Question on DIY Stonewash finish and scratched blade tip

[ravingDIODE]

Hi all,

My name is Riaan. I am a hobbyist knifemaker from Cape Town, South Africa. I have been at it for 6 months now, so I am still dipping my toes into this big pool of knife-making!

I built a DIY tumbler and using some ceramic media I have done a stone wash on a few blades now which came out good. I did a stonewash on a blade for a fellow knifemaker a while back where the tip of the blade looked really scratched. I thought it was the ferric-chloride dip that was maybe bad. I noticed the same thing happen to one of my small utility knives now.

It looks as if the tip of the blade is "washed" a lot more than the rest of the blade.

Has anyone had this happen to them while stone washing some blades?

Here is a pic of the tip of the utility knife and of my DIY tumbler:

Any ideas or insights would be appreciated

Regards,
Riaan

 

[The_Iron_Joe]

Hi there, welcome to the forums.

Assuming that you're using your setup as you'd use a "rotary" tumbler instead of a "vibratory" one, you'll probably see some improvement to to the finish if you introduced some fins to the inside of the barrel. Among other things, this encourages a cascading effect that'll more evenly affect whatever you're tumbling.

I'm also assuming that the entire piece of steel is of a relatively uniform hardness... otherwise, if the tip is softer than the rest of the piece, that'd explain the discrepancy in finish.

 

[A.McPherson]

Does your tube sit level in the turning device?

I've seen some that sit with the closed end lower than the open end.

If this is the case, and the tumbling media isn't full enough, your blade could get an uneven finish because it's not equally exposed to the media...

 

[ravingDIODE]

Hi there, welcome to the forums.

Assuming that you're using your setup as you'd use a "rotary" tumbler instead of a "vibratory" one, you'll probably see some improvement to to the finish if you introduced some fins to the inside of the barrel. Among other things, this encourages a cascading effect that'll more evenly affect whatever you're tumbling.

I'm also assuming that the entire piece of steel is of a relatively uniform hardness... otherwise, if the tip is softer than the rest of the piece, that'd explain the discrepancy in finish.

Correct, I use it like a rotary tumbler. The only "fins" that I have are those two wooden slates pop-riveted to the inside of the barrel. I am assuming that it is too flat and not effective.

I believe the hardness is uniform. I have one of them tested on a few spots.. They were soaked for 10-12mins in the often at temp, and then plate quenched. It is N690 Stainless steel.

Does your tube sit level in the turning device?

I've seen some that sit with the closed end lower than the open end.

If this is the case, and the tumbling media isn't full enough, your blade could get an uneven finish because it's not equally exposed to the media...

As far as I can tel it is level yes. I have a flat 20x20 aluminum profile frame with bearing blocks screwed in place and the steel rods with surgical tubing going through these blocks. The bottle also rarely moves up or down as it remains in place.

Some local friends suggested that the media and blade is slushing around and not tumbling enough, with the heavy part of the blade sitting in the media and the tip getting the most action.

I am going to try use other fins on the inside and slow down the speed. If that doesn't help, I'll try make a new tube to use.

This being new to me, I have no idea how the mechanics work inside. A little camera inside would be useful

 

[The_Iron_Joe]

Correct, I use it like a rotary tumbler. The only "fins" that I have are those two wooden slates pop-riveted to the inside of the barrel. I am assuming that it is too flat and not effective.

I think so, yes. If you look up images of rotary tumblers, you'll notice that many have a hexagonal shape; you shouldn't need a severe change in angle in order to see an improvement.

I believe the hardness is uniform. I have one of them tested on a few spots.. They were soaked for 10-12mins in the often at temp, and then plate quenched. It is N690 Stainless steel.

Good, probably one less thing to worry about!

If I can find a diagram or video explaining what should be happening, I'll link it later.

 

[ravingDIODE]

I think so, yes. If you look up images of rotary tumblers, you'll notice that many have a hexagonal shape; you shouldn't need a severe change in angle in order to see an improvement.


Good, probably one less thing to worry about!

If I can find a diagram or video explaining what should be happening, I'll link it later.

Thank you very much, I appreciate the help! I'll report back when I have made a change and noticed a change

 

[The_Iron_Joe]

Well, this is about as close as I could manage to find offhand that actually showed particles/media in use.

I know these are fins are placed centrally instead of raidially positioned from the walls of the cylinder, but the principles are similar enough. I think that, for ease of manufacturing and for general longevity, the more common type of small scale rotary tumblers are hexagonal inside instead.

 

[ravingDIODE]

Well, this is about as close as I could manage to find offhand that actually showed particles/media in use.

I know these are fins are placed centrally instead of raidially positioned from the walls of the cylinder, but the principles are similar enough. I think that, for ease of manufacturing and for general longevity, the more common type of small scale rotary tumblers are hexagonal inside instead.

That definitely helps. I am pretty sure now that my "fins" aren't "finny" enough lol. If that makes sense. I'm going to look at getting a different container and add decent fins inside instead of trying to alter the current container.

 

[The_Iron_Joe]

That definitely helps. I am pretty sure now that my "fins" aren't "finny" enough lol. If that makes sense. I'm going to look at getting a different container and add decent fins inside instead of trying to alter the current container.

You should experiment with different volumes of media once you've got the tumbler built, if you've got time. Often if you add any more or less media beyond a certain range you get less than optimal results in a given timeframe.

 

[kreole]

I've had one tip damaged (rounded) during tumbling, and it was a small one that managed to get wedged sideways during the cycle. I noticed that one is small and about the diameter of the tumbler; maybe something similar happened?

 

[Rick Marchand]

It could be that your fins are too square and not high enough at the same time. I can see the some of your ceramic media is wedged beside one of the fins. It could be that your utility blade is doing something similar and only exposing the tip, past the fin. I would suggest making the fin more triangular in cross section and a bit taller ... and maybe epoxy/caulk the joint so the tip or edge cant get under it. It also appears that your utility knife is almost the same length as the inner diameter of the tub.... it could begetting wedged that way as well.

 

[ravingDIODE]

You should experiment with different volumes of media once you've got the tumbler built, if you've got time. Often if you add any more or less media beyond a certain range you get less than optimal results in a given timeframe.

I think I should too. I am sure it will have an effect. While searching for DIY tumblers, I read that media should be about halfway in the container. So I never tried taking some out. Will add it to my list!

I've had one tip damaged (rounded) during tumbling, and it was a small one that managed to get wedged sideways during the cycle. I noticed that one is small and about the diameter of the tumbler; maybe something similar happened?

Quite possible. I thought it might wedge between the side and the wooden slate, but it is small enough to move around freely... could be that it is rotating sideways and the tip being beaten harder.

It could be that your fins are too square and not high enough at the same time. I can see the some of your ceramic media is wedged beside one of the fins. It could be that your utility blade is doing something similar and only exposing the tip, past the fin. I would suggest making the fin more triangular in cross section and a bit taller ... and maybe epoxy/caulk the joint so the tip or edge cant get under it. It also appears that your utility knife is almost the same length as the inner diameter of the tub.... it could begetting wedged that way as well.

Thank you, I am going to look into that gap yes. You all pointed out a few issues, so I got some testing to do. Hopefully I can get around to it end of the week. I will have a few blades to tumble soon, but need to sort it out first.