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Thread: Belt grinder vs. belt sander
02-22-2011, 08:51 PM #1
Belt grinder vs. belt sander
What distinguishes the mere sander from the metal-hogging grinder? Sfpm? Power behind them to prevent bogging?
I'm looking at buying/making/modifying something that will be a real grinder, and wondering where the line is drawn between machines that sand and smooth, and machines that remove significant amounts of metal.
02-22-2011, 09:11 PM #2
When sanding you want to remove minor surface imperfections, with grinding you want to remove some significant amount of stock. The former doesn't need a lot of power or high SFM to get the job done.
One of those KMGs is on my "make this some day" list, but that is a long list that doesn't seem to be getting much shorter.
02-23-2011, 12:34 AM #3
As you already have figured out it is the belt SFPM. Slower SFPM sanders are designed for sanding wood. If you were to sand wood with a high SFPM belt grinder it would work but you would very likely burn the wood; hence, the lower SFPM for some belt sanders. Conversely, you can use a low SFPM belt sander to grind metal but the removal rate is agonizingly slow. The best of both worlds would be a variable speed sander/grinder.
Another point to consider, if your goal is to really “hog” metal, then you want a grinder that has a contact wheel that you can grind against. The metal removal rate is much greater when grinding against a contact wheel than when grinding against a flat platen. There are many models of belt grinders that combine both a contact wheel and platen. This allows you to remove a lot of metal on the contact wheel and then square up the work piece on the platen.
As for power needed this is dependant on the area of the work piece contacting the belt and how hard you push it into the belt. Obviously, whether you are sanding wood or grinding metal, more power is better.
02-23-2011, 04:30 AM #4
For some applications, a slower SFPM is good, such as grinding/sanding Titanium. Improves belt life. I have seen a few belt grinders set up with DC vari-drives so the SFPM could be dialed in for the job, or belt used.
Also, there are different types of contact wheels. Rubber lined for general use, or hard, even grooved to run cooler for heavy grinding.
Last edited by CougarMountain; 02-23-2011 at 07:11 AM. Reason: spelling
02-23-2011, 04:40 AM #5
Belt grinders also come in various forms for different jobs. I have owned a knife grinder or two. Bader is one brand that makes grinders for knives. What application do you have in mind?
02-23-2011, 07:46 AM #6
02-23-2011, 08:37 AM #7
I have used a Burr King 2x72 knife grinder for many years. It is probably the most used tool in my shop. It came with a 1.5 hp single speed motor which I replaced with a variable speed motor after several years of use. I highly recommend a variable speed motor for general use. The variable speed motor is 1.5 hp and is rated at 2500 rpm. The grinder has sufficient power to hog off large mower blades using a coarse grit belt. I think that I still have the Baldor 1.5 hp single speed end mount motor around if anyone is interested it it.
Last edited by Jim Williams; 02-23-2011 at 08:47 AM. Reason: add information
02-23-2011, 09:33 AM #8
Sander / Grinder
By illistration in my shop I have an older 6" x 60" Sunstrand belt grinder. This is a 5 HP machine.
When set for 2000 sfm it's a fine sander for wood or graining Alum with the correct belt.
At 3300 sfm it is great for deburring and sanding steel.
At 6500 sfm, and coolant turned on it eats steel at an alarming rate, provided you don't have too much surface contact with the belt.
Grinding (belt or otherwise) is all about infeed pressure and HP, frankly 5 HP across a 6" belt is too little and 6500 sfm wet is too slow by about 500 sfm for really agressive wet grinding.
Abrasive machining has really come into it's own in the last 10-15 years, what was once considered a finishing process is now frequenly a process of choice for heavy material removal. The newer seeded abrasives that started with the Norton SG made this possible, where it was not with the older Aloxide's.
02-23-2011, 09:44 AM #9
2 in 1
When the motor on my 2x72 belt sander/grinder died, I replaced it with a TEFC 3 phase motor and VFD. It works great and you can set speed any where you want it. It has become one of the most used tools in the shop.
