I’m looking for some advice how to know when its time to throw out a bit and go with a fresh one. I am struggling to determine if carving issues are related to my speeds and feeds learning curve or the bit itself.
I was doing some carvings on Bubinga (a particularly dense wood) with a 30 deg V bit and was getting some chatter in some directions of carvings but not others. I tried dialing back the stepover and playing with speeds and feeds but couldn’t seem to get rid of that chatter. Cut quality was ok but not great - no burning.
What is your guys yard stick for when it time to chuck the bit and start with a fresh one?
There’s a few close up pics of the cutting edges in the e-book.
It’s worth remembering that the play and stiffness on the Shapeoko is not symmetric, also that the cutting forces through a real wood are asymmetric so it’s not surprising that chatter appears in some parts of the cut and not others.
Are you roughing and then coming back with a final light load finishing pass?
I normally relegate my bits to roughing once the edge goes dull and keep the new shiny ones for finishing. I find that a thumb (very) carefully dragged across (not along) the cutter can tell if the tip is still as sharp as the untouched parts of the edge further up.
Yes - using Vectric so doing a clearance pass with a 1/8in endmill first. The defaults for the V bit were like a 4% stepover, and I think .07in depth of cut and about 35ipm. I tweaked that to 10% stepover to prevent it from taking 10 hours to carve - I tried 20% first but that did not sound healthy at all.
Julien provided some helpful hints on examining a cutter in this thread.
If you still have a new, known sharp, similar cutter it might be worth running a small test toolpath back to back between that and the bit you’re suspicious of, you obviously know what chatter and unhappy cutter sound like. I mostly cut birch ply which means only carbide is worth using at all, I’m also a little cheap and use a diamond sharpening card to refresh the flat faces on the chamfer bits a few times before buying a new one.
Thanks - these are great pointers. All things considered I think it came out good, but I’m a perfectionist and am always looking to dial things in to a perfect cut without an immense time sacrifice. The clearance pass on this took about 50 minutes and the vcarve about 4 hours!
Update - I’m doing a similar carving on the same wood - I switched to a new bit and make speeds and feeds a touch more conservative. I tested the new bit by running my finger across the edge and comparing to the old one – it was clear that the fresh bit was scraping my finger and the dull one was more smooth to the touch. It is running super smooth now, so I’m pretty sure most of my issue was dull bit related.
