Question regarding convex grinds.

A

Almightyox

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Jul 29, 2014
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Hey folks. I and working on my next knife and have decided that I am going to try a convex grind on this one. My finish sanding technique in the past with has been limited to FFG so i was wondering what the best technique is for finishing sanding a convex bevel. Do you back your abrasive paper with something soft to help if conform to the curve of the bevel? I appreciate any words of wisdom that will help me out.
 
It might be helpful to let us know what tools or machinery you have at your disposal. There are different techniques depending on whatcha got.
 
I have files, a ton of sandpaper, and recently I purchased a belt grinder. I have the bevel cut already, I am just wondering how I can go about getting the same "near mirror" finish as I could with my sanding block and 1000 grit/3M pads on my flat grinds. I would back my abrasives with a flat stick to keep my finish uniform on flat grinds, but on a convex grind you end up with a curved surface. I only have belts up to 480 grit.
 
I do convex grinds almost exclusively, although I usually just do a belt finish up to 400 then give it a nice satin finish with a scotchbrite belt.

However, when I occasionally do hand sanding I'll use the technique described by Nick Wheeler in his video (you can find it in the video tutorials sticky, it is awesome!). Except instead of a hard backing, I use a small paint stirrer wrapped in one or two layers of garment leather. It's some dyed blue thin stuff that I think I got in a scrap bag, and it's pretty sponge-y, almost like imitation leather. But I'd bet any similar material will do. Anyhow, the thin wood of the paint stirrer will bend and curve a little around convex bevel, as will the soft leather backing wrapped around it. The only thing to be mindful of is that your edge will be dulled during the sanding because it will sink into the soft backing (although you can minimize this by resharpening after the coarser grits then using a lighter touch while hand sanding with the finer grits), so you'll have to give it a good sharpening when your done.

Hope that helps!
 
Ok, so.... Do you have just the flat grinds done or do you have it also convexed down to the cutting edge? If the question is only about how you sand the curve I would say the same way you do the flats. When sanding convexed edges I use a backing stick, brass in my case (but anything rigid should work) and just follow the contour. As you sand through the grits you will be changing directions and that will blend in any micro facets into a continuous sweeping convex slope. You can use a padded surface on your sanding stick like a piece of leather or thin neoprene rubber but only after you have laid down a good smooth foundation sanding with your harder backing sticks so that your flats are truly flat without ripples and your slopes are smooth. If you grind in your convexed edge on the belt sander, a 480 grit belt will give you a pretty smooth surface. Hand sanding from there is just polishing the blade. * I have also found that using a piece of 1/4" thick plexiglass gives me a hard enough stick with which to sand however it bends a bit and works nicely over convex edges.
 
Thanks a bunch guys. What you've both described seemed like the best bet for getting a uniform finish over the whole blade but I wasn't quite sure. In response to your question I have done a convex bevel about 75% of the way up the blade and then a small flat grind to the other 25% of the way up to the spine. This was literally the first grind I did on my grinder, everything before was with files, and I was afraid if I took it to the grinder again I would mess something up or get it too thin. Things go very fast on a grinder, including mistakes lol. I got my grind where I got it and wanted to do a bit of sanding on it post-HT to give it a real nice shine. I really appreciate all the help guys. Hopefully this knife comes out as good as I think it will.
 
I sure will. Workin on a sheath right now and waiting for something in the mail so I can finish it up. I've posted pics of all my completed knives so far.
 
Yes, looking forward to pics as well!

Btw, what type of grinder are you using? My first grinder was the HF 1x30, and I churned out a decent number of convex blades with it before upgrading. Now I use it for all my finish sharpening. It's been a trusty little workhorse!
 
I got my hands on a 2X42 Craftsman grinder. I love the look of the convex and I was able to accomplish a nice looking grind in a fraction of the time as when I was using my files. So far so good :)
 
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