I’m starting my ZHL SR build. The bulkheads slot nicely, but snugly into the keel. How important is removing char! Does it inhibit a good glue bond? Should I remove it from everything, or just areas where it will bee seen?
Thanks
Thanks
Hi Paul
I remember Chris Watton carrying out a trial when I was a member of the "other site".He glued three identical joints together.One with char fully removed,one partially and one untouched.There was no difference in the strength of all three joints.I dare say this depends on how clean the laser cut is.Invariably all the ash has fallen off in the machine and what you see is just surface discoloration.
Kind Regards
Nigel
I remember Chris Watton carrying out a trial when I was a member of the "other site".He glued three identical joints together.One with char fully removed,one partially and one untouched.There was no difference in the strength of all three joints.I dare say this depends on how clean the laser cut is.Invariably all the ash has fallen off in the machine and what you see is just surface discoloration.
Kind Regards
Nigel
Thanks Nigel, that's just what I needed.
Just add to what Nigel said. laser cuter don't cut straight 90 degrees, it a bit bevel (mostly depends on laser power and thickness of ply. It may not visible to the eyes but it is always there. So not as much as to clean char, but make parts glue together 90 degrees on those cuts, specifically on bullheads where you will need absolute 90 degrees against the false keel. 
Hi Jimsky!!! This is not true with all lasers.. perhaps in the early days but not now. However, I do agree the char needs to be removed for precise fitment and gluing.
Jim - Thanks for that. I will use my machinist square under magnification to examine how square the laser cuts are.
My experience suggests only remove char where it will be seen. If there is a residue a light sanding will clear that up. I have not observed any difference in glue strength between char vs no char. The issue of a clean, square, tight fitment of parts is a separate question. Always check for tight, square fit and adjust with sanding or filing as necessary.