filling holes?

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didjital
Posts: 21
Joined: Thu Jun 23, 2016 2:48 pm

filling holes?

#1 Post by didjital »

So this is probably a dumb question, but here goes:

I'm in the process of building 6 dr280s. In putting them together I've had a few parts that are warped with a twist. No problem, as I'm building jigs for stuff so far and I've been able to screw parts down to the jigs to flatten out as I assemble. So far so good....only problem is when I remove screws to take the assembly out I'm left with holes in the parts. I know the plans say to fill with pl, but I've already had some run ins with trying to sand pl with little success. I've seen where people have used bondo, but my question is whether or not that makes an airtight seal? I'm worried that my cabs will leak. Any suggestions?

While I have yer attention, I'd like to ask too about the pvc pipes in the back. I've been building rc planes since I was a kid and I've never been able to get hot glue to stick to pvc.... I've tried many times. My experience is that is seems to work, but can easily be pealed off cleanly in one big piece. What's the trick on that part of the dr280s? I'd hate for it to come loose since it's in such an inaccessible place. Is there another glue I could use? I was thinking pl, but was worried that the expanding might push it out of place. Any suggestions here?

Btw.... I'm documenting my build with pics and am planning to put up a build thread when I get a little further along.

CoronaOperator
Posts: 1648
Joined: Wed Mar 25, 2009 7:07 pm
Location: Medicine Hat, Alberta, Canada

Re: filling holes?

#2 Post by CoronaOperator »

If the holes are in a spot that won't be seen then there is no need to sand them. A random orbital with 50 or 120 grit can sand pl fairly easily. The trick with PL is to come back to the shop about 5 hours after gluing and then with a putty knife or a chisel to scrape or otherwise clean up the joint before it gets too hard to do so. Depending on your temp and humidity you might have to experiment with the time a bit. Once you get it down, the PL will be mostly set but still soft enough to scrape really easily.

With the pvc, sand the edges into a chamfer to make a trough for the hot melt to sit in.

Bondo is airtight but only use that where it will be visible and you want a nicer finish as the PL doesn't feather edge as nice as it is a little bit gummier. I use pl for the inside of the cab and Bondo for the visible areas.

See my build thread In my signature. I built dr250 ' s but the techniques are the same.
Built:
17" width 10" driver Autotuba
2 x 29" width dual Lab12 Tuba60
6 x DR250 2510/asd1001
In progress:
2 x DR250 2510/asd1001
For best results, point the loud end of the array towards the audience

didjital
Posts: 21
Joined: Thu Jun 23, 2016 2:48 pm

Re: filling holes?

#3 Post by didjital »

Thanks for the reply. I've been waiting about an hour on the pl here as it's very humid. I'm able to scrape away pretty easily. As far as holes, do you just squeeze it in and do the same thing? Wait a while and scrape it level?

As far as the hot glue on the pvc.... you haven't had any problems with adhesion? In my past experience it just peeled right off after it was cool...I mean it didn't FALL off, but it definitely wasn't a strong bond at all.

CoronaOperator
Posts: 1648
Joined: Wed Mar 25, 2009 7:07 pm
Location: Medicine Hat, Alberta, Canada

Re: filling holes?

#4 Post by CoronaOperator »

All of the glue joints are on rough cut edges and if you sand the edges at a 45 degree angle to make a chamfer you get more surface area for the hot melt as you now have a trough to fill. They are glued and locked in from all 4 sides so they don't have a chance to flex and break the glue joint. Try one out, you'll see as the troughs make a mechanical lock on it and it can't move.
Built:
17" width 10" driver Autotuba
2 x 29" width dual Lab12 Tuba60
6 x DR250 2510/asd1001
In progress:
2 x DR250 2510/asd1001
For best results, point the loud end of the array towards the audience

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Bill Fitzmaurice
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Joined: Tue May 02, 2006 5:59 pm

Re: filling holes?

#5 Post by Bill Fitzmaurice »

CoronaOperator wrote:If the holes are in a spot that won't be seen then there is no need to sand them. A random orbital with 50 or 120 grit can sand pl fairly easily.
I use 40 grit discs. With a DuraTex finish there's no need for anything finer.
if you sand the edges at a 45 degree angle to make a chamfer you get more surface area for the hot melt as you now have a trough to fill.
+1. It's in the plans. This also exposes pores in the PVC, giving the glue something to grab.

didjital
Posts: 21
Joined: Thu Jun 23, 2016 2:48 pm

Re: filling holes?

#6 Post by didjital »

yes, i did read the plans (several times in fact)- I was just still worried based on past experience with hot glue and pvc. Thanks for the quick responses guys!

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LelandCrooks
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Re: filling holes?

#7 Post by LelandCrooks »

Look for foamcore PVC. It glues well.
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