Will this work? - Grinder build

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KillerGriller

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Sep 4, 2018
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Recently, I’ve been reading up on 2x72 “ grinder builds (out of curiosity more than pressing need) to see what kind of options are out there.

This afternoon I came across a used dual-5”contact-wheel grinder for cheap, and was curious about using the motor to build a 2x72? DCKnives recommends a 1-3hp motor, this one is 3/4hp, 37xxrpm and is already setup for 110v; is a 3/4hp motor workable or just frustratingly underpowered? Not having to spin both contact wheels should has to be a plus for power concerns?

I’m currently running a 2x28” for knives/metal, and have a standard 4x31” with a 5” disc I use for wood. would something like this used grinder even be worth the effort?

Cheers
 
If you can find it or afford it, a VFD is really really nice to have. I was using a fixed speed grinder and now I have no idea how I lived without variable speed. Think of how you felt when you switch from dial up to high speed internet or when you got your first DVR. You'll question how you ever lived without it.
 
Thanks for the feedback everyone.

Stacy E. Apelt - Bladesmith said:
A two wheel bench grinder just isn't going to work. You should be able to get a regular 56C frame 1HP 110V motor cheaply
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Is the limitation the power or the motor or because the motor is setup to differently?

jweber said:
If you can find it or afford it, a VFD is really really nice to have. I was using a fixed speed grinder and now I have no idea how I lived without variable speed. Think of how you felt when you switch from dial up to high speed internet or when you got your first DVR. You'll question how you ever lived without it.
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Almost everything I've read agrees with you :D
 
KillerGriller said:
Thanks for the feedback everyone.

Is the limitation the power or the motor or because the motor is setup to differently?
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It's mostly the power of the motor. Grizzly makes a 2 wheeled grinder (G1015 IIRC?) that utilizes a similar style of motor/setup and is only about 1hp. It get's the job done, but still has a number of limitations, especially when compared 3 to 4 wheel "tool arm" style of grinder.

Your best bet would be something along the lines of a 1.5 to 2hp, direct drive setup. If you have a 220V circuit in your shop, you've got a number of pretty cost effective options in that power range. You can find decent Chinese VFDs on eBay all day long for about $75 to $120, and I've found 3 phase motors in great condition for anywhere from $50 to $150. If you want brand new, you can get a 3 phase IronHorse motor from Automation Direct for less than $200.

If you only have 110VAC, then you pretty much are just limited to about 1hp, unless you spend an extra couple hundred bucks for a Kbac-27d VFD, which will give you up to 1.5hp on 110. A direct drive 1hp motor on a VFD will work on a 3 or 4 wheel machine, but just don't expect to be leaning into it too heavily.

Of course, there's always the single speed, single phase option (which you're obviously already considering), but having built 3 grinders myself, and knowing what I know now, I'd rather have variable speed, even if it meant I had to sacrifice a little bit of power to get it.
 
Drew Riley said:
It's mostly the power of the motor. Grizzly makes a 2 wheeled grinder (G1015 IIRC?) that utilizes a similar style of motor/setup and is only about 1hp. It get's the job done, but still has a number of limitations, especially when compared 3 to 4 wheel "tool arm" style of grinder.

Your best bet would be something along the lines of a 1.5 to 2hp, direct drive setup. If you have a 220V circuit in your shop, you've got a number of pretty cost effective options in that power range. You can find decent Chinese VFDs on eBay all day long for about $75 to $120, and I've found 3 phase motors in great condition for anywhere from $50 to $150. If you want brand new, you can get a 3 phase IronHorse motor from Automation Direct for less than $200.

If you only have 110VAC, then you pretty much are just limited to about 1hp, unless you spend an extra couple hundred bucks for a Kbac-27d VFD, which will give you up to 1.5hp on 110. A direct drive 1hp motor on a VFD will work on a 3 or 4 wheel machine, but just don't expect to be leaning into it too heavily.

Of course, there's always the single speed, single phase option (which you're obviously already considering), but having built 3 grinders myself, and knowing what I know now, I'd rather have variable speed, even if it meant I had to sacrifice a little bit of power to get it.
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What's the purpose of the VFD other than running a 3ph motor off of 1 ph power?

Here's a 1 1/2 hp motor that will run off of 120 vac: https://www.surpluscenter.com/Elect...HP-115-230-Volt-AC-1725-RPM-Motor-10-1027.axd Pretty spendy of course.
 
The VFD gives you a adjustable speed control, If you work small B & T blades or small Scandi grinds, You can get it done with a 1 HP,, Only Cry ONCE! Is my Motto, Not every time you use it and say, Blankldy Blank Blah! :mad:...

Get a 1 1/2 HP Variable Or get some step Pulleys and go adjustable speed, I did that until I sold enough knives to buy a Variable control years ago, Generally ,, The finer the grit of the belt, the slower you want to run it..

Every belt Grit will have a sweet spot of speed & Pressure for each Maker!:)

My first and I still use for sharpening & lighter grinding was a 2 x 72 from

www.cootebeltgrinder.com. Ive had it and used it since 1997
 
Rhinoknives1 said:
The VFD gives you a adjustable speed control, If you work small B & T blades or small Scandi grinds, You can get it done with a 1 HP,, Only Cry ONCE! Is my Motto, Not every time you use it and say, Blankldy Blank Blah! :mad:...

