how fine to sand blade prior to h.t.?

F

fetz

Joined
Dec 30, 2003
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would'nt it make more sense to almost finish the blade while it is still annealed? i have read about some of you rough grinding and then heat treating and then finish grinding and sanding, i know there must be a reason for it, sooo please elaborate! thanks
 
My 2 cents on this one...

I tried taking them almost to finish years ago.The finding I had was that the real fine edge was waving in the quench,and if the blade did have a small warping problem I had no extra steel to remove the warp.Also I had heard that it takes a few sharpenings before a good blade reaches it's full cutting potential and by doing a finish grind it cut out the curve of extra sharpenings.I also don't grind in my back edges untill after the heat treat,this cut's down on warppage also.
Hope this helps some.
Bruce
 
It is all one big trade off between different difficulties. Some of the things determining this are how good you are at heat treating and what equipment you use to do it. If you are not real good and experienced in keeping the time at temp,in the wrong atmosphere, to a minimum you should probably do more finishing after the HT. I use the salt baths, so I take my blades to a hand finish (sometimes 600X) before the HT. But if you are going from a kiln or forge into oil you need to consider a few things.

One thing to consider is the possibility of stress risers caused from coarse scratches. For this reason I have always went to at least 200X before HT. But then if you are going to have scale, decarb or discoloration going much higher could be a waste of time since you will have to drop back to a coarser belt to clean things up for polishing.

Decarb is something to always consider. It is always wise to remove a bit from your very edge to be sure that you have good fresh steel where it counts, if you have not taken very elaborate measures to eliminate the possibility of decarb.

If I were doing it in a kiln or Forge I would sand to 200X and then pick things up again at 200X after the HT and then on to the polish. It really is not that bad. If you are spending many hours or days rubbing a finish on by hand after 400X belt, you should work on developing a smoother grind. I have found that just scratches come out in minutes not hours, but dips and waves in the grind take hours or days as you need to bring the entire blade down to that level to properly erase them.
 
fetz,

I leave my blades at 60 grit prior to HT but know many who take them just about to final finish. For me it is a personal preference. I like the extra resistance the HT'd steel has when I am going up through the grits trying to leave everything flat.

...pretty lame...I know..:D

Take Care
Dean
 
I rough grind at 50 grit and then go to 220 before HT, making sure to round ALL the edges off.
 
40 grit, 120, 240, 320, and then heat treat with molten salt. The blade is at about final dimensions. After tempering the blade, I go back to the grinder for clean up with 320 and then hand sand with 320 and then to 600, some times I go up to 1500 before I etch the blade.

Like Kevin said, alot has to do with your heat treat abilities and equipment. When I first started out, I would just profile the blade with a 40 grit and then HT and temper. Then I would grind all the bevels.
 
On carbon steel knives I like to leave it real thick before heat treat. .040 or so is typical.
For the few stainless blades I've done I took them up to about 400 grit and around .010 edge thickness.
It helps to make the edge round and smooth to prevent warping and cracking.
 
Bruce E. hit on something important for you if you edge quench.

I take mine to 400 grit, finer than the more experienced do. Even when I foil wrap I will have oxidation (oxidization) to grind down. If not atmoshere controlled there is decarburization or more that has to be grinded down. It makes little sence to have to go up in grit size after heat treating.

RL
 
Being new to knife making but not to working metal I have HTed my first few blades the same as I HT gun parts. I bring to a 400 finish and heat to about 400/600 and coat with Boric Acid then go through a normal edge quench. After removing the Boric Acid with boiling water I find the blade just as clean and smooth as before HT. Now the question -- do you think there is decarberization of the surface if a coating is used as I do? I have checked the edge with a file and it skates on the surface. I must be fair and add that so far I have only used carbon steel for blades and so far have experenced no warpage. I must also admit that even after making rifle stocks for about 50 years I still have more trouble with the handles than the blades.
Good luck and thanks for every ones help
 
Originally posted by Pete Allan
...Now the question -- do you think there is decarberization of the surface if a coating is used as I do? ...
Click to expand...

Anti scale compounds are another good way to go. I tried some for a while before I went to salts. It is hard to say how effectively you can eliminate decarb problems with coatings, there would be a lot of factors. I have to watch the salts real close to make sure they keep neutrality, or they will start to decarburize the steel in a nasty way. Sometimes, and I stress the Sometimes, a quick dip in an etchant can reveal the splotchy spots of decarburization. When the salts go out of neutrality the blades will come out with pretty silver polka dots:rolleyes:

Decarb is not a huge moster that will destroy every blade, but it is more prevalent than many folks think, and some methods get around it a lot better than others. It is just kind of embarassing when one of your knives have to be sharpened a couple of times before it will hold an edge the way you know it should.
 
I don't have any fancy equipment just a forge and some grinders. I had a problem with warping on ground blades after heat treating. I changed to forging to shape leaving the cutting edge a little less than 1/8" then doing the normalizing, quench, temper, sequence. End of warping, I have not had a blade warp in 8 or 9 years. Gib
 
Gib.

I had one blade bend even after I left it the same 1/8 inch thick.

