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07-26-2011, 08:30 AM   #31
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QuoteOriginally posted by Ex Finn. Quote
This is pretty good stuff for fixing things.
J-B Weld Company - J-B WELD Product Information
In my opinion. JB Weld should be outlawed. It works just o.k. for a while, but is has a very bad tendancy to crack apart as well as lose bond with whatever you have used it to fix.

08-04-2011, 08:04 AM   #32
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This should be an easy repair - I would consider these as options:

- Put JB weld into the stripped holes, with a wire or nail thinner than the original screws in the hole. Remove the wire before JB weld dries (1-2h), reassemble in 24h

(or)

- Redrill the affected holes on the metal mount and use larger (although just as long) screws salvaged from some other broken device. Use JB weld or Lock-Tite on the affected threads for extra holding

(or, if hopeless)

- Use JB weld to glue the mount ring to the camera. There is a bit of dead space behind the mount so you may have to manufacture a spacer. Make sure JB weld is only applied in spots where it will not interfere mechanically or electrically (i.e. away from leavers and contacts). Leave camera with the mount facing down during the curing of the glue.

(or, if totally desperate)

- I will happily purchase it from you - I always need a backup body

QuoteOriginally posted by rhodeswv Quote
Hi Everyone,

I wish I were posting regarding a slightly happier subject...I recently dropped my K-7 from about 3-4 feet onto pavement. The camera seemed pretty messed up at first. The body mount ring was hanging cockeyed off the camera body so that the autofocus drive and most of the other contacts to/from the lens were disconnected (namely the aperture contact). But I found that after pushing the body mount ring back into position, the autofocus drive re-engaged as did the aperture contact.

The problem is that 3 of the 5 mount ring screws stripped the plastic piece the mount ring attaches to, so that the screws will not screw back in and clamp the mount down anymore (in the photo, they're the 3 bottom holes). Basically, I'm trying to find a way to remount the mount ring. I've considered using some sort of epoxy to adhere the mount ring back to this plastic piece, or even to fill the screw holes so that they can be re-tapped somehow.

I figure this kind of repair would take weeks and cost almost as much as a new camera if I sent it in. Mainly because I think most of the internals mount to that one plastic piece that would need replaced. That's why I'm trying to figure out a DIY fix. Otherwise, the camera still seems to work great, which is pretty impressive, really.

Does anyone have any ideas or suggestions at all on how to reattach the mount ring? I know it needs to be very level and accurately placed for the optics to still work accurately, not to mention the contacts. I'd be grateful for any help I can get. Thanks in advance.
08-04-2011, 08:08 AM   #33
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I have used JB weld on stripped 80psi oil fittings (on an automotive engine), brass/aluminum interface. This was 5 years ago ... I also glued an aluminum oil pan that had a hole from a rock (temporary measure, mind you) a few months ago ... still holding. Call me lucky

JB weld is nothing but an epoxy with a powdered filler - has this cracking been documented somewhere?

QuoteOriginally posted by cyclone3d Quote
In my opinion. JB Weld should be outlawed. It works just o.k. for a while, but is has a very bad tendancy to crack apart as well as lose bond with whatever you have used it to fix.
08-04-2011, 02:18 PM   #34
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QuoteOriginally posted by cyclone3d Quote
In my opinion. JB Weld should be outlawed. It works just o.k. for a while, but is has a very bad tendancy to crack apart as well as lose bond with whatever you have used it to fix.
I have used JB-weld from fixing AmericanDoll furniture to patching WR-284 wave-guide, pressurized with sulphur hexafluoride. My mileage is good so far.

Cheers. Mike.

08-04-2011, 07:48 PM   #35
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QuoteOriginally posted by Ex Finn. Quote
I have used JB-weld from fixing AmericanDoll furniture to patching WR-284 wave-guide, pressurized with sulphur hexafluoride. My mileage is good so far.

Cheers. Mike.
I have also used JB weld. Its good stuff. But there are some considerations here. One is the ring most likely needs to go on before the cover. See the flange and oring. I mean something has to seal that big hole where does the oring press against? The inner side of the front panel!

The mount is super critical for a good picture, that is no blur in one corner or another side. Its so sensitive it has a torque sequence like a car tire, one across and back...


As I have said I have used JB Weld and know it comes in quick setting and regular. Seen it for years. And as you can see by looking at that mount putting just a hair too much JB weld in one area will render the camer useless, more than likely, and be hard to take off (if need be) without making a bit of a mess with stuff dropping down into the mirror chamber and on the shutter. I just don't see it working out for such a critical alignment part. Its not there just to hold the lens. It must hold the lens perfectly flat, and it must hold large long lens which will put a lot of pressure on the flange. And it seals the lens mount area with an o-ring!!!

No movement can occur. Stainless Steel, Magnesium and Polycarbonate have close to the same thermal properties as far as expansion/contraction.

Now knowing the above look at what he has to work with using JB weld to try and perfectly glue (or however) the lens mounting plate back on without disturbing any moving parts and without hampering weather sealing in any way.

Would you want to use heavy kinda runny (I know it thickens) JBWeld on this -


All Pentax service manuals shows putting the ring on first then the front cover. There appears to be a step up flange around the ring where the oring is. This makes sense; how else is that big hole sealed?

Note the manual says nothing can be around or on the oring no dust no nothing. Can your imagine if the repair is just a hair higher at one corner? This will compromise the seal. Assuming the K-5 is put together the same (it sounds like its not from his problem of the floating pins). The front cover is going to be pressed down onto it forming the seal for the front lens area. Take a look at your weather-sealed Pentax dSLR. Note how tight it is in that area and how its almost seamless considering the back part of the flange is pressing against the cover and oring to form and weather seal.



