What's the correct way to sand?

[Vifam7]

This sounds like a dumb question but - what's the correct way to sand away a seam line or sprue mark? I'm talking about the hand movement. ;;

Back and forth? Circular motion? One direction? While I'm pretty sure you're not supposed to go back & forth, I've read/seen tutorials using the circular motion and then others that say to go in one direction. And still others that say go in one direction at first then a different direction next.

Someone please enlighten me.

[DrunkenMaster2]

Me, I like to use a circular motion, only because it bends better, I found out that if you go back and forth you leave lines on the kit, so when you paint you can see it and the lines pop up like a sore thumb. If you paint after you use a circular motion you don't see anything.

This sounds like a dumb question but - what's the correct way to sand away a seam line or sprue mark? I'm talking about the hand movement. ;;

Back and forth? Circular motion? One direction? While I'm pretty sure you're not supposed to go back & forth, I've read/seen tutorials using the circular motion and then others that say to go in one direction. And still others that say go in one direction at first then a different direction next.

Someone please enlighten me.

[big F]

Circular works for me but sometimes you have to do straight because of position previous paint etc. That said I was using a needle file eairlier as this was the best for what I was doing.

[valkyriepilot]

wet sanding also works wonders for smooting down the surface. it also prevents the dust from flying around your work area.

as for direction, from my experience it's a case to case basis. back and forth works best with cylindrical or long parts for me (gunpod/rifle barrels, cannons) and big flat surfaces. circular works well for me for those smaller areas, since i find that using back and forth for these parts tend to eat away to much plastic from the edges, leaving the central portion thick and the edges sometimes a lot thinner.

as for sanding down sprue nubs, assuming you've been able to cut the gate pretty close (but not too close) to the surface, short back and forth strokes using rough grit (400 grade or so) sandpaper should start the sanding process. then work your way to the finer grades, 600 or 800 next, then circular with 1200 or so for finishing. keep the pressure confined to the area where the nub you are sanding down is, you don't want to sand away plastic from other adjacent areas.

for seamlines, the very first step should be alignment of parts that will be glued together. if you already misaligned the parts when you glued them together and there's no way to separate them short of damaging the parts, chances are you'd have to resort to putty or other fillers. otherwise sand down as you would a sprue nub. also to ensure that there would be no gap in the seams, you might wanna use an adhesive that melts down the plastic, so that it bonds both parts at the seam permanently. take great care using these kinds of adhesives, as there's no way to separate the parts again once they've bonded. if all goes well and the parts are aligned perfectly, you should have no need for fillers or putty and you just need to sand down the excess melted plastic that oozed out of the seam.

also, for curved areas or parts (like the valk's gunpod or the curved leg area), i use 3M sanding sponges. they use the same abrasive material as with sandpapers but this time they are applied on - you guessed it - sponge sheets. the sponge conforms to the curve of the piece you are sanding, so that there won't be any accidental flattening of a curved area, unlike if you use ordinary sandpapers or maybe files.

Edited January 8, 2009 by valkyriepilot

[big F]

also, for curved areas or parts (like the valk's gunpod or the curved leg area), i use 3M sanding sponges. they use the same abrasive material as with sandpapers but this time they are applied on - you guessed it - sponge sheets. the sponge conforms to the curve of the piece you are sanding, so that there won't be any accidental flattening of a curved area, unlike if you use ordinary sandpapers or maybe files.

These things are great and soooo cheap.

[valkyriepilot]

These things are great and soooo cheap.

i couldn't agree more a friend of mine who's into pla-modelling too (and very good at it hands down) managed to secure a very affordable source for our sanding sponges. Kotobukiya actually sells these sanding sponges too, but at a much higher price. so if you wanna get these cheap, try and contact your local 3M Distributor directly. oh yeah, here's some info from 3M's website: http://www.3m.com/Product/information/Sanding-Sponge.html

hope that helps

[big F]

3m are very approachable with this, i used to contract for them and they were able to order anything in the stock range mostly in bulk, I at the time wanted some Fluorinert to use in cooling my PC as its electrically inert and retailers were asking silly money for it. I was able to get up to a 50 Gal drum if I wanted.

The sanding pads IIRC come in retail boxes of 50 or less so would be ideal to get like that. If you have an actual 3M factory/office nearby get friendly with a staff member and they can get it for you via the staff purchase system.

[MechTech]

"Danielson, wax on- wax off." Seriously, I have a collection of sanding blocks. There's nothing better. My wife goes to beauty supply places every now and then. There's another great place to go (with your wife of course ). I think Sally Beauty supply is in both the UK and US. I just checked and they have a website too http://www.sallybeauty.com It should be under "Manicure" stuff. Just don't tell anyone your sanding block is pink! They're also a good source of acrylic for building stronger parts-stinks to high heaven though.