I was tempering it in the kitchen oven. It was at 350 for two hours.

just before the two hours was up I got a phone call and I had to go, so I grabbed the knife out of the hot oven and set it inside a drinking glass.

why?. Im not sure, but at the time that seemed to be the correct thing to do with it.

then i took the glass with the knife in it and right away placed it into the freezer.

Thats not what I wanted to do, most of the time I set the knife to cool to room temp, then into the freezer...but I didnt have time. so it went from oven to glass to freezer all in 10 seconds.

knife bent in the freezer somehow...
 
Kevin, how do you neutralize the salts? Replace it? What causes the problem? The steel; the atmosphere?

Thanks Kevin.

RL
 
I have a graphite powder that Park offers that is sprinkled on the top of the molten salts. This does a couple of things. First, it is carbon setting right on the top of the salts, you have probably heard a few salt users that talk about stirring with carbon rods and the like. Second this powder will form a solid barrier on the surface of the salts to keep contaminates out. This handy crust can easily be penetrated by blades but keeps dust and other crap out as well as virtually eliminating the salt vapors that waft about when they are at temperature and attack anything metallic in their vicinity.

Also for safty sake I will often scoop out a cup or so of the salts and add some fresh stuff. How do they go bad? The are more than a couple contributing factors. The worst is all of the metal and silica dust flying about in a bladesmiths shop, then there is whatever may be introduced on the blades that you didn't notice, and continued heating to 1500F can cause just about anything to start to get worn out.
 
Originally posted by Kevin R. Cashen
This handy crust can easily be penetrated by blades but keeps dust and other crap out as well as virtually eliminating the salt vapors that waft about when they are at temperature and attack anything metallic in their vicinity.
Click to expand...

So an electric salt pot setup, such as the ones Tim Zowada offers would be fine as long as the maker employed the use of the carbon powder? Kevin, you are famous amoung these forums for your preference for the gas-powered salt pots, but certainly you must agree that an electric model would have its benefits, yes? :D
 
I just apologized to Tim four days ago about this. You see Tim sells the kilns that can be used for this, but I have not been very good for drumming up new business for my friend. I do believe I have had the worst luck of any maker I know of with the salt not staying where it is supposed to. I apologized to Tim, who has had very good luck, for not being able to offer anything but horror stories about using electric kilns and salts.

Heck the reason I was on the phone with him was to check on the availability of replacement pats for my kilns. I have spent a small fortune replacing refractory bricks and elements over the years, and lost countless hours of shop time trying to keep things working. I totally abandoned the kilns for the high temp well over 3 years ago and had a couple of incidents with the low temp taht I finally have a handle on. Then just last week, one of those 2-3 year old contaminated bricks decided to release its deadly payload and blew an entire section of my kilns. I could tell it was high temp because of the tell-tale bright yellowish green color on the bad sections. Years later I am still paying for using the high temp. with electricity. I switched to gas in a desperate attempt to salvage my operation and sanity, but have since found so many advantages that I cannot deny that I am in love.

Now after saying all of that, I must add that there are many folks out here that have used the kilns for high temp for years without any incident and are very happy with the setup. This is mostly a case of -the universe is out to get Kevin Cashen, and Murphy's law is the only one that I can always count on.

I wished Tim would start selling gas units as well so I could be his best salesman. In the meantime, I think the kilns are great for low temp and cannot be beat for annealing operations.
 
There are commericially-available gas units out there, only they are intended for high production, and therefore are built like tanks and have exorbitantly high price tags ($8k). If someone offered a gas-powered saltpot setup, reliably built and sturdy, I would buy one.
 
Kevin R. Cashen
(I had a bit of trouble with my computer and my email this week, but if you remember you have asked me....)

"DaQo'tah Forge: Out of curiosity, what steel was your bent freezer blade made from?"

Kevin due to the advice I have received from the members of the Blade forum, I have switched to just useing John Deere Load shafts.

The blade in question was forged from a 1 and 1/8 inch thick shaft. I used my belt grinder and it was left over-sized along the future cutting edge to protect the inner steel from the heat-treatments.

after 3 heat/quenchings I tempered in the kitchen oven that is set at 350.

I wanted to have it in the oven for 2 hours but due to a phone call I had to go, so I took it out of the hot oven and placed it in a drinking glass (hey it was hot and I had to put it someplace) , then I placed the drinking glass into the freezer.


I returned home about 12 hours later and noticed right away that the knife had a bend in it that I just dont remember being there when I took it out of the oven.


Now it "could" have been bent coming out of the kitchen oven, but I just dont think so because of the way you clearly notice the bend right away when you look at it.

The knife was NOT bent going into the oven, was bent coming out of the freezer. Thats all I know for sure.


(I fixed the blade by grinding and making the knife shorter and you cant tell now there ever was a problem, however I still think about why that happend.

My ideas were: that you should not go from oven to freezer that fast?....or,

That when you place a hot knife to rest and cool down it should be not tilted?....or,

There is also the small chance that in that drinking glass there might have been some water, and if so, the water did a low temp quench on one side of the blade due to the tilt of the blade as it sat in the drinking glass?....or

just one of them things......
 
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