Glue for Delrin/acetal?

homebrewed

homebrewed

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I have some parts I machined from black Delrin that need to be glued to something else. In this case, to aluminum. The only other way would be to use grub screws but I'm concerned that the threads in Derlin would strip out -- at most, I can accommodate a 6-32-ish size set screw, and the Derlin isn't all that thick.

In the past I tried to glue Delrin using silicone glue/caulk and that didn't last very long (although that was in a very difficult environment, inside the gas flap of our old VW Jetta).

What have folks here used with good results? My current application is in a more benign environment, as part of an attachment for my mini lathe; but there is the possibility that it could be splashed with cutting oil on occasion. I don't do flood coolant. A Loctite product? Cyanoacrylate? Epoxy? Urethane?
 
Very few (or no) adhesives will stick well to Delrin. As somebody once said to me about gluing to plastics, "It's like trying to glue to grease." I would suggest (1) using a sandblaster on the Delrin surface to give it some "tooth." and (2) using JB Weld.

I think you're absolutely right about the screws, especially given the short thread depth.
 
I recall some information regarding DIY water rocket construction that might provide some clues for gluing difficult plastics. Water rocket enthusiasts often join multiple water bottles to make bigger rockets; and the air pressure used to propel the fuel (oddly enough, it's known as "water") can be quite high, 200-300PSI -- so the adhesive used to join bottles together would seem to be pretty strong. The preferred adhesive in the DIY water rocket community appears to be "PL premium construction adhesive". The thinner the glue line the better.

The current record height for a home-built water rocket is around 1,700 feet.

Water rockets don't benefit from the special Laval nozzle shape used for chemical rockets so there's no point in getting all that fancy when it comes to nozzles. The Laval nozzle's high performance depends on compressible flow, and water isn't compressible.

A popular nozzle/release mechanism is based on a plastic quick-disconnect made for garden hoses. 3D printed fins are popular now.

The water is expelled quite rapidly so most of the rocket's flight is just an unpowered coast up to its maximum height. They can lift a small payload like a wireless camera, altimeter etc to document your rocket's flight.
 
If you don't have any other luck, this stuff here is about as spooky as it comes (well, not as spooky as hot cyanoacrylate). It sticks to shiny surfaces and to plastics, so it's a good candidate. I think you're pushing your luck trying to glue acetal, however.
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I don't have the plastic parts so much on my models, I'm partial to brass. Working on a friend's locomotive, he had called and told me about a plastic that ACC wouldn't hold. I'm not sure it was delrin, although delrin is used very frequently in the hobby. My solution to the question was to use "Methyl Ethyl Ketone" as a plastic solvent. Blocking up everything firmly and letting the MEK wick into the broken piece. It left somewhat of a ridge or bulge but breaking that particular part implied careless handling so I had little sympathy.

The solution worked for delrin(?) to delrin. I'm sure it would not hold delrin to aluminium. The best I could offer there is to use a Nr4-36 machine screw. A coarser thread can be found on sheet metal screws, even more so on wood screws. Such small sheet metal screws are not hardware store items. I would suggest a fine woodworking supplier as a possible source.

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homebrewed said:
I have some parts I machined from black Delrin that need to be glued to something else. In this case, to aluminum. The only other way would be to use grub screws but I'm concerned that the threads in Delrin would strip out...
Click to expand...

If you can poke a aluminum cylinder-part into a hole (like for grub screw fixation), can you NPT-thread it?
If so, a bit of abrasive grit and any-old-glue will lubricate the threaded coupling, tighten until the
grit bites into both the aluminum and Delrin. When the glue dries, so the grit can't shift, it'll
hold (one hopes). Tapered pipe threads guarantee a snug fit without careful machining, I've found. (#blush)
 
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