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Sanding Seams


Lewis95
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Good Morning all, 

 

I am currently trying to rescue my Twin Otter build. I stalled when I couldn't get the top fuselage seam right. No matter how I go at it, it always seems to bulge. I'm currently going at it with Mr Dissolved Putty and a #1500 Flex-i-File. It seems better but I can still feel a definite ridge on the filler. Eliminating seems is not my strong suit at the best of times but I am really struggling with this one. Should I just got back to a really coarse grit (say 400?) and wipe out everything and start again? I'm also worried that I'm about to sand through the plastic altogether (A misstep that led to me binning a hobbyboss easy kit... yes, I got defeated by an easykit...). 

 

Any tips would be super helpful! 

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It might be worth checking to see if the seam itself has not split. Sometimes it is not always immediately apparent, but if the seam is not 'solid' then the filler will bulge. Is it a large gap you are trying to fill, as sometimes it is better to fill the gap with stripes of plastic (plastic strip, plastic card or stretched sprue. I have built a Twin Otter, but I cannot remember any issues with the fuselage, although there were a number of others. 

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24 minutes ago, Mr T said:

It might be worth checking to see if the seam itself has not split. Sometimes it is not always immediately apparent, but if the seam is not 'solid' then the filler will bulge. Is it a large gap you are trying to fill, as sometimes it is better to fill the gap with stripes of plastic (plastic strip, plastic card or stretched sprue. I have built a Twin Otter, but I cannot remember any issues with the fuselage, although there were a number of others. 

No issues with size or solidity. It's not a large gap, just a fuselage join that was noticeable under primer. It's now noticeably worse than when I started trying to sort it.

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Might be idea to use something a bit beefier as a filler. I am building a Mach2 Argosy, which has a few issues  with fit and I have used white Miliput to good effect. 

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11 minutes ago, Mr T said:

Might be idea to use something a bit beefier as a filler. I am building a Mach2 Argosy, which has a few issues  with fit and I have used white Miliput to good effect. 

I don't like using 2 part epoxies, never have for some reason. I did have some Humbrol but it dried out, hence the Mr DP. 

 

But it's the bulge that I'm struggling with. Whether it's Miliput or Humbrol or Nana's Toffee, I can't get rid of it without leaving tide marks (the edge of the filler) or oversanding and introducing the seam again.

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I rely on good quality Swiss-pattern needle files to eliminate bulges without causing collateral damage. For this use, I suggest an equalling file is for its rigid planar surface. Sanding paper will likely cause collateral damage around the filler. A sanding stick will tend to flex over the bulge or perhaps even be pushed into the seam. I'd start with a 4-cut file to knock the bulge down flush with the surface and then a 6-cut file for the final smooth finish.

 

Vallorbe (Grobet Vallorbe in the US) are excellent files. Not cheap but head and shoulders above the typical readily-available needle file set.

 

HTH

-- 

dnl

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2 hours ago, dnl42 said:

I rely on good quality Swiss-pattern needle files to eliminate bulges without causing collateral damage. For this use, I suggest an equalling file is for its rigid planar surface. Sanding paper will likely cause collateral damage around the filler. A sanding stick will tend to flex over the bulge or perhaps even be pushed into the seam. I'd start with a 4-cut file to knock the bulge down flush with the surface and then a 6-cut file for the final smooth finish.

 

Vallorbe (Grobet Vallorbe in the US) are excellent files. Not cheap but head and shoulders above the typical readily-available needle file set.

 

HTH

-- 

dnl

I have a cheapy Amazon set of needle files. They look like 1 swipe would go clean through the parts if I'm honest. 

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Mr DP is quite hard when it sets and if the surrounding plastic is softer you may be sanding that away before the Mr DP thus leaving a ridge.

Try a car glazing putty or Tamiya basic putty

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If the join is sound and the gap is small then something like Tamiya basic might work. It will produce a fin surface. I am a bit perplexed by the use of the term ridge or bulge. Are you saying that you are struggling to eliminate cleanly the excess filler over the seam? 

Like Alex, I think a photo would be helpful. 

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3 hours ago, colin said:

Mr DP is quite hard when it sets and if the surrounding plastic is softer you may be sanding that away before the Mr DP thus leaving a ridge.

Try a car glazing putty or Tamiya basic putty

Tamiya Basic Putty or the Tamiya Fine Putty? I need to order a tube and was going to order the fine. What's the difference between them if you don't mind me asking. The Mr DP was left overnight to go off and shrink back. All previous putties were either Humbrol or PPP on this one.

