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Is it better to do final sanding, polishing, etc. before or after heat treat? Even if going for a mirror finish. Seems like it may make it easier to remove scale from heat treat?? Appreciate the response.
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question- Finishing- final touches, sanding, polishing, etc
- Thread starter crazydad42
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Depends on your metal, if you are using a simple steel (1080 - 1095) go to 220, you will need a bunch of sanding after heat treat. If stainless and wrapped, I go to 400, there will be light oxidation and then you can go up in grit. After 400 the sanding is pretty easy, if you get out all the previous scratches. If you sand at different angles it makes seeing the previous grit scratches easier. If you take some shortcuts in sanding trying to go to a mirror finish you will spend many hours in sanding purgatory.
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It will also depend on what kind of knife you are making... some knives are best made with some of the grinding done after HT.
Stacy E. Apelt - Bladesmith
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As the fellows are pointing out, there is no one answer.
The main thing to consider is that ANY SCRATCHES left from pre-HT work will be five times as hard to remove after hardening. 400 grit pre-HT is the minimum in most cases. For a knife that will be mirror polished, I would take it to 800 or better before HT. For most stainless steels, you can take the blade to the final finish before HT and merely re-do the last couple steps afterward. My friend pre-polished his stainless blades before HT. After HT, just takes them to the buffer with black emery compound, then green.
Another big variable in the degree of pre-HT sanding is the edge thickness at HT. On a carbon steel blade you need to leave a bit more thickness. That means you have to take the whole bevel down some after HT. On stainless, the edge can be virtually at the finish thickness. This allows for only a minor clean-up after HT. For most carbon steel blades, I take the edge to .020-.030" before HT. Stainless I take to .005-.010". On thin blades that are below .060" thick at the spine, I usually grind the bevels after HT.
The main thing to consider is that ANY SCRATCHES left from pre-HT work will be five times as hard to remove after hardening. 400 grit pre-HT is the minimum in most cases. For a knife that will be mirror polished, I would take it to 800 or better before HT. For most stainless steels, you can take the blade to the final finish before HT and merely re-do the last couple steps afterward. My friend pre-polished his stainless blades before HT. After HT, just takes them to the buffer with black emery compound, then green.
Another big variable in the degree of pre-HT sanding is the edge thickness at HT. On a carbon steel blade you need to leave a bit more thickness. That means you have to take the whole bevel down some after HT. On stainless, the edge can be virtually at the finish thickness. This allows for only a minor clean-up after HT. For most carbon steel blades, I take the edge to .020-.030" before HT. Stainless I take to .005-.010". On thin blades that are below .060" thick at the spine, I usually grind the bevels after HT.
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It's unfortunately a moot point, regardless of steel type, if your knife requires a post heat treat grind.
In those cases, I try to take everything to as high of a grit as I can with my machines, and then hand finish the rest until I can finish everything on a buffer.
For any part of the knife that will be heat treated at or near it's final dimensions, you're ahead of the curve if you can take it close to it's final finish prior to heat treat.
In those cases, I try to take everything to as high of a grit as I can with my machines, and then hand finish the rest until I can finish everything on a buffer.
For any part of the knife that will be heat treated at or near it's final dimensions, you're ahead of the curve if you can take it close to it's final finish prior to heat treat.
Stacy E. Apelt - Bladesmith
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It would delay the quench too long to allow hardening for most carbon steels. A2 can be wrapped.
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Bladesmith said it very well. Any scratches left in the blade will be infinitely harder to remove after heat treating I always sand my blades out to at least a 600 or 800 grit finish before heat treating that way after heat treat all I have to do is spend some time @ the buffers.
Why is this the case? Are you just speaking in regards to the finish?
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Such great info! Thanks to everyone who responds. It's greatly appreciated.
Stacy E. Apelt - Bladesmith
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"It will also depend on what kind of knife you are making... some knives are best made with some of the grinding done after HT."
No, it affects far more than the finish:
In a very thin edge knife...or a very thin bladed knife...the bevel and edge are best ground after the HT. If you grind and sand them to their final thickness pre-HT you will have two problems.
1) Warping and twisting. In thin places the blade may twist and even get what is called a "bacon edge", which is a rippled edge. Leaving the edge or bevel thicker can prevent this.
2) Decarb - The steel surface on carbon steel looses its carbon over the entire surface to a shallow depth during HT. This is normally only about .002" thick, but if the edge is already thin, you may grind it too thin in clean-up. Most folks recommend taking at least .003" off the complete surface of a carbon blade after HT. In actuality, most post HT clean up removes far more steel than .003".
Additionally, any decarb left on the blade after finish sanding may/will look darker than the rest of the blade. Sometimes this is deliberately done for effect on the upper part of the blade, but it can also show up as splotches and irregular dark patches on the nice smooth blade bevel. That is why carbon steel needs more post-HT sanding than stainless steel.
No, it affects far more than the finish:
In a very thin edge knife...or a very thin bladed knife...the bevel and edge are best ground after the HT. If you grind and sand them to their final thickness pre-HT you will have two problems.
1) Warping and twisting. In thin places the blade may twist and even get what is called a "bacon edge", which is a rippled edge. Leaving the edge or bevel thicker can prevent this.
2) Decarb - The steel surface on carbon steel looses its carbon over the entire surface to a shallow depth during HT. This is normally only about .002" thick, but if the edge is already thin, you may grind it too thin in clean-up. Most folks recommend taking at least .003" off the complete surface of a carbon blade after HT. In actuality, most post HT clean up removes far more steel than .003".
Additionally, any decarb left on the blade after finish sanding may/will look darker than the rest of the blade. Sometimes this is deliberately done for effect on the upper part of the blade, but it can also show up as splotches and irregular dark patches on the nice smooth blade bevel. That is why carbon steel needs more post-HT sanding than stainless steel.