Grinding the belly on a big chopper

[JG Custom Metal Works]

So I've run into a problem with my grinding setup. The jig I made works great with smaller blades as the belly on most of them has been shallower. Here is the kind of jig I am using:

http://bushcraftusa.com/forum/showthread.php/81426-Scandi-Grinding-Jig-Tutorial

I have this big chopper in the jig and when I drag it across the belt it works great until I reach the belly. My question is, what is the best way to consistently grind the bevel while using this jig? The way I see it I have two options.

#1: The first would be to rotate the handle clockwise and down so the belly curves along the belt. This wouldn't work with the jig as the tool rest/table is in the way of the clockwise path. I'd prefer to use the jig if at all possible.

#2: The second would be to pull the handle towards me so that the edge would stay in contact with the belt throughout the belly. I have my grinder and tool rest/table setup now to do this. I just want to make sure this will cause any undesirable effects on my grind.

I know there are a lot of free hand purists on here and I think that's awesome, I just get more consistent results from using the jig.

 

[i4Marc]

Here is the thing. I can't speak for all freehand purists but I am not against the use of jigs if it helps speed up production. But jigs are like any other piece of technology designed to make our lives easier. If you don't learn how to do something yourself you are screwed when the technology fails. People tend to look to jigs to bypass the learning curve of freehand grinding but they don't realize jigs have a learning curve of their own and some limitations as well, as you know. Take the time to learn freehand. When you get comfortable with that you will be able to work through any grinding problem you have. As for you jig problem I would say get some junk steel from the big home stores and experiment. Don't experiment with blades you care about. Profile 5 or 6 junk steel blanks, mount them in your jig then try some of the different movements you mentioned.

 

[Bob Ohlemann]

I do a lot of machining and making fixtures and jigs is something that has always gone along with that. I am new to knifemaking and like most, have found the freehand grinding to be very challenging to learn. I've turned to jigs so that I can produce results the are up to my standards. In three months, I've made three different adjustable work rests and four jig blocks. Each jig is different because each blade is different. That it the thing about jigs, they are built for a specific purpose. Personally, I think the kind of jig you linked to is ineffective to begin with. It allows the blade to flex as it is pushed against the grinder. If you want to grind your big chopper in a jig, then you probably need to make a jig specifically for that purpose.

I agree completely with i4Marc on the freehand grinding. I find using the jigs to be limiting and time consuming. To improve my freehand grinding, I have cut a large stack of mild steel blanks and drawn a basic pattern on them. Every day when I go out to the shop, I start out by grabbing one of these blanks, profiling it and then grinding it either on the 10" wheel or the flat platen. I grind it as carefully as if I was working with a high dollar super steel. When I'm done, I throw it away and start working on my projects. I've gone through about a dozen of these blanks so far and I can see my grinding getting better; it is worth the time investment for me.

Bob

 

[Shawn Hatcher]

I know there are a lot of free hand purists on here and I think that's awesome, I just get more consistent results from using the jig.

I'm no purist, but the issue you're having is exactly why I learned to grind freehand. The jigs are just way too restrictive in my experience, especially if you like to make a wide variety of blade types.

It does take time to develop the skill, though. There's no getting around that. Good luck.

 

[JG Custom Metal Works]

I plan to get some junk steel or other metal to practice on. Anyone have advice on the cheapest metal to get that would be good to practice on? Heavy gauge sheet metal? Scrap of some sort?

Oh and BTW I got the bevels most of the way done on my big chopper. I just pulled the handle towards me so that the edge stayed on contact throughout the belly. Worked pretty good. I still have to blend everything together but that should be done here in a little bit. I'll post pics when it's done.

 

[JG Custom Metal Works]

Just got the bevels done. I ended up just convexing it at the end blending everything together with 120grit. I don't know if I'll go any higher than that before heat treat. Anyway here is my 2nd knife:

9.75in blade, 2in wide, 3/16in thick.



Kind of a shitty picture, sorry.

I'm pretty sure it's ready for heat treat aside from drilling pin holes. If anyone has advice as to what size holes I should drill and what size pins I should use I would appreciate it.

RichardJ was awesome about helping me out today too.

 

[Stacy E. Apelt - Bladesmith]

On a big chopper, use heavy size pins. 1/4" would be my suggestion. Drill the tang holes a bit larger than the pin/rivet. You want to drill the tang hole at least 25% larger than the rivet to allow some alignment slop ( If you drill them the same size as the rivet, it is almost a guarantee that the pins/rivets won't want to go thorough the tang during assembly).

Personally, on that knife I would use three large size Corby bolt ( 5/16" head) and drill the tang holes at 1/4". That would provide a solid handle and a good look. You would need the matching counterbore to the Corby bolt size you use.

 

[Dan Pierson]

I kind of question the value of grinding on cheap practice steel because that only addresses
one of your three major costs while guaranteeing a worthless result. The three costs are:

- steel
- belts, you really have to use sharp belts for proper practice and you'll go through a lot
of them. They'll cost more than the steel unless you're wasting something exotic.
- your time

 

[Shawn Hatcher]

I kind of question the value of grinding on cheap practice steel because that only addresses
one of your three major costs while guaranteeing a worthless result.

Just to add to Dan's excellent points . . . there is much more to making a knife than just grinding the bevels. All of these different steps require skills that are honed with practice. It makes more sense to me to start with high-carbon steel and start getting good at making knives, not just grinding bevels. You can pick up some very good steels like 5160, 1080/1084, 1095 for very little money from places like www.alphaknifesupply.com or www.newjerseysteelbaron.com.

Here's a great vid by Walter Sorrells on this subject of knifemaker progression. I love his phrase of "failing your way to success":

[video=youtube;tY6wp_Wsr0o]http://www.youtube.com/watch?v=tY6wp_Wsr0o#t=0[/video]

 

[JG Custom Metal Works]

Good point. I've also found that I'm getting better at fixing things. I had almost scrapped a couple of my first blades and recently I've went back through them and have been able to fix them. I'm just gonna try and go slow.

 

[Shawn Hatcher]

Good point. I've also found that I'm getting better at fixing things. I had almost scrapped a couple of my first blades and recently I've went back through them and have been able to fix them. I'm just gonna try and go slow.

Yes, making a knife is really just a series of corrected mistakes (for me anyway). It's impressive how a nano-second mistake can ruin hours and hours of work!!

 

[Will Batayte]

Since i read that you have been making a bunch of custom rests and such, maybe you could build a jig and rest that have an inherent curve to them so it follows the belly of the blade. Then you don't have to freehand the curves.

 

[JG Custom Metal Works]

Since i read that you have been making a bunch of custom rests and such, maybe you could build a jig and rest that have an inherent curve to them so it follows the belly of the blade. Then you don't have to freehand the curves.

Actually the rest was far from custom and was made using two pieces of angled aluminum. It works fine while grinding the belly, all I had to do was pull the handle towards myself once the belt comes in contact with the belt. I'm real happy with how things turned out. I blended everything together at the end freehand but that was easy with a slack belt/no platen.