CA glue retention

[PeterT]

This isn't my idea. I've seen it employed on other forums, particularly Clickspring on YouTube. Basically you machine a holder fixture or face in-situ so its running perfectly true. Then use CA glue (cyanoacrylate aka Crazy Glue) to attach a part to the fixture. Do the machining to the part. Then remove & heat the assembly past the glue's rating & with a light tap-tap, off she comes. Any excess glue easily comes off with acetone. Very handy when parts are thin, fiddly to otherwise difficult to hold. My heat source was a propane torch. I didn't measure temp but maybe 5-10 secs. I found this worked better than a heat gun but my gun is kind of gutless.

IMO this technique is OK for relatively light cutting, fine feeds & ideally not interrupted. If the surface area is too small or you get too aggressive, it might go bye-bye. I use CA a lot for other hobbies. I like medium or thick viscosity in this application. Clean surfaces well with acetone or methanol, apply the glue, align & I like 'kicker' (accelerant) to help lock it down because curing can be delayed with metals,

I've also seen hardware store 5-min epoxy used. It is thicker so you might have to factor that in. But in certain applications teh fillet can add rigidity. I'm going to try taht next. My examples are an aluminum washer & second operations to a steel gear.

 

[PeterT]

Steel gear, aluminum pot chuck. Going from 5mm ID to 10mm, then width reduction.

 

[Alexander]

How long should CA be left to dry if you are using it without kicker?

 

[PeterT]

That's a good question, Alex. I left a part for 2 min that had about 1 in2 of area, it came off. But it was also seeing interrupted cutting from the irregular band sawed face. I glued it back on with more glue (a dot every 5mm), left it 10 min & it stuck for the remainder. I only took 0.010" passes at higher speed just to err on safe side. Also avoid heat from machining, but CA is impervious to cutting oils that I can tell.

CA is weird stuff. It prefers porosity or texture for faster cure. That's why when you put a drop on something like balsa wood you can see the fumes come off as it goes nuts & exotherms. 2 seconds later its like glass. Put the same drop on something inert like metal & it will sit that way for quite a well, like several minutes. Thin CA sets faster than thick, but for positioning I want working time. So I think kicker is worth having around. You can apply glue to one side & kicker to the other. Now in this mode when the 2 come together as a sandwich they will instantly fuse together. Don't do this if you need to align a bit, it'll be too late. But if the kicker hits any glue, even on the edge, it tends to carry on & help cure the remainder.

Some guys use Loctite in this application claiming CA is Loctite & vise-versa. That's not quite true, or 'It depends'. But they sell what they call 'primers' which kind of do the same thing. I found Loctite almost too strong on a test piece, it did not want to let go & it was pretty hot. That's why I was saying have a plan to give it a tap, or an exposed beveled edge to get a chisel in there - anything that can part the joint just a smidge.

I've also seen guys use el-cheap0 hardware store 5-min epoxy. Glue the metal to MDF substrate. Cure for 10 min, then machine away. Similarly heat to release joint. It goes kind of waxy at the right temp, beyond that its a burning stench. Epoxy is thicker so factor that in your net thickness. It will also therefore form fillets around the edge, maybe helps with clamping strength.