Replies

1. 
   AdamCherubini | Jun 04, 2006 02:08pm | #1

   I'm interested in a grinder too. Wouldn't the speed of an 8" grinder be faster than a 6"? Doesn't that sorta defeat the purpose of a slow speed machine? Also, the 8" would leave a smaller hollow. Not sure if that's better or worse.

   I'm looking forward to your responses,

   Adam

1. 
   Patto | Jun 05, 2006 09:26am | #2

   Adam,

   The old wheels were much bigger than 8" for just that reason.  (Speed)

   In my opinion, an 8' grinder will require fewer returns to the grinder between sharpening on whatever stone system you use. This is beacuse it takes longer for your honed bevel to become too large to work easily. For turning tools, you also probably have better contact with the bevel close to the cutting edge.

   The downside is that the metal is thinner a fair way back from the edge. If you are touching up plane irons and paring chisels with a low grind (25-30*) you will find that it is very easy to blue the corners because there is just nothing to transfer the heat.

   periodic dipping in water is not sufficient - smooth, light passes across the whole width of both iron and wheel work. I rest a bare finger about 1/2" back from the edge. If this gets hot then you will burn the steel.

   Dave

1. 
   AdamCherubini | Jun 06, 2006 12:33am | #4

   "an 8" grinder will require fewer returns to the grinder between sharpening on whatever stone system you use. This is beacuse it takes longer for your honed bevel to become too large to work easily. "Isn't it just the opposite? Both bevels are the same. Same angle. But the smaller wheel has a deeper hollow in it. So you can hone many times, keeping your hollow. When the bevel is flat, hollow, gone, then (as legend has it) you go back to the grinder. No?Help me.Adam

1. 
   Patto | Jun 06, 2006 01:59am | #5

   Adam,

   Depends on how you measure the 30*. If it is the cord between the back of the hone to the top face of the iron, you are right as shown in the attached. if it is tangential to the wheel then it is the other way. In either case the difference is pretty marginal. I guess that I just like the flatter grind.

   If you are grinding to a cord angle and hone untill bevel is flat there is no difference because the grind intersects the top at the same place.

   Would certainly support the argument for a solid grinder. I have an Abbot and Ashby. You can rest a 20c piece on edge on top of it while running.

   I hate these threads- now I have to go and see just how I set up the grinder.

   David

   Edited 6/5/2006 7:01 pm ET by Patto

1. 
   AdamCherubini | Jun 06, 2006 02:17am | #6

   I get it and I don't get it. I get the part about the tangential grind, but how would you ever hone something like that?Adam

2. 
   Patto | Jun 06, 2006 06:02am | #7

   You Wouldn't - it was me trying to solve geometry in my head (I should know better) and getting it wrong, I just didnt say it very well.

   Dave

3. 
   hdgis1 | Jun 06, 2006 06:18am | #8

   Given that the thickness of the chisel and the angle of the grind are the same, the length of the bevel will also remain the same from wheel to wheel. However, what will differ, is the depth of the hollow and the thickness of the remaining steel. 8 is thicker and (assuming the same outside RPM of both wheels) seems that it will blue slower. I read a damn good explanation of blade geometry and wheel size a long time ago but cant remember where it was. Maybe in Leonard Lee's book? Try a professional sharpener and see what they say.

2. 
   jc21 | Jun 05, 2006 04:05pm | #3

   "what advantage (if any) an 8" grinder gives over a 6" model." ...............none to quite a few depending on what you buy. In the shop at work we have a Northern Tool 8" grinder and a HF 8" grinder/buffer- wouldn't give you a nickel for the both of them. The Northern is gutless and both vibrate losing parts time to time. Both are 3600 rpm- imho too fast; too easy to overheat the steel. For my own use I've got Delta's 23-275 http://www.7corners.com/7c_store/showdetl.cfm?DID=1&offerings_ID=-1162244437&ObjectGroup_ID=71&CATID=16 and have been pleasantly surprised. It's a costs more ($175) but I think worth it. Slow speed, heavier, quieter, smoother and  more powerful ( 8 amp) than a six incher, it's one of the better Far East imports I've used. It's not perfect; one of the stock wheels was seriously out of wack and the tool rests require a wrench for adjustment as well as a little tweaking to make them parellel to the wheel. If you've got the $ (I didn't), get a US made Baldor which you will probrably be able to  pass down to your kids.

3. 
   mike4244 | Jun 06, 2006 05:25pm | #9

   Look for an 8" 1750 rpm grinder. The larger the wheel the less hollow grind you get. 6" grinding wheels give you a more pronounced hollow grind,not as desirable as an 8" wheel grind. When grinding plane irons and chisels and turning tools you only need a shallow hollow grind. I have used both, I own a 6" 3450 rpm. I bought this grinder 40 years ago,still waiting for it to die so I can buy an 8" grinder.

   mike