Hey, now my wife can order her stuff online and I don't have to wait around bored!

Most of mine are 3M. I went through several course ones building the Daedalus lower hulls. They just seem to smooth out better than anything else overall. Add water and your golden! - MT

[protostar8]

So using a 1000+ grade of sand paper should make it nice and shiny/smooth just like untouched plastic, right? I don't paint models very often and I really hate those little areas of "dull" plastic left after I use the exacto to clean the sprue mark.

[jardann]

Yeah, use the highest count (finest) sandpaper you can get. To get a nice polished look, you may want to try polishing the part with an old (almost worn out and very soft) t-shirt or similar undergarment type cloth.

[protostar8]

Yeah, use the highest count (finest) sandpaper you can get. To get a nice polished look, you may want to try polishing the part with an old (almost worn out and very soft) t-shirt or similar undergarment type cloth.

Cool, got plenty of old socks and cotton t-shirts that are just starting to get to the point where I'm gonna toss them. Might hold onto them for another month instead.

Thanks for the info too!

[protostar8]

Well, I bought some 2000grit sand paper at Autozone today. I'm less than thrilled at the moment. I tried it out on a blue gundam part (the bottom side of it that doesn't really show up once attached. All it did was scuff the hell out of it. It didn't leave it shiny or polished looking in any way. Maybe I'm doing it wrong?

Edit: Tried it on a grey part too, same result. Scuffs it and makes it dull. I am either doing it wrong or there is no way to get that nice shine back.

As I don't plan to paint the model, I hope I'm just doing it wrong.

Edit 2: When I buff, it doesn't really do anything. Should I be using something in conjunction with the soft cotton to act as an abrasive (like toothpaste or something)?

Edited February 4, 2009 by protostar8

[shiroikaze]

Maybe this will shed some light for you:

http://www.macrossworld.com/mwf/index.php?...=5881&st=20

It's WM Cheng's step-by-step on his VF-0S. He included steps for sanding down seams and polishing his canopy. I guess this can probably help...

Edited February 5, 2009 by shiroikaze

[Vifam7]

Well, I bought some 2000grit sand paper at Autozone today. I'm less than thrilled at the moment. I tried it out on a blue gundam part (the bottom side of it that doesn't really show up once attached. All it did was scuff the hell out of it. It didn't leave it shiny or polished looking in any way. Maybe I'm doing it wrong?

Edit: Tried it on a grey part too, same result. Scuffs it and makes it dull. I am either doing it wrong or there is no way to get that nice shine back.

As I don't plan to paint the model, I hope I'm just doing it wrong.

Edit 2: When I buff, it doesn't really do anything. Should I be using something in conjunction with the soft cotton to act as an abrasive (like toothpaste or something)?

What are you trying to sand? Sandpaper should generally be used to "sand down" something. The highest grit sandpaper being the last to use to bring it as smooth as possible. If you're looking to polish the plastic back to it's shiny self, something like Tamiya Polishing Compound is more for that purpose.

I wouldn't worry about light scuff marks and dull areas. Once you spray clear flat, those things get less obvious. (Yes, it's a cheat)

In fact if you're not painting and/or not going to spray clear flat, it might actually be better to lightly sand the whole model. That'll might make the model a bit less toy-like. Not recommended ofcourse if you like the bright colors.

Edited February 5, 2009 by Vifam7

[protostar8]

Maybe this will shed some light for you:

http://www.macrossworld.com/mwf/index.php?...=5881&st=20

It's WM Cheng's step-by-step on his VF-0S. He included steps for sanding down seams and polishing his canopy. I guess this can probably help...

Okay. I tried using some toothpaste then and saw how that works. I read a few places that suggested toothpaste as the abrasive. Polishing with cotton worked okay, but it had a little bit of scuffing left. After the toothpaste, it was better and pretty shiny. I guess the abrasive paste was the key.

I'll try starting with a much lower grade of sand paper first instead of just going from my exacto to 2000 grit. Even though I cut pretty much flush with the exacto, I get some odd scratch/scuff marks showing up with the 2000 grit, so maybe a lower grit sand paper first will help eliminate them? I guess it's really one big learning process, so I'll keep at it and post a follow-up IF I can perfect it and I'll note what I did.

Edit: Toothpaste seems to work for polishing. It made the parts all nice and shiny again. There are still those new scratch marks, but that may be because of my amateur sanding technique. I'm gonna build another model before Luca likely ships, so I'll gets lots more practice and try to see what works best.

