Author Topic: plasting welding fluke scopemeter chassis  (Read 635 times)

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Online coppercone2

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plasting welding fluke scopemeter chassis
« on: March 28, 2021, 05:21:24 am »
Ok so my scope meter Fluke 99 is electrically fine but the chassis is all sorts of fucked up. It needs new stand offs, many cracks fixed, etc.

So this is what I can't easily figure out:

1) What should I do with the bad standoffs? I can use a dremel to make the bottom flat from crumbled plastic, but what is something I can put there? I thought maybe 3d printer guys might have some kinda fancy standoff thing or good technique, I don't think I can glue em back together they break even when I use loctite medical grade superglue sensitizing surface tension changing primer with the best loctite glues. I don't mind changing screws and using metal inserts ones but I have no idea whats going to work, its mad frustrating, its thin and there is no room to work in, it needs to be super strong

2) can the exterior plastic shells be welded with some kind of plastic welding system? I have the best glues (DP8810, DP8805) for plastic that I know of, but their not going to cut the mustard here. I need some serious strength the word on the tip of my tongue is weld that shit up. I see them fix big ass trash cans and bumpers on youtube using a plastic welding system (its like tig or mig with hot air), I wanna do this kind of repair here, I don't think anything else is gonna hold.

I fixed a few cracks with glue and they keep manifesting and spreading out, I wanna do a real weld job where i use a die grinder /dremel burr to make a channel and actually fill it up with filler. It keeps spreading its like being on thin ice it just keeps moving outwards
« Last Edit: March 28, 2021, 05:23:58 am by coppercone2 »
 

Offline spostma

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Re: plasting welding fluke scopemeter chassis
« Reply #1 on: March 29, 2021, 09:51:10 pm »

Super glue + baking soda can be  used to build up material;
Ty-raps and a not too hot soldering iron can be used to weld plastic cracks, see




Threaded Brass Inserts for platic are available from RS and AliExpress
 

Online coppercone2

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Re: plasting welding fluke scopemeter chassis
« Reply #2 on: March 29, 2021, 10:56:21 pm »
nah the super glue is not cutting it, I have tried it with baking soda also for 'fast cure'. I just think its not strong enough, I need to weld.

I saw a more advanced video where he bevels it with a burr and then fills the whole thing in with a rod, but does anyone know what rod is used for whatever fluke uses? I think they need to be compatible. I am not sure the best choice of filler rod.
« Last Edit: March 29, 2021, 10:57:56 pm by coppercone2 »
 

Offline SilverSolder

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Re: plasting welding fluke scopemeter chassis
« Reply #3 on: March 30, 2021, 03:21:37 am »

I had to cut the door panels open on my car, and plastic weld the whole thing back together again, in order to re-apply the leather trim that had come off.  What worked the best for me was my hot air soldering station! - using the hot air from that, with plastic welding rods (should be the same type of plastic as the object you are working on).

Unlike working with metal, I found it best to heat the rod quite a bit, as well as the object being welded, and "feed" the rod into the seam.

It didn't look too bad in the end, but this was all done on the back of the door panel...  I wouldn't attempt to weld anything that had to look good afterwards, unless you are OK with sanding the whole thing down and painting it...

 

Offline SilverSolder

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Re: plasting welding fluke scopemeter chassis
« Reply #4 on: March 30, 2021, 03:35:17 am »

3M makes some eye-bleedingly expensive adhesives for plastics that are actually very good - but they don't act as fillers...  they will only fill very small gaps, good for putting cracked stuff back together.

A less expensive but also superb adhesive is Devcon 22045 Plastic Welder.  This is a urethane type adhesive, smells so evil that you almost can't believe it can be legal to sell it -  but it works fantastically well, and this stuff will fill gaps too.

 

Offline jpanhalt

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Re: plasting welding fluke scopemeter chassis
« Reply #5 on: March 30, 2021, 10:41:58 am »
but does anyone know what rod is used for whatever fluke uses? I think they need to be compatible.

The plastic welding I have done with hot air is better if the plastics are compatible.  It is a combination of simple fusion and fill welding. Unlike metal welding, one doesn't work a puddle, but rather heats the filler and pushes it into the base material.  I never tried using vastly different filler than the base plastic.

