Many kendama players delve deeper into kendama and learn more about wood itself (especially those who turn their own kendamas). Saw the grain on my RWB Sesh cups today and noticed this and got a bit worried So that got me thinking. What clues could kendama players look for on their kendamas that could indicate poor craftsmanship or anything that can affect the playability or life of the kendama negatively?
It’s a bit hard to see the detail of your photo but it looks like there are small linear nicks/chips/voids in the dish. Is that your concern? Perhaps I'm reading your post incorrectly but it appears you are asking two questions; 1) What characteristics in the wood itself might lead to appearance and performance differences and 2) What manufacturing cues might indicate poor craftsmanship or quality control. (Maybe a third question would be how the two relate to each other.) I guess examples of the first would be knots, insect trails, how it was cured, disease in the wood, etc. Also some woods weep oils or sap or are prone to chipping or plucking (don’t know the correct word here but working it can pull little bits/plugs out like what appears in your photo). Also Janka scale and other measurements will give hints of possible performance abilities or weaknesses. Although my limited lathe and woodworking experience was a long while back and never made kendama specifically I still feel like I inherited my current "wood nut" interests from my grandfather. His big thing was always sharp tools. His tools were well worn but the cutting edges were shiny and sharp. On the other hand he wasn’t turning out a ton of product either so there is almost certainly a range of acceptable tool wear the bigger production companies will tolerate before they resharpen or replace a tool. A lot of the “imperfections” I’ve seen appear to come from tool sharpness; chatter, nicks, burrs. Some could also happen when switching woods say from a softer to harder or vice versa since a tool will react differently between them; a tool sharp enough for one might not be for the other. One additional concern for the repeatability of the cuts is wear of the tool in general. Each sharpening and machine setup can slightly change the angle/shape of the cut so adjustments have to be made. For example repeated sharpening will shorten the blade and if it’s set into the jig in the same way as a fresh blade the cutting result will be a bit different. Additionally in the larger operations I’m thinking that the craftsmanship and quality control aspects are somewhat if not completely separated. If someone has to make 100s of parts a day it’s probably more efficient to have them make the parts and someone else QC (and refinish) the parts. There have been kendama I’ve seen where the QC was a bit lacking; wood splits or cuts, mismatched parts, burrs, incorrectly drilled, inconsistent size/shape, or other anomalies. Like I mentioned above it’s been a while since I’ve been working with raw wood so I’m sure more active woodworking members will be able to correct or supplement my comments.