Hollow Grind Machine

David Wesner

David Wesner

Joined
Jan 5, 2005
Messages
2,531
Just wondering if any of the veterans have built , used , or seen Bernard G. Pavlik's Wet Hollow Grind Machine?I have a few questions for any one that has.First,are the prints well done and worth the price?#2 The reply I received from Bernard stated that the Blade radius developed is 15 inches.I noticed from some of the images posted on his website advertising the plans that the "6 inch dia. bench grinding wheel he uses to develop the radius is mounted perpendicular to the blade which would only create a max. 3" radius that would slowly get smaller every time you re-dressed the wheel.If the wheel was mounted parallel to the blade I could see how you could dress any given radii on the wheel and basically form grind the hollow grind.Am I missing something or a feature that is not evident from the pics on the website?Any replys or explanations would be greatly appreciated.Thanks in advance for any replys.I'm off to work for a while so I wont be able to respond to any posts for a few hours.Have a great day guys.Anxiously awaiting some education.Oh BTW heres a link to what Im talking about (i think you can cut and paste it to your browser address bar . )http://members.aol.com/pavl5/myhomepage/business.html
 
I haven't made one, nor would I even consider it. A 6" wheel just isn't a decent size for making a knife blade over 2-3" in length. Couple that with the lack of flexibility in the grind and you have a machine that has become obsolete very quickly. Jigs and contraptions like this come and go, but there is no substitute for a crisp, fresh belt and a small measure of skill.

:)
 
Not to be a naysayer, but I'm not particularly impressed. The blade samples provided, if ground on this machine, suck. Well, they suck anyway, and who'd want to invest so much time and money building a machine that does such poor work? Yuck.

Much better to just bite the bullet and start grinding freehand. Even the most rank novice is likely to do a better grinding job than that...

If you're set on grinding jigs, check out Gene Osborne's video, "How to Make a Hunter". The grind produced by Gene's jig is even and consistent, and should be much less expensive and easier to build than this...thing.

Just my two cents. ;)
 
A wast of time and money. Free hand grinding a hollow ground blade is the easiest of all the grinds to do. Gib
 
What they said!

Learn to walk with a crutch, and you'll never be able to walk on your own.
 
Don't do it.

Take it from someone who spent the last 5 years making knives on a bench grinder. Its not worth the investment to make one of those things. For one, like the other guys said, you can do more things, and do a better job free hand.
For another, those wheels wear fairly quickly. That machine is set up like you'd knock out knives in large numbers, of the same pattern. The grind will change slightly with every knife. When you went back to re-grind after heat treating, the wheel would no longer match the contour of the blade. I never did a batch larger than 3 blades on my bench grinders for this very reason.

The finish also sucks. You have so much hand work to do. The wheel has a little bit of a gouging effect. It takes a lot of elbow grease to put a good finish on. The finish from a 120 grit stone wheel is maybe comparable to an 80 grit belt.

If you have the money to build one of those machines, just spend it on a belt grinder instead. I finally saved enough to buy a 2X72 belt grinder after all these years on a benchgrinder with stone wheels. I'm not sorry I went that route at all. The transition was easy, and the benchgrinders still serve me well for tool sharpening and rough profiling. But if I had had the money in the beginning I'd have gotten the belt grinder. Its worlds above the stone wheel. I ground 2 knives on it last night and its smooth as glass, runs cooler, and grinds much cleaner.
If your short on funds, get a benchgrinder or small beltsander and learn on that. When you finally get a real belt grinder, it will seem easy. If you have the money right now, then go for the real thing.
 
Hollow grinding on a regular grinding wheel is much more dangerous than a belt grinder. What you gents have said about it is absolutely true. I have done a lot of hard steel wheel grinding and it's a nervous endeavour when the grinding stone wheel is biting into a large surface. Even though you are using a tool rest, it's just too dangerous to continue. Some day, guaranteed, your luck is going to run out and you could get seriously injured. You won't want to be anywhere near a wheel when one breaks and explodes, either.
 
Don't hollow. Never tried. Don't know how. That said, the best way is to just get up to the grinder and do it. My opinion is that is the way to learn regarless of grind. No tool rest. no nothin. Just you and the belt platen. That is the only way I believe you can develope the touch.

RL
 
I agree with all the above also. Freehand is the way to go. I don't even use the tool rest that came with my KMG and never will. Just like Mike said, if you learn to walk with a crutch, you'll never learn to walk. It takes time but you'll be better off in the end. BTW Roger, if you don't hollow grind, how do you grind your WSKnives?
Scott
 
rlinger said:
Don't hollow. Never tried. Don't know how. That said, the best way is to just get up to the grinder and do it. My opinion is that is the way to learn regarless of grind. No tool rest. no nothin. Just you and the belt platen. That is the only way I believe you can develope the touch.

RL
Click to expand...
From the looks of your grinds, Roger, nobody will complain!
 
UH, I thinkst the preacher is not so good at what he preaches. It takes me a coon's age to grind a blade, any blade. It is not like I just belly up and knock it out. I am lucky to do a couple an evening. Thats just grinding bevels - not counting profiling. That part takes me another good day. Slow is part of the reason my utilities are often treatening to terminate me. However, I do believe the best way to learn is to just get up there and shove it in.

RL
 
Thanks for all the replies.Just so you vets know,I dont want to start out with a crutch for sure.I am an experienced machinist with 20 plus yrs of working with state of the art equipment.I have a very high work ethic and take a LOT of pride in my work.I am just trying to find the best way to get to the end product.I have to admit that some of the hand grinds I have seen here are VERY impressive.The symmetry(is that spelled correctly?) that you fellows aquire is truly amazing and I want it, bad.Dont expect to get rid of me here any time soon as I am like a big sponge for knowledge and new techniques.I posted the question because I am getting ready to take the plunge on a "real" grinder very soon.Looks to me like it will be a bader B111 or the KMG.A hollow grind specific grinder didnt really appeal to me but I was curious about that particular machine.If you will re-read my first post you will see that with my machining experience there are a few things that just dont make sense on the design.I dont mean to be redundent but I still cant figure out how he is able to get up to a 15" radius grind out of a 6" wheel mounted perpendiclar to the blade.The math just doesnt add up.Thanks again for all the replys,you guys are really amazing.and someday,with lots of practice I WILL perfect my grinding skills too.
 
With your background you're going to do some fine work. Some of the best of the best are machinists by trade, and that is experience well spent. You'll be making folders in no time. ;)

I've thought about the radius part too. Only two things it could be: He's wrong; or somehow he moves the blade to take a second and third cut. Either way, you don't want it.

I have a BIII; for your money I think you'd be ahead with the KMG. Just my .02.

Good luck, looking forward to seeing what you do.
 
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