3 hours ago, Alex Gordon said:

Would there be any chance of a photo? That might help with properly understanding the snag.

There's a moderate chance of a photo...

1 hour ago, Mr T said:

If the join is sound and the gap is small then something like Tamiya basic might work. It will produce a fin surface. I am a bit perplexed by the use of the term ridge or bulge. Are you saying that you are struggling to eliminate cleanly the excess filler over the seam? 

Like Alex, I think a photo would be helpful. 

Sort of. The seam is pretty much eliminated at this point but I can't seem to get the filler to feather into the plastic. 

 

I'll try to nab a photo when it's not gone my bedtime haha!

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I use Green Stuff Green Putty.  I find it is very fine and best of all it's water based.  So you can thin it to milk consistency and apply it with a paint brush in layers.  You can even inject (into seams in the model...) with syringes you find on eBay.  As it's water based, you can just wipe off the excess with a moist cloth.  Sands very easily.  It might help with the feathering if it's diluted...

 

Can't buy it in Oz though, so just bought 8 tubes from the manufacturer...https://www.greenstuffworld.com/en/green-stuff/1220-green-putty.html

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This is where I would use gloop (sprue dissolved in Tamiya thin) - it forms a proper plastic weld and has the same finish and strength as the surrounding plastic making a consistent finish across the join easier.

 

I too would go with files for removing/shaping excess, moving to fine sandpaper only for the final finish

 

Cheers

 

Colin

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2 hours ago, ckw said:

This is where I would use gloop (sprue dissolved in Tamiya thin) - it forms a proper plastic weld and has the same finish and strength as the surrounding plastic making a consistent finish across the join easier.

 

 

Cheers

 

Colin

That's basically what Mr Dissolve putty is anyway

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4 hours ago, Flat Chat said:

I use Green Stuff Green Putty.  I find it is very fine and best of all it's water based.  So you can thin it to milk consistency and apply it with a paint brush in layers.  You can even inject (into seams in the model...) with syringes you find on eBay.  As it's water based, you can just wipe off the excess with a moist cloth.  Sands very easily.  It might help with the feathering if it's diluted...

 

Can't buy it in Oz though, so just bought 8 tubes from the manufacturer...https://www.greenstuffworld.com/en/green-stuff/1220-green-putty.html

The same stuff citadel used to sell? 

3 hours ago, ckw said:

This is where I would use gloop (sprue dissolved in Tamiya thin) - it forms a proper plastic weld and has the same finish and strength as the surrounding plastic making a consistent finish across the join easier.

 

I too would go with files for removing/shaping excess, moving to fine sandpaper only for the final finish

 

Cheers

 

Colin

When I've got dregs in my TET bottle, I plan on making some. 

 

 

But we digress, this thread is aiming more towards recommending different fillers and putties which is helpful but not quite what I was asking. I was more asking in regards to the techniques in the black art of seam elimination or I'll still have the same issues if I use sprue glue, Tamiya or car glazing putty at the moment. 

 

The tips regarding files are useful so I'll have a look into that but what about with sanding? I never seem to get the sanding part right except by fluke when I sand it up to a gloss finish.

 

 

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Just to add to some of the suggestions, have you tried using a flat sanding stick to get rid of the lump?  Sometimes flexible sanding sticks and especially the foam stick can make lumps linger, because they conform to the surface, sanding everything at the same time, so you keep the bump, it just ends up slightly less noticeable.  I've recently got some sanding tools from Galaxy Model, which are flat aluminium pieces (think float trowel) that you stick the self-adhesive sanding material to, and it will give you a perfectly flat finish.  I'm not advocating using them for the whole of the job, just to get the bump off.  Careful sanding of just the bump should minimise it, after which your flex-i-file should have a better chance of getting the job done.  Another tool that is also good for sanding curved surfaces is the Flex-i-file sanding "thing".  I can't think of the name, but think of a C-shaped aluminium tube with pins on each end.  You put special sanding bands over the pins, and there's enough flex in them to allow you to sand curves.  You still need to move it around a bit, but it's better than a flat stick.  You can get refills and different grades of band, which seem quite long-lasting.