As for the plastic type, have you contacted Fluke?  If that is a dead end, you can do a variety of tests on pieces that have broken off.  By that I mean you can test what solvents might work might soften or dissolve.  Look up "flame test."  Many plastics give characteristic odors and flames when burned. Some examples are nylon, polypropylene, noryl, styrene, and ABS. 
 

Offline TheSteve

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Re: plasting welding fluke scopemeter chassis
« Reply #6 on: April 01, 2021, 04:45:45 am »
Plastruct Plastic Weld works great if the plastic is compatible - it contains MEK which is magic stuff.
VE7FM
 

Offline Old Grey

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Re: plasting welding fluke scopemeter chassis
« Reply #7 on: April 08, 2021, 09:36:04 pm »
I've welded plastic fuel tanks, and it's just a soldering iron and a strip of plastic cut form a engine oil container as filler rod.

As for glue, Selleys Urethane Bond is the strongest I've found. The problem is that they don't make it anymore so you'll have to chase old stock if it exists.

It's $20 for a small tube.
You have to hold stuff together for 6 hours - I use tape -  because it's slow to cure.
You have to wear gloves because it's so sticky and gets everywhere.
It can't be used long term in sunlight - I glued a lot of plastic in my dash and after maybe 5 years it got brittle and snapped off -.
It expands and bubbles a little.

I once glued a split wooden golf club head with it, and it's still fine 20 years latter.
 

Online coppercone2

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Re: plasting welding fluke scopemeter chassis
« Reply #8 on: April 09, 2021, 01:00:07 am »
My best glue for plastics is DP8805 and DP8810. They are very expensive 2 part acrylic epoxies with glass bead fillters to ensure proper bond thickness, the only caviat (irrelevant) is however they will not dry/cure if the joint is open, it basically needs to be tight and the stuff on top can be wiped off like a paste later.

The loctite prism sensitizer is also expensive, it allows me to glue polyproplyene to plexiglass even with superglue.

The only problem is the damn chassis is thin, and all these glues.. even the best ones.. i think the tensile strength is just too low compared to the base material when its all floppy. I really think that I need to do some drilling (crack propagation stop) and welding to solve this problem.


Its not that the glue joint is failing either! the problem is there is new cracks forming at the end of the glued junction in different directions. I put it back together with a battery and it was just a hair tight with the screws and then I got a giant crack propagation in a different region.

I was really hoping I can try to weld it up, otherwise it was basically going to be put into a old alarm box to make a battery powered floating bench multimeter thing.

I thought maybe if I melted it all back together it might stop propagating.


So again, in short, not to be angry, just pointing it out
the glue bonds pretty much hold but I got a containment problem, like richard nixon

I don't really understand why it keeps disintegrating more.


Maybe I should just poke the end of the cracks with a soldering iron, then glue it all up with the acrylic epoxy? I know they drill holes in cast iron and glass on the end of the crack because it spreads out like this. Maybe I can just spot melt it in that point and then use glue since it is strong enough for the bulk of the crack?

Like I had a crack near the screw hole of the battery compartment, filled it up, I look 6 months later and the battery compartment is like cracked in half.

What I anticipate is that when I fix it up this time, I will look in a few months and the ends of the cracks will be going in different directions some how.


I do have a 2 part poly-urathane epoxy also.. I can try it, it sounds similar to the glues you are mentioning.

Maybe I will bite the bullet and buy one of these exotic solvent glues.

Does a THF one sound any good for welding this up? I have a THF based Lexan glue. And I no longer have any, but I was thinking about buying more  plexiglass glue (similar to the lexan glue with different solvents ratio and additions).



« Last Edit: April 09, 2021, 01:11:06 am by coppercone2 »
 

Online coppercone2

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Re: plasting welding fluke scopemeter chassis
« Reply #9 on: April 09, 2021, 01:12:51 am »
BTW, people with glue suggestions in this thread,

Do these glues keep OK? I have managed satisfactory control of my 3M Epoxy stockpile in a refrigerator. I HATE buying glue because it expires, I almost don't like any 1 part glue because they always expire before I use em. This object is pretty expensive, but if these glues have a good shelf life from your experience, I can maybe find a unique engineering application for them as not to feel like I am pissing away money.

