Skiving Machine Woe's.

[SonderingSusan]

 

Hey Everyone,

 

Sometimes being alone with all this machinery can be trying ! My sewing machine techniian was just here today about one problem and now i have another.

 

I have put a thick sharpie mark on my bell knife to see what is happening when i sharpen it, as my knife is cutting into the leather and ruining it. 

 

What i have discovered is that the sharpie mark is only half removed after a long time of sharpening - 5 mins. The black sharpie mark is still totally intact closest t the edge of the knife - and the sharpie is removed further in on the blade. 

 

Does this mean my sharpening thing is not hitting the blade at the right angle ? What can i do about this ? Any / all advice welcome and greatly appreciated!!!

 

Thanks in advance,

S

[TinkerTailor]

So good call on the sharpie trick. I use that one all the time. You are absolutely correct that if the sharpener is not getting to the edge, and is hitting the wrong spot, something is out of wack.  Not sure now new this machine, or its blade is, and what make/model it is so the following it somewhat speculation:

Digging in can be due to a dull knife, but it can also be due to incorrect cutting edge angle/grind. Cutting machines, whether for leather/wood/metal all have specific edge angles needed to cut a given angle. It is always a balance between material removal rate and preventing the tool from digging in. This is why it is important to ensure you are starting with the correct angle, and the blade is not off due to previous poor sharpenings.

Now why is the question. It could either be the sharpener is out of wack, or the angle of the edge on the knife is out of wack from previous poor sharpening, or the stone is not flat/true. Without pictures or a manual i suggest accurately checking if the angle of the blade as it sits is correct with some measuring device, or check it against a brand new knife if you have one. If you push a piece of plastercene or clay up to the edge, you can get an impression of the angle of the edge. This is sometimes easier and safer than measuring the actual edge. Compare this to the factory specs. The idea is to check the knife to ensure it is right with the world, if the angle is correct, you need to correct the angles of the sharpener, or sharpen in a different position. If the angle is off, you should sharpen the knife to the correct angle or replace it.. The other thing is the stone needs to present a flat surface to the metal at the correct angle. If the stone is worn with ridges in it or something, you will need to either dress the stone or replace it.

Good news is, if the angle of the knife is out of wack,and provided you have enough knife left, you should be able to sharpen it correctly by ensuring the sharpener is working at the correct angle and going to town. It may take a while to get it grinding right to the edge, but it will eventually get there. If you end up going this route, take your time and take breaks. You do not want to overheat the knife grinding it too fast.

here is a tutorial, watch at 1:45

 

[Sonydaze]

If you have advanced the bell knife towards the presser foot, it changes where the stone engages the bell knife.  Bigger advancement, bigger change.  If you have been sharpening without advancing the knife, the angle of the grind becomes steeper and creates a lot more friction on the leather coming off the edge.  My thoughts (from the other side of the world) is to set the bell the correct distance from the presser foot then regrind the edge until the Sharpy mark goes away right to the edge.  When I was newer to this kind of skiver, I made the mistake of not consistently advancing... trying to make the bell last longer.  The regrind took about 1/2 an hour,  I suggest dressing the grinding wheel before you start.