What Is the Best Grinder ?

[Mark Johnson]

You need a heavy grinder for removing over 1/4" thick materials. Something rotary and with a hard pad and 36 grit! This is rare... For 90% of my boatbuilding, I use a Porter Cable model 7336, 6" soft pad, random orbit sander. It will take ten years of 70 hour weeks. (Don't ask how I know).
It is perfect for feathering glass edges, fine sanding before a paint job, prepping the deck for epoxy, or bottom jobs! Unlike rotary 8" soft pad sanders, (with a 5 minute sanding disc life before it gets dull or loads up), this random orbit sander doesn't load up or dull quickly, so disc last 30 minutes... If I had known this, on my boat project previous to the last one, I could've saved thousands in sandpaper!

Mark

[Coolruns]

I agree with joey69, Metabo makes excellent angle grinders. Used them for years in the paper mills. Versatile and really take a good punishing.

[bangkaboat]

Originally Posted by boden36

If you are doing a lot for work, consider a 9" grinder and also a 5" grinder. If you get the same spindle diameter ,then the worn out disk ofr the big one will be like a new disk for the little one.
Regards,
Richard.

That is a very dangerous suggestion. A 9" disc is not made to run at the speeds of a 5".

[GordMay]

Originally Posted by boden36

If you are doing a lot for work, consider a 9" grinder and also a 5" grinder. If you get the same spindle diameter ,then the worn out disk ofr the big one will be like a new disk for the little one.
Regards,
Richard.

Originally Posted by bangkaboat

That is a very dangerous suggestion. A 9" disc is not made to run at the speeds of a 5".

Actually, I think they're made to run at about the same surface cutting speeds.

Although the 9" diameter angle grinders operate at slower spindle speeds (6600 RPM) than do the 5" grinders (10000 RPM); the slower 9" cutting wheel travels at a slightly faster surface cutting speed (1,500 -vs- 1,300 Surface Ft per Min) than does the faster 5" wheel.

SFM = RPM x DIAMETER in inches x 0.262
10,000RPM x 5" x 0.262 = 1,310 SFM
6600RPM x 9" x 0.262 = 1,556 SFM

[SabreKai]

The surface rate may be nearly the same but spinning a 9 inch disk at 10,000 rpm even after cutting it down will likely cause it to fly apart. If you are going to try it, tie the grinder down in a solid box of some sort and stand back before you plug it in. Cutting it down may impose slight imbalances amplified by the high rotation speed.

Sabre

[delmarrey]

Gord Crunch the numbers.

Originally Posted by boden36

If you are doing a lot for work, consider a 9" grinder and also a 5" grinder. If you get the same spindle diameter ,then the worn out disk ofr the big one will be like a new disk for the little one.
Regards,
Richard.

Another thing that has to be considered is the bonding agent. Grinding wheels are rated for material types. A wheel for steel will have a harder/more heat resistant bond, whereas for aluminum or bronze the bond will be softer/less heat resistant to allow the wheel to self-dress. But unless one specifically asks they get the generic wheel, for steel.

The problem I've found with FG is the wheels load up quickly. When the wheel gets hot the resin starts loading the wheel and then quits cutting, loading the wheel even more. A catch 22.
One thing I found for deck work only is to use water while grinding but it's really sloppy. The other is to use course sanding pads. They load up too but can be taken off and slapped on a board to release some of the resin. Plus they are less expensive. Once a wheel loads up, one has to grind on some steel to resharpen the abrasive and knock out the resin.

BTW, most grinding wheel arbors are a 5/8"-11. So it's good to check sizes before one buys.

[Bruce Bevan]

I would agree with Hellosailor NOT to restrict the air flow through electric power grinders. Heat is the biggest killer of electric tools. Blow out the fibreglass particles regularly to keep the cooling passages clear.

You mentioned in your post that you planned to sand off the bottom paint. I would caution you against this as the fine dust is easily inhaled and could possibly severely shorten your life. Consider using a couple of hand paint scrapers with a sharp flat file and some really good friends. Keep the scrapers sharp and you should find the paint will come off quite quickly thus significantly reducing fine inhaleable particulate. Do use a good dust mask, gloves and coverall. Not my most favorite job in the world, but someone must do it I suppose.

BB

[boden36]

Interested in the comments re using the worn out 9" wheel in a 5" grinder. I must check the specs when I get home and may stop doing it.
Having said that, during steel boat building I have done many hours using worn 9" cut off wheels in 5" grinders, without a single failure. Maybe I have been courting disaster!
Regards,
Richard.

