Bond 316 stainless to UHMW using Loctite 648?

I have a 1/2 diameter 316 stainless pin about 8 inches long where about 3 inches of that pin is press fit into UHMW. The pin does not extend through the bottom of the UHMW.

I need to make sure that pin doesn't come out. It's used on a tent side pole where wind will lift up on the pin and it needs to hold. There is no good way to mechanically attach the pin.

I talked to a loctite engineer who recommended using the 7649 primer on the hole in the UHMW and then using loctite 648 on the stainless pin.

I am wondering if anyone has had experience with this and can vouch that it holds well?

Well, I would trust the loctite engineer before listening to me, but:

nothing in a smooth hole designed to stop pullout is really ok in a mission critical app. If the primary load was to the side and falling out was incidental, sure.

Also adhesives usually want space, a press fit wipes all the adhesive off.

Would trust a friendly set screw before any loctite.

rons said:

Would trust a friendly set screw before any loctite.

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Not in this application, too low a modulus of elasticity in the plastic.

I think Gustafson has a good point, double-check with Loctite about the design clearance for their adhesive, and try to ensure a fine texture is left in the hole from whatever drilling/boring method you use.

Milland said:

Not in this application, too low a modulus of elasticity in the plastic.

I think Gustafson has a good point, double-check with Loctite about the design clearance for their adhesive, and try to ensure a fine texture is left in the hole from whatever drilling/boring method you use.

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I mean a set screw that would intersect into a through hole in the shaft. It wouldn't start moving until the plastic started to melt...

what about a good roll pin? Press fit + locktite + roll pin.

Whenever I think of glued in pins I think Boston Harbor Tunnel........

ATV said:

I have a 1/2 diameter 316 stainless pin about 8 inches long where about 3 inches of that pin is press fit into UHMW. The pin does not extend through the bottom of the UHMW.

I need to make sure that pin doesn't come out. It's used on a tent side pole where wind will lift up on the pin and it needs to hold. There is no good way to mechanically attach the pin.

I talked to a loctite engineer who recommended using the 7649 primer on the hole in the UHMW and then using loctite 648 on the stainless pin.

I am wondering if anyone has had experience with this and can vouch that it holds well?

Click to expand...

I'm suspicious of any kind of glue with any kind of polyethylene.

I'd be tempted to turn the 1/2" type 316 rod diameter down to 7/16" or so in the middle, leaving a full diameter head at the end that will bottom in the hole in the UHMW, with a neck about 1.75 inches long. Chamfer the bottom tip and neck upper end for easy pressing. Leave neck bottom edge square, to make it hard to pull out. Press this into the hole. The UHMW will spring back in the neck region, capturing the full-diameter head. One can also heat it to speed things up.

Or, press into hot UHMW.

I have not had good luck gluing anything to UHMW. I actually had to do something similar to what you are describing not long ago. If you had access to a boring bar you can turn a groove in the bottom of the hole. If you had a lathe you can then turn a snap ring groove in the bar a little deeper then normal. Put a snap ring in the groove in the bar and use the hole as kind of a ring compressor and push it down the hole in the UHMW. When it gets to the groove at the bottom of the hole it will snap into it. This is a one shot deal since there is no way to compress the snap ring again. I have to guess that you don't have a boring head or a lathe however. If you do then I apologize for assuming you do not. I would want some mechanical advantage in holding that pin in your UHMW. You could use a file to create some barbs on the pin. Think hose fittings but as sharp as you can get them. Take a hacksaw and cut a slot in the end of the barbed shaft about two inches long. Go to the hardware store and get a wedge used in securing a hammer handle to the head. Put the wedge in the slot you cut, drop a penny down in the hole, glue the crap out of it and drive the bar down into the hole. The wedge will spread the slot and cause the barbs to dig into the UHMW. This is an old school way of securing dowels and such into blind holes.

I second the ring groove and snap ring. Works great. How about a course thread?

Or cross-drill and pin?

I have been looking for a glue for UHMW for many years now. Locktite, 3M, epoxies, glue, nothing holds.

I agree with a mechanical lock if you want strength.

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I just did an experiment on bonding acetyl using cyanoacrylate adhesive. Acetyl is a low surface energy plastic. I don't know how it compares to UHMW. I made a saw cut into a 1/2" thick bar of acetyl 1/4" deep to make a stress riser, then snapped it. I didn't measure the force it took to snap it, but it was really easy. Then I used Loctite SF770 primer and Loctite Ultragel to glue it back together. Then I supported the bar between two blocks about 12" apart with the saw cut facing down and started adding weight on top of the bond. I ran out of weights at 35 lbs and it help up. I thought it was pretty amazing.