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I'm noticing that when I turn really hard woods, even with brand-new and very sharp carbide bits, sometimes I'll see these long scratches on the surface. scratches on outside surface of curly maple bowl scratches on inside surface of curly maple bowl Often they'll only become apparent once I've started sanding, and no amount of sanding seems to be able to mitigate or remove them. Do I really need to re-surface the bowl with a chisel?

I pretty exclusively use Easy Wood Tools (carbide-tipped) since I don't have the space for a sharpening system. Generally, I use the circular bit (which they call the finisher) for roughing, then try to get a fine surface finish with a square or radiused-square bit.

I'm attaching some pictures that show the scratches I'm talking about.

Since my tools are very sharp, and I'm seeing the scratches no matter what speed I set my lathe at, I'm wondering if they're happening because the speed at which I move the tool along the wood is slightly inconsistent - could this be the case? (I find it really hard to move the tool at a super-consistent speed, as it seems like there are "slippery" and "sticky" parts on the surface of my toolrest).

Any tips or tricks would be much appreciated - I note, this doesn't seem to happen nearly as much on softer woods like walnut.

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    There's this rule of thumb with certain things, you get what you get. This is what you're getting with your carbide tools as sharp as they are currently, being used as they are currently. Ergo you need to change one of the parameters — get 'em sharper, use them slightly differently (more of a shearing cut with an edge rather than corner?) or switch tools. – Graphus Feb 6 at 8:17
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    "and no amount of sanding seems to be able to mitigate or remove them." Now not to be glib but, sand more :-) – Graphus Feb 6 at 8:19
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    Just a quick note on carbide tools - they are know for their edge retention, not absolute sharpness. Typically steel cutting edges can be made quite a bit sharper than carbide (at the expanse of requiring much more frequent sharpening). You could try with a (well honed) steel chisel for comparison. – Eli Iser Feb 6 at 12:52
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    I was actually going to suggest you try a card scraper to see if you could get past the marks left by the carbide, then switch to sanding after (presumably) the marks have been removed. If you try this approach I think you'll get the best results with a sharp edge (no burr) or with a very small burr produced by just one or two strokes of the burnisher, fine enough that it's just about possible to feel but no larger (my thinking is that if larger it could be too fragile as well as more prone to catching). – Graphus Feb 6 at 16:51
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    Re. just using sanding, what grit have you been starting at? Sanding on the lathe is rather famous for how easy it is because the moving workpiece takes so much effort out of it but it can still be important to start coarse enough before moving to a finer paper that removes very little material, and I think this is one of those cases. Even though it'll seem like a step back it might be worth starting at 100 (if this were a tabletop I'd be recommending 80), then move to 120 or 150, then 220, 320 and 400 or however high you like to go. – Graphus Feb 6 at 16:54
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As some people already pointed out, the carbide tool is not as sharp as a HSS bowl gouge can be. The scratches on the outside can only prevent by a shearing cut with a very sharp tool because the grain needs to be cut in almost 90 degrees. Sanding will not help much, depending how deep the chunking is...

The scratches on the inner part look more like sanding scratches which appear when you do not move the sanding paper quickly enough on the rotating bowl or the bowl turns to fast while sanding. In general, the sanding paper should never hold still at any point!

I mostly start with 80 grid paper to get rid of most tool marks and correcting some minor curves or whatever... Only if I am happy with the surface after this process, I proceed with smaller grids and go through them very quickly.
Also it helps to sand in fibre direction by hand which eliminates all the marks you show in the second picture...

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