Grinder on full speed up to what grit?!

zzknives

zzknives

Well-Known Member
Hey guys,

Will get a bigger more powerful ( 3 hp) grinder soon :D

Only problem... no variable speed

So I was wondering to what grit you grind on full speed

I´ll still have my smaller variable speed grinder right next to the bigger one so I´ll probably use the bigger one for profiling,rough shaping and to start grinds only til I have enough money saved to get a variable speed unit

Anyway I tried to do some flatgrinding on full speed up to 240 grit on my 3/4 hp grinder today and the results were not that good.

(usually grind only on full speed with the 36 or 60 grit belts)

plunge lines didn´t end up where I wanted them to be :eek:

belts were worn out in notime...:bud:

60 grit worked (as usual)
120 was worn out quickly and ruined the plunge lines
240 grit,well made a weird knocking noise and felt weird

So am I right and getting finer belts then 150 grit for the bigger grinder won´t make any sense because they won´t work on full speed anyway?

Or am I wrong and a 3 hp grinder built like a KMG with 2x72" belts is not as powerful as I think

OR are ther makers out there who grind on full speed all the way and it´s just something you have to get used to???

THX

AL

P.s which belts from Tracy Mickleys shop would you recommend Thanks a LOT!
 
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My Square Wheel Grinder is one hp. It has more power than I can use. I have never in 32 years even slowed it down by grinding anything.
 
Well so looks like you only have to get used to it and then it works as good as a variable speed one...

p.s like your website and knives!
 
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Personally, I rarely grind past 120 grit, and I knock the grit down on the edges the belt with an old file first. I have ruined more blades on 120 grit belts than all other grits combined, for some reason.
I start hand-finishing at 120 grit on granite backing, this is the only way I can get my bevels consistently flat and it is hard to screw up your plunges this way.
 
I was grinding today with my 1.5 h grinder at 100% and I keep slowing it down with the 10 inch wheel. I have no doubt I could stop it grinding


I want a 3 hp bad! :)

I try to grind as fast as possible... ;)
 
I have 2 hp running at 3450. I really have to push to get it to slow the RPM's on high.. I also use a 4 step pulley setup that runs quite fast on high, and quite slow on low. I like my setup. It will run slow enough to use my 400 grit cork belt, or fast enough for 36 grit.
 
There are too many variables to really answere your question. First of all, what is the speed of the motor that you'll be using? Then, what is the size of your drive wheel? Both of those will effect the sfpm (surface feet per minute) of the belt. I have a motor that spins at about 3600rpm with a ten inch drive wheel. That puts the sfpm way up there with a 1:1 ratio between the pulleys on the drive shaft and the drive wheel. I cut the speed way down by putting a 1.5" pulley sleeve on the drive shaft and a 5" sleeve on the drive wheel. That cuts the speed by almost 75% and increases the torc. If your motor speed is slow enough, for an 8 or 10" drive wheel about 1800rpm, you can use a step pulley like Arrow does for a poor man's speed adjustment.

Just a suggestion, speed is over rated and you might do better with a slower speed, especially with course grits. Higher sfpm will get the job done faster but requires more control. Speed will also help you screw up a blade real fast.

As far as how fine of a belt you can use at higher speeds, you can use any grit that you want. You just have to remember that you will have to watch overheating your heat treated blades a lot more closely. As in make one pass on the grinder and then cool the blade in a bucket of water. Also hold your blade with bare hands so that it will get too hot to handle before you take the temper out of it with built up heat. You may well raise a few blisters on you fingers but that will just help you learn, besides it's traditional. Just like cutting yourself as you grind in the final edge. There's a reason that burn cream and bandaids are considered expendable knife making supplies.

Doug Lester
 
well I don´t know anything about the motor yet.

all I know is that it has 3 hp and that the grinder maker knows what he is doing... 2thumbs

so I have to wait until it gets here to check and then decided if I can /want use a step pulley

wow Les you must really be pushing 2guns

Thanks Doug but I don´t use a grinder on heat treated blades
So that wouldn´t be a problem.

Like Justin I start hand finishing at about 150 which is my most flexible belt

But do have some 240 and 320 grit belts as wel which i only use ocassionally

Thanks again guys! 2thumbs
 
I have noticed that if I speed up a 240 or 320 to full speed they seem to get the blade way to hot. I profile and start my bevel grind on a 60G belt at about 70%
 
Did some further grinding last night on full speed..that was aaaahhhh lets say fun *haha*

a medium sized EDC blank I started with almost looked like a knife 3 design and size changes later LOL


A new 240 grit belt worked on full speed as well

Most have been something wrong with the belt I used before...


Anyway YES the blade got hot and YES I burned my fingers :)

Don´t feel that comfortable working on full speed yet but might get used to it...


Les I tried and could easily stop my grinder grinding too ...

Figured out what´s the secret behind our superman power ... austrian women...they feed us well LOL
 
I have a 2hp VS KMG. I will not run full-out past 120-grit. This is as high as I go pre-HT; and after HT, I won't run much of anything at full speed to avoid heat build-up.
 
I never run over 60%. Usually around 30-40% on my 1.5 hp Bader III. If you want a motor you can't bog down, get a 3 phase motor. DC motors will bog down.
-John
 
Mine is a 3 phase motor but with only 3/4 hp

So you can easily stop it if you want.

Did some further fullspeed grinding... rough grinding up to 240-grit works quite well now but when it come to the plunge lines I´d not recommend it *haha*
 
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