Topic: Gluing Plastic and fillers

[Monkfish81]

Hi All

I am starting my first ever boat build and have joined the forum for some advice.

I have done some RC aircraft modelling so am not a complete novice - although embarking on this project I am feeling more of one.....

Despite it not being the easiest model to start out on, its the one I will enjoy sailing and having on display in my study.

I have started out building the funnels and the first question I have is how do you get a seamless joins between pieces of plastic ? Using these funnels as an example, I have assembled them, filled any gaps with Filler (Revell Plastico) and sanded down, but you can still see the join lines and sanding marks.  I think they will still show even being primed and painted.  I have seen other modellers work on here, and there are no visible joins so what am I not doing right ?  Is it a case of adding more filler and sanding more ( I have various grit grades upto 1500) but I can still see sanding marks even when primed.  Is there a better technique for sanding or a better filler to use ?

Second question I have is that I bought a Dremmel for trimming the hull, but is the circular cutter the best attachment for the job, as on a small test area it has quite a thick cutting edge.  Would it be better to use a sanding tool and grind it down ?  Also what is the best way of getting nice rectangular holes in the Hull for the fairlead openings ?  Fibreglass by its very nature tends to split etc so how are you guys getting perfectly square and straight cuts in it ?

Look forward to any help / advice ..........

[colin]

Let's see if I might be able to help...

About the joints of plastic, my first question back at you, which plastic glue do you use, most of theses glues melt the plastic to form the joint, but the plastic although it has bonded does not harden until about 12-24 hours later..
Most of my joints on a corner have slight overhang on one side.. once the glue/plastic has sett, I file this back to the non producing side, with micro fine files, no sanding.. no filling..

As for the side of the Hull, I prefer to use a sanding disc/tool a round drum of sanding paper.. also normally found in a basic dremmel starter box..

As for the freeing ports.. I have numerous types of files, square, flat, half round, and round, in various grades..
A hole is drilled, or a multiple of holes, then opened out with the files..

Maybe this might help you..

[Monkfish81]

Thanks Colin
I have been using Rocket Max Cyano glue for the plastic - its quick setting (as in about 20 seconds)
From what you have mentioned I think I need to get myself a decent set of files....
Any recommendations for filler or are the all much or a muchness ?  I have bought some P38 car body filler for the bigger jobs on the Hull but for the smaller items would tubes of filler like the Revell Plasto filler suffice ?

[colin]

Any fillers can be used, the car body repair ones, are okay for the hull and an thing to do with the hull..

But for filling in gaps on plastic then you would be better of with plasto or the Humbrol equivalent.. as they melt into the plastic..

I would never ever use cyno glue for glueing plastic.. any sort of plastic weld.. the one from revel works fine.. or Humbrol or UHU ..

Have a read...
http://www.deansmarine.co.uk/index.php?topic=152

[Monkfish81]

I will change glue for a stronger / better bond...

I'm still curious how you get such a seamless join though from just gluing the plastic together and then fine sanding with a file.  The edges of the plastic pieces (however carefully cut out) will never be an exact match and there will be small gaps.  What do you do in these instances  - use filler and the fine file again or something else ?

Its really useful to know all this as I want the get as good a finish as possible ......

[colin]

Because of the glue I use, and the capillary action that occurs when pressing the parts together...
You see the plastic melting, which fills in any gaps that might of occurred while cutting the part out or preparing it for gluing..
Once dryed and harden,  you are not just filing glue, but melted and moulded plastic..
The slight overhang of the parts before filing can definitely be seen In my builds..
Have a look at this photo..
http://www.deansmarine.co.uk/index.php?topic=66.msg131#msg131

Why not try this method on some spare plastic..

[Monkfish81]

Thanks again Colin - I will indeed. Very interested to try this approach and I’m sure the end result will be better. Glad I asked the question before starting on any of the other plastic superstructure etc