Bonding Nylon to Metal

[Yojevol]

I've embarked on some refurbishment to my newly acquired Denford CNC machine. 2 of the 3 sets of sliders which allow the router to move in the 3 axes are worn and in need of a bit of TLC. This is one of them (I've got 8 to do):-

The plastic inserts are worn and need replacing. I'm intending to machine the slot in some 8mm nylon rod (ordered) and then bond them into the housings.
So the question is - has anyone tried bonding nylon to metal? I've looked at 3M's chart and they seem to say that epoxy or CA will do the job.
Brian

 

[Jelly]

Loctite AA 326 or Loctite 603 would be my go-to options in this instance, with the AA326 being the better option.

 

[AES]

That's a tough one IMO. Any idea how the OEM did it/what they used? Not heard of AA 326, but have used Loctite 603. IME, it MIGHT work! But it doesn't have a very good "peel" strength, and that's what you're looking for in that job (I don't know that machine but am assuming that block in your pic slides longitudinally along some sort of "rod way/s"?).

 

[Jelly]

That's a tough one IMO. Any idea how the OEM did it/what they used? Not heard of AA 326, but have used Loctite 603. IME, it MIGHT work! But it doesn't have a very good "peel" strength, and that's what you're looking for in that job (I don't know that machine but am assuming that block in your pic slides longitudinally along some sort of "rod way/s"?).

AA326 is specifically for structural bonding of dissimilar materials, and has the peel strength he'd be looking for.

I think the 603 could work if the fit-up between the parts was good, and he found a way to apply good even pressure to exclude any air whilst it cured; given it only really works well if the parts it's holding are already a location fit or transitional fit.

 

[AES]

Thanks for the info Jelly. I hadn't heard of AA 326 before. Is it freely available?

Yup, although I guess it will depend on how tight the fit is between those two pads and (I presume) the rod/s way, it was peel strength that worried me a bit - 603 isn't marvellous in that respect, especially if the two parts involved are "only" a location fit.

 

[xy mosian]

That image has me wondering if the nylon is 'snapped' in. I could see the lugs in the metal casting mating with cut outs formed in the plastic inserts. Of course, if that is the case, they could be there purely to help with alignment during some glueing process.
xy

 

[Jelly]

Thanks for the info Jelly. I hadn't heard of AA 326 before. Is it freely available?

It's available online but only in the largest (50ml) bottles, cheapest I've seen is about £30-35 so it's about as pricey as 603.

I believe it's was originally intended for securing high strength magnets into high-tech polymer assemblies.

 

[andy48]

Another option might be to make up a filler piece (wood?) to fill the central gap, then accurately fix the slider in place on the guide bars and fill the space between slider and bars with Turcite or similar. Its designed for machine sliding surfaces.

 

[Cabinetman]

That image has me wondering if the nylon is 'snapped' in. I could see the lugs in the metal casting mating with cut outs formed in the plastic inserts. Of course, if that is the case, they could be there purely to help with alignment during some glueing process.
xy

I agree, and probably they aren’t even glued at all as the lugs would stop the plastic sliding up-and-down anyway, another thought is that perhaps you could take up the slack by inserting a bit of card or similar between the existing plastic and the metal? Ian

 

[Ollie78]

They are probably IGUS linear bearings the catalogue is vast, you might be able to get new ones which is the best thing really, the precision relies upon a perfect fit.
I think its likely that you can get replacement carriages.

They look like part of the drylin W range to me, is there a part number on them anywhere ?

Look on here drylin® linear bearing and linear guide systems

Ollie

 

[Jonm]

This article is suggesting a combination of plasticweld on the nylon and superglue on the metal.

https://gluereview.com/best-glue-for-nylon/
Not tried it myself.

 

[Fergie 307]

Firstly not sure I'd use Nylon. Maybe Delrin or PTFE. The slots mid way along, which look to be at top and bottom suggest to me that they probably clip in place, possibly with a small shoulder at each end to keep them in place longitudinally. Have you tried inserting something suitable in the slot and see if they just pop out?

 

[Yojevol]

Thanks guys for your thoughts, very useful. A few points of clarification and further thoughts of my own.
1. @xy mosian You're right to assume that the present ones are held in mechanically by lugs and the notch that can be seen in the pic.
2. They were originally sprung into place.
3. I don't think peeling off would be possible because the rails will tend to prevent that.
4. The lateral forces will be small and only due to friction which these inserts are designed to minimise.
5. The original supplier was Reliance but this design is not now in their range, probably obsolete. They supplied the whole transmission system.