02-23-2011, 10:03 AM #10
In searching older threads, and in some other forums, I came across a "rule-of-thumb" of about 1 hp. per inch of belt width, as a minimum for stock-removal. Does this make sense?
02-23-2011, 10:40 AM #11
I'd call that a minimum, yes. I prefer my 2HP 1" machine, and can still stall it if grinding a long section on the platen.
02-23-2011, 11:40 AM #12
02-23-2011, 12:24 PM #13
I have what is to me the holy grail of belt sanders, a Porter-Cable G8 wet/dry 5HP machine. I use 9 x 108 Norton belts, although there's enough width for a 10" belt. I've never tried using it wet. I believe the drive drum turns at 800 rpm and that it is approximately 10" in diameter. I never paid too much attention to details or sfpm because the beast always did what I wanted.
This sander will remove a fearsome amount of metal. I used it for beveling steel for welding, general shaping, etc. and never had a complaint. This is a pretty basic vertical belt sander. The table is fixed perpendicular to the platen, so grinding to anything approaching a precision angle is out, but then belt sanders are by definition not precision machines.
I had a Burr King 1 1/2HP sander at one time. I hated that thing. It ran blazingly fast with its 3500 rpm motor and scared the hell out of me. It's awfully light for any serious work but if you can get past the high speed and generally unsafe feel of the machine, it's okay for smaller work, I guess. I got rid of mine and never missed it.
The G8, by contrast, is very sedate and confidence-inspiring, while still hogging away a prodigious amount of metal. The problem will be finding one of the old things, since they haven't been built in ages. I believe Hammond made/makes similar heavy machines. I'd recommend calling around to various machinery dealers or checking plant liquidations. That's how I got mine, about 30 years ago. You may get lucky and find one too.
02-23-2011, 02:33 PM #14
belt sander belt shredding
when i was younger and didn't know any better i was belt sanding some 1/2" plate as hard as i could on a 9" wide belt.
was grinding too hard in one spot not trying to move piece side to side so i burnt the belt in a spot roughly in center of belt.
then pushed real hard so right half of belt broke free of left half and flapping edges got caught on table. so i ended up with a shredded belt disintegrating and getting thrown in my chest and face. one that happens once i would never push a metal piece into a dry belt sander full force or at least not without a face shield and a bullet proof vest.
i would be wary of pushing a belt sander with extreme pressure especially grinding dry.
02-23-2011, 03:53 PM #15
02-23-2011, 11:38 PM #16
Months ago I was asking myself the same Question. I have had a ¾ hp 6x48 belt sander for many years and although useful, it did not foster the enthusiasm that some folks have for their grinders. I needed to re bearing the thing and while I had it apart, as an experiment, I changed the pulleys to approximately double the speed, about 5400 SFPM. I can honestly tell you that I was surprised and truly impressed as to how much material, steel, that thing can remove. It has quickly become one of the most used and useful tools in the shop. Same belts, same motor, so to answer your question, the difference seems to be a much higher belt speed. Note that this is the same speed, 5400 ish, that most grinders are at their best. Get one.
02-24-2011, 02:33 PM #17
Awake, and anyone else interested,
I dug out the Baldor motor from the Burr King 2x72 knife grinder. The horsepower is 1, 1725 rpm, 215/208-230 volts. It is mounted on a Burr King pedestal base, has a 115 volt cord and plug, is TEFC, and is painted a pristine Burr King green. It had very little use before I went to the variable speed and is near new in condition. I would suggest not more than half the price of a new motor alone, or reasonable offer. I will try to check E-bay for suggested prices. Awake has first dibs, since he asked first. It would be nice to have it picked up, although it is in the box the replacement came in. I had misquoted the hp as 1.5 as I had not seen it in a while.
02-24-2011, 11:21 PM #18
Anyone familiar with the Kar-Ry belt grinder? Company seems to be out of business. . . .