Converting sander/polisher to grinder

[Darwins Child]

I have recently patched some salt-spalling on the low-point of our garage floor using quikrete sand/topping mix and, try as I might, I could not level them with the rest of the surface of the floor. The patches are raised above the floor approximately 1/16", or perhaps as much as 1/8", which makes squeegeeing the floor more difficult than it should be.

I'd like to grind the patches down to pretty much even with the floor surrounding them and then finish that part of the floor with some epoxy floor-coating specific for garage floors. The area of the floor that contains the patches is no more than 9 ft2. The patches themselves add up to a total of maybe 4 ft2.

I figure that the patches can be ground down with a grinder in under 15 minutes. A rental place has quoted $47 for a so-called dustless grinder and $25 for the grinding disk for 1/2 day, plus tax. I'm seeking an alternative.

I have tried our son-in-law's belt sander, but it's inappropriate for this job.

I've seen some youtube videos of water-lubricated concrete countertop grinder/polishers, but nobody rents them around here.

I've got the very nice variable speed 7" Hitachi sander / polisher shown in the photo below. I also have a shop vac to suck up dust as it is created.

Is there a kit that converts a polisher / sander into a grinder of any diameter?

Thanks.

[barncobob]

Maybe a Ryobi 4" angle grinder would work, I bought one at HD for $27..im guessing they have abrasive wheels for concrete as well as steel.

[SouthArk370Z]

Finding an adapter shouldn't be difficult at just about any store that sells power tools.

The polisher should work well, but I would be very careful to not let it overheat. Give it frequent long breaks. Don't push it - if it is getting hot quickly, stop and get the right tool.

Edit: Dust is going to be a big problem. Be prepared.

Edit 2: The load of grinding concrete is probably going to be substantially more than polishing. I'd go with grinding discs that are smaller than 7". The smaller discs will take longer to do the job. But they don't sling dust as far as bigger ones, so that's a plus.

[ChaseZ]

This is the type of bit you need. It is a diamond concrete polisher. Concrete finishing stores sell them, and fits right in to an angle grinder.

X2 on dust!
Though these won't be as bad since they are what is intended for the job. Pretty much aching else will throw up clouds of the stuff that gets into and coats EVERYTHING.

[SouthArk370Z]

Originally Posted by ChaseZ

This is the type of bit you need. ...

I've never used one of those but it looks like it would do a MUCH better job of keeping things smooth/level than a grinding disc.

[Darwins Child]

Thanks, guys.

I've checked prices of diamond grinding cups and concrete / masonry grinding wheels. The cups are very expensive. The wheels, not so much. For example:

https://www.lowes.ca/grinding-polish..._g1198226.html
or
https://www.lowes.ca/grinding-polish..._g1198210.html

They have good reviews and I'm almost certain one will last long enough to grind down what little area has to be leveled.

Because I had to run someone to the airport this morning, I've yet to call a tool place to see about an adapter for our sander / polisher, but here's an example of an inexpensive 6A, 4-1/2" grinder:
4-1/2 in. Angle Grinder | Princess Auto

So, for the cost of a rental, I could have a new tool (that I need like a hole in the head) and a grinding disk.

But for this one simple, quick job, I was hoping to get an even less expensive adapter for our 11A sander and install one of the above concrete grinding disks.

Regardless of which tool I end up using, because of the certainty of a lot of dust, this will be a two-person operation. My wife will hold the large-diameter hose of our hearing-destroying shop-vac (that sucks like the black hole at the center of our galaxy) right where the disk will grind and eject the concrete. If the hose is kept close to the contact point, this should reduce the dust to a bare minimum. (Add this to the list of Famous Last Words.) Just to be safe, I'll move our Outlander and Z out of the garage and down the street some safe distance from any potential dust.

Thanks again, folks.

[SouthArk370Z]

Originally Posted by Darwins Child

... So, for the cost of a rental, I could have a new tool (that I need like a hole in the head) and a grinding disk. ...

Originally Posted by Darwins Child

... dust, ...

I highly recommend that you exhaust the vac outside. Either move the unit or use some tubing to duct it. Most shop vac filters are designed to trap rather large particles (saw dust, chunks of mud, &c) and the finer cement dust will blow right through.

[Darwins Child]

A Hitachi-brand wheel-guard assembly by itself is going to be around $25, or so, so a new, inexpensive 4-1/2" grinder it will have to be.

[Darwins Child]

Originally Posted by SouthArk370Z

I highly recommend that you exhaust the vac outside. Either move the unit or use some tubing to duct it. Most shop vac filters are designed to trap rather large particles (saw dust, chunks of mud, &c) and the finer cement dust will blow right through.

Good idea. Will do. Thanks.

[ChaseZ]

Yeah the diamond grinding cups are not cheap. Infinitely better, but not cheap. Did you check if princess auto has a knock off version? Never know with them what they have. I noticed a week or two ago they had the big helicopter concrete finishers now so maybe they do have more like products.

