Please help me best set up my new KMG

B

Bobbybirds

Joined
Aug 17, 2012
Messages
180
Hi All,

I have just taken deliver on my new KMG Chassis and I have lined up a 3hp motor and VFD and I am trying to determine the best way to set it up.

Just for a bit of background, up until now I have only been working with a cheap 1x42 frame and a 1/2 HP motor and I have zero experience dealing with speed control etc.

I have been trying to read up on RPM vs drive wheel size etc as well as desirable surface speed and I think I am overwhelmed and starting to get cross-eyed over the calculations and was hoping you experienced folks could maybe help simplify things a bit for me.

What is the range of surface speeds that most often will be worked with? If it matters I am building smaller to average sized knives and will not be looking to make swords or the like and will work with a range of materials from 1084 to the stainless steels. The reason I am asking is the motor is a 3550 RPM motor and the drive wheel on the KMG is a 4" wheel and I am trying to decide if I should be using a 1 to 1 pulley to the drive shaft and if so, what diameter of pulley to best control the speed of the motor within the ideal ranges.

Am I overthinking this? Does the fact I am using VFD negate this concern all together? I just keep thinking that 3550 to a 4 inch wheel is ridiculously fast and it might make sense to lower the speed with the pulley even before considering the VFD...

Thanks in advance for any advice!
 
3550 top end speed isn't too fast. Once you get used to it you may find that you want to go even faster.
Are you using the kbac vfd?
 
Josh Rider said:
3550 top end speed isn't too fast. Once you get used to it you may find that you want to go even faster.
Are you using the kbac vfd?
Click to expand...

The VFD is a Lenze AC Tech SM Vector and the motor is a new version of the pic below... I am actually getting these for free from a good buddy who's family business is building pumps for the oil and gas industry and they end up with odds and ends like this when big O&G companies make configuration mistakes when ordering pumps and they end up just re-ordering the correct pieces and don't care about keeping the wrong stuff (must be nice to have so much money that stuff like this isn't worth the effort to re-purpose! lol!). I take care of his entire families wheel and tire needs though my company so they are returning the favour.

smv-300_870x630_5.jpg


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I'm not familiar with that vfd. Hopefully someone with more knowledge than me will come along. If it has open vents you're going to want to protect it first and foremost or it will die on you. The metal dust from grinding will kill it.
 
Josh Rider said:
I'm not familiar with that vfd. Hopefully someone with more knowledge than me will come along. If it has open vents you're going to want to protect it first and foremost or it will die on you. The metal dust from grinding will kill it.
Click to expand...
I asked that and was told it should be a sealed unit inside, but I will confirm and protect if necessary for sure!
 
Josh Rider said:
It's pretty easy to protect it. Do you already have pulleys?
Click to expand...
No not yet, hence the reason why I want to establish what size and ratio I should be considering, like should I use a 1 to 1, 4" pulley so it is the same as if I was running direct drive to the 4 inch drive wheel?
 
I have a 3450 RPM 3HP motor and VFD on my KMG and I went 1 to 1 thinking I could change down the road just to get it up and running. I never used a 2x72 when I got it. I've now used about 5 different 2x72s of various configurations and haven't changed it.

Its really going to be a personal preference and the upside of a vfd is you get nearly infinite speed selection. Now if you find you prefer grinding really slow or fast you may want to gear it up or down accordingly. Don't over think it!

-Clint
 
I think Jose at Pheer grinders offers that VFD as an upgrade on his grinder packages. He may be able to provide some info.
 
Bobbybirds said:
No not yet, hence the reason why I want to establish what size and ratio I should be considering, like should I use a 1 to 1, 4" pulley so it is the same as if I was running direct drive to the 4 inch drive wheel?
Click to expand...

I see. I don't have a list of the shaft sizes for different frames but I've seen it here before. Like Augus7us says, with a vfd you'll have infinite speed with the vfd and 1 to 1 pulleys. The thing you may want down the road is more torque at the higher speeds and that is where a bigger drive wheel or pulley may help. (If I'm not mistaken ).
 
If you are going to run good ceramic belts, such as the Norton's or 3M's; they are built to take belt speeds in the 7,000 SFM. They also work best when heavy pressure is used. I run a 3hp on one of my KMG'S which has a 2-3-4 pulley system. I changed the 4" drive wheel for the 6" size; with the 3hp being a 1750 rpm motor, belt speed is 5400 SFM.

Ceramic belts is all about speed and pressure if you want to get everything out of this type of belt. The 36 and 60 grits tend to load up and the crystals round over instead of staying sharp. I run the 3M cubitron 984f belts which many makers on this site will agree are one of the very best belts available.
 
No reason to gear it down unless you need the torque advantage. Shouldn't be a problem with your 3HP motor. It'll run happy and have the same power at lower speeds.
I usually top out around 1.5K-2K SFPM for belt speed, I might work at a slower pace than some of the others here.

To make your SFPM easier and stop your head from swimming in the math, just multiply the circumference of the drive wheel by the RPM it's spinning. Your 4" wheel has a 12.6" circumference. If it spins at 1000RPM it will feed 12.5K inches of belt a minute, or about 1K surface feet. Easy!
 
Bobbybirds, I used to think that I needed to go faster and I did. Now I realize that for myself 4500SFM is the top speed I need to grind at and most of the time at a much lower speed. The set up you have now would be fine for me. I would use the extra speed by using a 5 inch drive wheel for grinding the profile only and 3600 SFM would do just fine for grinding bevels. If you need to go faster just use a courser belt like a 50 grit or a 40 grit or just buy a 5 inch drive wheel. Just my opinion again. I think that you should be able to make great knives with what you have. Larry
 
Thanks again guys... My worries a lessing now reading more answers. I was just worried about being too fast and cooking blades easily, but I can see that should not end up a concern with this set up assuming good belts and techniques of course...
 
I don't use the highest speed on my grinder with a VFD, I thought I would but I typically run in the 2000 range for more control and less "oops I just ground off too much."


Sent from my iPhone using Tapatalk
 
Most VFDs have an option to exceed 60hz to drive the motor faster than rated. Do NOT do this with your motor. Since it is a two pole motor, it will already be running at 3500 RPM at 60Hz. Exceeding 3500 RPM will not make the motor bearings very happy. If you want to achieve high FPM (7000 for example), use a 2 - 1 ratio. I recommend using Steel Pulleys. Grainger sometimes has some good deals on their website. Powertwist Link belts are also good to use. -Doug
 
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