Sweeping plunge

R

Rob!

Joined
Feb 9, 2000
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Can someone offer any guidance on how acheive a wonderful sweeping plunge like this? I read something about small wheels but it wasn't very specific.
ironwood-damascus-irish.jpg



It is a flat grind and Thomas is famous for it. I think Knives of Alaska are doing something similar now with some of their offerings.

Thanks for any guidance.

Rob!
 
Rob!

From what I understand, Thomas does this on a 9" disc grinder turned on edge (wheel face up). You should give him a call and go see his shop.

Nathan
 
Ditto on that Rob. Thomas is very forthcoming about his methods! Plus he's only a hop, skip and a jump from the south House of Tools (aka: Toys 'r us).

Hugh
 
Thought I jump in here. I don't use a disc grinder for grinding my sweeping grinds at all, tried it, but did not work for me. The problem with the disc grinder is that it does not allow one to flow the grind out on the heel (handle end) of the edge.

I am doing it all on a 2 x 72 Burr King with the flat platen. The grinds are not easy to do and take longer then a regular grind. Hard to describe in words. If you are in my neck of the woods give me a call and I can give you a brief demo on how I do it.

Have a read in Knives Illustrated December 2004 page 18 for more info on the sweeping grind.

Cheers,

Thomas

www.haslinger-knives.com
 
Whoops :foot: guess I was wrong. Uncle kelly keeps telling me I should go see you too. Maybe I'll have to make some time when I have some time.:confused: (of which I seem to have little). Thanks a lot Thomas!
 
I do these plunges on a flat platen as well. basically, i do the following:
-Scribe two sets of lines to designate pre-ht grind thickness.
-Pick where you want your cutting edge to begin and where you want your sweeping plunge to begin.
-This should line out for you the "width" of your sweeping plunge
-Start your plunge and evenly feather the plunge from both sides from your "back" line towards the ricasso to your scribed center lines where you want your edge to begin.

Heres an example on an integral but its the same idea. Think of the curve you want....that curve should be reflected in the cross section at the plunge. A straight plunge will show a perpindicular cross section, a curved plunge will show a curved cross section:
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Is easier to see than explain, but thats how I've done it.
 
Why don't you write to Thomas and ask him? He is a terrific guy and very approachable. His address is thomas@haslinger-knives.com (from the Canadian Knifemakers Guild site). I've seen him do it, and must confess I have not been able to turn out anything like that.
Mike
 
I just had a though that simplifies all this. Just look at the first pic in this thread again and think about what a grind line really is. Its just the apex of the bevel. You already know how to move that line around by putting more or less pressure on the spine side. This is just incrementing and feathering that pressure at the ricasso rather than using even pressure stright to the spine. Flowing plunges like this end up with a different blade geometry cross section at the ricasso end of the blade...anyways, ill leave the rest to someone else. it makes sense to me but I think I am being unclear...
 
Thomas demonstrated this at Ed Storch's symposium last year. It was the single thing I wanted to learn most last year. I got called to our sales tent by someone who was about to leave - and by the time I got back, Thomas was doing finishing touches :(

I've been kicking myself for nearly a year now. I've never been to his shop but I guess it's time to ask for a visit. Hey Thomas - still following the thread? :)

Rob!
 
Back in the 70's I made probably 100 blades like that. I used a craftsman 6X48 belt sander because that's all I had and didn't really know what I was doing. But, I couldn't make them fast enough for the demand. Haven't made a knife for years now but want to start again. Wanderer70
 
Necropost:
Heres one im working on. No smallwheels or dscs used. Just gold ole flat platen and feathering....

15" OAL knife, so its a good 2" high curve. MUCH harder than your average plunge IMHO:
1.jpg
 
Charlie Ochs does his sweepng plunge grind by setting the radius withan angle grinder and then grinding vertically on a 3 inch contact wheel and flattening on a 9 inch horizontal disc. As anyone who has ever tried the vertical grinding knows, you can end up with some serious ripples. I have never been completely sure how guys like Charlie and Bill Moran did that and still ended up with flat even bevels...lol I know that Bill Moran had some wheels covered in soft rubber foam for grinding handles so that he wouldn't dig holes or flat spots.
 
