Deep grind marks won't come out

C

clivehamilton77

Joined
Aug 16, 2012
Messages
104
Uber new guy here.

I dont have a picture so I will try to be as detailed as possible.

I am using a 2 x 42 grinder with a not so good platen that has rolled edges. I notice that after all is said and done i have these areas that have streaks or otherwise tiny lines that must have been casued by the sander.

After HT, I put the blade through the grinder at 120 and 220 grit. I then hand sand with 320, 400, 600. I have been through stacks of sandpaper at 80 grit and can't seem to get these little streaks/divots/gouges out.

Am I just not sanding enough? Or how are they caused in the first place? Bouncing off the platen?

Thanks in advance for any of y'alls help.
 
Hard to say without a picture, and what you're describing is probably hard to photograph.
Sometimes I find streaks in the steel itself which are not actually scratches while sanding. I can't recall offhand if that's before or after heat-treat. If after, I would presume uneven or just barely adequate cooling rates would be the culprit.

Are you doing all this hand-sanding before or after cooking the blade?
 
Are you sanding in the same direction that the grinding was done? Have you tried sanding at 90 degree angles from the direction the grinding was done?
 
Mr Tryppyr's suggestion cannot be over emphasized. The 90 degree change makes all the difference in the world.
 
clivehamilton77 said:
Or how are they caused in the first place? Bouncing off the platen?

Thanks in advance for any of y'alls help.
Click to expand...

They are usually caused by not approaching the platen in a perfectly parallel manner. If you are slightly angled going in one side of the sandpaper will "dig" into your blade in that instant while getting the bevel against the platen. If your technique is being repeated for every pass this can make a big low spot.

Just remember you are not trying to remove the scratch. You are trying to remove all the material that is not the scratch. ;)
 
Carl_First_Timer said:
Just remember you are not trying to remove the scratch. You are trying to remove all the material that is not the scratch. ;)
Click to expand...

quoted for truth. gotta bring the surface down to the level of the bottom of the deepest scratch.
 
Oh god. Welcome to the insanity that scratches will inflict on you.

Are you using sharp belts? Also, try coloring the whole blade black with a chisel tip marker, then grinding or sanding a bit- if it is indeed a scratch, it will show up as a black line.
 
Very Ghandi like quote there Carl_First_Timer. I like it.

Daizee - I am sanding after complete HT

Tryppyr - I believe I am. After grinding blade up across the blade I hand sand the length of the blade so yes it would be 90 degrees

Salem - I currently get my nelts from TruGrit and they take forever to get down here to the deep south (New Orleans). So im kind of stuck with a bunch of half used 60 grit belts as they are my sharpest. Then some fresh 80 grit and 120 grit. Everything else is 3M wet/dry sandpaper.

Thanks everyone for y'all's advice. i really appreciate a forum like this to help a new timer like me. This source is indispensable.
 
clivehamilton77 said:
Very Ghandi like quote there Carl_First_Timer. I like it.

Daizee - I am sanding after complete HT

Tryppyr - I believe I am. After grinding blade up across the blade I hand sand the length of the blade so yes it would be 90 degrees
Click to expand...

Ahhhhhhh..... or not....??

What Tryppyr was referring to is all post grind sanding, and every other grit(for me: 220, 320, 400, 600, 800, 1000)is done in opposing directions so you can clearly(sometimes not so clearly) see the previous scratch pattern.

-Peter
 
The best way to approach this is to sand as much as you need to---prior to HT. If you try sanding marks out of hardened steel it's just a plain PITA.
 
Bigblue17 said:
Ahhhhhhh..... or not....??

What Tryppyr was referring to is all post grind sanding, and every other grit(for me: 220, 320, 400, 600, 800, 1000)is done in opposing directions so you can clearly(sometimes not so clearly) see the previous scratch pattern.

-Peter
Click to expand...


Yeah. you want to be reasonably close to your finish grit BEFORE heat-treat, and at a minimum make sure it's FLAT.
I grind at 60 or 80, then hand-sand with a block at 180, 280, 360. THEN heat-treat now that you know it's flat.
The decarb depth depends on the heat-treat method, and can vary from lots to negligible.
For 'lots' methods I'll only pre-sand to 180 or 280, then go back and clean up with 180 and step up to 600 or 1000.
For 'negligible' methods I'll pre-sand to 360, then post-sand from 360-1000.
 
Peter- Thanks for clearing that up. I know exactly what you and Daizee are talking about now and now come to think of it I dont do that.

David - Im starting to figure that out thanks, haha

Daizee - Thanks, I guess I need to do a lot more work before HT in the future. I send my blades to Peters HT in PA.

Thanks everyone. I appreciate all of the info.

Since I have everyone's attention and this is on my mind. Where would I buy a sheet of 1/8" or 3/16" steel to make biggers knives? More specifically a Tomahawk?
Ill post some other time as anew thread if this doesnt get any hits.

Thanks again everyone for y'all's help. Id be lost with piles of worthless steel surrounding if it wasnt for this website and others.
 
clivehamilton77 said:
Peter- Thanks for clearing that up. I know exactly what you and Daizee are talking about now and now come to think of it I dont do that.

David - Im starting to figure that out thanks, haha

Daizee - Thanks, I guess I need to do a lot more work before HT in the future. I send my blades to Peters HT in PA.

Thanks everyone. I appreciate all of the info.

Since I have everyone's attention and this is on my mind. Where would I buy a sheet of 1/8" or 3/16" steel to make biggers knives? More specifically a Tomahawk?
Ill post some other time as anew thread if this doesnt get any hits.

Thanks again everyone for y'all's help. Id be lost with piles of worthless steel surrounding if it wasnt for this website and others.
Click to expand...

You're well on your way.
pre-heat-treat work is soooo much easier. think of it as working faster and look forward to how much less work there will be once it comes back from the furnace.

the usual steel purveyers can usually supply something large enough for full-tang hawks.
and, of course, there's always Aldo. :D
http://njsteelbaron.com
 
Thanks Daizee. I recently just found out about Aldo after much searching. Im sure that shows how new I am at this as I've found out that Aldo is very well known around these parts. I appreciate your help. Thanks very much.
 
I'm late to the party but a couple of things I'll toss in:
* Good shop lighting & cross-lighting - it's amazing how well scratches will stand out with the proper lighting - and you definitely want to get all the scratches from the /last/ grit out before moving to the /next/ grit. That's where changing direction between grits pays off.
* Felt marker cheating - if in doubt, take a fat felt marking pen and paint the blade - when you sand or grind, the plateaus will clean up shiny, leaving the scratch canyons marked in felt-tip colors.

And +1 on the great advice above.

~~ Michael Kemp
 
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