30 May 2008, 03:03 PM
Join Date: Mar 2006
Location: Melbourne, Australia
Originally Posted by brisfitworks
On our Camel we used laser cut 4130N sheet. Obiously, we have no data from it on fatigue life and cracks appearing but the discussion about bending inducing cracking or micro cracks is revelent.
When I first started bending up brackets, especially the fwd attachment clips on the stab (Sopwith dwg. A-2481) I got cracking in the corners of the bend at the cut edge. There was no signs of over stressing on the outside face of the bend even when viewed with a 10x glass.
Because of edge hardening by the laser, we had a lot of issues with drilling out or reaming holes (I drew them a bit undersized to drill or ream out for a better finish against the bolts and clevis pins). So I suspected edge hardening from the laser was a cause of cracking at edges of bends.
I had talked to the heat treatment/hardening shop we use at work about bulk annealing parts before forming but they were concerned about warpage from uneven heating. If I had stacks of 20-50 of each, they said, they could be tightly wired together to make them more like a block of metal to avoid warpage. Since I was only building one Camel I went for old fashion torch annealing.
For remaing brackets I used a oxy-acetylene torch to anneal the edges and got much better results - none or minimal cracking which was then repaired.
When I got cracking at the bend I went over the edge at the bend with a TIG torch to melt back and seal the surface.
If I had to do again and what I am investigating with the F2b is waterjet cutting accuracy and costs versus some sort of sandwhiching plate for annealing and normalizing laser cut parts.
Sorry, a bit late for where you are today, but I will tell you this from my experience with our museum aircraft - I am always amazed at what my training tells me will fail yet lasts just fine for decades of use. I have seen misuse of materials and all sorts of workmanship failures and most failures are due to other causes.
Point is, I am not convinced you need be as worried and have to strip all the your carefully finished parts.
Oh to be in mass production of all these bits and planes and so easily afford destructively testing everything ;-)
Many thanks for your input Bill.
I think I also with any further fittings I get cut will go the water jet way. I made the same mistake pre cutting with smaller holes and then drilling them to size. Once hardened by laser cutting it's a heck of a job drilling them out. Also the amount of work required grinding down all the edges before bending is very time consuming.