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

rfrink

rfrink

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Aug 1, 2000
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Over the past 4 years or so...I've gone through the exercise of laying out a big wheel grinder. Something with a huge-mungus wheel...say 36".

I have a handful of designs that I've done in the past...but never built one.

I have some new resources that might be able to make this happen. There are several design questions to be solved. The main question is what size wheel and what size belt. For example if a 72" belt is used, then the wheel is limited to about 20". However, if we jump up to a 132" belt, then a 36" wheel is possible. This means a different inventory of belt length to go along with your standard 72's hanging on the wall.

I see this machine more as a dedicated hollow grinder...not a general work horse like the KMG. The new machine won't have the flexibility of attachments..

I vision a 2 wheel design..... like the Burrking with a 36" wheel...and maybe a platen between the contact wheel and idler. The contact wheel will be driven.....ummmm...and who knows ....I'm just making this up as I type.

So here is the question...do you want a 36" wheel ...or a 20" wheel?


Whatta ya think?


Sincerely,
Rob
 
Rob,

As big as you can make it would be good. Or you could make custom platens for whatever size wheel you wanted. I think Bruce Evans has a platen which replicates the arc of a 12' wheel.

Do you remember the way my grinder tracks? with the drive motor pivoting up and down. seems to work pretty good. if you coould incorporate the tracking and tensioning into the drive system you'd have it.
 
You already know my answer, Rob! LOL!

I say that a dedicated hollow-grinder is just what our industry needs, and the jump to a 132" belt would be doable, and most-likley be more supported by the supply-houses if you have a grinder out there to use them with. This definitely wouldn't be a beginner's grinder, but a lot of us verterans would simply HAVE to have one! Here is a short list of my immediate thoughts:

1. Motor size. To turn a 36" wheel, the motor would have to be beefy, and my suggestion would be an AC gearmotor in the 1 hp or better range, with a high gear ratio for more torgue. Grinding a huge hollow on a big bowie or sword would bog that thing down to nothing if the motor and drive torque were inadequate. I haven't done the math yet, but with a 36" wheel, it would take very low rpms to provide a nice feet-per-minute speed to the belt surface of the contact wheel. I'm guess right off that a gearbox with 50 rpm would give a decent amount of grinding speed. I suppose I can dig around my Machinery's Handbook and figure it out of you want. Slower is generally better for hollow-grinding in my experience.

2. Physical size. Getting into a bigger wheel and longer belt means bigger size. I would design it to be vertical, rather than horizontal like the KMG. I also believe this design would warrant it to be a freestanding unit.

3. Price. If you could keep your price break below $1800, I think you'd sell quite a few.
 
I still wish you could come up with a manual feed surface grinder for a good price. Nothing to exacting tolerances , just to flatten pretty close.
 
I like the idea of the biggest thing you can make but you will need to turn that motor way down or the whole thing will be spinning so fast it goes into orbit!
 
Rob, if you haven't seen it before, on that TV show "Swords, Axes, & Knives" on History Channel, there was a shot of folks at Victorinox grinding on some large-diameter wheeled belt grinders.

I would be most interested in such a device. I doubt it would ever be a really large seller, of course, but there would be a market for them.
 
Rob, Mark brings up a good idea. In addition to the great grinders you offer, you should try to develop some type of device that would work like a mini surface grinder. Most of us knife makers have a need for a surface grinder, but not necessarily a need for the huge surface grinders that we run across. Also, purchasing one new is out of the question for many of us. What would be ideal is something smaller that could run belts and maybe be based on the same principle of a cross slide vice. It's just an idea, but it could be a great seller for you. -chris

__________________
Chris Crawford Knives

 
Rob,

While I'm still saving my pennies for my first KMG, I'll jump in here and say that an affordable surface grinder would be very high on my list! Probably right behind the Hydraulic Press and KMG that I'm saving for.

- Mike
 
Mark,

I have a Frink secret weapon - a curved platen that simulates a 20" wheel!!!!

Yes-siree boys! How do you think I can do a 20" hollow grind?

