Issues going up grits on the grinder

T

Technohedge

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Sep 9, 2018
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Trying to improve my 'off the grinder' finish as hand sanding forever is really something hate doing!

Issue is when I go from 120 grit to 240 grit then to 400, it all looks great until I try and hit it with 240 paper to finish it off. Seems to reveal loads of much deeper scratches I thought id got rid of but obviously haven't.

I have tried covering the steel in engineers ink and then grinding until its gone but this doesn't seem to work. Also tried etching in FC but that doesn't seem to take in the deep scratches.

Any other tips guys?
 
Don't go to the next grit until all lower grit scratches are gone.

What happens in machine sanding is you sort of burnish over the scratches because the belt moves only one way. The parallel lines tend to hide things.. Then when you hand sand you reveal them again.

Ways to deal with that:
1) Try changing the angle of the blade to the belt between grits. This shows where the previous lines are.
2) Use good light ... lots of it. When examining the blade for scratches, have the light come at an angle. Higher Kelvin light sources are also better. 5K to 7K will show a lot more scratches than a soft white 4K bulb. A gooseneck lamp with a 75W 6K LED bulb is a great examination lamp.
3) Use magnification. A jewelers hood, called an Optivisor, is a valuable tool. What looks perfect by eye may show it isn't done yet with a magnifier hood on. The lenses can be changed or you order the magnification you want. The higher the number, the closer you have to hold the object to you. #5 is a good lens number for most shop examination, with 2.5 magnification and a focal length of 8".
 
Get a cheap orbital sander. The kind that takes a third sheet or quarter sheet of sandpaper. Take off the soft backer and put on a hard backer made of micarta. Put the sandpaper on as tight as you can get it. Start with a grit lower than the last grit you were using on the grinder. Clamp the orbital sander upside down in your vise or clamp it to the table somehow so that the sanding surface is facing up. With the orbital motion there is no one single way that it pulls your knife so that it's easy to keep the bevels flat against the sanding surface. I think this idea came from Ed caffery. When I first tried it it was a miracle for me in flattening bevels and reducing hand sanding!
 
Stacy E. Apelt - Bladesmith said:
Use good light ... lots of it.
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This. And make sure you look at the blade form all angles as well as move the blade angle around when looking from each direction for scratches. As you get to higher grits, the smaller scratches sometimes only show up at one specific angle. I can't tell you how many times I've spent 2-3+ minutes looking at a blade to locate any errant scratches before finding that one last scratch.
 
You want to see the scratches? Just take a picture of it it's amazing how a camera will bring out the scratches sometimes that you can't even see.
 
My guess is you are using your belts way past their effective time. Once a belt get worn to a certain point it doesn't cut but just spears the surface covering up deep scratches. It may look like you're makeing progress but you're not. Worn belts cause most new makers problems.
 
weo said:
Stacy, do you know if you can get these that fit on the outside of a 3M 6800 series full face respirators?
View attachment 1594920
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I would no recommend scratch/finish inspection of the blade while wearing a respirator. The diffusion of the shield would be a problem. Take the hood off, pop the Optivisor on, and check it close up and under bright light.

A large hand magnifier glass (reading glass) might work sort-of-OK for checking while wearing the respirator.
 
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weo said:
got it, so you use them for this, exclusively...I was thinking that if my 1.75 readers made grinding easier for me than my normal 1.25 readers, then 3-5X would be even easier.
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Focal distance shrinks with increasing magnification on Optivisors. It gets weird when you're face is 6-8 inches from the grinder. Tried it! :)

I have a PAPR and am seeking a solution, too, weo weo . I'll let you know if I ever discover anything.
 
fitzo said:
am seeking a solution, too, weo weo .
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What seems to work well enough for me is that I took the earpieces off a pair of readers and replaced them with some elastic bands. This allows the mask to seal around the elastic pretty well. It's not the most comfortable, but not bad.
20210705_122540.jpg
 
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fitzo said:
Focal distance shrinks with increasing magnification on Optivisors. It gets weird when you're face is 6-8 inches from the grinder. Tried it! :)

I have a PAPR and am seeking a solution, too, weo weo . I'll let you know if I ever discover anything.
Click to expand...
I use the #3 and #4 lens for some work where I want a bit of enlargement but can't safely get my face too close. These work good for engraving without a scope. 14" and 10" focal length with about 2X magnification.
 
weo said:
What seems to work well enough for me is that I took the earpieces off a pair of readers and replaced them with some elastic bands. This allows the mask to seal around the elastic pretty well. It's not the most comfortable, but not bad.
View attachment 1595113
Click to expand...

That's an excellent idea when a seal is necessary. I like it! I wear readers (2.25) inside the PAPR now but it is insufficient. About my only solution now is to turn to 2.50 or 2.75 inside the hood. That's weird when one looks up, though.

I have considered having a magnifier on a stand next to me so I can flip the blade under there for a little closer view. Set of magnifiers that'd flip down from the PAPR hood thing would be a great boon.
 
Stacy E. Apelt - Bladesmith said:
I use the #3 and #4 lens for some work where I want a bit of enlargement but can't safely get my face too close. These work good for engraving without a scope. 14" and 10" focal length with about 2X magnification.
Click to expand...

I am having problems with my spinal curvature and sitting at the 'scope for engraving. At that fineness, so to speak, I find I have slightly different focus in the eyes, and the mono-focus of my beloved Optivisors are being a problem there. To that end, I am considering a set of Keplerian magnifiers used by doctors and dentists. I want to engrave again even more than make knives, and I really want to make knives.
 
Fitzo ......To that end, I am considering a set of Keplerian magnifiers used by doctors and dentists. .....

Like these?

1625516723667.jpeg

I set this using them yesterday:

1625516806228.jpeg

Here is my engraving bench:

1625516918281.jpeg
 
Those are Galilean optics, but very same idea. Kep.'s look more like mini-telescopes and the Zeiss I am looking at have a headgear as opposed to eye frames. They are the Pro-Mag 5. I think the big difference is in eye positioning. I need something where the eyes will adjust separately, so my Optivisors are a little off for engraving. In some respects, the style you have may be better for my messed up neck. The Engraver's Forum (Steve Lindsay) says call them up, they are very helpful and offer a test run, so I will eventually.

Thanks for a pic of your bench! Very cool to look at, as much as seeing another knife maker's shop. That's actually a wet-grinder for faceting jewels, isn't it? Very neat, another thing I'd have loved to have tried. Lots of cool stuff down on that left hand bottom shelf. And i see the blacking lamp up above. I also like that badass cape on your chair. And the bench is to die for.

Fun to see. Thanks, Stacy!

Edit to add: Well, my idea may stay on hold a good while. The Lindsay site says the magnifiers were "$1499" but when I start looking I see $3495. I need to call them.
 
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