[delmarrey]

Originally Posted by Bruce Bevan

I would agree with Hellosailor NOT to restrict the air flow through electric power grinders. Heat is the biggest killer of electric tools. Blow out the fibreglass particles regularly to keep the cooling passages clear.

That's why I recommend the gray Scotch pads, there is little to no air flow resistance. Grit and FG dust will eat up an armature, brushes and possibly bearings.

I've used and repaired grinders for over 40 years and have the scarS to prove it.

[SabreKai]

I had a 4 inch disk disintegrate on me when I put it on a grinder that turned 13,500 rpm. The disk was only rated at 10k. Don't know why it was rated at such a low rpm but I never checked it before putting it on. It was a cheap brand bought from Canadian Tire, Work Mate if I remember correctly. Sure there's supposed to be a safety factor in the numbers but having seen it happen once, and pieces fly across the room and stick into a wooden skid convinced me not to tempt fate anymore. Life is already too interesting.


Sabre

[bangkaboat]

Originally Posted by GordMay

Actually, I think they're made to run at about the same surface cutting speeds.

Although the 9" diameter angle grinders operate at slower spindle speeds (6600 RPM) than do the 5" grinders (10000 RPM); the slower 9" cutting wheel travels at a slightly faster surface cutting speed (1,500 -vs- 1,300 Surface Ft per Min) than does the faster 5" wheel.

SFM = RPM x DIAMETER in inches x 0.262
10,000RPM x 5" x 0.262 = 1,310 SFM
6600RPM x 9" x 0.262 = 1,556 SFM

I can only comment on the basis of my own experience & education. A few years ago, the nice people from Walker spent a day educating us(Vancouver Drydock) on all of the equipment they were supplying, after one of our labourers hurt himself. As we steelworkers were using their 5" grinders, exclusively, we were surprised that they spent so much time on the issue of mixing disks in the afore-suggested manner. Still, as we were paid to be there, no one complained. Now, after about 35 years of using grinders, formally & informally, I now have a piece of paper that says that I know how to use one.

However, when I was 19 & a steel fab. apprentice, I used the remnants of a 9" disk in a 7" grinder & ended up with 162 stitches in my left thigh, when the disk exploded. I had a lot of time to think about it while riding to the hospital with a first aid attendant's thumb holding my artery against my femur. So, once again, I suggest that this is an ill-advised practice.

Mike

[hellosailor]

Not to digress from grinders, but since the wheels CAN explode...I suppose a leather shop apron is still a good idea but I see kevlar and the new "bullet proof" materials have made the scene:

National Safety Apparel NSA-24"x26" Kevlar Twill Bib Apron-A02KV24I36I#

A kevlar apron designed for glass workers, but I'd bet there are better ones out there.

Memo to self...Dear Santa.<G> Cheap investment in damage control!

[HappySeagull]

Originally Posted by delmarrey

Gord Crunch the numbers.



Another thing that has to be considered is the bonding agent. Grinding wheels are rated for material types. A wheel for steel will have a harder/more heat resistant bond, whereas for aluminum or bronze the bond will be softer/less heat resistant to allow the wheel to self-dress. But unless one specifically asks they get the generic wheel, for steel.

The problem I've found with FG is the wheels load up quickly. When the wheel gets hot the resin starts loading the wheel and then quits cutting, loading the wheel even more. A catch 22.
One thing I found for deck work only is to use water while grinding but it's really sloppy. The other is to use course sanding pads. They load up too but can be taken off and slapped on a board to release some of the resin. Plus they are less expensive. Once a wheel loads up, one has to grind on some steel to resharpen the abrasive and knock out the resin.

BTW, most grinding wheel arbors are a 5/8"-11. So it's good to check sizes before one buys.

I tried a grinder (when I went after blisters in a refit 20years ago) but gave up really quick because the discs clogged so quick.It was the heat of hi-speed. And it was gouging too..A friend lent me an orbital sander and that actually worked,and didn't clog.But slow.
Great tips!Boat's due for a fixup!

[Bash]

Am I the only one who thinks of winch apes when I see this thread title?

My idea of the best grinder is someone who brings his own sandwiches, never complains about the type of beer you serve, keeps calm during the pre-start maneuvers, never gets tired, never gets seasick, sits fat on the rail, and helps fold the sails at the end of the race.

The perfect grinder would be someone who fulfills all of the above, and is not ambitious to be promoted to tactician by the end of the season.

[tager]

I was going to say "someone else."