The Most Incredible Knife Sharpener I Have Ever Used

[Nathan the Machinist]

I have 3 master electricians and 1 engineer in the family. But none are knife people. What type of VFD is available that could be used to run very slowly on a 1 x 30 set up? Any leads? I will build 1 or 2 or 3....

I am not familiar with that industry, but surely someone here is?

a variable frequency drive running a 3-phase motor at 5-10 Hertz coupled to a 2:1 belt drive system can run a knife grinder pretty slow. My grinder goes down to 3 hertz. we use Leeson inverter duty motors that tolerate the lower speeds without excessive cogging.

 

[Lorien]

You have plenty enough spare parts and you can do it. Here's a hint for a V low RPM type set up:

that makes way more sense to me than a belt grinder for what we're talking about

 

[Azula Gun Holsters]

Wanted to see what I could do with a couple of kitchen knives with broken tips. Have had these kitchen knives for many years and they were dull, a little bent and the tips were broken. My wife is a little hard on knives.
Ran through belts 130, 220, 800, 1000 and then the leather strop belt. Just curved up at the end to create a new tip which worked. The new tip is rounded but sharp to the very end. I used a tub of water to dip the blade into between every pass on the 130 and 220 belt and every couple of passes on the 800 and 1000 belts. The blade felt cool the whole process. I ran the AMK-75 at a slower speed and made a fast pass each time over the belt
The two kitchen knives were sharpened at 15 degrees each side and are extremely sharp. Really sharp.

I also ran a used scrapyard 411 over the sharpener , using the water dunk between passes. The 411 came out very sharp as well and the tip easily cut 6oz leather.

I have enjoyed using the AMK-75 and my knives are sharper than they have ever been.
My only concern would be heat build up as Nathan mentioned. Need to confirm if the water dunk is sufficient to control heat build up.

BROKEN TIP KITCHEN KNIFE CLAMPED UP AND READY TO GO

DUNKED IN WATER BETWEEN PASSES TO CONTROL HEAT BUILD UP

BROKEN TIP ON TOP VERSUS REPROFILED TIP ON BOTTOM

KITCHEN KNIVES HAIR POPPING SHARP

SCRAPYARD 411 VERY SHARP

SCRAPYARD 411 TIP CUTTING THROUGH 6oz LEATHER WITH EASE

 

[bluemax_1]

I hope this post is appropriate, seeing how there's an ongoing discussion of sharpening systems vis-a-vis their potential for overheating an edge:

Nate, AGH asked if dipping the knife in water before each pass is enough to potentially avoid overheating the edge. Based on your post about burned edges, and the tiny mass at the very edge, coupled with the AMK-75's slowest speed of 1000rpm, I'm thinking that this might not be enough to prevent overheating the edge?

What about something like a Tormek wet grindstone (stone spins in a water tray, and operates at 90rpm)?

 

[Tim the Wizard]

Love the potential of machinery but i'm sticking to waterstones. Happy to sharpen a knife or two here for community members that have put their Carothers to good use.

 

[Nathan the Machinist]

I hope this post is appropriate, seeing how there's an ongoing discussion of sharpening systems vis-a-vis their potential for overheating an edge:

Nate, AGH asked if dipping the knife in water before each pass is enough to potentially avoid overheating the edge. Based on your post about burned edges, and the tiny mass at the very edge, coupled with the AMK-75's slowest speed of 1000rpm, I'm thinking that this might not be enough to prevent overheating the edge?

What about something like a Tormek wet grindstone (stone spins in a water tray, and operates at 90rpm)?

Yeah dipping in water won't do much, that's not the same as wet grinding, it will take an edge that was already overheated and has already cooled back down (takes a fraction of a second) and get it wet. Nothing accomplished. I'm speaking from real first hand experience here. The only utility would be if the edge stays wet and if the belt gets damps. While it is possible to burn an edge on a wet belt it is harder to do.

To be safe you should use a reasonably sharp belt, avoid heavy grinding pressure, keeps things moving and use a low belt speed. Water helps but isn't critical on resharpening unless you're removing a lot of material.

We use water here but we're also trying to do the job in a few minutes.

 

[WhitleyStu]

To be safe you should use a reasonably sharp belt, avoid heavy grinding pressure, keeps things moving and use a low belt speed

The very basics of a good grind right here. Good belt, proper pressure, keep the blade moving to decrease grind lines and low speed belt surface feed. I seldom run my 2x72 at over 40%-50% thus keeping the edge cool. Now if I were a blade maker and hogging off steel then the speed would be much higher.