grinder speed, size and sharpening


I am looking at grinders to sharpen stuff including lathe chisels.
Most books/resources suggest the bigger the wheel the better say 8-10 inch by 3/4-1 inch wide.
I heard some cases that it may be best to go with a variable speed 2000-3450 rpm or a slower one (about 1750 rpm) grinder for more control and or less chance of burn.
The dilemma is that I can get a 8" grinder pretty cheap (40.00 with the rough wheels) and wondering which is better to go with, bigger and faster or smaller, but more control. Variable speed @ 6" is about double the price in canada (but it comes with one cool wheel) and going to an 8" variable speed is about 3x, so if I can make an informed decision, it would be great. Sure, I can buy the 8" variable and cover all the bases but why spend more if I can meet my needs with cheaper.
I also heard that even running cool wheels (white ones), it should run at 3450 high speed for the wheel to break off its top layer and stay sharp.
Any thoughts/resources would be very welcom
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First, check out rec. woodturning. Most of the turners I know use the 8 inch slow speed grinders. On the rough side (scrapers) they use a 60 or 80 grit wheel. On the smooth side usually a 120 grit wheel. Most use a slow speed grinder, but some use a high speed grinder. With the M2 high speed steel, overheating is not supposed to be a problem (I don't know that much about metals, I just grind a lot of it). For your bench chisels and planes, you can over heat them. Every one uses different wheels. I have had white, grey, and pink with similar results. The wheels must be dressed to clean them up. Getting too much metal on them prevents good cutting action. I setteled on CBN (cubic boric nitride) wheels, They cost about $300 for a 1 x 8 inch wheel, and are made to order in whatever grit you want. They will outlast the other wheels by 5 to 10 to 1. robo hippy
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Well, slow speed and 6x1 wheels here. Rationale is that it's tougher to overgrind with the slower wheels. Used high speed and 8x1 at the school, just had to be careful to not remove too much.
Wouldn't use a white wheel on HSS. Waste of time. HSS is high-speed because it can take more heat. So why are you worried about losing a bit of sharpness if it won't overheat the tool anyway? Nice for carbon steel, though not really necessary. It's pressure that causes most of the heat. Less pressure, less friction. If you're impatient to remove a lot of steel, go coarser or to a belt.
My lathe tools, HSS and Carbon, are sharpened on the green SiC wheels from Woodworkers' Supply. They say it excels with HSS because it removes so little, and they're right. That's what I'm after, not a fresh grind, just a fresh edge. Doesn't disappear into a pile of sand in two months, either.
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so sounds like I should save the go with 8 " high speed
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Slow speed, 1120rpm, they only have the 6" right now but usually have the 8" as well:
http://www.garrettwade.com/shopping/product/detailmain.jsp?itemID 1879&itemType=PRODUCT&iMainCat395&iSubCat400&iProductID1879 You could ask them when their next shipment is.
Grizzly:
http://www.grizzly.com/products/G1036 two speeds, two wheels 1345 / 10" wheel is 70 rpm http://www.grizzly.com/products/H7759 10" wheels 1750 RPM
Lowest speed possible or you could blue the HCS steel and ruin it. As far as the speed of the grinder and the tolerances of HSS, you have all other possibilities of sharpening HCS, as well.
--
Alex - "newbie_neander" woodworker
cravdraa_at-yahoo_dot-com
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Unfortunar\tely you are looking to trade off between two factors that are both becessary, but for different reasons. To put it simply simply you want a larger wheel to decrease the depth of the concavity on the hollow grind - to deep a concavity will yield a weaker tool. This is opposed to wheel speed which factors into the liklihood or risk of overheating and burning the tool being ground. So to put it simply, for most woodworking applications you want as large a wheel as possible (8 inch dia) with the proper composition wheel White (or pink or light blue) Al Oxide wheen as opposed tot he standard grey carborundum wheels which usually come as standard on most grinders.
Yo0u want as low a speed as possible to reduce heat build up at the grind.. Buy the Delta 8 in 1725 rpm grinder and replace one or both wheels with white Al Oxide wheels, 2 grits
Another alternative would be one of the low speed water cooled wheels. They are slow to grind an original shape on a tool blank but can't be beat for plane, chisel and turning tools.
Save the 3750 rpm grinder with the grey wheels for lawnmower blades and screwdrivers!!

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Uh, wouldn't that depend on the length of the section being ground?
Have you, or other perpetrators of this myth ever figured out what the difference in depth is over a 1/4 inch?
Guess we should all get flat stones.
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I have an eight inch variable speed. I've never turned it down. Don't see why I ever would.

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Woodcraft does have a nice 8 inch slow speed grinder that I think is under $100. The only thing that I didn't like about it was that if you put very much pressure on it, it would stall the motor. This can help prevent overheating. The Baldor, 1 hp, at closer to $500, you can put a lot of pressure on it, and it won't slow down at all. robo hippy
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