How to repair a stripped screw hole in a DX Chogokin toy

[brouken]

Hi MWers! I've tried searching the threads, but was not able to find a topic/solution regarding this.

I noticed that one of the screws on my DX Chogokin YF-29 Ozma was loose. I tried tightening it, but apparently, the plastic hole was stripped and the screw wouldn't tighten in anymore. I tried dropping in a dab of Tamiya plastic cement in the hole to try and tighten it up. But the screw just won't bite.

Any suggestions on what to do? Is there some kind of putty that I can use to fill up the hole so that the screw can tighten?

Any help would be most appreciated. Thanks!

[spanner]

I would imagine you would have to use some kind of plastic filler or a certain type of glue perhaps that you can fill the hole in entirely and re-drill a new hole so the screw can thread in again..

There are plenty of knowledgeable folks in here who would know a lot more about this than I do and im sure someone will give you the advice / direction you need!

Edited December 16, 2014 by spanner76

[wmkjr]

Got a pic to use as a reference? Maybe you can use some plastic bag or ziploc or plumbers tape, cut a small enough piece to fit around the screw and use that as a wedge. How about Loctite or CA glue?

[brouken]

Thanks for the replies!

The screw hole location is on the plastic part that connects to the die-cast part of the left arm assembly to the main body of the valk (i.e. the shoulder part). I'll try to take a clear pic of it for reference.

As an update and a warning: DO NOT USE TAMIYA PLASTIC CEMENT TO FIX A PROBLEM LIKE THIS. I didn't read the instructions on the bottle clearly and apparently Tamiya Cement uses a solvent to bond plastic. So what happened was that the cement actually dissolved the plastic in the hole, making the problem worse.

So now my only recourse is to refill the hole up with plastic repair putty and just carefully drill in a new hole for the screw. I guess I'm off to the hardware store to look for a suitable putty.

Oh, and I did try using a piece of plastic bag wrapped around the thread of the screw. But the screw is so small that the plastic bag just keeps slipping off. As for Loctite or CA glue, I'm hesitant to use them because they might melt the plastic further. I think I'll just fill up the hole with some epoxy filler for plastic.

[ArtTem]

Thanks for the replies!

The screw hole location is on the plastic part that connects to the die-cast part of the left arm assembly to the main body of the valk (i.e. the shoulder part). I'll try to take a clear pic of it for reference.

As an update and a warning: DO NOT USE TAMIYA PLASTIC CEMENT TO FIX A PROBLEM LIKE THIS. I didn't read the instructions on the bottle clearly and apparently Tamiya Cement uses a solvent to bond plastic. So what happened was that the cement actually dissolved the plastic in the hole, making the problem worse.

So now my only recourse is to refill the hole up with plastic repair putty and just carefully drill in a new hole for the screw. I guess I'm off to the hardware store to look for a suitable putty.

Oh, and I did try using a piece of plastic bag wrapped around the thread of the screw. But the screw is so small that the plastic bag just keeps slipping off. As for Loctite or CA glue, I'm hesitant to use them because they might melt the plastic further. I think I'll just fill up the hole with some epoxy filler for plastic.

As i remember, many parts in DX is from ABS. Because it's more stronger than usual PS (styrene). So, did you try that:

?

Edited December 16, 2014 by ArtTem

[mechaninac]

Two ways to deal with a stripped screw boss on something made of plastic (ABS in this case):

1) Fill the hole with slivers or shavings of the same ABS and use plastic weld to bond it all together. The fill material can be acquired from the toy itself by removing some ABS from some internal, hidden, surface.

2) Source a slightly larger diameter screw of the same length and head size to use on the stripped boss. It'll cut/form it's own thread as it's worked into the screw boss, which will not be stripped as far as the fatter screw is concerned. The through-hole in the mating part may need to be drilled larger to accommodate the new, slightly wider, screw.

[brouken]

@ArtTem, spaciba for the tip about using ABS Cement my friend. :-) I'll consider this, but I've been having a difficult time getting Tamiya ABS cement as its always out of stock in our local hobby shop. :-(

@mechaninac, thanks also for the tip. This will be my backup plan just in case the epoxy filler doesn't work. Step two will be a little difficult though because the screw being used is so darn small. Finding a slightly larger diameter one of the same length and head will be quite a challenge.

After going to a nearby ACE Hardware shop, I managed to get some JB Weld KwikWeld Quick Setting Steel reinforced Epoxy rated at 2424 PSI. It also cures at a dark grey color which is the same color as the 29 Ozma. :-) I'm going to perform the operation tomorrow and see if I can fill up the hole enough to make new threads for the existing screw. Hopefully all goes well. :-)

[brouken]

Okay, I've made a photo collage of the damaged hole as well as the repair that I made. Hopefully, this will help others who might experience the same problem.

Here is a wide angle shot of the damaged hole for the shoulder joint:


As you can see in this close-up photo, the hole got eaten away even more after I tried putting in some Tamiya Cement (the non-ABS one). As I mentioned in my earlier post: DO NOT USE TAMIYA CEMENT FOR THIS REPAIR.


Here is the photo of the arm assembly. The arrow points to the part where the screw goes in to join with the hole in the previous pics:


Enter JB Weld's Kwikweld Steel Reinforced Epoxy! Bought from ACE Hardware. It's fortunate that it cures in the same color as the plastic in my valk.


Here is the pic of the repair (compared to the unbroken hole on the right). I only used small beads of the epoxy mix to first cover up the hole using a paper clip tip and a toothpick. After letting it dry up a bit, I used the paper clip to make a new slightly smaller hole. It looks kind of messy, but this is the best I can work with using the material and tools that I have.


After letting the epoxy dry for a few more minutes, I re-assembled the shoulder joint and put in the screw, slowly tightening it so that it will make new threads in the epoxy. I didn't tighten it all the way in yet. I just want the screw to go in just enough so that the epoxy will cure around it. The instructions say that it will fully cure in 4 to 6 hours, so I'll know by then if my fix worked. I'll provide an update to show the completed repair by then.

The epoxy has a working time frame of six minutes. After that, it hardens considerably. It's important to slowly shape the epoxy while its drying. Too early and the epoxy will just stick to your shaping tool (in this case, a paper clip and toothpick). I also cut a bit of flat plastic to help shape the epoxy. Others may want to use a precision flat head screwdriver, but you have to lubricate it first with something so that the epoxy won't stick to it permanently and ruin the tool.

I've studied the shoulder mechanism on my valk and observed that the reason why the screw loosened up is because the metal joint that allows for vertical movement of the arm is too tight. I tried to loosen it a bit so that it will not stress the screw hole too much.

I also thought about the engineering of this assembly and I honestly think that it could be improved. At first, I thought that the metal part was meant to rotate on the plastic during transformation. But it seems that it doesn't. It's really meant to be fixed in place while another joint of the shoulder does the rotating for the transformation. The problem as I mentioned, is that if the vertical joint is too tight, then it places quite a bit of stress onto the plastic hole where the metal part of the shoulder assembly is screwed in.

Anyway, thanks for the inputs guys! Hopefully, the repair will be a success. I'll know for certain in about six hours.