Allan Bennett Posted May 9, 2020 Share Posted May 9, 2020 I'm at the stage now where I've structurally completed a traditional balsa model, but am having my usual problem of how to achieve a perfectly smooth round fuselage. Some parts of it have been planked with long sheets spanning several formers, and others with separate sheets between each former. Anyway, my perenial problem at this stage is how to sand them down to a smooth finish. Whatever I do the glue lines, be it CA, white wood glue, or epoxy, always stand proud. My usual sequence is to sand (file?) them down with a flat Permagrit tool before then using finer sandpaper or sanding blocks to achieve a nice round finish. But invariably I can still feel ridges with my fingertips, so can anyone suggest a simple way to speed up my progress towards perfect roundness? Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted May 9, 2020 Share Posted May 9, 2020 Hi Allan, Obviously, your glue lines should be wiped off before they set. Easy to do with a damp small brush if it's water based or with acetone in the case of epoxy. This is a sanding method I pinched from Andy B. In fact you create yourself a sanding tool with a few layers of cardboard laminated together with a sanding paper at the bottom. Several pads with different grits glued on works best. Cover your fuse with some protective cling film, wet your cardboard bits & sandpaper for the bottom and laminate them together with PVA glue. Keep them taped to your fuse until dry. You just obtained a sanding tool with the curve of your fuse. Make yourself a few pads with different grits. I use some strips of sanding paper on top to give some 'grip' to my hand when sanding. Works a threat... Et voilà... Hope this helps... Cheers Chris Quote Link to comment Share on other sites More sharing options...
Trevor Posted May 9, 2020 Share Posted May 9, 2020 If the problem is caused by your glue lines being harder than the surrounding balsa, it helps to harden up the balsa before sanding. There are a number of ways to do this but I’ve just been introduced to Deluxe Materials’ Eze-Kote which does the job well, and doesn’t interfere with subsequent film covering. Trevor Quote Link to comment Share on other sites More sharing options...
Pete Collins Posted May 9, 2020 Share Posted May 9, 2020 Won't help with this build, but for future reference it might be worth trying Aliphatic Resin when planking. Sands better than most other glues. Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted May 9, 2020 Share Posted May 9, 2020 Posted by Pete Collins on 09/05/2020 12:11:51: Won't help with this build, but for future reference it might be worth trying Aliphatic Resin when planking. Sands better than most other glues. Aliphatic is made for the job Quote Link to comment Share on other sites More sharing options...
Former Member Posted May 9, 2020 Share Posted May 9, 2020 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
Allan Bennett Posted May 9, 2020 Author Share Posted May 9, 2020 Thanks for those quick replies. I'm not talking about blotches of dried glue that I should have wiped off when wet, but the actual glue that's between the planks is still a hard spot that I find makes finishing difficult. I've tried aliphatic in the past, and I don't recall it being any better than regular white glue in that respect. I might look at Gorilla white for the next build, though basically I find that any glue is harder than the balsa, so causes the ridges. Maybe hardening up the balsa with 'sanding sealer' will help. But won't that (or Eze-Kote) add weight, and will it be detrimental to the glassing that I propose to do? I like the idea of making curved sanding pads from cardboard, so I'll try it, thank you. Quote Link to comment Share on other sites More sharing options...
Steven S Posted May 9, 2020 Share Posted May 9, 2020 Eze -Kote is made for glassing https://www.youtube.com/watch?v=r_oZlHrdSpA Quote Link to comment Share on other sites More sharing options...
John Lee Posted May 9, 2020 Share Posted May 9, 2020 There are lots of different Gorilla glues but having run out of my favourite Titebond aliphatic during my current project I turned to 'Gorilla Wood Glue' which is white, but dries clear. I had some in stock which I picked up previously from Aldi. It is an excellent adhesive but dries rock hard and crystalline and I found it very hard to sand. Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted May 9, 2020 Share Posted May 9, 2020 As others have said, aliphatic has never given me ‘hard’ joins between sheets and sands really well. Most recently used on my Rascal refurb and you really can’t see the joins! Quote Link to comment Share on other sites More sharing options...
Mike T Posted May 10, 2020 Share Posted May 10, 2020 If you have any glue, even the thinnest line, anywhere near the surface, then you are knackered. Plank with 3/32 or 1/8 and when fixing, ensure only the bottom edges of the butting faces have glue on them - i.e. no glue anywhere near the surface. You can sand back aggressively when you've finished and any voids filled with lightweight filler. If you do end up with glue ridges, you can eliminate them with careful use of a hard sanding block and medium-ish paper (say 180 grit) or the finer side of a Permagrit bar, but don't try and work down to a finer finish with a finer paper, or you'll just end up back at square one as the finer paper won't touch the glue but will hollow out your balsa! As someone else has said - firm up the timber to get the surface to uniform hardness and proceed from there. Quote Link to comment Share on other sites More sharing options...
