KMG style grinder upgrade help

This is data for your new motor .

1725 rpm/5 inch drive wheel = 11 m/s belt speed
2500 rpm/5 inch drive wheel = 16 m/s belt speed
3000 rpm/5 inch drive wheel = 20 m/s belt speed which is enough ...
If we slow down.......
1300 rpm/5 inch drive wheel = 8.6 m/s
1000 rpm/5 inch drive wheel = 6.5 m/s
800 rpm/5inch drive wheel = 5 m/s
 
Natlek, I didn't realize 20m/s (around 4,000 SFPM) was fast enough for ceramic belts to really work. I was under the impression ceramics really wanted something on the order of 6,000+ SFPM ( 30 m/s) speed to really start to work and really shined at 7,000 SFPM (36 M/S) speeds.

The KMG with shaft/pulley Timos is currently using has a max speed around 4500 SFPM (23 m/s), so meets your number of 20 m/s required speed for ceramics.

Understand, I don't normally use ceramic belts - I've used them a couple of times but never felt I was getting full benefit of ceramics since my max speed is 4,000 SFPM (20 m/s). Maybe I wasn't putting enough pressure?
 
Natlek, Thank you so much. So If I use the 2X jumper on the VFD and a 5" drive I can get the 20m/s speed I need. Along with fixing my belt slip problems this should be an improvement.

Since I already have a sturdy unused pedestal and my old 1.5HP 1PH 1800RPM motor and step pulley I can use that to make a hogging grinder . If I use a 2 wheel setup I should really be able to max my surface speed? Does anyone know of any good 2 wheel grinder plans I should model mine after? I think It might be real nice to have a VFD flat platen setup alongside a 2 wheel with a work rest. I do not currently have a contact wheel at all.
 
Ken H> said:
Natlek, I didn't realize 20m/s (around 4,000 SFPM) was fast enough for ceramic belts to really work. I was under the impression ceramics really wanted something on the order of 6,000+ SFPM ( 30 m/s) speed to really start to work and really shined at 7,000 SFPM (36 M/S) speeds.

The KMG with shaft/pulley Timos is currently using has a max speed around 4500 SFPM (23 m/s), so meets your number of 20 m/s required speed for ceramics.

Understand, I don't normally use ceramic belts - I've used them a couple of times but never felt I was getting full benefit of ceramics since my max speed is 4,000 SFPM (20 m/s). Maybe I wasn't putting enough pressure?
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I m not familiar with KMG with shaft/pulley so I don t have data for speed he already have ...
Well , first I wrote almost enough ... and then deleted that almost .But many knifemaker here use that speed ... You are right .........7000- 8000 is speed where ceramic shine .I will try
these days to film short video how it looks grinding on 8000+ SFPM .
 
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If I remember correctly, the KMG comes with a 3 step pulley with the high speed position is around a 2 to 1 ratio putting the shaft around 3400 RPM giving around 4500 SFPM belt speed. Perhaps Timos will chime in to his actual pulley ratios.

Depending on the type of VFD drive, a 1750 rpm motor could be overspeed to 4,000 rpm, or maybe even the max of 5,000 rpm. At 5,000 rpm with a 5" drive wheel the belt speed would be around 6500 SFPM which would work nicely with ceramic belts. With a 5" drive wheel and the motor at 500 rpm you would have around 600 SFPM belt speed which is slow enough for fine grit belts.
 
You will still need to address the belt slipping on your drive wheel.
Looking at your setup, a 30lb spring or different tension system might be your next move in eliminating the slipping.
If you can find an old motorcycle innertube to cut a piece from and stretch over your drive wheel you could at least get a sense of what your grinder can do with proper traction.
 
timos- said:
Natlek, Thank you so much. So If I use the 2X jumper on the VFD and a 5" drive I can get the 20m/s speed I need. Along with fixing my belt slip problems this should be an improvement.