Get a 1 1/2 HP Variable Or get some step Pulleys and go adjustable speed, I did that until I sold enough knives to buy a Variable control years ago, Generally ,, The finer the grit of the belt, the slower you want to run it..

Every belt Grit will have a sweet spot of speed & Pressure for each Maker!:)

My first and I still use for sharpening & lighter grinding was a 2 x 72 from

www.cootebeltgrinder.com. Ive had it and used it since 1997
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So does it require a 3 ph motor (on 1 ph power) or can you use a 1 ph motor (on 1 ph power)?

Sorry if this is a hijack.
 
I bought a KMG with a 3-pulley setup, and already had found a used 1.5HP 110V motor locally for $50. It works ok, but even on a 20A circuit, I can't run all my tools at the fastest pulley configuration, because the startup draw blows the breaker with the platen or 10" wheel. I can bog the machine down a bit too, but it's not TOO bad. And it was a cheap start. Allowed me to get 2 contact wheels, platen, base-plate, tool rest, and tool storage tree for ~$1700 (several years ago now).

Now I have a KBAC-27(D?) and a 3ph 2HP motor gifted from a friend ready to replace it, just need to get the 220V line wired in my shop.

So I guess what I'm saying is that 1-1.5HP on 110V *will* work. It will also be limited in noticeable ways. If you can afford to go VFD out of the gate, you'll save money in the long run unless you get very lucky with parts.
 
I can't imagine working without a VFD, period. (I learned on the ubiquitous cheapo single-speed 1x30 (mine is Rikon but exact clone of the Harbor Freight) -- which taught me up front what would've taken me a lot longer to learn on a 2x72 - not that I'd recommend going that route!)

I picked up a brand-new 3-phase 1hp 1725 rpm motor from AutomationDirect (not an endorsement, although they were great) for $153 all-in (w/ shipping), and a KBAC-24D (not 27D - can't remember why, but the price was $238 vs. $357 from Amazon, shipping included 'cause I have Prime), so total was $391 including tax & shipping. I'm on 110v -- the VFD handles the phase conversion (you can use a VFD only with a 3-phase motor*) and the motor can be wired for either 110/220 - I wired it for 110 obviously.

I'm running the motor with the VFD set to double the RPMs, so it spins at 3450 rpm. I mostly flat grind on the platen (I make chef knives), although occasionally use a 10" rubber contact wheel, but generally only for surface finishing. I don't notice any problem with torque with the 1hp and 2x setting unless I'm really trying to hog off metal and really leaning into a piece of 2" wide hardened - but I pretty much don't do that 'cause I'm working with 0.082 anyhow and like to keep my temper. If I were making Bowies or machetes I'd probably care a lot about torque, but I'm not. :-)

Again, I vote strongly with all the folks who say you've just got to go with a 3-phase and a VFD. I remember I've seen somewhat less expensive VFDs out there - can't remember why I ponied up for the KBAC although I think it was that all the cheaper ones couldn't handle 1hp. You should definitely be able to find a used 3-phase 1 - 1.5 horse motor out there for cheap though - try Craigslist or even better check out Freecycle.org for your area. I almost guarantee there's a business somewhere within a 25 mile radius (unless you're in the boonies) that's got a motor they haven't used in 5 years. Try HVAC installation and repair places too, maybe? They may be upgrading systems or have some ideas for you.

Best,
Andrew

* While you can, sort of, alter the speed of a single-phase motor through rather exotic means, for practical purposes, you can't -- no, not with a ceiling fan controller, or a Variac, or a light dimmer, or a ____ .... Look, if you could, people would. Problem is, these are induction motors, not brushed/universal motors, so fiddling with the voltage going into them is meaningless
 
KBAC-24D is for 3 phase motors up to 1HP w/ either 115/230 VAC, KBAC-27D is for up to 2HP w/ either 115/230 VAC, KBAC-29 for up to 3 HP w/ 230 VAC. Those are the most common VFD's for belt grinders.

Also remember that if you have a GFCI outlet, the standard VFD's will not function correctly they make separate models that are GFCI compatible.
 
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I thought id post here instead of starting a new thread. Ive been researching alot about using a 2 wheel bench grinder for knife making(as a hobbiest). From what i gathered, it seems that they tend to be underpowered and that variable speed is a problem. So the hp and speed are the problem, correct?

Would a 3 phase, variable speed, 1-2 hp bench grinder work fine then?

I could make a 4 wheel attachment for one side of it if i needed to, or was considering one of those 2 wheel multitool attachments for starters. Im just persistent on the bench grinder idea because i would have other non knife making reasons for it.
 
There are "bench grinder" style belt grinders out there, usually with about a 1 hp motor. A 2 hp 3 phase motor on a VFD is the way to go though. Much more power, and end of the day will get you a lot more versatility, simply by nature of your interchangeable tool arms.
 
A dedicated 3 phase bench grinder will run close to $800 (probably Baldor) without a VFD or attachments for knife making. Smart money is buy a $50 bench grinder for other project work and concentrate on a 2" X 72" designed for knife work.
 
Yeah, i think im seeing it all now. As far as 3 phase, variable speeds go, i found a 1hp for $500, and 1.5hp-3hp for $800-1000. At that price point i could build pretty nice knife belt grinder myself. Thanks for the feedback guys!
 
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