Selleys Urethane Bond
Devcon

I know Urathane glue is some aviation stuff.

I have Scotch Weld DP604 I believe, that is a 2 part epoxy urathane. But it does not sound the same as these solvent glues, I think all the scotch weld products will not weld the plastic, only bond it.


As for the experiment, how should I conduct it? I thought maybe to make a pile of scrapings then mix them with small quantities of glue to make a putty/paste and see which one is the strongest? I can rip off some of those plastic screw studs to experiment on, since they need to be replaced anyway. If I get some kind of thing I can glue in there with a big lap joint, I think the epoxy might be the best choice there, but it might not be the best choice for crack filling, where you want the solvent action of these more unique glues.

If I can trim down some hex standoffs on the milling machine to make replacement screw inserts, I can glue those on with DP8805 and I think it will be super strong, I have very good results on my antenna bracket stuff I made with it, i.e. gluing copper to plastic.

So my plan is
1) for replacement standoffs use one of the good epoxies I know works good from large scale tests, I am confident in the lap joint strength of the acrylic 2 part epoxy between plastic and metal now after trying to dismantle some of the plastic metal bracket parts I made for antrnnas.

2) for crack propagation try one of the solvent glues mentioned in this thread and some how figure out which one is best, hopefully it will melt the tip of the crack closed with a real weld. (no experience with solvent based glues other then making a few lexan and plexiglass joints)
« Last Edit: April 09, 2021, 01:22:15 am by coppercone2 »
 

Offline SilverSolder

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Re: plasting welding fluke scopemeter chassis
« Reply #10 on: April 09, 2021, 01:07:26 pm »
The Devcon stuff is inexpensive and will keep for about a year...  so it is economical even for a single project.

Here's an example of where I used it successfully:  the paddles broke off the Amplitude and Power switches (the Amplitude switch is supposed to look just like the Power switch, both circled):





To fix them, I cleaned the surfaces and glued the paddles back on the "stump" with Devcon.  This is a reasonably challenging job for an adhesive, since the forces acting on the joint are quite high in normal use.  I am happy with the result, it has worked flawlessly for several years.


Another example: a guy I know makes custom car interiors.  He compared the Devcon with some high-end 3M products on some plastic interior panels and found it stuck just as good as the expensive stuff.

 

Online coppercone2

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Re: plasting welding fluke scopemeter chassis
« Reply #11 on: April 09, 2021, 02:47:06 pm »
Maybe the glue I have is matched too well with plastics that don't glue well at all and this glue has a higher tensile strength with semi glue-able plastics.

I think the 3m acrylic epoxies have ~1/2 of the tensile strength of that stuff when used on most things other then aluminum, but the bonds came out much stronger on plastics like Corian and plexiglass, but those generally don't glue well at all with anything. I see the SDS is very different, but it does seem to be doing something with acryl type molecules.

I think I focused too hard on doing the impossible with my glue choice, this job requires doing medium really good..

There is also permatex black plastic bonder, but it smells foul and the shelf life is trash for a 2 part product. I ALWAYS threw this stuff out even when I thought I was in the clear...
 

Offline SilverSolder

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Re: plasting welding fluke scopemeter chassis
« Reply #12 on: April 09, 2021, 03:35:40 pm »
Maybe the glue I have is matched too well with plastics that don't glue well at all and this glue has a higher tensile strength with semi glue-able plastics.

I think the 3m acrylic epoxies have ~1/2 of the tensile strength of that stuff when used on most things other then aluminum, but the bonds came out much stronger on plastics like Corian and plexiglass, but those generally don't glue well at all with anything. I see the SDS is very different, but it does seem to be doing something with acryl type molecules.

I think I focused too hard on doing the impossible with my glue choice, this job requires doing medium really good..

There is also permatex black plastic bonder, but it smells foul and the shelf life is trash for a 2 part product. I ALWAYS threw this stuff out even when I thought I was in the clear...

