Using 4-1/2" angle grinder as sander/polisher

[joeswamp]

I have a bunch of old crusty body hammers I'd like to polish up, and I also have an electric 4-1/2" angle grinder. My grinder is single speed and runs at 10000 rpm.

I was thinking about taking the guard off and getting one of these:

https://www.amazon.com/dp/B01JKA0KN2/?tag=atomicindus08-20

and then just ordering a whole bunch of hook and loop disks. I figure start with 50 or 80 grit to get the dings out and then just progress up the range. 5" disks go up to something like 2000 grit. They also offer these extra soft pads that go between the disk and original pad, so you don't change the shape of what you're sanding.

The disk pad is rated for 10000 rpm, but are these disks going to just fly off like frisbees if I attempt to do this? Do I need to get or borrow a 5" variable speed grinder?

Also is it unwise to attempt this with a regular grinder? Should I be using a DA polisher?

 

[rlitman]

Hook and loop discs at half that speed will fly off dangerously. Forget about trying them at 10000 RPM. Yes, a variable speed grinder would be better.

 

[PugetDude]

If you do this, wear eye protection and post a video.

 

[joeswamp]

I will wear a full face shield and possibly a suit of armor.

Hook and loop sanding disks (and the pad) are rated to some pretty high rpms, I was curious as to what the practical range is.

 

[Stooge]

I have a hook & loop pad for some coarse surface conditioning discs I use on a grinder. The discs themselves are woven and semi rigid but a little pliable. They work fine at first but catch a slightly off angle and the pad will go flying, (spun off and caught my leg once but it hurt as much as being hit with a small piece of balsa wood or thick cardboard) and can damage the backing pad then nothing is going to stick to it. I think I bought the first one from Lehigh Valley Abrasives and was pretty short lived, then I bought a few from McMaster or MSC and they have been fine.

I've only used them on car bodies though, the discs go flying pretty quickly on anything that isn't a flat surface, and even sometimes with places that are. i don't think they would work well for refinishing hammers.

 

[dogdog]

I think grinders are mostly brushed AC/DC motors , will work with those HF router speed controllers for cheap (works up to certain slow speed, weak torque at lower speed)... besides that HF have that polisher for cheap.. at least it can do some what orbital actions... Yes I have two, and it works fine...

 

[rlitman]

I think grinders are mostly brushed AC/DC motors , will work with those HF router speed controllers for cheap (works up to certain slow speed, weak torque at lower speed)... besides that HF have that polisher for cheap.. at least it can do some what orbital actions... Yes I have two, and it works fine...

The HF router speed controllers are ****. At 90% of your RPM, you've lost 50% of your torque, and it only gets worse from there.

The polisher is a better idea.

 

[OhioRandy]

What about using a flap disc? They work well and can leave a smooth surface.

 

[Tinner]

Hook and loop discs at half that speed will fly off dangerously. Forget about trying them at 10000 RPM. Yes, a variable speed grinder would be better.

Have you ever used one? We use them at work on a regular basis. They work fine, we use them on 7" and 4 1/2" grinders, 7-11,000 rpm. The discs occasionally come off, usually due to operator error. There isn't enough mass there to do any real damage.

 

[Krang]

Flap discs (the actual flappy kind) would be ideal. You can get them in some very fine grits too, and work with those higher speeds. Just keep in mind your going to be removing a ton of material


Sent from my iPhone using Garage Journal

 

[Krang]

Like this kind:



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[sqznby]

I have a bunch of old crusty body hammers I'd like to polish up, and I also have an electric 4-1/2" angle grinder. My grinder is single speed and runs at 10000 rpm.

I was thinking about taking the guard off and getting one of these:

https://www.amazon.com/dp/B01JKA0KN2/?tag=atomicindus08-20

and then just ordering a whole bunch of hook and loop disks. I figure start with 50 or 80 grit to get the dings out and then just progress up the range. 5" disks go up to something like 2000 grit. They also offer these extra soft pads that go between the disk and original pad, so you don't change the shape of what you're sanding.

The disk pad is rated for 10000 rpm, but are these disks going to just fly off like frisbees if I attempt to do this? Do I need to get or borrow a 5" variable speed grinder?

Also is it unwise to attempt this with a regular grinder? Should I be using a DA polisher?

If all you're doing is cleaning up these tools, I'd try a DA sander/polisher.
You can get every grit under the sun from 40 to 8000.
If you have a bench grinder with a wire wheel, knock everything down with it then go to town with the DA. Or grab a wire wheel for the 4.5 grinder and go to town.

 

[joeswamp]

I ordered the pad from Amazon and will try it on a piece of scrap. If it blows up I'll look into getting a DA sander/polisher.

Never thought about a flap wheel, I've never used one. Seems like it would work, although it looks like you can't get the really high grits.

 

[terryo1965]

I run a similar pad on an angle grinder with hook & look discs, never had a problem with discs flying off unless I put them on half assed to begin with. I like flap discs too, but sometimes you need to run finer grades than 120.

 

[joeswamp]

Tried it out this morning, here's the verdict: The discs don't fly off, they work fine. However it is almost impossible to have any degree of control at 10000 rpm, metal just gets removed way too fast. With an 80 grit disc I think I removed 1mm of steel in about a half second.

I was trying to avoid changing the shape of the hammer face, so I used a soft interface pad (an extra soft pad between the yellow pad and the disk) to conform to the surface. However I still changed the shape of an old junk hammer head. I also managed to sharpen the edge of the hammer face (supposed to be rounded), and I can't round edges with this setup -- disc will catch and come apart. It is easy to catch the edge of the disc on the work and then the edge of the soft pad gets chewed up.

I think what I need here is a slow angle grinder with a coarse fiber disc to shape the head, then I need this soft pad sandpaper setup (again at slow speed) to polish the faces.

 

[sqznby]

I thought it would be handful, 10k rpm is fast and will work quickly at removing material. The DA would be a better option but will not be able to reach into the nooks and crannies but, it would do a great at finishing and prepping for polishing, especially with the pads available.
Another option would be a Dremel type tool or maybe am electric die grinder. You'd have plenty of options for tooling and bits with that, that's for sure.

 

[OhioRandy]

Try clamping your grinder in a vise as apply the hammer to it. Might have more control.

 

[PugetDude]

Soft Steel or Brass wire wheel in the drill press will get into the nooks and crannies.
Clamp something to use as a tool rest to leverage against to prevent the tool from going airborne and taking out your teeth.

 

[engineer2]

I wonder if the HF variable speed control would work to slow it down:
https://www.harborfreight.com/router-speed-control-43060.html

 

[mike13u]

We polish everyday with 4.5 grinders. You just need to buy the grinder models that have variable speeds and slow it down. Both hook-and-loop and sticky back abrasive paper work fine. I like the diskit brand pads similar to the yellow ones above.
If you know what you are doing, you can polish that hammer face to a mirror finish with a VS grinder, a backing pad as you show above and papers 180-600g.