all to hell but it's still not what I'd consider acceptable on thin plate, tubing etc for some applications. I've found one of those Silicon Carbide Paint/Rust stripping discs to be the best solution for removing scale very fast and without changing the dimensions of your metal. But I've found if I'm removing welds on metal that still has the scale on it, you can clog a flap disc way too quickly if you're not careful.

Some brands work much much better than others, and the lifespan while relatively short also ranges quite a bit though.


I think the importance of a larger grinder over a 4 incher for heavy metal work is really understated, at least online, maybe because to those who do it for a living it's simply an obvious fact. Maybe after some more discussion I can edit the original post to be a sort of "Grinding for newbies FAQ" type post that consolidates some of it.

[Spartan]

I'm probably going to catch some crap for this, but I use a standard thin cut off wheel on a 4.5" grinder as my go-to method for removing particularly tough mill scale, especially on plate and square tubing where you can sometimes get that bit of a dip in the metal where the mill scale is extra thick. The thin cut off wheels flex nicely to prevent much of the gouging, but are also aggressive enough to get the job done quickly and don't load up at all. You do need to have a light touch, though....to protect the wheels if nothing else.

It's technically not the safe choice, but I've never had a disk fly apart on me and only do it with the disks that have thick fiberglass reinforcement. I also always wear full PPE when grinding, so it is within my risk tolerance. Your mileage may vary on whether or not it is safe for you and your shop, but it works GREAT for me and mine.

[sbaker56]

I'm probably going to catch some crap for this, but I use a standard thin cut off wheel on a 4.5" grinder as my go-to method for removing particularly tough mill scale, especially on plate and square tubing where you can sometimes get that bit of a dip in the metal where the mill scale is extra thick. The thin cut off wheels flex nicely to prevent much of the gouging, but are also aggressive enough to get the job done quickly and don't load up at all. You do need to have a light touch, though....to protect the wheels if nothing else.

It's technically not the safe choice, but I've never had a disk fly apart on me and only do it with the disks that have thick fiberglass reinforcement. I also always wear full PPE when grinding, so it is within my risk tolerance. Your mileage may vary on whether or not it is safe for you and your shop, but it works GREAT for me and mine.

Please tell me you at least have a guard on I'll admit I've occasionally used a cutting disc to shave off tacks and other things that tread the line between grinding and cutting including shaving a bit of paint off to tack a piece or strike an arc. But cut off wheels do explode, and they do so with enough force to severely injure and kill, sometimes even enough to piece through PPE. I always cut with a guard and make sure my body isn't inline in any way to be struck if the blade were to fail because the damage they can cause is frequently far more than superficial.

Glasses.jpg (58.79 KiB) Viewed 3849 times

[Spartan]

Yup always a guard in place and making sure my face and critical bits aren't ever in line with the disk. It has worked well for me for many years, and if you only use the edge and light pressure it just wears down on the edge like normal. Those exploding disks are from people doing things other than what I describe.

However, people should always follow the manufacturers safety recommendations if they are so inclined, and only do things they feel are safe for them and in their shop. Just sharing a very cheap and effective solution that works well for me. I've tried many of those discs specific for mill scale or other similar abrading, and man are they expensive, quick to load up, or take forever to get down to the base metal. I use what works for me, and it works quite well.

[Oscar]

On finished weld beads, If you need to remove metal fast= 3M fiber discs with Cubitron II abrasive, coarse grit 24-36. 2nd best = 3M Cubitron II Flap disc, 24-36 grit.

If you need to remove metal fast before welding, I prefer the 3M Cubitron II hard grinding discs, but it's tougher to keep the level surface because it really gouges it out.

I've heard a lot about 3M's Cubitron line, especially the resin discs, After seeing the video below I'm convinced if they're half as fast as they seem they're worth picking up a few. The downside is they seem to be packaged in commercial sizes, I don't need a whole 200$ box worth of discs

pDTln6BnIX0

The gouging problem is why I dislike removing mill scale with a hard rock in most applications. The larger grinder is much better in removing scale from a reasonably large area in a timely manner without grooving and gouging the plate all to hell but it's still not what I'd consider acceptable on thin plate, tubing etc for some applications. I've found one of those Silicon Carbide Paint/Rust stripping discs to be the best solution for removing scale very fast and without changing the dimensions of your metal. But I've found if I'm removing welds on metal that still has the scale on it, you can clog a flap disc way too quickly if you're not careful.

Some brands work much much better than others, and the lifespan while relatively short also ranges quite a bit though.


I think the importance of a larger grinder over a 4 incher for heavy metal work is really understated, at least online, maybe because to those who do it for a living it's simply an obvious fact. Maybe after some more discussion I can edit the original post to be a sort of "Grinding for newbies FAQ" type post that consolidates some of it.

You can find individual disc packages on Ebay and Zoro.com. I like using the hard grinding disc for mill-scale but only if it is a low-quality fine-grain disc. Like the ones that come pre-packaged with grinders. They are so horrible at actually removing metal, but that makes them perfect for removing millscale without gouging. Another good hard disc is the 3M Green Corps disc. It's fine-grain disc that wears very slowly and doesn't remove too much metal, so it's great for quick prep on hot rolled steel.