If you use a disk to grind it hose down the floor first. It will help catch dust and make cleanup easier. Still use the shop vac as well of course.

[Darwins Child]

Originally Posted by ChaseZ

Yeah the diamond grinding cups are not cheap. Infinitely better, but not cheap. Did you check if princess auto has a knock off version? Never know with them what they have. I noticed a week or two ago they had the big helicopter concrete finishers now so maybe they do have more like products.

If you use a disk to grind it hose down the floor first. It will help catch dust and make cleanup easier. Still use the shop vac as well of course.

Thanks.

This is about as close as PA gets to a diamond cup-grinder:
4-1/2 in. Carbide Tungsten Flat Disc-Flat | Princess Auto

I just noticed that PA has some 4.5" masonry grinding disks for $3.99, so I'll give one of them a try first-off.

I'll probably buy this grinder:
Mastercraft 4-1/2-in 6A Angle Grinder with Bo | Canadian Tire

[ChaseZ]

Originally Posted by Darwins Child

Thanks.

This is about as close as PA gets to a diamond cup-grinder:
4-1/2 in. Carbide Tungsten Flat Disc-Flat | Princess Auto

I just noticed that PA has some 4.5" masonry grinding disks for $3.99, so I'll give one of them a try first-off.

I'll probably buy this grinder:
Mastercraft 4-1/2-in 6A Angle Grinder with Bo | Canadian Tire

I'd be tempted to give that first linked one from PA a try. Good thing about them is if it doesn't work to your satisfaction they will return it no questions asked.

I've had a zillion of the cheapy Mastercraft and Power Fist angle grinders over the years. Mastercraft no long has lifetime warranty on them. PA as mentioned will return anything. In some cases it's worth buying a decent one but not always. Given that super fine dust you're going to subject this one too I'd get the cheapest one you can as it will have a truncated lifespan to be sure.

[Darwins Child]

Originally Posted by ChaseZ

I'd be tempted to give that first linked one from PA a try. Good thing about them is if it doesn't work to your satisfaction they will return it no questions asked.

I've had a zillion of the cheapy Mastercraft and Power Fist angle grinders over the years. Mastercraft no long has lifetime warranty on them. PA as mentioned will return anything. In some cases it's worth buying a decent one but not always. Given that super fine dust you're going to subject this one too I'd get the cheapest one you can as it will have a truncated lifespan to be sure.

Thanks for the advice, Chase. I appreciate it.

I contacted a Hitachi tool service center this morning, described what I proposed to do with our Hitachi sander / polisher and then went there with the tool so that the tech could more adequately advise me.

In short, my tool's max. 3400 rpm and an arbor that does not have flat spots on its side near the gearbox make it inappropriate for even occasional conversion to use as a grinder.

The good thing is that after having explained to the guy exactly what temporary task I wanted to accomplish with a grinder, he marched over to a shelf full of used tools that were for sale, picked up a grinder, handed it to me and said "here, you can borrow this until Monday". "Borrow"! Now, there's a word you don't here too often at a business nowadays. Not only that, but no deposit or credit card was required and he even refused my offer to leave my Hitachi as collateral.

To sum up, I took him up on his offer, shook his hand, walked out the door and drove to PA, where I bought a 4.5" masonry grinding disk for just over $4. So this job is going to cost $4, plus some gas to take me back and forth a couple of times to the tool service place. How's that for a happy ending?

The only possible downside is that he also said "if you break it, you've bought it, OK?" And I agreed. This means that for this job, this particular tool is going to be treated probably the best it has in its entire life.

BTW, the guy said that a grinder is one of the most useful power hand tools that one can buy, and went on to explain some of its various uses. I was impressed to the point that I might actually buy one of the things.

[Darwins Child]

I'd like to open up this thread to a discussion of the tasks that can be accomplished with a good grinder / cutter. I need some additional incentive to buy one.

For example, I have recently "machined" some custom-design jacking blocks for the Z using 2 x 2 aluminum bar and doing the "machining" with a manual hacksaw, a really good file and lots of blood, sweat, but no tears. How much of the work that is typically done with a hack saw can be done with a grinder? Specifically, could a sober you cut a fairly accurate 1/2" wide x 1/2" deep slot in a block of aluminum and, if so, how?

What imaginative things have you done with your grinder and what have you learned, good and bad, by your experience?

Do any of you have variable-speed grinders and, if so, what do you think of it and what advantages does it have over a fixed-speed unit? In particular, what do you think of the Makita variable speed grinders?

Thanks for any comments about your grinder ownership.

[SouthArk370Z]

A handheld grinder would not be my choice for work that requires any precision. They work well enough for rough work but are hard to control. Great for removing a lot of metal but they also tend to generate a lot more heat than, say, a bandsaw - this can cause Aluminum to oxidize and steel to lose it's temper if you are not very careful.

That said, you can:
Use it as a chop-off saw for pipe, tubing, angle iron, &c
With a wire wheel/cup, remove paint/rust in a hurry
Deburr cuts made with saw a lot faster than using a file