Since I already have a sturdy unused pedestal and my old 1.5HP 1PH 1800RPM motor and step pulley I can use that to make a hogging grinder . If I use a 2 wheel setup I should really be able to max my surface speed? Does anyone know of any good 2 wheel grinder plans I should model mine after? I think It might be real nice to have a VFD flat platen setup alongside a 2 wheel with a work rest. I do not currently have a contact wheel at all.
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Now you've got the right idea - if you're wanting to use ceramic belts you need a single speed hogging grinder for them. Wouldn't waste a 3 ph motor/VFD setup for that. Find a 2 hp single phase 3450 rpm motor somewhere and set it to direct drive using a 7" to 8" drive wheel - you might need a 3 hp motor for really hogging at that step up in speed. With an 8" drive wheel I wouldn't think you'd have to worry about belt slippage much at all, even with a solid aluminum wheel.

The idea of using a small innertube to slide over drive wheel is a good idea - I might try that if I can find an old tube around 2" to 3" diameter.
 
The belt slip happens as I apply pressure against the flat platen. I think what has been going on is as the fresh belt wears a bit I apply more pressure to fracture the grain but this never ends up happening becuase of the belt being pinched against the flat platen. This happens even more as I am grinding in full distal taper with a large chef knife making full contact vertically against the platen. Recently I discovered that I can get more belt life if I slack belt grind the majority of material off (i guess this makes sense since the belt is not being stalled) but the problem with this is I end up with too much material being worn off the spine side of the blade.

It sounds like a ratcheting tension system helps to prevent this but also sounds like I might get some belts to break if I go too tight.
 
The slipping is your #1 problem. Speed is secondary. If you can get 6k+ fpm belt speed, you will see a HUGE improvement in material removal and belt life. There's no reason AT ALL that you cant grind at least 2-3 10" hardened kitchen blanks with a single belt.
This will also be dependent on your ability to apply enough pressure when grinding. The belts WILL NOT "rub" steel away with any efficiency.
 
Well, I wonder then, wouldn't a steel (for mass) drive wheel with a polyurethane outer (for grip) be an ideal drive wheel? polyurethane can be made to a very specific hardness. Maybe something like D55 hardness?
 
You can get an air shock and mounting hardware pretty cheap from McMaster Carr. It helps tracking quite a bit. Your direct drive is going to make a world of difference.
 
If/when you get a new shock, consider getting one with threaded ball studs and mounting it on the left side of your grinder instead of the top. Try to get your tracking arm horizontal to the tool arm.
Not only will this help with tracking, but you'll get a bit more belt contact with the drive wheel if the tracking wheel is sitting lower.
 
If you end up swapping the motor, I'd probably look for a 56C, face mounting motor, and get a direct drive mounting plate from Matthew Gregory's friend, if he's still making them.

A rubber drive wheel will give more "grab" for the belt, but you should be able to get sufficient torque with your aluminum wheel. As for breaking belts, as long as you're buying new, quality belts, I don't think it'll be a problem. I have a 100lb gas spring on my grinder and haven't popped a belt yet. I'm confident I could go to even a 120lb spring without issue. For the KMG design, I probably wouldn't go that heavy, unless you made a longer handle for tensioning (which you may want to do anyway), but you'll probably see some improvement even with a 50 or 60lb spring.

Another option would be a pneumatic cylinder with an on/off valve. You could get up to 90 psi or so on these, and changing belts is as simple as the flip of a switch. Gonna need the valve, regulator, and a couple other odd parts, and it is a bit more expensive than just a regular gas spring/strut, but I'd say it's probably worth the extra cost.
 
Josh Rider said:
You can get an air shock and mounting hardware pretty cheap from McMaster Carr. It helps tracking quite a bit. Your direct drive is going to make a world of difference.
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I have both , pulley system and direct drive .I can t see difference .Can you elaborate what you mind with bold part of your post ? What is that that make world of difference , except possibility to easy change belt speed with VFD on direct drive ?
 
