The secret to good plunge lines?

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AlienAutopsy

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I've been wondering... what's the secret to those beautiful plunge lines I'm used to seeing on custom knives? Is there a way to refine a plunge after grinding or is there a specific technique I can use to get a nice plunge?
 
After I heat treat the blade I'll throw a 220 grit belt on the grinder and leave a little more than 1/8 of inch of the belt over hanging off one side( the side I'm going to be bumping the plunge into) as I'm cleaning the scale off and getting the 80 grit scratches out I'll run that plunge all the way into the corner of the wheel a few times and take a look at it to see where more pressure is needed. I grind a little different than most people though. I grind with the belt going away from and the cutting edge down but that's the way I clean the plunge it works every time for me
 
I do the same but my belt travels toward me. I may even you a more coarse or finer belt but yes the same as Robert. Frank
 
I do them last
Most of the newer makers I have seen try to get their plunges perfect first and then grind the rest of the blade. Then they slip and screw them up. Start just in front and grind the blade perfectly, then go back and set your plunges exactly where you want them. Do one and then use that to line up the other side with the edge of the belt.
This along with the advice given above.
Thanks,
Del
 
I never start with the plunge. I will start grinding mid blade and then move left and right. I actually do the "plunge" last, working closer and closer to where I want it to be. Patience and a ceramic platten help too.
 
Like many of the others I start forward of where I want my plunge line to be and move it back as I work through the grits. I fine tune it on the last grit I use before HT with a very light touch but still hitting all the blade to avoid the 2" disease:o

Another tip I was given was to flip the belt so you are using the same edge of the belt for both plunge lines. While working with a small grinder, 1X30, this made a huge difference. I don't notice it as much on the 2X72, but I still do it.
 
If you use what you guys call a "file guide" you can get crisp plunge lines.
I don't care for sweeping plunges. I use a guide made of 2 pieces of angle iron screwed together. You can't grind past it.
 
I get them as close as I can with the belt, then if necessary switch to needle files and sandpaper wrapped dowells.
 
I have to admit that I have never been able to get happy with my plunges straight off the grinder and I dress them by hand on the corner of my sanding plate, with sandpaper wrapped over it. Maybe I just haven't tried the right grinding belt to do them properly on the grinder, I can never get the belt to flex consistently enough over the edge of the platen to end up with the same radius on both sides, at least not while the plunges are still in the spot I wanted them. 20 minutes of hand lapping beats a 10-second screw up on the grinder any day, in my book.
 
I use one of these. Set the edge of the clamp where you want the plunge lines to be and grind away.

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Plunges are super important! A true deal-breaker... a crappy one will stick out like a sore thumb, even on a knife that's almost perfect otherwise.

I usually use a file-guide to set my plunges by hand, then grind the bevels*. The trick is, don't go quite as far up the blade, or as deep as you think you need to when setting the plunge. This allows just a bit of wiggle-room for blending the bevel into the plunge, and hand-work to get any deep scratches out when everything is set. The worst is when you set what you think is a perfect plunge to start from, and by the time you get the bevels and taper ground, you find there's a small but ugly divot on the spine, where the ricasso meets the blade. :grumpy:

Also, Marvin Winn showed me to lap/polish the ricasso area after the plunge and bevels are set, to help keep a nice crisp transition from the flat part to the plunge. :thumbup:

*Having said that, the other fellows' tips about grinding the bevels, then cleaning up the plunge makes a lot of sense! Regardless, I find a file-guide, edge scribe and calipers essential to keeping things clean and even on both sides. I'm getting better at keeping everything centered by "calibrated eyeball" but good measuring tools are still pretty important in my shop.
 
Buy a carbide faced file guide and wail away.:D Also, i ahev been doing what Del said for a while and it helps. I actually cut the plunge grinds on a lot of knives using a higher grit "hogger" belt like 80 instead of the 36 or 40.
 
Maybe some one can post pictures of bad plunges and good plunges for the newbs to see. I may be guilty of a bad plunge myself I'm not familiar with what a bad one looks like
 
Justin King said:
I have to admit that I have never been able to get happy with my plunges straight off the grinder and I dress them by hand on the corner of my sanding plate, with sandpaper wrapped over it. Maybe I just haven't tried the right grinding belt to do them properly on the grinder, I can never get the belt to flex consistently enough over the edge of the platen to end up with the same radius on both sides, at least not while the plunges are still in the spot I wanted them. 20 minutes of hand lapping beats a 10-second screw up on the grinder any day, in my book.
Click to expand...

Justin
You might try a jflex weight belt. These are very flexible and will allow you to roll the plung. I do as most others here, adjusting the plunge last and running the belt about an 1/8" over the edge of the wheel.
 
Robert Carter said:
I may be guilty of a bad plunge myself I'm not familiar with what a bad one looks like
Click to expand...

You'll know it when you see it :D Take a closer look at almost any factory knife for examples. Oddly, a really good plunge seems hardly noticeable at all.

Nasty scratches, not being even and matched on both sides of the blade, harsh transition from the bevel to the ricasso, rolling over the spine, "leaning" back toward the handle... all these things will jump out and scream "don't buy me!".
 
+1 to the bevel clamps - I made a smaller one for paring knives I was making from 1/16" stock - it solved the problem of the belt rolling up the tiny plunge.

Also, it helps if you don't get too emotionally attached to a perfect outcome, just let good things happen...
 
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