stirrin' the pot ...thinking of a new grinder....

Holy Smokes!.....I didn't expect to much action here....whew, slow down guys!

Very good info getting posted.

Mark, it looks like your the guilty bastid for hijacking the thread from hollow grinders to surface grinders :D :D (Thank you for the order BTW).

I looked into surface grinders in the past. And actually looked a few designs that guys sent me. After looking....I concluded that it is hard to beat the little grizzly surface grinder model. I think it runs $1200-$1500. Has micrometer Z, and both X-Y slides, precision ways...single phase input....etc. I don't know how you could get this much value or precision starting from scratch with a new machine design.



Back to hollow grinders:

A 36" wheel will turn slow.....I'm thinking about 400-500rpm for hogging. There is no issue on torque, hp and speed. They are all related and one trades-off with the other. HP is the product of speed and torque. For a given hp, if you reduce the speed, you increase the torque..and so on. A drive train that reduces the speed will proportionally increase the torque. It is the basic input=output thing. If we put 2 hp worth of electrical power into the machine, we will get 2 hp out...in one form or another.

I'm really leaning toward a 36" wheel myself......why stop at 20..? heck if you want a flat grind then bigger is better...but 36" is the limit based on machine tools needed to make it....otherwise we could keep going.

A few issues regarding driven or coasting contact wheel....

If the contact wheel is a coaster ...then there is trouble starting the grinder. The probelm is that the drive wheel spins and throws the belt off because the big wheel has too much inertia and takes a while to spool up. I see this on KMG with 14" wheels and high powered motors (5hp). A solution would be a motor controller (VFD) with a ramped accel for starting...or soft start. Then, what about tracking?... it is much easier to use an idler wheel for tracking adjustment... I think it would be impractical to steer the big contact wheel. Small adjustments would make BIG changes in the belt position. If you use specialty fixtures, you might not want to move the wheel after the fixture is set. ....hmmm...more thinkin' to do...... Maybe move the motor with the drive wheel for tracking....and for tension

.... gotta think about it more.....

Keep the ideas rolling...

Sincerely,
Rob
 
Heck Rob,

If you had the drive motor on a mounting plate like my grinder. You could use a screw drive to make the adjustments. I'll do a drawing and send it to you.

How about a gear driven 72" wheel that has an inflatable contact wheel. Just slide on a belt . Hit it with a bump of air and off you go. The gears could be on the inside of the hub or even as little as a half inch below the contact surface. Now where dreamin BIG.
 
Lighten the load of the big wheel. Make it spoked. Five big sturdy spokes would lighten it considerably, and if the contact area is thick enough (1/4 inch or so) it will not flex under pressure.

There is a thought.....

Doc
 
Rob I like the idea of a 36" wheel but I would be happy for now if I had a 36-48" curved platen for my Burr King. I dont have VS on it yet. The platen would be affordable and an alternative to a buying another grinder for some of us. I have another idler on my burr king so I can use 72" or 132" belts. It goes almost to the ceiling but those 132" belts last a good long time.
 
Is it reasonable to design it so that it can function as a large-radius hollow-grinder with the option of adding attachments to do surface grinding? You are at the specification stage now and it would be the simplest and least expensive to put in these capabilities now.

It seems that you are thinking of an arrangement with one large contact wheel and one small idler/tracking wheel. One way of driving the contact wheel would be to use a third rubber coated drive wheel the size normally used in one of the two wheel grinders, like the Grizzly. The drive wheel would be positioned somewhere inside the loop of the belt and in contact with the contact wheel only. The torque would be transmitted around the rim of the contact wheel. The drive wheel can be mounted directly on the shaft of the motor, eliminating the need for another set of bearings. Speed adjustment would have to be made using a VFD (see below). The axle of the contact wheel would only have to be strong enough to support the weight of the wheel and the pressure applied when grinding. It would not be subjected to any torque.

It will be very difficult or expensive to avoid having a lot of rotational inertia due to the mass of the large contact wheel. If you use a small motor, it may stall and blow fuses/breakers all the time. Using a very large motor, say 5 hp, would likely exceed the supply capability of most potential users. Also, using a big motor to get the big, heavy wheel spinning, without ramping up the speed, would put greater stresses on all the parts of the machine making it necessary to use stronger, heavier, more expensive parts and bearings.

VFDs are commonly used to start such high-inertia loads in industry and it is probably your best and least expensive solution. It seems that this grinder would be fairly specialized and would not likely be someone's first grinder. The extra cost of the VFD component would then be easier to justify for a customer who is an established, full-time (likely) knife-maker who wants this for a dedicated application and already has one or two other grinders for more general use. It is likely that the customer has already installed VFD's on his other grinders. It should also be possible to run multiple grinders, one at a time, using hte same VFD by using appropriate switches/contactors or plugs and sockets. It may even be possible for someone to start out with a simpler, cheaper grinder, then sell it and buy one of these, as his one grinder, when he knows that he will stick with it and has more cash. Offering a surface grinder option would make it much more attractive as an "only grinder".

One more question. Can your rotary-platten perform the hollow grinding function, or can it be modified to do it?

Just my 2 cents worth.

Phil
 
It would be fun just to put something together out of junk , just to try it. I bet if we put Don (peter nap) to the challenge, he could do it. :)
 
Yes Mark! I really like the design that you have on your grinder. It is just so simple......I'm thinking it is the way to go.


