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    • Alan Longmire

      IMPORTANT Registration rules   02/12/2017

      Use your real name or you will NOT get in.  No aliases or nicknames, no numerals in your name. Do not use the words knives, blades, swords, forge, smith (unless that is your name of course) etc. We are all bladesmiths and knifemakers here.  If you feel you need an exception or are having difficulty registering, send a personal email to the forum registrar here.  

Grinder question

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I'm not an expert in motors, at least not where knowledge between brands and such is concerned. I know enough to make a system that works.

A few things to understand. First what power outlets are available to you? I'm limited to 120V, so that narrows my choices when choosing a motor/VFD. I can still get them, but realistically I'm limited to a 1.5HP motor. Some of those choices have a 240V input for the VFD and some have a 120V. Second, some of those motors are non-vented (TENV), which considering that grinders will be run for long periods of time, having a fan to keep it cool would imo be mandatory. The magic letters I look for are TEFC (totally enclosed fan cooled). I'm not saying for sure that TENV can't be used, just that I don't know if they're the best choice. Third, keep the motor frame type in mind. That's going to determine the size of the arbor for when you're looking at drive wheels. Third, I don't know if the packages are different, but generally when getting the motor you're going to have to wire it yourself. That means wiring/crimping tools and a basic understanding of wiring diagrams. The motors will come with one, often on the motor itself, and so will the VFD. Like I said before, I like the OBM chassis, just it requires some effort on your part.

When I put mine together I followed the advice this gentleman put on his review. I used this VFD and while I couldn't find my exact motor it was almost identical to this one. To directly answer your question, if I had to pick between those options I would choose either this one if I had a 230V power source or this one if I was limited to 120V. Same motor, different VFD for different voltage inputs. Why? TEFC, 3600RPM, 1.5HP, price looks fair. I don't like the first one simply because the motor is 1800RPM, I prefer 3600RPM. Personal preference, you can make a sheave system to compensate for it, I just prefer the simplicity of a direct drive wheel. I can't say if Leesons are any better, I don't know brands too well.

Just a little more reading material to take up your time, I read this guys material all the time and it has all been extremely useful to me. This one explains electric motors/vfds for grinders, this one explains the importance of belt speed, and this one is a calculator he made to help you get the speed you're looking for. It helped me, hopefully it helps you as well. There's a lot of guys here who really are experts with AC motors, so hopefully they'll chime in and give you some good advice as well.

Edited by P Jones

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Thank you so much for the info.

I have been spending lots of time reading.

But that leads me to more question.

Do you like the LED display?  Is is a knob only style better?

Currently I can do either 110 or 220 in my shop.

So is the bigger motor better?

Is 1HP enough or is 1.5 better?  Now on some 1.5 motors they and go both ways.  

Looks like not to much price difference between the 1 and 1.5 motors.  Looks like a bigger jump in price with the VFDs.

The sealed VFDs are kinda pricey.  But looks like I can get the OBM, VFD, motor, and small wheel attachment for the cost of the KMG 3 speed machine.

I ll just add the big wheel later.  

Also some guys are saying that they wear a groove in the platen.  They put a peace of glass on th eplaten to prevent this.

What's your thought on this?

I have not wear a grove in my home made grinder so ....

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MORE POWER! :lol:  Seriously though, I can stall my 1hp motor if I really lean on it.  As for the glass (actually pyroceramic, much harder than glass), I have worn a groove in mine.  Only took 12 years of sporadic use.  I've been meaning to get a new one for the last few years, but it's only now becoming a small issue.  I imagine if I used it hard every day it would only last a year or less.  And it's cheaper to replace than steel.  Or easier, at any rate.  I have heard of guys using hardened O-1 platens, but again, the pyroceram is easier.  Just bolt a shallow shelf to the base of the platen as insurance and attach the pyroceram with JB weld.  I have heard of using double-sided carpet tape as well, but since there will be a mess somewhere (inside or outside the pants) if it lets go I went with the more permanent idea.

There are ways around a sealed VFD, such as putting it in another room with long leads to a panel on the grinder, putting it in a box with filters and a CPU cooling fan, etc.  Whatever works for you.  Just remember an open VFD will evaporate in a puff of expensive smoke if any metal dust gets inside.

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So I was doing some reading on D Comeau Custom Knives.  Like above, Thanks P Jones.

He says this set up could be run 110 or 220.

When I click the link I only see 208-230/460 VAC.

Before I spend is this going to be ok?

Or I could just go the 110 rout he listed for the 1.5HP motor.  Of course it says the same thing about that motor as well.

I think I ll just call them tomorrow.

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OK shows what I know.  Not a lot.  LOL

It's the VFD that can take 220 single phase and convert to 220 3 phase or 110 single phase and convert to 220 3 phase.

So both motors I am looking at are about the same.  The difference is in the VFD.


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