I smoothed all the ripples by using a steady hand while grinding and a light touch, then it was good old elbow grease and sandpaper to make it even. I think the key is using finer grits and taking your time vs hogging. Trying to hog in a curved plunge vertically, you just end up with a mess of deep grooves. Step that up to 400 grit and take your time with a rounded platen edge, and its a different monster. Id say this plunge took me at least 3X the time a normal straight plunge since theres so much more to worry about.
 
I guess just thinking about the dimensional nature of it is making me a bit crazy. I can't draw on the computer worth a darn, so I'll try words.

Lets presume - at the edge that the transition from ricasso to what will eventually be working edge takes - oh maybe 3/8 of and inch. (Probably much less) I understand how the upper part of the plunge will sweep over that 3/8 inch. But I'm looking for a plunge that sweeps - I dunno - maybe 2 3/8 inches across the top.

Now picture a cross section of the blade right near the beginning of that area - right after the first 3/8 inches. At this point, the plunge cut is only going maybe half the height of the blade or even less and the angle from the edge to that half heigh mark is pretty steep.

Insert a few more steps here that I won't describe. The idea being that this is a smooth transition and not just the two points I'll be describing.

Now, consider the distal end of that sweeping plunge - toward the point and maybe 2 3/8 inches away from the ricasso. Now, the cross section is a straight line from the edge - all the way to the spine - and not nearly so steep as the first cross section.

The rest of the cross sections from there to the tip will be a similar angle, except for some allowances for drop point or distal taper that would hurt my brain to calculate.

Now imagine this transition from ricasso - to steep angle - gradually to shallow angle and then more or less consistent shallow. Does it help to liken this to a golf green?

How the heck does a guy finish that putt with a flat disc sander??? :confused: :confused:

If anyone can translate my warped thoughts for others, I'd apprecaite the help.

Thanks

Rob!
 
I was thinking that you could do it on one of the KMG rotary platens grinding lengthwise. The stiff belt should eliminate the rippling prblems that you get on a contact wheel.
 
Rob, I think the same idea whether 3/8" transition or 2 3/8 doesnt make a difference, you just get a longer transition to the final angle from edge to spine. AKA, your main bevel angle will vary until the grind reaches its apex regardless of how long it takes to get there.

As far as finishing goes, i dont do any finishing grits on the grinder. I do it all by hand. I am not sure at all how to finish that kind of grind on a sander....you could do it vertically by just carefully re-tracing your grinds, but I dont have the zenlike skills to match those curves through multiple grits without losing the curve and ending up with a more straight plunge by habit.

For this curved plunge, from the edge of the plunge to the apex is almost 2" (10" blade) I did it all by hand beyond 200 grit...tough work but it pays off....
 
No Argument there David. They sure do look nice. Maybe I just have to stop thinking and do it.

Rob!
 
That sweeping plunge is also a signature style of MS Rob Hudson. He does them on a 2 x 72. Rob has not made many knives lately, but his are definitely classic styles which will never grow old, in my opinion.

Rgds,
Allgonquin
 
Allgonquin said:
That sweeping plunge is also a signature style of MS Rob Hudson. He does them on a 2 x 72. Rob has not made many knives lately, but his are definitely classic styles which will never grow old, in my opinion.

Rgds,
Allgonquin
Click to expand...
I own one of Rob's hunters from the early 90's which is when I met him at the Guild show during it's first stay in Orlando. That was about the time he made that wild multi bar damascus Viking dagger with the flame patern edges....still amazing even today. I heard that he had a pretty serious car accident sometime after that. Is that why he doesn't make that many knives today or did he go back to doing primarily high dollar ornamental iron for a living?
 
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