Finally think if the lens plate with oring goes on first with the front cover pressing down onto it, this enhances its holding power from long lens a lot! Its being held down by screws and a flange!

I do note there is not a lot of material to work with on the bottom screw hole. But there has to be a way to do this without JB-Weld. Even though I like JB-Weld myself its just not for this job IMO...

I could be wrong?

Only way I would try JBWeld. -

1. Put JBweld into screw holes, smooth over flush.

2. Put on lens flange with what screw holes were still OK. than put on front K-5 metal cover and make sure it flush and flat over the lens flange.

3. Use white lens cap but cut off all material but for the part that goes into the mirror chamber and a tiny bit for a flange. You know count around so its still seals the mirror chamber but you can get to the screws.

4. Drill with appropriate size drill to use a tap and re-thread screws or just use self tapping screws or your choice and your done hope for the best. I would pull it back apart once I got the screw holes drilled just to make sure no material is in the camera.

Hope you get the idea. Put plate back on with good screw and bad holes filled. Put front cover back over, make a seal with white body cap, cut down so you can work on the screws and not get anything into the camera...

Last edited by jamesm007; 08-04-2011 at 08:35 PM.
08-10-2011, 09:35 PM   #36
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Hey everyone. Sorry I haven't been able to post for a while, but I have made some progress with the repair. Here's what I've done:

First, I ran some tests on adhesives. I found that the plastic chassis was most likely made of polycarbonate, so I wanted something that would work well on polycarbonate. But the other really important aspects were strength, workability, and rigidity.

Basically, I drilled some holes in a piece of wood and filled them with the different glues. Then, I tried drilling some holes just slightly smaller than the screws so I could see how well they'd hold.

The results:
1) Loctite plastic epoxy is too flexible, almost rubbery. Definitely not dimensionally stable enough.
2) JB Weld didn't provide quite enough strength when I tried to pull the screw out. Seems a little brittle. As a side note, the package says it works on SOME plastics. It works great for metal, wood, and all. But I've used it on plastic before, and it didn't really adhere.
3) ABS cement cured to a very strong, tough, and rigid consistency. The screws threaded in great, and couldn't be pulled out.

So, I went with the ABS cement, even though the mounts aren't ABS. Another big benefit is that I was able to dip the screws in the cement, then screw them straight into the body. The screws then come right out--they don't bond to the cement. So, the threads are formed perfectly in the glue before it cures.

Jamesm007, I looked into the helicoils, and I still think it's a great idea in general, but I found that the screws in the K-7 (and I suspect all other Pentax SLRs) are a strange variety. First off, they are not only metric but JIS (not technically phillips head). Second, they're actually a really coarse thread for their diameter of 2mm (something like 0.8mm pitch), no doubt to keep good purchase in the plastic. Finally, they aren't even circular in cross section! They're actually slightly triangular. I thought that was weird, but it's probably another feature for threading into the plastic better or to prevent them from vibrating out.

Anyway, I got the screws in with the cement to re-form the threads, and the lens mount ring is back on. There's still a slight electrical issue with the aperture control that causes the lens to lose contact if it's bumped upward (torqued up toward the flash), but is fine if it's not bumped. I've taken photos, and it appears that the IQ is just fine. No unevenly soft corners or anything.

My only issue now is that the lens mount ring is actually bent just slightly, so that there's a tiny gap at the bottom of the ring, maybe about 0.2mm. I think that's what's causing the problem with the aperture contact. Since it can be affected so predictably by bending the lens up or down, I think it's actually a mechanical problem related to the bent ring. Does anyone know how to get this as a replacement part? I'd love to replace it.

Also, Jamesm007 thanks for all the diagrams and tips. By the way, the o-ring isn't a big issue, because it seals against the side of the body, so it still seals whenever you take the lens ring off and put it back on. The body doesn't have to go on after the ring. And, it turns out, the contacts on my camera weren't broken. It seemed like they were moving a bunch, but they only had a little play, which I think it intended to aid in alignment when the ring is put back on.

Thanks again for all your advice, guys. I really do appreciate it. Just getting ideas flowing helps a ton. And thanks for the offer to buy the camera, vw_michael. I think I'll be holding on to it, but I'll keep you in mind in case that changes.

Thanks again. This forum is a great place!
08-11-2011, 05:07 AM   #37
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Isn't the ring you mention the same on all Pentax DSLRs? Or is there something different about weather sealing? Have you called Pentax parts? Could you get one from a non functional Pentax DSLR? I've seen in the past dead Pentax DSLRs for sale on ebay. You could buy a broken K10 or something and switch rings, then sell the broken K10 again.
Have you tried to fix it? New plate glass is usually pretty flat. You could use a piece of plate glass as a guide to judge flatness.
08-11-2011, 07:48 AM   #38
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Well, I've tried to fix it. Good thing is, it's actually pretty strong and doesn't take to bending very easily. But that makes it tough to fix. I think I made it a little better, but I won't ever be able to get it as flat as it should be.

I'm not sure if the ring is the same on all Pentax dSLRs. I'm sure they are mechanically, but as you say, the weather sealing may be different. Good idea about salvaging from a dead camera. I'll look into it. Also, I'm going to call Pentax parts today. Thanks.

08-11-2011, 06:27 PM   #39
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> I've taken photos, and it appears that the IQ is just fine. No unevenly soft corners or anything.

Congratulations! Its amazing you have no degradation in IQ. You must have done a superb job,really. Yea that oring kept throwing me off. In some pics it looks flush, in a couple it looked like there is a flange there. So when you said the contacts were floating around I figured it may be because of...

Glad you got back to us. Now we know how the ring goes on and how to repair if it happens to me or others. Your post and repair will help others for years to come

Thanks
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