 

Another filler that I often use is CA aka Super Glue.  As long as you sand it straight away, you can get a strong, flat seam that doesn't absorb paint, and is able to be scribed over without any shelling.  Not great for very soft plastic, and if you leave it overnight it will reach full strength, and be quite hard to sand after that.  more strings to your seam filling bow, one of them almost literally :)

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13 minutes ago, Mike said:

Just to add to some of the suggestions, have you tried using a flat sanding stick to get rid of the lump

Forgive me picking apart your lengthy reply haha 

 

The part regarding no flex sanding equipment.... Now that sounds like it could be useful. I'd need to DIY it with a bit of wood or rigid XPS (the solid supports they used to send with Wedi board when I worked in the tile industry) but that may work. 

 

Any recommendations for grits?

14 minutes ago, Mike said:

Super Glue.

 

Beyond wary of superglue. I can't even keep my tubes alive let alone use it properly lol

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1 hour ago, Lewis95 said:

Beyond wary of superglue. I can't even keep my tubes alive let alone use it properly lol

:lol: I buy 20g bottles, and leave them open on my desk. They'll last 6 months to a year before they go a bit thick, probably because the pin-hole in the nozzle is really small. :)

 

1 hour ago, Lewis95 said:

Any recommendations for grits?

 

If you're going to DIY it, you could make a few with different grades, then start with the coarsest going along the seam, step down and go across, step down again and go along the seam etc., alternating the direction of stroke so you get rid of all the scratches.  Finally, polish it off with a really fine grit, which I usually do with a nail buffer, as that will show up any lumps & bumps.  Another way of testing your work is by applying either metallic paint, or a gloss black, although you can generally see even with a grey primer.

 

Just so you know, sanding seams isn't as easy as it's made out.  I've said "So I filled the seams with CA and sanded them back" in the past, which sounds like a moment's work.  The reality is that it takes longer.  Sometimes quite a bit longer.  I once filled my seams with a brand of CA that isn't around any more (thankfully), got a nice clean seam, and a few days later that sucker shrank and left a trough.  I think I amended my review on that one, and eventually removed it from the site because it wasn't good, and other people were having similar problems.  I'm currently using a bottle of Everbuild medium viscosity, but some brands their medium is too gloopy, so it's suck it and see.  No discernable shrinkage on the Everbuild :yes:

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As someone who struggles with seams too, it's a bit rich of me weighing in, but just to add more random noise for you to filter through 😄, I agree going with soft foamy abrasives can just leave the lumps and take away the detail next to them. Certainly try not to use downward pressure, and try to sand in the same direction with light long strokes. But best to save for the final 'curving' of the surface that is already continuous, and use a more solid abrasive surface to get rid of the bump demarcations first.

 

If it's an issue of the filler standing proud, you could try (depending on how curved the surface is) scraping it down along the direction of the seam with a scalpel blade angled sideways and backwards a little and see if that works better for you. Just be careful not to take too much off.

 

Other alternatives are to remove the filler by dissolving it rather than abrading it, so water for something like perfect plastic putty, or MLT for something like mr surfacer 500 (which I like a lot for small seam line indentations which are hard to get thicker filler to go into).

 

I've never had much luck with glue putties. They make a permanent weld which I tend to find can be somewhat porous and require further remedial work, where surface putties can easily be wiped away to try again. But I'm sure that's down to my lack of expertise. 

 

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3 hours ago, Mike said:

I buy 20g bottles, and leave them open on my desk. They'll last 6 months to a year before they go a bit thick, probably because the pin-hole in the nozzle is really small. :)

Might have a look at those Everbuild ones then.

3 hours ago, Mike said:

few with different grades

Which grades? I think my "coarse" sanding stick is around 1500 grit. Should I be going to 800 maybe?

3 hours ago, Ngantek said:

you could try (depending on how curved the surface is)

The surface in this instance is actually dead flat aside from minor lippage. It's the top seam on a Twin Otter which is a boxy SOAB at the best of times 🤣

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28 minutes ago, Lewis95 said:

The surface in this instance is actually dead flat aside from minor lippage. It's the top seam on a Twin Otter which is a boxy SOAB at the best of times


A rigid flat sander would be ideal in this instance then :yes:

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1 hour ago, dromia said:

800 grit is my usual finishing grade.

 

180, 220, are coarse.

Whoa.... For plastic? 180 would shred wouldn't it?

1 hour ago, Mike said:

 


A rigid flat sander would be ideal in this instance then :yes:

Aye, at the moment I do seem to have a few tide marks but the bulginess seems to be gone. 

 

And yes, I know bulginess isn't a word haha

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24 minutes ago, Lewis95 said:

And yes, I know bulginess isn't a word haha

The important thing is we understand what you mean ;)

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