It slips right in where the flat platen goes. And has top and bottom clamps for graphite belts.

The only 'issue' is that there is more friction than a flat platen, so the motor is working a bit harder. But I'm not working any harder ;). It probably wouldn't work out for a commercial machine seeing 8 hours of continuous use, but for a knife maker it's just perfect.

On the finished blade it''s really hard to tell if it's flat grind or hollow. You have to feel it with your fingers. But when you use the knife you know!



Steve
 
I have to agree, a small shop size American surface grinder would just rock.
I still say if you designed a quality, under 1200# knee mill or dovetail head mill you wouldn't be able to keep up with orders at any price.
 
I think it's Neil Blackwood that uses the 132" belts. Seems they werre a standard where he worked or something. IIRC

You'd get a lot more grinding time from a 132" over the 72"

Course it's a moot point if you cain't find the belts.
 
You'd get a lot more grinding time from a 132" over the 72"
I agree,,
and
with Jeff's thinking yes a motor change but if you drive the belt and let the belt drive the wheel you don't have to change ratio as with the square wheel wilton.
so that's the easy way out in that department.

I don't see any more drag than you get in a flat grind against a fixed flat platen, you'd have less I'm sure you know with a moving wheel that is supporting the belt.

I do agree , you'd sell more surface grinders. more need for it... :)
 
Dan Gray said:

I don't see any more drag than you get in a flat grind against a fixed flat platen, you'd have less I'm sure you know with a moving wheel that is supporting the belt.

Click to expand...



Dan, I assume you're refering to the curved platen. You wouldn't think so would you, but there sure is! Had to switch the KMG from a 15 shared amp to 20 amp dedicated curcuit. I THINK it's because on a flat platen the belt isn't in hard contact with the platen all the way down the face. For the most part (until you press with a the blade) it's kinda floating over the middle part. No so on the curved one.

Steve
 
Would you guys prefer a belt setup over a stone? I have been working that one out in my head with a stone, but a belt setup doesn't seem like it would be that difficult to do to me. I am sure Frink has a better design in his head than I do as far as that is concerned....

Doc
 
I have a cheapie surface grinder (HF) that I converted to 72" belt, ala Ed Cafrey's design, but I'd buy a 20" rig if it's offered. So there Rob, there's an order (well, sort of, based on the final cost of the unit).
 
Sando said:
Dan, I assume you're refering to the curved platen. You wouldn't think so would you, but there sure is! Had to switch the KMG from a 15 shared amp to 20 amp dedicated curcuit. I THINK it's because on a flat platen the belt isn't in hard contact with the platen all the way down the face. For the most part (until you press with a the blade) it's kinda floating over the middle part. No so on the curved one.

Steve
Click to expand...

absolutely Steve,
until you press with a the blade on the flat platen the two wheels are helping
and more of a problem on the curved platen from the tension of the belt plus more while grinding.

pinching the belt in any way is like adding brakes to it. on the hollow grinding wheel
it's mainly pure grinding pressure stopping the motor.
more like a half of a brake :)
 
Well, one good thing Rob. I'll help out with some R and D money. I talked it over with the boss and I would like to order a grinder :)

Sorry I got your grinder thread drifted into a surface grinder thread. You can do it.
 
Just from a mechanical/cost standpoint I'd go with a driven belt rather than the contact wheel. For one, like Dan and Jeff were getting into, you don't need a specialty motor to adjust your belt speed if you have a normal sized wheel driving the belt. That allows you to sell with or without a motor and we can use whatever motors we have if we want (like maybe someone is buying this grinder and retiring one that has a servicable motor).
The other fact is the amount of power you'd have to have to drive that big wheel. Your placing the load 18" from the center, which is going to take a lot more torque. I know gear reduction can solve that problem, but that ups the price on your motor quite a bit and makes the whole thing more complicated. If you have a small wheel driving the belt the only increase in load over a normal sized grinder would be a little more friction in the whole system, since your not giving the load a mechanical advantage.

You can count me in the class of folks who would be interested in one of these, but won't be able to afford it for at least 20 years :D
 
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