Lapping/Truing Poltava Metallic Bonded Stones with Silicon Carbide

OhioApexing

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I recently picked up some Poltava Diamond Tools metallic-bond diamond and metallic-bond CBN stones, in addition to some resin-bond CBN stones. They were purchased with ease and great customer service from Practical Sharpening. They're all fantastic, but I truly love the metallic-bonded CBN stones and promptly ordered four more to add to my rotation.

The common practice for lapping/refreshing the metallic-bond stones seems to be an etch with ferric chloride, which kept me away from trying them until I began using FC to acid/stonewash knives for clients. It is a really straightforward process, but I digress.

The ferric chloride does an excellent job of exposing fresh abrasive but I became concerned with flatness over time, especially as I was looking to mount the stones on EP blanks (the metallic-bonded stones come unmounted from Practical Sharpening so that each side of the stone can be used, the resin bonded stones are mounted).

I did a bit of digging on Poltava’s website and found that they recommend vitrified-bonded silicon carbide to dress/true their metallic-bonded wheels:

https://pdtools.com.ua/en/inform_po...he-use-truing-and-dressing-of-diamond-wheels/

Not having vitrified-bonded SiC at my disposal, I decided to try loose silicon carbide on glass in an even, fairly heavy application. I expected it to be an extremely arduous process but was very pleasantly surprised.

I decided to go after the 100-grit (JIS) metallic-bonded diamond, the 150-grit (JIS) metallic-bonded CBN, and the 300-grit (JIS) CBN.

For the 100 and 150 grit, I used 60-grit (FEPA) and worked it until the grains had broken down into an even, relatively fine layer across the glass. I did the same for the 300-grit stone but finished with 120-grit (FEPA) SiC to finish the surface. I spent maybe 60 seconds on each side of the stones. Here are before/after results -- the uneven coloration in the last photo is due to the stone not yet being completely dry:

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Conclusion: I have yet to sharpen with them since lapping, but I got them mounted to Gritomatic blanks. The stones feel great to the touch and seemed very flat when placed on the back of my Atoma 400 bench stone. I wish I had gotten the before/after measurements with my calipers to see what kind of material loss I incurred but eye-test says that it was nominal at best. I noticed no appreciable loss. I'll try to remember to follow up after use. For now, I see loose SiC on glass as being a viable alternative to ferric chloride etching as a means of truing the stones. I may use continue to use FC to expose fresh abrasive as needed (as I would use a nagura on resin-bonded stones) and SiC to bring them back flat as needed.
 
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With the coaser grit I was using 60/80 SiC powder. The 400 and up I was using 120grit SiC.

The finer grits I still had to burn down with ferric choride to get the abrasive poking out more.

My experience has been that you don't want to dress them with a stone, that tears out the CBN abrasive.

I just condition them with ferric choride, neutralize with baking soda. When the brass bonding starts to dish enough, I reset with SiC powder again. I noticed the 120 and 50 grit Metallic bonded stones didn't seem to need the ferric choride after SiC powder lapping, but the finer grits need more love to get the grains poking up after lapping.

I like to use a granite tile from home Depot. Got the idea from @Diemaker

I broke the glass I was using. The tile is more robust and cheap.
 
With the coaser grit I was using 60/80 SiC powder. The 400 and up I was using 120grit SiC.

The finer grits I still had to burn down with ferric choride to get the abrasive poking out more.

I like to use a granite tile from home Depot. Got the idea from @Diemaker

I broke the glass I was using. The tile is more robust and cheap.

Thanks for this — I’ve got JIS 500, 1000, and 2200 (as well as JIS 80) coming today or Monday in metallic-bonded CBN. Will definitely try the ferric chloride on the finer stuff.

I’ve still got the glass from my EP flattening kit which has that nice rubber ring around it to stop abrasive and water from going everywhere and thus, allows me to lap indoors without my girlfriend losing her mind, lol. Will definitely try the tile once that wears out.
 
DeadboxHero DeadboxHero How long did you let your sit in the ferric chloride to etch them,I haven't etched mine yet but plan to in the near future.

With the coaser grit I was using 60/80 SiC powder. The 400 and up I was using 120grit SiC.

The finer grits I still had to burn down with ferric choride to get the abrasive poking out more.

My experience has been that you don't want to dress them with a stone, that tears out the CBN abrasive.

I just condition them with ferric choride, neutralize with baking soda. When the brass bonding starts to dish enough, I reset with SiC powder again. I noticed the 120 and 50 grit Metallic bonded stones didn't seem to need the ferric choride after SiC powder lapping, but the finer grits need more love to get the grains poking up after lapping.

I like to use a granite tile from home Depot. Got the idea from @Diemaker

I broke the glass I was using. The tile is more robust and cheap.
 
Nah, use gloves and swap with a small piece of shop towel, let it burn for 2-5 min, rinse and neutralize with bicarb, repeat to desired effect. Just use the MG chemical stuff on Amazon.

DeadboxHero DeadboxHero How long did you let your sit in the ferric chloride to etch them,I haven't etched mine yet but plan to in the near future.
 
This is good to know. I have the 300 and 1k and plan on getting more. I like their resin bonded stuff too though so we'll see.
 
I'll give it a try that way and see how it goes.

Nah, use gloves and swap with a small piece of shop towel, let it burn for 2-5 min, rinse and neutralize with bicarb, repeat to desired effect. Just use the MG chemical stuff on Amazon.
 
If you like their resin stuff you would like the Venev more for sure,I have some of the Poltava resin stuff and it's not bad but it wears faster then the Venev stuff,I'm really impressed with the OCB stuff from Venev that I have tried so far,I have 2 400 CB stones coming my way and a 15K Metallic CBN stone as well on route to me,should be here Monday Tuesday.

This is good to know. I have the 300 and 1k and plan on getting more. I like their resin bonded stuff too though so we'll see.
 
Got the JIS 80, 500, 1000, and 2200 metallic bonded CBN lapped/etched/mounted today, joining their JIS 150 and 300 counterparts. I got sidetracked after that by cutting/mounting/sanding/loading a few strops, so, no time to sharpen. I’ve got a new M4 PM2 that I’m planning to walk through the full progression tomorrow. Looking forward to it.
 
I looked up vitrified bonded SiC and it's SiC in a bar or stone. In fact, it looks like a SiC sharpening stone. Vitrified means to convert something into glass or a glass like substance so, in this state I doubt it would embed any SiC in the bonding. Some sources such as Gritomatic do not recommend flattening with SiC powder as they say it will get embedded in the stone and then leave scratches in the blade. It seems to me that by etching with ferric chloride after lapping any SiC that has become embedded in the binding would be eliminated. So, if Gritomatic is right about the SiC becoming embedded then etching with ferric chloride is a must with the finer stones if for no other reason than to remove the embedded SiC. I can see why etching would not be necessary with coarser grits. I have a 400 grit Poltava metallic CBN that has developed a saddle since using on Magnacut and CTS-XP blades and I think I will try the lapping/etching method on it.
 
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