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mike-E said:
The slipping is your #1 problem. Speed is secondary. If you can get 6k+ fpm belt speed, you will see a HUGE improvement in material removal and belt life. There's no reason AT ALL that you cant grind at least 2-3 10" hardened kitchen blanks with a single belt.
This will also be dependent on your ability to apply enough pressure when grinding. The belts WILL NOT "rub" steel away with any efficiency.
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This is 3mm thick 15n20 steel and about 44 Hrc . I use square tube for jig . Just two pass and five seconds and one side is done ....................on 8000SFPM .I have no one around me now , but for other side I will try to make short video .....Many here don t understand what they are missing ............
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So, Ideally I should return the 1800RPM 1.5HP 3PH motor for a 3450RPM 2HP 3PH motor. That will give me close to 8000 sfpm with the 2X jumper on the VFD. Additionally if I get a 100lb ball end thread type gas spring I can mount that lower to get a better positioned tracking arm. I can also fit a sleeve over my existing drive wheel and lock it on with some cap screws. I can cut out a notch from the base plate to accommodate a 5" or 6" drive wheel. Ive got access to some pretty advanced hi wear plastics for that. My only worry was that I would have much lower torque with the higher RPM motor. But it seems speed of drive wheel and pressure on the belt is far more important than torque.
 
Natlek said:
I have both , pulley system and direct drive .I can t see difference .Can you elaborate what you mind with bold part of your post ? What is that that make world of difference , except possibility to easy change belt speed with VFD on direct drive ?
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How big are your motors with each set up? A belt and pulley system (apart from adding the possibility of a slipping v-belt and additional vibration) does absorb additional power/torque from the motor. Similar to if you've ever used an extension on an impact wrench, vs directly attaching the socket.

Of course, if you have plenty of "head room" (l.e., a large motor, good belt, pulleys and bearings, etc...) you probably won't notice as easily. If it's only a 1 to 1.5 hp motor and your trying to surface a large knife on your flat platen, where there's the most possible surface area contact, you may start to notice.
 
Grinding bevels at 8,000 SFPM speed is for the true experts, Check with Stacy, and a few of the other experienced knifemakers and see how many grind at 8,000 SFPM. Natlek certainly has the skill to grind at that speed, no way I'm interested in grinding at 8,000 SFPM, not even 6,000 SFPM. My 4,000 SFPM is plenty for me, and still allows my grinder to slow to 300 SFPM for those delicate grinds with fine grit, and sharpening tasks.

Won't ceramic belts work just fine at 6,000 SFPM speeds and high pressure? A platen eats up a good bit of power compared to a contact wheel. You want to really move some metal, use a 10" contact wheel at high speed.

On the concern of lower torque with a 3600 rpm motor is only at lower RPM, at the full 3600+ rpm where you need all the power the motor has, you'll still have the same torque. The only place you'll lose torque with a 3600 rpm motor is at low speeds where you're not using much power anyway so it's not a concern.

To me, the big advantage of direct drive is how much quieter and less vibration they run. I used a step pulley system for a yr or so, then built a 2X72 with direct drive/VFD and was amazed just how much quieter and smoother it ran.
 
timos- said:
So, Ideally I should return the 1800RPM 1.5HP 3PH motor for a 3450RPM 2HP 3PH motor. That will give me close to 8000 sfpm with the 2X jumper on the VFD. Additionally if I get a 100lb ball end thread type gas spring I can mount that lower to get a better positioned tracking arm. I can also fit a sleeve over my existing drive wheel and lock it on with some cap screws. I can cut out a notch from the base plate to accommodate a 5" or 6" drive wheel. Ive got access to some pretty advanced hi wear plastics for that. My only worry was that I would have much lower torque with the higher RPM motor. But it seems speed of drive wheel and pressure on the belt is far more important than torque.
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On my direct drive two wheel grinder I have 2HP 2800 rpm and 22cm dia. drive wheel .Never noticed lack of torque......On my new one grinder I have 1.5 HP and 2790 RPM motor with pulley .I just grind that blade on picture on 8000 sfpm .That mind that I use 1/2 ratio ..... motor/pulley . I would like to see one can stall that 1.5 Hp motor ...I have no idea for there come that idea that you lose torque in some circumstances...........I strongly believe that whenever someone stated that he stall motor or have no torque ...HAVE belt slipping !
 
Natlek said:
I have both , pulley system and direct drive .I can t see difference .Can you elaborate what you mind with bold part of your post ? What is that that make world of difference , except possibility to easy change belt speed with VFD on direct drive ?
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In addition to the variable speed it eliminated my belt slippage.
Tracking improved with the shock system and vibration was reduced tremendously.
I was shaking tools off the bench when I had a 3 speed setup.
 
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