Poor Man's surface grinder

Thanks, Anthony, your prediction is about to come true, I'm building this weekend! Anyone know where to get the magnets?

Wayne
 
Here are some nice bar magnets: http://www.amazon.com/dp/B004R0C7CS/

Here are the magnets I used because it was easier to drill round holes: http://www.amazon.com/dp/B001KUURP2

Since the RPM is only around 2K to max of 3K I don't think there's much danger at all.... but as in all things, use common sense and BE CAREFUL!!!!

I would think a flap disk might leave a smoother finish, but since it is flexible, not sure how close it would hold to truly flat?

I had no idea this would get this many folks so interested.

Ken H>
 
Great idea! Thinking outside the box, and building something like this great stuff to read about!

I would think the round magnets with a few pins would be sufficient. Just don't go too big on the magnets. You have to be extremely careful around the bigger rare earths. Even a pair of 1" rounds 1" long can't be separated by hand. In the process of reuniting them, they will tear meat off your fingers if you're not careful! Ask me how I know... :(

Dan
 
Dan, you are correct on those rare earth magnets - they are STRONG!!!! When they say "Not for Children" - heed that advice! They will pinch your fingers enough to raise a blood blister. Ask me how I know - that phrase is getting as well used as "Hey, watch this"!!

Ken H>
 
Is there a possibility of the disk overcoming the force of the magnets and flinging the blade into your belly? At least with a surface grinder the piece goes flying to the side and not back at you. I had a machinist in my shop one day and he gave me some flack when he saw I was face milling with a magnetic chuck, that is what made me think of this. I really don't know the answer.
 
That concern is why I put pins in the magnetic base to hold blade. There is at least one hole in the tang that slides over the pin, and another pin up toward the tip that allows blade to rest against to prevent blade flying off. Now, with that said, I still stand to the back where if the blade did fly off, it wouldn't fly toward me.

With only .005" depth cut, and low RPM, there's not that much force on blade, but again - BE CAREFUL!!!

Ken H>
 
Ken, there are companies in Europe that make a swing arm surface grinder that works just like what you have here. The arm has heavy duty bearings in it and it swings just like a pantagraph. They use a cup style grinding stone/wheel. They are very accurate.
 
Tom, that was my first direction, to use a cup grinding wheel. I just didn't find anything like I wanted, so started using what I had on hand. Back in my college years I worked in a machine shop where I ran a surface grinder and those wheels/cupped wheels were VERY accurate - half a thou was nothing!

With the proper cupped grinding wheel, I'd think a milling machine would be more accurate than what I'm getting with that 7" metal disk. It's not very accurate - looking at it you can see the surface wobble a bit. BUT - since the feed is slow it sorta balances out. It's at least better than my free hand grinding to even sides of blades, and does a better job of a distal taper.

Ken H>
 
I will give this a try. I think I will make a aluminum disc put a nut through it . As long as it is true that should work . Them you can use spray adhesive and use any paper you want. Glad I stopped by.
 
Mark, Be sure to let us know how the aluminum disk works out. Not sure how well the sandpaper will work for removing a good bit of metal as in distal taper, but I do think it just might make a nice finishing cut. I'll wait for you to try it, and if it works pretty good, I'll try it also. I've got some 3/8"X5" plate I could cut a 5" disk from, but not at all sure that's large enough. Hey, I've got a 8" steel disk I could rig up....

Ken H>
 
Hey you guys are giving me the itch ! I still make the occasional small tool but I'm no longer into trying the bigger stuff. I am trying hard to get a fellow knife maker into doing one, though.
Frank
 
Folks, I've got so much help and guidance from KD's that I'm glad I was able to give back to the group with a good idea on this "poor man's surface grinder". As I've cautioned before, it's at best a "get by" since I have no surface grinder.

Ken H>
 
Wish I did this but don't have a mill, I use a 5 inch disk chucked in my drill press, this looks like it works better. And what caffrey said you might have problems with rigidity but I usually use mine for small things not long blades such gaurd faces and it works fine been using it for about four years now. Search neat trick disk sander don't now if I left pics up.
 
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Ken, how would you rate your results on this compared to using a disc grinder? (Obviously your method provides for parallel surfaces whereas using a disc grinder by hand won't.) I'm still trying to improve my technique on the disc grinder and I don't have a cross slide vice for my drill press. As a total noob, I'm still trying to find cost effective ways to get decent and repeatable results.

I've just begun making culinary knives and just like you said, getting a good distal taper on a flat platen is no small feat. I've also tried using my 10in wheel and running the blade fore/aft lengthwise (similar to the way David Boye shows in his book, minus the work rest), which is actually giving me better results than trying to do it on the flat platen, but it's also really easy to make one heck of a wavy section in the blade.
 
I picked up one of these but havent tried it yet.

81J5CwXW6KL._SL1500_.jpg
 
I have a mill on order and am looking forward to giving this a try. I was looking at grinding wheels, but haven't decided which to get

Exitium-curious to hear how that wheel does.

Jeremy
 
John, when you mention "disc grinder" are you referring to "side grinder" or sometimes called angle grinder? Are you talking about clamping the blade in a vise, then holding grinder by hand and grinding? There is no comparison to the results "I" get when grinding by hand, or if disc is held in milling machine! I do some really cruddy hand grinding with a side/disc/angle grinder. That is for "hogging" metal in the roughest form.

Yes, the contact will will cut much faster than flat platen. After contact wheel, then use flat platen to level out the "waves" left by contact wheel.

I'm familiar with those DeWalt type grinding wheels and was thinking about one to try, but didn't see one right off, and realized I had the 7" discs on hand so used them. I'm liking the idea of the aluminum plate mentioned before and might try one of those also.

Ken H>
 
Sorry, Ken. I'm referring to disc grinder as in a KMG vertical disc.

My question is whether a grinding disc chucked up in a mill or drill and using a cross slide vise will give you as flat a surface as using a vertical/horizontal disc grinder. My logical brain is saying that it should be, but I'm wondering what kind of runout the bolt mount causes, or issues with the flatness of the abrasive disc itself. And what kind of surface are you left with? My other big issue right now is discovering faint 60grit or 120grit scratches...about the time I've hand sanded to 320.
 
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