Deep grind marks won't come out

[clivehamilton77]

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.

[Doug Lester]

It is really hard to say without being able to see what we are talking about here but it is quite possible that you are not getting all the previous grinding/sanding marks out before going to the next grit. On the grinder, try marking the blade with a magic marker when you go to the next finer grit and then grind until all the black marks are gone. Also don't try to get that last little bit of use out of your belts. When they start to feel dull switch them. With the sand paper sand at right angles to the way you sanded with the last grit until all of the scratches from the previous grit is gone. Close enough may be good enough for government work but it's not close enough for finishing a blade. Don't try to get that last little bit of use out of your sandpaper either.

Doug

[clivehamilton77]

Thanks Doug I appreciate it. I must not be sanding enough. I've always heard you guys say it takes elbow grease but i thought it would end sometime. Thanks for your advice. Ill put it to good use.

[Doug Lester]

Don't use cheap sandpaper, get the stuff meant for doing auto body work, not woodwork. The difference is in the material that is used for the abrasive grit. Some the stuff for wood is just not quite hard enough to stand up to hardened steel.

Doug

[clivehamilton77]

O ok. Thanks Doug. I go from using the stuff at AutoZone and when Im at Home Depot I pick up what ever I can. Ill have to stick with the stuff at CarQuest or Autozone. I appreciate all your input.

[Bowman]

Clive,

I just went through this recently and I can not recommend buying good quality sandpaper enough for your blades. I thought the same thing and it took forever using a pile of paper with little to show for results.

[Ed Tipton]

CliveHamilton77...Ditto everything that has been said previously....but....I picked up on something you said about your blade "bouncing" against the platen.
I had a problem with "blade bounce" that drove me nuts until I finally corrected the problem. If your blade is "bouncing" against the platen, then changing to a finer grit belt is probably not going to help unless doing that eliminates the bounce. In my case, I finally had to overlay the existing platen with a piece of 1/4 " glass. I attached the glass with JB Weld epoxy, and that cured the problem. I was never able to determine exactly what was causing the blade to bounce, but it was... and it was very obvious and very annoying.
Assuming there is no "blade bounce", then your problem is probably that you are simply not giving the finer grit belts enough time to work their magic. Also, you really didn't say, but if you're grinding after your HT, then the entire process is going to take much longer, and it will also wear out your belts much quicker. I try and get my pre-ht grind all the way down to 220 grit. Doing this when the steel is still softer makes a great difference, and it also helps to reduce or eliminate stress risers in your blade, and that helps in reducing both warping and cracked blades....not to mention the savings in time.
I don't know what technique you're using when hand sanding, but if you can clamp the blade to a workbench, and then take a piece of sandpaper and wrap it around a piece of wood, it then becomes very easy to keep all of your sanding scratches in a straight line and it is also very easy to apply much greater force than it is if you simply hold the blade and sandpaper in your hand.....just a thought.
It's all part of the learning process...and the sad thing is that without actually seeing you work and actually seeing the results....all of this really amounts to a shot in the dark.
Hopefully, somebody will suggest something that will get you on the straight and narrow.....Ed

[AUBE]

As they said...without a pic its hard to say.

But out of curiosity how big of a blade are you working on, what material is it, and how long have you spent hand sanding?

Also do these streaks/divots/gouges run the same way the sanding scratches do or they go the opposite direction? Are they straight, or do they zigzag? I've seen people find flaws in the steel, or heat treatment, that they thought were scratches but were actually part of the steel...for example small inclusions can form zigzag streaks that look like scratches and run pretty deep in the steel....you'll never hand sand them out. One guy was overheating the blades during heat treat and getting alloy banding, then spent hours trying to sand it out.

Basically if you are doing a blade around 4" long, around 1 1/4" wide from something like 1095, and using good sandpaper/technique it should take you maybe an hour to remove all scratches from a 150grit belt. Thats using maybe 2-3 sheets of good sandpaper.

(edit: My post just reminded me of a situation we had about a year ago. I have an apprentice/worker that works for us 9-5. Well I'm typically up late so I will set aside tasks for him then sleep in til noon. I had set aside a pile of blades for him to hand sand through the day. At this point he had done a lot of hand sanding so I thought he would be fine alone. I wake up and ask how many blades hes done...hes on the same one he started with. I ask whats taking so long he says "I can't get this darn line out!" I look at the blade and realized that he had never done sanding on a hamon lined knife and he had spent hours trying to sand a hamon out of the steel(impossible). I felt a bit bad about that one, had to buy him lunch.)

[clivehamilton77]

Bowman. Thanks man.

Ed - Not a shot in the dark at all. You pretty much hit the nail on the head. Thanks so much for the insight and advice. As far as the platen goes what do you think of using a piece of ceramic tile to secure to the platen instead of glass? Would that hold up?

Also, for my hand sanding, I have a piece of 2 x 4 and I lay the knife down on one side and secure it with a wood screw through the thong hole and clamp the 2 x 4 down. I then secure the sand paper in a rubber sanding grip type thing.

Sorry for not having pistures. Ill hopefully get some soon. I posted some pictures of my recent work on a thread a few down from this one. If it helps they are usually on the bevel.

AUBE - I am working on O-1. 1/8" x 1.5" and a length of about 7.5". I have hand sanded about 4 hours now and I keep the blade cool as well by dabbing it with a wet towel. As far as the direction they run the same way that my grinding belt does when I am grinding edge up. So that's why I thought it was due to bouncing blade. And they are straight as an arrow.

Jeez, I am sanding way longer than an hour. That is a funny story AUBE. Something that I would probably do being a Newb and all.

I cant tell you all how much I appreciate the advice and guidance. I dont know how you old timers did it without a resource like this. If not for this, I'd be using that steel from Home Depot and thinking I was the next Gill Hibben or Loveless. Thanks again.

[clivehamilton77]

Link that I mentioned in previous post

http://www.knifenetwork.com/forum/sh...ad.php?t=60342