Hi Scott

 

I'm talking ideal conditions here.  The reality is that the Lancairs for the most part stick together pretty well, less one well discussed Legacy.  So while all preparation may not have been ideal, chances are they were adequate.  As an example, your 5/8" wide bond if done on a 24" long rib has 15 sq. inches of bond area.  Using a low figure of 500 psi for bond on the 15 sq. inches yields and impressive 7500 pounds to break the skin off of the rib.  Divide it in half and you still exceed the weight of the aircraft.  Of course that assumes very simplistically that the load is evenly distributed over the whole rib as in a straight tensile load as opposed to a peel type load where lineal inches of bond count.

 

Also in regard to solvents, I tend to agree that Methylene Chloride used every now and then is probably pretty harmless.  I've read that water swallowed in sufficient quantities becomes toxic so the dose does make the poison.  I've used MC for years with no ill effects but it was all incidental exposure.  Note that all of these tend to dissolve latex gloves.  There are also a lot of other solvents that cut grease very effectively and more so than acetone, paint thinner and kerosene among them.  But likewise, MC, paint thinner and kerosene don't dissolve many other types of contaminates like mold release wax as effectively as acetone. It has to do with polarity of the molecule and acetone isn't very polar.  Soap and water on the other hand is very polar with one end of the molecule bonding to water and the other end binding to oils and grease.  If you actually have significant quantities of grease on the part to be bonded, you really need to soap and water it until it's about as clean as that could get, then try other solvents to get the grease film off then maybe some 'tone followed by grinding and more acetone.  The point is to expose fresh surface without smearing the grease or other contaminate to the bond area.  Either one should work fine if you really clean it before the grinding.  It shouldn't make any difference if they are reasonably pure and when they evaporate, leave 0.0% residue (not possible with any solvent with other than 100% volitiles).

 

Would I sweat bonds that were less than absolutely perfectly prepared with laboratory pure acetone, sanded by virgins and blessed by the Pope?  No, but the techniques I talk about tend to get more bond strength and are a bit more reliable routinely.  As I said before, the Jeffco tech I talked to prepped their bonds with Jasco hardware store acetone.  In the lab I worked in, we only used technical grade acetone since there were less contaminates and it was not re-used acetone from solvent condensers at some weird plant cranking out who knows what.

 

But a blessing by the Pope might still not be a bad idea...

 

Dan