Another Question- Grinding

[izafireman]

All smiles yesterday as I got my first order of 72 inch belts for when I collect my new grinder next week )))
But I was grinding a hardened Elmax blank out last night, 4 degree a side flat. Roughed out at 40 grit and then 120 grit..all went well. But I only had an oxide 220 for the next stage so opted to skip to a 400 Trizact instead..so 40,120 then 400. This is where my problems occurred in that the belt seemed to be cutting in mainly one place, so I altered the angle of the work table but even so this still did not get me taking material off the whole surface. What I had to do in the end was finish off free hand.
Am I right in thinking that going to the 400 was too bigger jump or could there have been another reason the 400 was not cutting over the whole area of the blade as I also thought it was because as I went up the grades the belts get thinner.

Edit...just realised, I forgot to say initially I was using a jig, might help make more sense.

Thanks

 

[Tom Lewis]

I mainly grind CPM 154 and W-2 steel. What works well for me is 36 grit, 60 grit, 120 grit, 220 grit, 400 grit, 22 Norax. Then I start hand sanding long ways on the blade with 400 grit and work up to 1200 grit. Skipping any of these grits would make the job much harder.

 

[izafireman]

Thanks for the reply Tom. I suppose I need to do the same grind again now I have the grits I didn't have before and see if this time it goes as planned.
Thanks

Pete

 

[JeremyBartlett]

All smiles yesterday as I got my first order of 72 inch belts for when I collect my new grinder next week )))
But I was grinding a hardened Elmax blank out last night, 4 degree a side flat. Roughed out at 40 grit and then 120 grit..all went well. But I only had an oxide 220 for the next stage so opted to skip to a 400 Trizact instead..so 40,120 then 400. This is where my problems occurred in that the belt seemed to be cutting in mainly one place, so I altered the angle of the work table but even so this still did not get me taking material off the whole surface. What I had to do in the end was finish off free hand.
Am I right in thinking that going to the 400 was too bigger jump or could there have been another reason the 400 was not cutting over the whole area of the blade as I also thought it was because as I went up the grades the belts get thinner.

Edit...just realised, I forgot to say initially I was using a jig, might help make more sense.

Thanks

My guess is that your initial bevel with the lower grits was uneven, so when you jumped to the 400 grit you were just polishing the high spots. My progression is 36, 60, 120, 220, 400, 600. The 36, 60, and 120 in ceramic, and all the higher ones in aluminum oxide. Hope this helps

 

[JeremyBartlett]

My guess is that your initial bevel with the lower grits was uneven, so when you jumped to the 400 grit you were just polishing the high spots. My progression is 36, 60, 120, 220, 400, 600. The 36, 60, and 120 in ceramic, and all the higher ones in aluminum oxide. Hope this helps

Another thing to consider, were you using a regular trizact or was it a trizact gator. The regular trizact are a lot thinner than your ceramic belts, try putting a another belt on behind it to give it a little more thickness and some extra give.

 

[izafireman]

Thanks for the reply and what your saying makes sense and is what I think was happening. Yes they are regular Trizact but I have just bought 85 mixed belts and made sure that included Gators from 60 grit to 600 grit on the advice of a pal. He swears by them and I cannot believe how long they last. I will though try the trick with the normal Trizacts as they to seem to go on forever and have lots of bite left in them.

Cheers

Pete

I forgot to say I got round the problem by a bit of free hand grinding ( which is new for me) and then am not proficient at free hand I hand to blend everything in using 2 inch random orbital ait sander with various grits. I can hear the purists cursing lol but I had to rescue the blade rather than bin it. It is actually turning out very nice and the random orbital is one great way to cheat for a an eventual mirror finish )))

 

[kgmacpherson]

Iza
I have a disability where hand sanding for any longer than 10 minutes has me crying like a little girl. To assist, I also use a random orbital sander with various grits. It has saved me tons of time and if it allows me to make knives which I love to do then I make no apologies.

 

[Smallshop]

Another thing to consider, were you using a regular trizact or was it a trizact gator. The regular trizact are a lot thinner than your ceramic belts, try putting a another belt on behind it to give it a little more thickness and some extra give.

Have you tried this jeremy? Great idea if you have and it works!!

 

[JeremyBartlett]

Have you tried this jeremy? Great idea if you have and it works!!

Yes I have, there is one trick to it though, both belts need to be pretty much new, you really have no idea how much belts stretch under tension on the grinder. I like to use a 400 grit trizact gator with a 400 or 600 grit AO belt on top of it, really gives a nice finish. I'm working on a few knives right now, maybe tomorrow I can post a pic of a finish done like that.