I believe the Permatex product is the same as the Devcon...  it just costs more!  :D

Yeah, it is annoying having to throw it out.  Maybe a better way is to look around for things to fix, and use the whole pack in one sitting...   The Devcon is only like $6 or $7, not like paying $50 for a 3M product that only comes in big packs.
« Last Edit: April 09, 2021, 03:37:26 pm by SilverSolder »
 

Online coppercone2

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Re: plasting welding fluke scopemeter chassis
« Reply #13 on: April 09, 2021, 04:34:10 pm »
no, the permatex has pyridine or one of those chemicals similar in it. It smells most noxious and foul, I don't see it on the SDS, but then when I look at the SDS of the black plastic bonder, I don't see it either, perhaps they changed it.. but I am sure of what I saw and smelled. Unmistakable, must be good for gluing but holy shit that glue WORKS your nose, granted its a beast glue that can do something like fix a black vacuum cleaner wheel...... normally impossible for something that gets trashed around that much. I saw pyridine or pysomething on the ingredients list (its NOT the one in pepper), and it was burned into my mind. I would say, maybe its capable of repairing a chair, but I would not repair a chair because its too dangerous..

That glue I will only use literary outside with a fan, its like if you made 'rancid ammonia' into a 'war gas' level of potency. It instantly makes me think of dying and cancer. Way more foul then even concentrated ammonia, all mineral acids, halogens, etc. I don't think its quite so bad for you (may be naturally occurring in your body in small amounts) as those chemicals listed, but the smell is dire.

I need a good work plan if I wanna use that black plastic bonder, I felt uneasy/paranoid about my health/sick after smelling it. I would rather do something really dumb like weld zinc steel then smell that again lol. It gives me similar feelings to 'on fire plastic' smell.. you just think 'this is sooooooooo fucking bad for me'. Maybe you can compare it to ''fresh ESD mat smell mixed with ammonia on steroids'. MEK and the new non methylene chloride paint stripper makes me a little sick too, but this one takes the cake 100%. Like 5 seconds of this stuff makes me feel worse then scrubbing something down with MEK soaked rags for like 5 minutes.
« Last Edit: April 09, 2021, 04:44:59 pm by coppercone2 »
 

Offline SilverSolder

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Re: plasting welding fluke scopemeter chassis
« Reply #14 on: April 09, 2021, 09:07:48 pm »
Your description of the Permatex is close to how I would describe the Devcon:  pure, crystallized evil that drains your soul out through your nose!  :D

With a smell like that, you just know it has to be effective...

Devcon and Permatex have the same parent company, so I suspect these two are the same:

https://www.amazon.com/Permatex-84115-5-minute-Plastic-Adhesive/dp/B000ALBZK8

https://www.amazon.com/Devcon-22045-Plastic-Welder-Dev-Tube/dp/B003NUGL9S

Notice how the specs are remarkably similar...  only the color is different.
« Last Edit: April 09, 2021, 09:11:00 pm by SilverSolder »
 

Offline langwadt

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Re: plasting welding fluke scopemeter chassis
« Reply #15 on: April 09, 2021, 09:26:05 pm »

I had to cut the door panels open on my car, and plastic weld the whole thing back together again, in order to re-apply the leather trim that had come off.  What worked the best for me was my hot air soldering station! - using the hot air from that, with plastic welding rods (should be the same type of plastic as the object you are working on).

Unlike working with metal, I found it best to heat the rod quite a bit, as well as the object being welded, and "feed" the rod into the seam.

It didn't look too bad in the end, but this was all done on the back of the door panel...  I wouldn't attempt to weld anything that had to look good afterwards, unless you are OK with sanding the whole thing down and painting it...

hot air gun is basically what the pros use, https://youtu.be/w837L8RTZd8

 

Offline SilverSolder

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Re: plasting welding fluke scopemeter chassis
« Reply #16 on: April 09, 2021, 10:36:24 pm »
This is what it looked like after using my soldering hot air station to weld polypropylene (which is almost impossible to glue/fill).  This is actually a subwoofer enclosure behind the door panel, so it has to be not only strong, but also air tight! - it turned out really nice, it almost looks original.




Butt weld:
« Last Edit: April 09, 2021, 10:42:04 pm by SilverSolder »
 


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