My further thoughts:-
6. The internal surfaces of the insert housing bores are as cast so probably not the best for bonding to, so I will drill them through to clean up and remove the locating lugs.
7. Provide an alternative method of mechanical restraint. Possibilities:-
7.1. metal clip that hangs over the both ends to convince the insert that thoughts of escape are futile. To hold such a clip I could utilise the existing mounting screws or drill and tap new holes in the middle. Making the clips is going to be a fiddly job and I would need 16 of them!
7.2. Drill and tap a new hole in the sides such that a screw would engage in a location hole in the back of the insert. Would need to be careful about screw lengths.
7.3. My favourite. Drill a central hole down from the top (as in the pic) surface such that it just breaks through into the insert bore. Insert the insert and keep in place with a self-tapping screw
8. I will have a surplus of nylon rod so I can experiment with glues/bonding agents, although I'm reluctant to splash out 30 odd quid for the 326 which will probably never be used again. The JB Plastic Weld/CA combination referred to by @Jonm looks interesting. I might have a go.
9. @Cabinetman - I had a go at some packing but it was very difficult impossible to reinsert. The old plastic is now fairly weak and it split along corner of the slot.

Any more thoughts are welcome
Brian

 

[xy mosian]

Thanks guys for your thoughts, very useful. A few points of clarification and further thoughts of my own.
1. @xy mosian You're right to assume that the present ones are held in mechanically by lugs and the notch that can be seen in the pic.
2. They were originally sprung into place.
3. I don't think peeling off would be possible because the rails will tend to prevent that.
4. The lateral forces will be small and only due to friction which these inserts are designed to minimise.
5. The original supplier was Reliance but this design is not now in their range, probably obsolete. They supplied the whole transmission system.

My further thoughts:-
6. The internal surfaces of the insert housing bores are as cast so probably not the best for bonding to, so I will drill them through to clean up and remove the locating lugs.
7. Provide an alternative method of mechanical restraint. Possibilities:-
7.1. metal clip that hangs over the both ends to convince the insert that thoughts of escape are futile. To hold such a clip I could utilise the existing mounting screws or drill and tap new holes in the middle. Making the clips is going to be a fiddly job and I would need 16 of them!
7.2. Drill and tap a new hole in the sides such that a screw would engage in a location hole in the back of the insert. Would need to be careful about screw lengths.
7.3. My favourite. Drill a central hole down from the top (as in the pic) surface such that it just breaks through into the insert bore. Insert the insert and keep in place with a self-tapping screw
8. I will have a surplus of nylon rod so I can experiment with glues/bonding agents, although I'm reluctant to splash out 30 odd quid for the 326 which will probably never be used again. The JB Plastic Weld/CA combination referred to by @Jonm looks interesting. I might have a go.
9. @Cabinetman - I had a go at some packing but it was very difficult impossible to reinsert. The old plastic is now fairly weak and it split along corner of the slot.

Any more thoughts are welcome
Brian

Hi Brian,
That sounds as if you have thought everything through well.
Had you considered the possibilty of making cpoies of the original? Without seeing the 'naked' liner it is tricky to see just how awkward that would be.
Just sprung into my head. How about making the inserts as you intend, but having them short of the housing. Maybe it would be possible to raise a burr, at each end, to stop the insert escaping.
Have fun, xy

 

[Inspector]

How much of a load is on these things? Could you machine an entirely new one from UHMW Polyethylene? It is after all a block with a T slot and four holes.

Pete

 

[Fergie 307]

Have you thought about getting someone to 3d print replacements? You should be able to copy them very precisely.

 

[Yojevol]

Have you thought about getting someone to 3d print replacements? You should be able to copy them very precisely.

Yes I have but I want to get on with it. I'm hoping the nylon rod material will be here tomorrow.
Brian

 

[Ollie78]

I suspect they are a self lubricating low friction blend specifically for the purpose.
Obviously you have the knowhow to do the job, I just worry you could put a lot of effort in and end up with a sub par result due to the material itself.

Let us know how it goes.

Ollie

 

[Keith 66]

Another option might be to make up a filler piece (wood?) to fill the central gap, then accurately fix the slider in place on the guide bars and fill the space between slider and bars with Turcite or similar. Its designed for machine sliding surfaces.

I had a lathe bed & saddle reground a couple of years ago, parts of the saddle were turcited, the stuff is famously slippery & needs a specialised glue that is astronomically expensive. Does a good job though!

 

[Yojevol]

Just to close this thread.
I made my nylon inserts and glued them in with J-B Weld Plastic Bonder. Very good adhesion to the nylon and the zinc casting. I tried their Plastic Weld product but I had a problem with it in that it wouldn't cure. It's an epoxy which they claim goes off in 5mins. Mine took at least a couple of hours just to get moderately secure. Even after 48 hours it was still not fully hardened. I complained to the supplier and got a refund. The Plastic Bonder is a 2 part urethane adhesive which is claimed to go off in 30mins and sandable after 2 hours. This is very optimistic. I waited for 2 hours by which time it was handleable.
After some days Plastic Weld had made a good bond with the nylon but not so good with the metal. @Jonm's suggestion above to use superglue as an interface may work if that's all you have to hand. Otherwise purchasing the Bonder would be a good bet.
Brian