Allan Bennett Posted May 10, 2020 Author Share Posted May 10, 2020 Posted by Steven Shaw on 09/05/2020 14:17:02: Eze -Kote is made for glassing https://www.youtube.com/watch?v=r_oZlHrdSpA I see that Eze-Kote is in fact a resin, so maybe I could use my regular 2-part glassing resin as a wood hardener before sanding and glassing? I'll try that first on the nose section of my current build before it gets too much hanger-rash, prior to final finishing off with McG 6969's curved sanders, and then glassing. Mike T, ensuring no glue anywhere near the surface is, for me, easier said than done. If my planks/strips are a nice close fit then whatever glue I use will wick up, or be squeezed up, to the surface. How do you prevent that? The best I can do (and do do) is to wipe off the surplus immediately. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted May 11, 2020 Share Posted May 11, 2020 I can't say I've ever had a problem sanding planking fixed with aliphatic - I wonder how long it takes to harden completely - not just the surface? Perhaps leaving it a bit longer before sanding might help? Quote Link to comment Share on other sites More sharing options...
Craig Carr Posted May 11, 2020 Share Posted May 11, 2020 I’m same as you Martin. I primarily use Aliphatic and never have a problem sanding at all. but your right it must be allowed to dry thoroughly (I personally leave parts overnight - I’m in no hurry these days for some reason ) and Immediately wipe off any excess (I use baby wipes) that squeezes out. I planked this model that way and it sanded down like a good un Edited By Craig Carr on 11/05/2020 06:27:54 Quote Link to comment Share on other sites More sharing options...
FlyinBrian Posted May 11, 2020 Share Posted May 11, 2020 Balsa cement sands well! Quote Link to comment Share on other sites More sharing options...
Andy Stephenson Posted May 11, 2020 Share Posted May 11, 2020 I was thinking of going back to balsa cement as I have trouble with aliphatic showing as a distinct line after sanding. It always seems to set slightly rubbery which doesn't have the same sanding properties as the wood it holds together. A. Quote Link to comment Share on other sites More sharing options...
Allan Bennett Posted May 11, 2020 Author Share Posted May 11, 2020 Posted by Andy Stephenson on 11/05/2020 09:56:57: I was thinking of going back to balsa cement as I have trouble with aliphatic showing as a distinct line after sanding. It always seems to set slightly rubbery which doesn't have the same sanding properties as the wood it holds together. A. Your experience is the same as mine -- the fact is no glue that I've come across has the same properties as balsa wood. I haven't made a curved sander yet, but attacking the glue lines with a coarse sander, and then using a curved sander with finer paper, sounds like the optimum approach if one can't avoid having glue lines. Quote Link to comment Share on other sites More sharing options...
Mike T Posted May 13, 2020 Share Posted May 13, 2020 Posted by Allan Bennett on 10/05/2020 20:58:38: Mike T, ensuring no glue anywhere near the surface is, for me, easier said than done. If my planks/strips are a nice close fit then whatever glue I use will wick up, or be squeezed up, to the surface. How do you prevent that? The best I can do (and do do) is to wipe off the surplus immediately. The last time I planked, I ensured that the edge of each plank was a good fit to its neighbour, then glued it only to the underlying formers. However, I did it this way because I intended to glass cloth over the top, knowing the resin would join the planks as part of the process. If you are using thin (say 1/16" ) planks, then I agree it will be difficult to avoid the glue creeping up, but giving it your best shot should minimise the problem. Re aliphatics - I'm using Titebond which is relatively thick and while it is easy to wipe off obvious surpluses, still leaves a fine coating, hence my earlier comment. If you use the very thin Deluxe Materials stuff, then I agree it sands well, but I find that it tends to bead up on the surface when being applied and needs encouragement with a finger or brush to flow. I reiterate though, unless you are using very hard timber (which is unlikely if you are planking), then any suitable glue is going to be harder than it, so it's best kep from your top surface as much as possible. Edited By Mike T on 13/05/2020 14:32:24 Edited By Mike T on 13/05/2020 14:32:58 Quote Link to comment Share on other sites More sharing options...
Andy Stephenson Posted May 13, 2020 Share Posted May 13, 2020 I use Deluxe Materials Aliphatic and find that it isn't harder than balsa, it's just rubbery which has different sanding properties. What I am after is a glue that sets hard enough but is still sandable. A. Quote Link to comment Share on other sites More sharing options...
Trevor Posted May 13, 2020 Share Posted May 13, 2020 If you use aliphatic to join sheets of balsa edge to edge, and then sand them flat on the board, I bet you have no difficulty achieving a smooth glue line. In which case, could it be that the reason it’s not working for your planking is that you are expecting the glue to work as a filler? 😇 Quote Link to comment Share on other sites More sharing options...
Andy Stephenson Posted May 13, 2020 Share Posted May 13, 2020 It's not just planking or sheeting it's general glue joints of every description where I see a line through the covering whether they are tight or not. A. Quote Link to comment Share on other sites More sharing options...
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