Inlays, blade angles and hardwoods and my "what the heck moment?"!

[Blaughn]

I am making Christmas presents for the 6 Grandchildren inlaying their initials into red oak.  (Pictures to follow when the finishing is done.) 

The first 3 were done with walnut inlays which went well. 

The last three I decided to use jatoba (aka Brazilian cherry) for the inlay with the end grain showing. 

Starting with a new blade and using it for all 3 initials -  the dropouts were cut first and they were too loose - lots of filling with sanding dust and white glue.  The first letter fit perfectly.  The second letter went 3/4's of the way in and the third letter was 1/2 way in.  I was convinced that my blade angle was changing.  The fact that I had no problems with the walnut inlays should have been a bigger clue. 

My analysis:  The jatoba wood is extremely hard (#10 on the list of the world's hardest woods).  I am convinced that the first cuts on the dropouts using a new blade were impacted by the wired edge on the blade creating a wider kerf.  The 2nd cut the wired edge was wearing away - thus a narrower kerf.  The 3rd and 4th cuts the wired edge was essentially gone.  Using a high quality micrometer I found the blade thickness was .0140" in areas above and below the cutting area.  In the section of the blade doing the cutting the width was .0130".  This trend was repeatable with a new blade and subsequent cutting.  Additionally with the hard wood the blade dulls more quickly and it cuts slower.  I did not have this problem with the walnut (which is softer than the oak).  Solution:  Use a new blade for each letter if your inlay is extremely hard.

I share this in the hope that it may save someone else from creating a significant pile of expensive fireplace kindling.  

Edited November 26, 2022 by Blaughn