Plunge Line Problem

[Hugh Buchanan]

I have been making knives for only a short time. I am having a problem creating symmetrical plunge lines.

• I use a 4x36 grinder with the side rails cut out, creating a 4" platen.
• I use a jig made of steel angle to hold the work at a constant angle.
• I built a large table and base, with a steel top on which to manipulate the jig. The grinder is bolted into this table and base.
• I am using aluminum oxide belts from Combat Abrasives.

My problem is that I am unable to control the shape of the plunge line from one side of the blade to the other. One side will have a vertical and square plunge line, while the other side will develop a curved, sweeping plunge line. I have tried to control the shape by hanging the belt past the edge of the platen. According to Walter Sorrels, this should produce a curved, rather than a straight and vertical line. This doesn't seem to provide consistent results. The shape of my plunge lines seems to depend as much on the phase of the moon as it does on the overhang of the belt.

Any suggestions will be appreciated. I am reluctant to grind one more piece of metal until I know how to control the shape of my lines.

Many thanks!

 

[danbot]

I have been making knives for only a short time. I am having a problem creating symmetrical plunge lines.

• I use a 4x36 grinder with the side rails cut out, creating a 4" platen.
• I use a jig made of steel angle to hold the work at a constant angle.
• I built a large table and base, with a steel top on which to manipulate the jig. The grinder is bolted into this table and base.
• I am using aluminum oxide belts from Combat Abrasives.

My problem is that I am unable to control the shape of the plunge line from one side of the blade to the other. One side will have a vertical and square plunge line, while the other side will develop a curved, sweeping plunge line. I have tried to control the shape by hanging the belt past the edge of the platen. According to Walter Sorrels, this should produce a curved, rather than a straight and vertical line. This doesn't seem to provide consistent results. The shape of my plunge lines seems to depend as much on the phase of the moon as it does on the overhang of the belt.

Any suggestions will be appreciated. I am reluctant to grind one more piece of metal until I know how to control the shape of my lines.

Many thanks!

https://bladeforums.com/forums/shop-talk-bladesmith-questions-and-answers.741/
You can report your post and ask a mod to move it to this ^^^ subforum. you will get good answers there!

 

[thebrain]

Many makers will file the plunge line then grind in to blend, if that makes sense. That goes for square or rounded plunge lines.

 

[Hugh Buchanan]

It makes sense. I would consider that to be a fall-back plan, if I can't do it all on the grinder.

Thank you for taking the time to make a suggestion!

 

[thebrain]

No problem , you would probably get more and better responses in the knifemakers subforum. I remember reading about Justin Gingrich (iirc)using files to cut in the plunge like I described. Lots of makers use a carbide filing jig but they can be expensive.