Primary bevel on belt grinder...

T

TJ88

Joined
Apr 28, 2016
Messages
25
So i got my jig lined out and it seems to be doing awesome. Its starting a really decent plunge line but... its grinding this really weird semi circle grind up twoards the spine. What the hell is causing this? How do i fix it or can i?

20160727_145617.jpg
 
Spend more time in the middle, adjust the center of pressure to the middle of the blade as you pass the middle with your push stick.
Are you using a work table, or grinding free with a bubble jig?
 
Looks to me like you are not contacting the belt straight on and maybe tilting the blade into the plunge when you begin the pass. Its very important to keep the whole knife parallel to the platen at all times. For now, just focus on where the grind line is drooping down towards the edge until it comes up to match and its straight, and then give it a couple of very straight passes to even everything out.
 
One big drawback of using a basic jig is it can only follow one plane. As you follow the edge plane, the bevel is ground. The edge is curved ... so the grind is curved.

A bubble jig will help you learn to grind freehand, which will eliminate the problem of the jig.
 
Are you using grind lines on your blade or even one in the center? After each pass look at this. Where is the metal being removed and where not. This should tell you where to grind more or less with more or less pressure and or just length of stroke.
Frank
 
I think you are right BKT. I have where the plunge line starts ground farther than anywhere. My setup is basically a leveled plank of wood clamped to the tiny factory aluminum table. Im not using a bubble jig just one i made.
20160728_124416.jpg

20160728_124501.jpg
 
Yes for now just start right there in the middle and that line will creep right up towards the spine and level everything out.

I am a believer that using jigs will make learning to grind blades much slower. Sometimes you will have to just be able to do things outside the limitations that a jig puts on you. Depending on the jig it can cause more harm than good. If you really need a jig, I would just establish flats with a jig and then remove it. Once you get a feel for how the belt moves steel, you will no longer need a jig and will have a deeper understanding of how grinding a blade works that may have never been apparent when using a jig.

Some makers use jigs their whole career and there is nothing wrong with that, but personally I like the freedom and feel of freehand grinding. You will make more mistakes but it will make you a stronger knife maker in the long run.
 
Is there anyway to take away how far the bevel has bit twoards the spine on the tip half in my knife? I keep looking at it and i think i went too far up and past where i wanted it to stop.
 
TJ88 said:
Is there anyway to take away how far the bevel has bit twoards the spine on the tip half in my knife? I keep looking at it and i think i went too far up and past where i wanted it to stop.
Click to expand...

No.... Now you straighten the grind height to match the height of the grind near the plunge. Then match it on the other side.
Also make sure your stock is straight before you start. Chasing THAT problem on the grinder is a losing battle.

Seldom do you end up making the knife you planned to at the start.

Some practice moving that bevel around without the jig will serve you tremendously, because it will teach you how to adjust and dial things in, as well as compensate for the inevitable whoopsies.
 
Uneven/curved grind lines can be caused by a number of things, but the main culprits are usually as follows:

1: uneven grinding pressure, or leaning into the corner/side of the belt/platen. Watch your sparks, they'll tell you where your belt is cutting.

2: the stock is not flat: if the bar your grinding on is bowed/warped at all, and you're grinding flat on a a platen, you're not going to be contacting the belt evenly, and this will cause the grind to curve up or down based on whether you are grinding the concave side or convex side.

3: dull belts: if you have sharper/more grit on one side, and are dull on the other, this will affect your material removal rate, and it will not be even or flat. Change to a fresh sharp belt and see if this helps.

Those are probably the 3 most common, though flatness of your table/workrest, and/or your platen can factor in as well.

My opinions on jigs have evolved somewhat over the years, but one thing will always be true: They won't grind the knife for you. Some jigs are better than others, but they all have their limitations, and really (at best) will only take the guess work out of ONE plane of grinding. You still have to think about the other two planes. I encourage any maker to learn how to free hand grind, even before using jigs, if possible, as you get a much clearer picture of what the mechanics of grinding actually are, as well as being able to understand more about the limitations of jigs.
 
AVigil said:
Everyone uses a jig, some are made of metal some are made of flesh.

The trick is learning how to use that jig correctly.
Click to expand...

Bingo!

As far as the problem with the OP I would guess the stock is bowed in the region where the bevel drops. Making sure your stock is nice and flat will help with just about every aspect of your production process.

Blessings,
Joshua
 
here is something that might help. i keep permanent marker and mark the edge of the blade before i grind so i can see where i ground and where i missed. i do the same thing when sharpening.
scott
 
You must log in or register to reply here.
Back
Top