Gluing metal to plastic

[Jol Wilkinson]

I need to glue some (about sixty) n/s canopy brackets to station buildings made up from the Grand Junction (Parkside Dundas) moulded panels.

The roof/canopies will be removeable for storage/transit. etc. so the brackets will be fixed to the buildings only. This will leave them a little susceptible to damage when working on the layout so a robust joint is needed. I have to hand Zap-a-gap cyano and one hour epoxy.

I am inclined to use the latter but does anyone have an experienced based view on which would be better, or any better suggestions?

Jol

[JFS]

Jol,

For plastic / metal joints, I have been using Loctite 435 which is an industrial grade of cyanoactrylate. With appropriate preparation, the resulting joint is stronger than the plastic, and of course with a suitably "thin" joint, it goes off in seconds. An aerosol primer is also available for "difficult" plastics. Only, snag is that a smallish bottle will set you back 20 quid ie:- http://www.cromwell.co.uk/LOC7255027Z but it won't let you down.

Hope that helps.

Howard

[Tim V]

Cyano etc - nasty stuff.

Any chance of modifying the bracket so they sit in a slot - thus increasing the contact area?

I would use epoxy myself.

[Will L]

Can't agree with that Tim. I find Super glue very useful for metal/plastic joints, but there is a nack to it and I wouldn't recommend the thick ones which I suspect the Zap a Gap is. Epoxy will do the job but I for one find it hard to do as neat and tidy a job as I can do with Superglue.

Superglue from the local hardware store is perfectly adequate, though I do find anything but the smallest pack will go off long before I've used it all. I recently found a pack of Loctite in three 1 gram tubes, as opposed to a single 3 gram tube, for £3.50. Hopefully the unopened tubs will outlast the opened one.

To make superglue work for you you need to proceed as following
1. Only use it on suitable joints, i.e. where there is a good tight fit between the parts. This stuff isn't a good gap filler, despite the fact that they sell thick gluppy varieties with this in mind
2. Therefore use a thin runny variety
3. Make sure everything to be joined is really clean, I like to get metal mechanically and chemically clean (i.e. polish with the fibre glass brush and wipe it of with a solvent cleaner) but plastic may not take well to this treatment, so settle for mechanically clean. Once it's clean keep your fingers off.
4. Squeeze out a blob of superglue out of the tube on to smooth non-absorbent surface
5. Assemble the joint dry
6. Pick up a small drop of glue on the tip of a bit of fine wire, or my favourite, the vanishingly small jewellers screwdriver from in the set
7. Apply the glue to the assembled joint where capillary action will suck it in. This is why you need the thin runny variety.
8. if you get too much on the joint, it takes longer to go off. If there is an excess sitting round the joint, mop it up with the edge of a bit of loo paper.
9. Blow on the joint. Superglues go off best in the presence of moisture and the absence of air.

Get it right and the action is near instant and will produce a strong joint with no mess.

Will

[Tim V]

It's that instantaneous action that is at fault here - what happens if it's in the wrong place? Plus I've found that super-glue fails after a while - and specially with dissimilar materials.

[Jol Wilkinson]

Thanks gentlemen,

I've been concerned that the brackets will be susceptible to damage when the roofs are not in place, e.g. getting knocked during track cleaning, erecting the layout, etc. In thinking about gluing them in place I've also realised that there is just sufficient clearance above the brackets at their outer ends to solder a thin strip of brass alomg the whole length to act as a "barrier" to hands, cuffs, etc. catching on them. That way any impact will also be spread along all the joints.

Howard,
thanks for the recommendation on Loctite 435, shame that they don't do it in a 3ml size like some of their other products such as 401. I took a look at the Loctite site and found it full of wonderful things, but rather confusing with so many options.

Tim,
photo of brackets temporarily in place, they have to be surface mounted but with a stiffening strip along the outer ends I think that I'll be able to resolve my concerns.

Canopy brackets.jpg

(amazing the detail shown in a big close up)

Will,
thanks for the guidance. Zap-A-Gap is a gap filling cyano that I usually find succesful but occasionally it doesn't work at all, cleanliness probably being the cause from your comprehensive notes.

Jol

[Will L]

It's that instantaneous action that is at fault here - what happens if it's in the wrong place?

Might be a problem if you use the apply glue hold together and hope approach but I specifically didn't suggested that.

Plus I've found that super-glue fails after a while - and specially with dissimilar materials.

I leaned to superglue before I leaned to solder. It's long time ago now (70's) but the results are still with me. Get it right and the results are perfectly durable.

Will

[wally]

For those who shudder at the price (and shelf life) of Loctite products here is a tip I picked up whilst ii was still working and sourcing such things for extensive workshop use.

Look for the Bondlok range,this was started by a group of chemists who worked for Locktite before branching out on their own.

They use the same type/refence numbers and the prices are considerably lower. The range is avaiable from many engineers suppliers.

Wally

[Will L]

For those who shudder at the price (and shelf life) of Loctite products ...

I didn't think £3.50 was excessive and as I say I'm hoping the septate 1 gm tubs will help with shelf life. Actually most Loctite products, the thread lockers and retainers last a very long time. Even the superglues last a lot lot longer the originals did in the 60s/70s. If your really concerned keep it in the fridge.

Will

[Terry Bendall]

My usual solution to the sort of situation that Jol has is to drill holes in the metal part, solder in a suitable size piece of brass wire and drill corresponding holes in the suface to which the component is to be fixed. This will reinforce the joint. Even something as small as 0.3mm brass wire wil help and if you can a larger size is better. I then use standard super glue. If the part is large enough, small screws can be used instead of the wire with a nut on the inside.

Brackets such as these would normally be bolted to the wall so if you feel so moved you can let the wire protrude through the front of the bracket and file it to a hexagonal or square bolt head.

Terry Bendall

[JFS]

Look for the Bondlok range,this was started by a group of chemists who worked for Locktite before branching out on their own.

Turns out that should be bondloc:-

http://www.bondloc.co.uk/#/cyanoacrylates/4542997832

Many thanks for the tip - will look into it further

Regards,

Howard.

[beachboy]

Taking Terry's method, if the rod used is say 0.5mm, then drill a 0.45mm hole & push the item in for a compression fit.
If the plastic is thick enough a rebate around the drilled hole on the inside, allows for an area a glue to make a bond without being squezed out.

Works well with small parts like wagon door bangs, which with just CA glue, can be knocked off without knowing until there gone.

Steve.