Help with SiC lapping

[Craig James]

All, just a little advice please.

On the recommendations of Mr. Wizard and an excellent video by HeavyHanded I've recently ordered myself a Zandstra Foss speed skating stone.

In order to maintain it, I've brought a cheap float glass chopping board and will be about to order some 60 grit SiC powder.

I also have JIS 800, 2000, 6000 stones that I would also like to maintain in this way. What additional grits of power would you recommend to maintain these additional stones?

Also, how much of this stuff do I actually need? 200g, 0.5 kg, 1 kg? I get the feeling 1kg would probably last me a lifetime...

Thanks

 

[Mr.Wizard]

You may be able to use the same #60 grit for all the stones if you flatten in sequence from coarse to fine. This is because silicon carbide is friable—it breaks down finer and finer as you use it. If you take care to use all the grit you sprinkled out as you flatten/condition the coarse stone there should be no full size #60 grit left to scratch your finer stones. If you expect to flatten your 2000 and especially 6000 stones by themselves I think you'll want some finer grit; I have some #320 that I use sometimes for this.

200 grams is probably enough, but a little more of the #60 wouldn't hurt and the marginal cost is usually low.

By the way rock tumbling hobby shops should have a "kit" that includes several grits (if you decide to get more than one) but check the quantity of the grit itself if you get one of these; "grit for a four pound tumbler" does not mean four pounds of grit.

 

[HeavyHanded]

I'd pick up a kg, is surprising how often you might turn to this once you get used to the process.

Personally I don't like to use loose grit on most of my waterstones. A 180mesh or so lapidary disk works a lot better since you don't have to worry about glazing anyway. Save the SIC grit for hard vitreous or Arkansas stones.

But yes, it breaks down and can be used on successively finer stones, perfectly valid way to go about it.

 

[Mr.Wizard]

HeavyHanded I agree that on something like a King 1200 "you don't have to worry about glazing" but I based my recommendation on his description here:

I own 4 stones, a DMT coarse, a Chosera 800 and a no name 2000/6000. The latter is shocking, coarser than the grit suggests it should be, super hard so that it tends to glaze after a couple of knives and loads up like a MF.

 

[Craig James]

Thanks both, and yeah my finer stones seriously are that bad. I keep meaning to invest but there is always something else in the house my money is better spent on.

Personally I don't like to use loose grit on most of my waterstones. A 180mesh or so lapidary disk works a lot better since you don't have to worry about glazing anyway. Save the SIC grit for hard vitreous or Arkansas stones.

i take it this is just personal preference rather than anything untoward happening to the stones? I’d hate to damage my Chosera, although it has seen quite a bit of use and despite it being a hard stone does need to be flattened. I don’t like taking my DMT to it and don’t own a lapidary disk...

 

[HeavyHanded]

Thanks both, and yeah my finer stones seriously are that bad. I keep meaning to invest but there is always something else in the house my money is better spent on.




i take it this is just personal preference rather than anything untoward happening to the stones? I’d hate to damage my Chosera, although it has seen quite a bit of use and despite it being a hard stone does need to be flattened. I don’t like taking my DMT to it and don’t own a lapidary disk...

Personal preference, I can just flatten the stones right at my bath and not have to set up for a heavier lapping operation with a separate bucket.

 

[Gritomatic]

You may be able to use the same #60 grit for all the stones if you flatten in sequence from coarse to fine. This is because silicon carbide is friable—it breaks down finer and finer as you use it.

According to my experience, #60 powder is slower than #120 due to the diminishing return effect. We recommend #120 as the first step in stone flattening with the exception of some extra coarse stones like Boride Ruby #60 to #100.

 

[Mr.Wizard]

Gritomatic The FOSS is a coarse stone that should be finished aggressively. I believe even #80 will be too fine to return its best performance.

 

[HeavyHanded]

Gritomatic The FOSS is a coarse stone that should be finished aggressively. I believe even #80 will be too fine to return its best performance.

Yeah, 60 or 30 for the coarse side.
120 is good to have around for finer stones, maybe even 220. Have never had good luck with anything finer.