Loctite For Delrin?

[William ChithamParticipant @williamchitham75949]

Reading Tim Stevens' thread on making a gear for a Colchester thread indicator it was suggested that he might turn down the splined hub of a damaged gear and make a new toothed outer to fix on with Loctite. It was also suggested that he might make a new gear out of Delrin or similar. I think these were separate suggestions but could they be combined? Would Loctite 638, say, stick Delrin to cast iron?

William.

[William ChithamParticipant @williamchitham75949]

[Jeff DaymanParticipant @jeffdayman43397]

In my experience there is no adhesive that will work on Delrin / acetal. One of its' most useful properties is its' anti friction self lubricating quality, particularly when run against metals.

It will need to be pinned or clamped mechanically to a mandrel. Washers made from sandpaper can help.

[not done it yetParticipant @notdoneityet]

I would drill and tap a coarse thread in the gear on a circle, to which I would machine the gear to leave half of it. Make the delrin ring and drill and tap while held in position. Grub screws can be loctited to the metal, no bother.

[Mick B1Participant @mickb1]

Possibly turn and straight-knurl the hub, bore the delrin to a drive fit on the knurl, then mount the hub and delrin assy to a suitable shaft, to finish turn the delrin outer and cut the teeth.

Edited By Mick B1 on 24/03/2021 15:52:57

[Michael GilliganParticipant @michaelgilligan61133]

For what it’s worth … I have great respect for technical advice from Permabond

So this is probably as good as it gets : **LINK**

Bonding Acetal with Adhesive

MichaelG.

[William ChithamParticipant @williamchitham75949]

Posted by Michael Gilligan on 24/03/2021 16:39:42:

For what it’s worth … I have great respect for technical advice from Permabond

Thanks Michael, that's a really useful link. Just to clarify my original post, this is a hypothetical question that occurred to me on reading another thread. Sticking metal components together with Loctite seems to have become a common technique, I was just wondering if it could be done with parts made from dissimilar materials, eg Delrin/CI.

William.

[Jeff DaymanParticipant @jeffdayman43397]

You can buy a lot of expensive adhesives from people whose job it is to sell it, and spend lots of time experimenting, only to find out:

1. it kind of just barely adheres to the low surface energy acetal parts, a very weak bond.

2. if the parts flex at all, or any load is applied, weak bond breaks.

3. If the temperature changes, weak bond breaks.

4. You then spend many hours in calls to the manufacturer / salesmen listening to excuses about field conditions being different from test lab conditions, questions about did you get it clean enough, dry enough, rough enough, with the right additives / accelerants etc, did you wait long enough, and looking at beautiful test charts. Bonding Failures will always be your fault, not the adhesive makers.

5. The salesmen will start to suggest special treatments to change the surface energy of the parts, like laser etching or corona discharge. If you go down this route, expect huge equipment costs and no tangible improvement, and no warranties or return policy whatsoever on the equipment.

6. After some time interval doing the above you will not be able to reach the sales people any more, or you will be told they have moved on to a company selling toilet cleaner, artificial fingernails, cars, etc (or prophylactics, in one case)

The above is based on multiple experiences trying to glue polymers in industry, much of the time spent trying to glue acetals and polyethylenes .

Acetal is NOT like other plastics that glue well, or metals that bond well with anaerobic adhesives.

[Michael GilliganParticipant @michaelgilligan61133]

All I can say in answer, Jeff, is please read what I wrote:

” … this is probably as good as it gets”

More than 30 years ago, I attended a short course by Bill Lees, who was then Technical Director of Permabond.

He basically talked us through the content of his book “Adhesives in Engineering Design” and the DOS-based ‘expert system’ that he had devised for Adhesive selection.

This little book remains one of my treasured possessions, and to my knowledge has never been bettered for its honest no-nonsense Engineering approach.

**LINK** : https://www.springer.com/gp/book/9783662110348

I’m not saying that bonding Delrin is easy … just that I would trust Permabond’s advice above that of any competitor.

MichaelG.

[Neil LickfoldParticipant @neillickfold44316]

I have used permabond products, who were the first to make a proper glue for aluminium alloys. Their primer works well with their cyano glues and tells you the correct clearance required for a max bond strength. In my experience the bond can not take constant shock loadings, so would need to have some mechanical means of retaining and the bonding to keep it assembled. A cue tip being glued to a delrin ferrule, will stay in place if they only did centre shots. As soon as side spin is put on, after a few, it fails. A cue tip that has a recess for the ferrule to spigot into the cue tip to mechanically secure any sideways movement, will stay adhered. Their polyolfine primer or pop is really good stuff.

Edited By Neil Lickfold on 25/03/2021 18:10:04

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