You got it Doc....the contact wheel will have a cast aluminum wheel....so it can be any design to fit the function.......I'm thinking custom chopper influences here. It could be straight spokes...or curvey spokes....or naked ladies holding the rim above thier heads...kinda art-deco like. The limitation in size is a lathe to turn the casting....and a rubber press to mold the tire.

A 72" expand-a-wheel.....hmmm... how would you ship that bad boy? :( ..that is the simplest idea!...but that takes a 226" belt....

A 42" wheel would take a 132" belt...that might be practical....


Ohhh boyyy....I'll never get to sleep tonight :D

Rob
 
Rob,

I have one your KMG grinders with a 14" wheel and absolutley LOVE IT!!!!
If a 36" (or bigger) wheel had been available that's what I would've ordered.

Keep that thinking cap screwed on tight..........can't wait to see what you come up with.

Mike
 
matt have you seen the wilton's drive..?
the grinding belt is the drive belt.
so no matter how big the wheel is the belt speed and hp will always remain the same. Jeff was talking about a different animal. :)

I have a expandable rubber wheel while not rotating you slide a belt over it once spinning it expands locking it in place maybe something like that? :)
 
Rob, if you build that thing, you simply have to have a nakid lady spoke option - ala American Chopper and then have the Tutils swap that shop bader out for a new monster KMG.
 
So what would you have to do to make a 20" or 36" wheel fit on a kmg, using 132" belts? Maybe by-pass the idler wheel? Would that not rock if the same machine could use both sizes of belts? I would then have to sell a kidney or something to get a KMG.
Did anyone mention building a surface grinder? ;) :D
 
My thought is this.....what do you need a big wheel on a grinder for?:confused: If you can't grind on a flat platen why even bother???? Just kidding folks...don't get the ropes just yet. If it can be done, you can bet Rob will do it.
 
Guys,
I've been following along here, and I would like to ask why is it that such a huge wheel is desired for a hollow grinder? Could someone please explain? Thanks.
 
Razerhunter, Many of the original bowies were ground on a huge wheel. It is easier to replicate them if we can match the shallow hollow grind. It is like having the best of both grinds.
 
Okay Rob, I'll chime in here with my vote of confidence. You build a grinder with a 36" wheel, and I'll find a way to own one.

Bader builds a 132" grinder, "Bader Space Saver", but I didn't pay enough attention to how it was set up the one time I saw a pic. I think it'll take that large of wheels too but it's in the $10K range; not my range. ;) I think it was set up much like the BIII and would accept various wheel diameters. But cripes it was years ago when I saw the picture and I just can't bring it back into focus now. Being old sucks!

I've been enjoying the discussion of curved platens too, since I built one I haven't used yet (still gotta build a way to mount it). Mine is a 2.5' radius, still kinda small for replicating the old bowies. But it does have appeal. :D
 
Dan Gray said:
matt have you seen the wilton's drive..?
the grinding belt is the drive belt.
so no matter how big the wheel is the belt speed and hp will always remain the same. Jeff was talking about a different animal. :)
Click to expand...
Yeah Dan, don't argue, I was agreeing with you :D
I mentioned Jeff too cause you guys were talking about the same problem, belt speed and power. He suggested a gear reduction. That would work to get the speed and increase torque but I was saying it brings up a lot of other complications. You end up needing a specialty motor, and you've got a much more complicated peice of equipment with more things to go wrong.
I also think your giving the load a mechanical advantage over the motor by applying power directly to the big wheel too. Kind of like putting an 18" wrench on it.
I would rather see it with a set up like the wilton. No gear ratios to fool with if you want to change the speed, and you can use just about any motor you want.

Rob is right about the inertia thing though, I hadn't thought of that. I think that could be pretty easily solved with a soft start or something. Will those big motors turn by hand? You could always give the wheel a good shove before turning the motor on. May not be OSHA approved but hardly anything I do is :D
I like the naked lady spoke idea too :eek:
 
rfrink said:
Yes Mark! I really like the design that you have on your grinder. It is just so simple......I'm thinking it is the way to go.


You got it Doc....the contact wheel will have a cast aluminum wheel....so it can be any design to fit the function.......I'm thinking custom chopper influences here. It could be straight spokes...or curvey spokes....or naked ladies holding the rim above thier heads...kinda art-deco like. The limitation in size is a lathe to turn the casting....and a rubber press to mold the tire.

A 72" expand-a-wheel.....hmmm... how would you ship that bad boy? :( ..that is the simplest idea!...but that takes a 226" belt....

A 42" wheel would take a 132" belt...that might be practical....


Ohhh boyyy....I'll never get to sleep tonight :D

Rob
Click to expand...

Not to poopoo on Doc's idea for the spoked wheel, but spokes would also provide a place for fingers and whatnot to get caught in. I would recommend a solid-disc center, just thin to save on weight. Spokes would be pretty, but not safe when a large mass is rotating under torque. Loss of fingers could happen.

I also like Mark's idea about swiveling the drive motor with a pivot point and a fine-adjust screw of some kind. A threaded screw rod, and a small hand-wheel would be excellent to achieve this.

Another design idea would be to connect a right-angled gearmotor directly to the contact wheel, and then you could have a bar, adjustable idler, and spring arrangment just like the KMG, except in reverse!
 
I still think it would be feasable to have the big wheel driven by a smaller wheel that rides on the inside of the wheel hub. You would just have to figure out what size would give the best speed/torque. The Idler could be both tension and tracking with the screw adjustment. That would allow just a two wheel setup.

Oh and the 72" expando wheel was circumference. ;)
 
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