Whats going on with my grinds?

[David Schott]

I think you're probably just using the same pressure with finer grits as when you're hogging. Those rough belts really rip into the steel, almost helping you keep the grind in place. Once you're using a smoother belt, it's easier to slip around a bit and unevenly apply pressure. I step belt speeds down and apply less pressure as I go up in grit.

 

[AVigil]

Build a jig to hold the blade at the desired angle and grind with that. It will show if it is mechanical or technique

 

[unky_gumbi]

OK so I made a fair number of changes, and things worked out much better this time. Only problem is I change so many things at once I don't know what fixed the problem either way this is what I I did this morning, there are 18 pictures showing what I did.

Laid out some grind lines

Using a used 36 grit belt I broke in the edges at about 45° stopping just above my edge thickness marks

strong side

Weak side

I then switched to a new 36 and started working my way up to my guide marks

weak side

strong side (yeah wobbly grind, it appears that my strong side is weak today, but that side is the worst of my elbows)

 

[unky_gumbi]

Then I started working up through the grits, 60-120-220-320. I started the progression at 60% of full speed and dropped 10% with each grit. I used a very light touch on each grit too.

Weak side

Strong Side

You will notice a nice little bobble here, someone came in the driveway and honked the horn while I was grinding, startling me:grumpy: I don't know who they were and they just wanted directions, but I gave them a nice lecture on startling someone while they were operating machinery, then I told them where to go

The grind lines are sharp even in the bobbled area, I am going to take a file and see if I can even that out without taking too much material off. Like I said I don't know what tip it was that made the difference, but one did so I will just thank everyone equally for their input on this. I have two other knives I want to get cut out and ground today so I best get back out there.

Thanks
George

 

[David Stifle]

George,

Looking Good!

You know you can improve even more if you bow three times to the North, three to the South, West and East don't you? A little know Bladesmith's secret passed down through the eons.

 

[unky_gumbi]

I never thought the bowing thing applied to me because I am just a metal dust maker that has knife byproducts

 

[Fred.Rowe]

The best advice I ever received on grinding: grind the the tip along with the entire radius of a blade "after" the straight area of the bevel is close to rough ground. The single straight draw with out the twist and turn used to shape the tip is best done by itself. Once the straight bevels are close to complete its much easier to grind the tip.

Fred

 

[Frank Niro]

Well there is your problem. With the worn spots the softer belts go into the grooves , change belt speed and bunch up to destroy your woirk. If the light comes through the platen needs replacing. That was my first thought when I read your thread. You may be salvage the platen and turn it over. Use heat and a putty knife plus gloves and you may save it to turn over.Not unusual by any means but difficult to find. Frank

 

[unky_gumbi]

My glass platen is one of the ones from USA Knife Maker and is clear. The scratches in it are under .001" deep (I used Ernie G's thumb tack method to measure the scratch) so not any problem with the belt getting in them as far as I can tell, I think the threads in the backing of the belts are thicker than that and the belt was basically new, used only once before for less than 5 minutes total grinding time. I will probably replace the glass platen this spring, but I wont be ordering it online because I can get it at Princess Auto and my brother can cut it to size for a fraction of the cost.

 

[A C Richards]

From the picture you posted it looks like a control issue rather than a belt issue. It is easy to let the blade rock ever so slightly. This will wash out the grind lines. Once you get to 220 grit or maybe 400 I go to hand sanding. This brings it all in evenly, at least for me.

 

[unky_gumbi]

I agree with you, it was a problem with the operator and not the machine I think it may have been a combination of the speed and pressure causing the blade to rock and washout the grind line, both operator errors. I changed a bunch of things so I can't say what in particular was the true cause Combine too much pressure and belt speed with my numb hands it is real easy to see how the blade can twist like you say. It also explains why what would normally be my strong side being the weak side yesterday because my dominate arm has been the worst of the two for numbness over the last couple of days

For the record I don't think I have gone past 220 grit on the grinder that often even though I have a couple of Norax U264 X45 (320G) and Norax U264 X22 (750G) belts. On a normal grinding session for me, once I hit 220 on a blade it doesn't see the grinder again, even after HT.

I was going to try and get a couple more blades done today using the suggestions from this thread, but it looks like I have been volunteered to finish packing up an apartment today. Too bad because it looks like it is going to be a beautiful day to be outside