However, I plan to clip the sprues with flush cutters (but I cut a little ways off so it doesn't mess up the plastic. I also plan to use an exacto to trim the remainder of the sprue off. I might try hitting it with some 440-ish grit sand paper first to see if it makes a difference over using 2000grit directly. I'm usually very good at cutting flush with the exacto though, so I'm not sure how the odd scratches are being made.

Edited February 5, 2009 by protostar8

[jardann]

I don't know, but it may be possible that the sandpaper you picked up at the auto store just isn't of good enough quality, or the grit is still of a different type and not gentle enough for your purpose.

Check out a hobby shop for some very fine wet-or-dry sandpaper. Testors sells a small pack that has an assortment of different colored sheets of different grit papers. It is a pretty common item, so even if you don't have a true model shop around, places like Hobby Lobby, Michaels or other craft stores or even WalMart usually has this little pack by the model kits.

Also, are you wet sanding? Wet the surface and the paper and keep it wet as you sand so that the sanding residue forms into a kind of slush of water and plastic particles. This will help keep your sandpaper clear and will greatly help with the final finish on the part. IF you don't have the wet-or-dry paper, you'll know pretty quick because the paper will turn soggy and the grit will start to flake right off.

I know this little detail wasn't explained much in this thread up until now. Sorry about that. Hope this helps.

Edited February 5, 2009 by jardann

[protostar8]

Just an update. I found that the wet sanding helped a lot. Also, buffing with toothpaste makes it nice and shiny again. Only issue now is that I still a little whiteness where the sprue is left. Any way to get rid of that white are where the sprue was? I really want my Luca to look great (and the Michael too), so I'm trying to get some practice in on another kit (another gundam kit in 1/144 scale).

Again, my technique is to use the flush cutters to cut close to where the sprue meets the part. Then trim the remainder with an exacto knife. After that, I hit it with a lower grade of sandpaper (I'd guess 200-ish), then wet it and hit it with the 2000 grit sand paper. Following that is wiping with a wet paper towel, buffing with toothpaste and cotton, and another wet paper towel wipedown to remove any toothpaste or missed plastic shavings. But on some parts that little white area where the sprue was persists???

Thanks for all the help and suggestions btw!

[shiroikaze]

...Autozone is still around?

[Mallet21]

Any way to get rid of that white are where the sprue was? I really want my Luca to look great (and the Michael too), so I'm trying to get some practice in on another kit (another gundam kit in 1/144 scale).

Paint ?

[protostar8]

Okay. Just a quick update. I've now built two Gundam kits using the following method:

Cut sprue with "flush cutters"

Trim remaining sprue with Exacto Knife

Sand with 600 grit WET (liberal amount of H2O) sandpaper in CIRCULAR motions

Wipe away water/plastic

Sand with 2000 grit WET (liberal amount of H2O) sandpaper in CIRCULAR motions

Wipe away

Buff with an old sock.

If it is still a little rough or not shiny, then I put some toothpaste on the part and rebuff

Usually they end up perfectly shiny with no real marks and look like the sprue was never there. However...

The exacto knife can sometimes leave nasty cut lines where I trim the sprue down, so be cautious when using one (I wasn't being super careful b/c I didn't really care too much about these kits and was using them just for practice). Another thing is the white area left by sprues from time to time...I have a hard time getting rid of them. I've tried several ways of getting rid of the sprue, but all end up with about equal results. Sanding them a little helps, but not always. Not really sure how to get rid of them without paint.

[MechTech]

The ONLY way to get rid of the white stress marks from sprue cutaway is heat. Which when applied will probably screw up your part. But heat will allow the plastic to contract to it's molded shape and return to normal color. If you have to sand the area and you are REAL CAREFUL, you can get a heat gun or blue section of a candle/lighter and move it close ever so slowly and carefully. Otherwise paint is a winner (and safer) every time. - MT

[Vifam7]

The exacto knife can sometimes leave nasty cut lines where I trim the sprue down, so be cautious when using one (I wasn't being super careful b/c I didn't really care too much about these kits and was using them just for practice). Another thing is the white area left by sprues from time to time...I have a hard time getting rid of them. I've tried several ways of getting rid of the sprue, but all end up with about equal results. Sanding them a little helps, but not always. Not really sure how to get rid of them without paint.

There are 3 other ways I deal with such marks -

1. If it's a dark area, I just dab at little bit of gray Gundam marker on it.

2. Dab some glue on the edges of the mark, wait a few seconds, then rub the area with a toothpick. Basically melting the plastic and rubbing some of the surrounding plastic onto the mark.

3. Melt a teeny tiny piece of plastic on top of it. Take a minute slice of plastic of same color from the sprue, dip it in Tamiya cement for a few minutes, then spread the gooey melting plastic on the white sprue mark. Wait for it to dry, then sand.

Not sure if the last 2 tricks are correct things to do, but it worked for me a few times.