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Tractrix Horn Crack Repair - Type of Plastic?


pdxwaker

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My Forte II tratrix midrange horns have developed cracks.

 

I'm looking for repair recommendations... considering plastic welding, plastic epoxy (ex: JB weld), 'black toughened' cyanoacrylate.  Right now, leaning toward a plastic weld (on back side of horn) with epoxy as needed for filler (applied with toothpick).  Other suggestions welcome!

 

For plastic welding or epoxy, it would be good to know the type of plastic used for the horn body... any help here?

 

 

crack.jpeg

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I would weld the back using copper wire as "rebar" to make it more solid.  If you're not familiar, practice on something else.  I used to do this a lot for car body repairs.  Then fill the front with JB.  Like you suggested in OP.  

Drilling a small hole at the end of the crack, stops it from spreading. 

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Unless you have a lot of skill in hot plastic welding, I would avoid it. And you really need to know what the plastic is...

 

If the plastic is ABS, I would use Plastex or Plastifix. It is a chemical weld process and works superbly, have used it much.

 

Otherwise epoxy or iso-cyanoacrylate are adhesives and maybe your best bet to make it stick, but the appearance may be less than desirable.

 

I have tried this adhesive and it works well. I have used it to bond glass to steel (non-porous surfaces) as well as wood to glass, wood to plastic (porous), but haven't tried plastic to plastic but can't see why it wouldn't work... The description here doesn't mention plastics, but the bottle lists it...

 

High-Temperature Glue, 4 FL. oz. Bottle | McMaster-Carr

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1 hour ago, pdxwaker said:

My Forte II tratrix midrange horns have developed cracks.

 

I would use ABS cement for the ABS horn. Press some masking tape over the face side of the cracks to keep cement from oozing out onto the visible side. Then using a small applicator, force the plumbers ABS cement (from Home Depot, Lowes or Menards, etc.) into the backside of the cracks. Keep the screw hole clean, promptly wiping excess cement with a Q-tip if needed.

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5 hours ago, Khornukopia said:

 

I would use ABS cement for the ABS horn. Press some masking tape over the face side of the cracks to keep cement from oozing out onto the visible side. Then using a small applicator, force the plumbers ABS cement (from Home Depot, Lowes or Menards, etc.) into the backside of the cracks. Keep the screw hole clean, promptly wiping excess cement with a Q-tip if needed.

So are you saying that these are ABS plastic?  As others have suggested, knowing the type of plastic seems key to the optimal repair.  

Edited by pdxwaker
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  • 2 weeks later...

I used ABS cement for the fix.  It is pretty thick stuff... tried to blow it into the crack by spreading it / using compressed air.  It seemed to work ok.  On the back side, added a glob of abs cement along the crack and allowed it to dry.  We'll see how it holds up.

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Just a point for future reference - as with any welding (chemical, arc welding etc.) you should use a filler material of the same or proven compatible substance. If you just "melt" the parts together (with either chemicals or heat), there will be a loss of thickness, and a high potential for mis-shaped parts when cured. ABS cement is simply ABS solvent with a few binding materials to give it higher viscosity

 

That is why I suggested Plastifix or Plastex if the horn is ABS. It uses an ABS solvent to melt the parts, plus a filler material. You could also use any ABS solvent and grind up ABS and either apply the powder like the two products I mentioned or dissolve it in the solvent then apply.

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