For certain shapes like round parts, I like using the 3M Scotchbritet Clean n Strip silicon carbide stripping wheel. Lasts a really long time. I have it on a Grizzly 3/8" Air drill @ 2800 RPMs. I like it over the other style that mounts akin to a flap disc to an angle grinder because on this one you use the outer edge as opposed to the flat part (I feel the latter makes the disc wear out too fast).






Here is a link to one on Ebay that comes with the roloc holder attachment.


This is the fiberdisc I use. The backerpad I bought at Home depot, as I could not figure out which 3M backer pad had a softer composition:

[sbaker56]

I really need to pick up an air drill/die grinder or other similar tool for using roloc discs and the like.

Benchmark Abrasives is my general go to for a large selection of decent abrasives at a very cheap price. They have quite a selection of roloc pads and surface prep options such as "scotchbright" like discs. But often for certain tasks I'm willing to pay the premium for the best just to get the dang grinding done even a little bit faster. I'm definitely going to pick up at least 1 or 2 of the discs in the cubitron line for special use or to see if It's worth switching over entirely.

It would be interesting to compare similar discs between MFGs in a semi quantifiable manner, but short of a jig similar to what project farm does, It would be easy to skew things a lot via differences in downward pressure and such.

[TraditionalToolworks]

I use a bunch of different disks, The Walter Zip discs are good for cutoffs, they seem to last as long as most. In general the Walter stuff is good, IMO, for grinding discs also. I'm talking mostly about the angle grinder wheels.

I have 2 Metabos and 1 Milwaukee, bought all of them used. The Metabos are the best, IMO. I use a 6" mostly.

I like to keep a cutoff disc on one, a flap and/or grinding disc on the other, and the Milwaukee is only a 4.5" so I keep a wire wheel on that one mostly.

I have had pretty good luck with the flap discs from Lehigh Abrasives in PA. Always looking for ones that last longer, the flap discs seem to wear out faster than most people would like.

I use both zirconia and ceramic, ceramic seems to work better for wood, and zirconia for metal. But I haven't done any scientific comparisons, they both wear out.

https://www.lehighvalleyabrasives.com/a ... s-zirconia

https://www.lehighvalleyabrasives.com/a ... cs-ceramic

[TraditionalToolworks]

somehow a double post

[Simclardy]

I'm probably going to catch some crap for this, but I use a standard thin cut off wheel on a 4.5" grinder as my go-to method for removing particularly tough mill scale, especially on plate and square tubing where you can sometimes get that bit of a dip in the metal where the mill scale is extra thick. The thin cut off wheels flex nicely to prevent much of the gouging, but are also aggressive enough to get the job done quickly and don't load up at all. You do need to have a light touch, though....to protect the wheels if nothing else.

It's technically not the safe choice, but I've never had a disk fly apart on me and only do it with the disks that have thick fiberglass reinforcement. I also always wear full PPE when grinding, so it is within my risk tolerance. Your mileage may vary on whether or not it is safe for you and your shop, but it works GREAT for me and mine.

Please tell me you at least have a guard on I'll admit I've occasionally used a cutting disc to shave off tacks and other things that tread the line between grinding and cutting including shaving a bit of paint off to tack a piece or strike an arc. But cut off wheels do explode, and they do so with enough force to severely injure and kill, sometimes even enough to piece through PPE. I always cut with a guard and make sure my body isn't inline in any way to be struck if the blade were to fail because the damage they can cause is frequently far more than superficial.

Glasses.jpg

This looks like he lost control and the grinder fell into his face. It seems like the glasses are melted a bit.
I'd hate to think that could happen on a shattered blade

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[sbaker56]

This looks like he lost control and the grinder fell into his face. It seems like the glasses are melted a bit.
I'd hate to think that could happen on a shattered blade
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I found it a bit surprising such a large piece without a jagged edge would embed into glasses like that too polycarbonate safety glasses are TOUGH. It'll stop an air rifle pellet at 1000 FPS. But shattered discs really can embed into glasses as well as flesh and bone. Here is another picture where it's a bit more clear, A google search will turn up a lot more graphic pictures as well, but I wanted to spare everyone the picture of a cutoff disc embedded into somebody's face.

disc.jpg (58.79 KiB) Viewed 3741 times

I'm no safety sally, in fact I probably am a bit more lax about things than most people, but grinders are probably by far the most dangerous tool all welders including hobby welders use on a daily basis, Acetylene is probably worse, but every hobbyist in the country isn't using one of those on a daily basis.

[TraditionalToolworks]

However, people should always follow the manufacturers safety recommendations if they are so inclined, and only do things they feel are safe for them and in their shop. Just sharing a very cheap and effective solution that works well for me.

At least you had safety glasses on! One of the most dangerous things is grinding without safety glasses. Lucky you did!

I've had enough of those cut-off discs break on me that I tend to be careful with them, I don't use them in any way that would cause them to bend, as I have learned better...

No worries, I think you may have learned something out of all of it.