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Sandpaper grits

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  • Member since
    January 2021
  • From: Somewhere near Chicago
Sandpaper grits
Posted by Teenage Modeler on Tuesday, May 11, 2021 7:29 PM

I was recently shopping at Menards, and saw 400 grit sandpaper. I saw that it was super fine.

The thing that got me wondering was, how come 400 grit is super fine and for polishing, whilst in scale models, it is considered gritty, and not used for polishing?

 

We use around 4000 grit sandpaper to polish the topcoat of car models, to make it shiny. If we were to use 400 grit instead, then it would make deep scratches. How come 400 grit sanpaper is labeled as super fine, whereas if you use it in car models, it would scratch it?

No signature needed, just my head!

 

 

  • Member since
    May 2004
  • From: Land of Lakes
Posted by cbaltrin on Tuesday, May 11, 2021 8:46 PM

I would not get hung up on advertising labels. 400 grit may be indeed super fine for wood-working... Just bug the grits you need. 

On the Bench:

  • Airfix 1/72 Fw-190D (1976)
  • Hasegawa 1/72 Skyraider 
  • Monogram 1/72 F-4J
  • Monogram F-14A
  • Monogram P-51D
  • Revel 1/72 HH-3 Jolly Green Giant
  • Monogram P-47D Done!
  • Italeri F-100D 1/72  Done!
  • Member since
    November 2009
  • From: Twin Cities of Minnesota
Posted by Don Stauffer on Wednesday, May 12, 2021 7:41 AM

When painting 1:1 cars when you go below 600 you go to rubbing compound rather than sand paper.  Names are not consistant even between brands so ignore it and go by number, which has a technical specification.

I bought an assortment of grits down to 10,000.  Old habit, I guess- I don't use anything below 1000- I go to polishing compounds.

Don Stauffer in Minnesota

  • Member since
    April 2020
Posted by Eaglecash867 on Wednesday, May 12, 2021 8:10 AM

Its just about the difference in materials and the finish you're trying to achieve.  With wood, you're not really looking to "polish" anything to a high sheen like you are on a car model...you're just wanting to get it so its smooth to the touch.

I have built car models on rare occasions, but I'm mostly about building things that fly, which usually don't require the high polish that cars do.  But, I still have full sets of MicroMesh paper, pads, and boards that range in grits from 1500 to 12000.  I use those as part of my routine for polishing canopies, but I also find them great for eliminating seams between parts.  Going all the way up to 12000 grit puts a mirror-like finish on the bare plastic, which makes it really easy to spot any tiny gaps that may need a little extra attention before putting primer and paint on the model.  All you have to do is shine a bright light at just the right angle across the joint and the mirror finish will make any low spots immediately visible.  But, the polishing many times completely eliminates the need for any kind of filler because it completely eliminates gaps in most cases.

"You can have my illegal fireworks when you pry them from my cold, dead fingers...which are...over there somewhere."

  • Member since
    October 2010
Posted by hypertex on Thursday, May 13, 2021 4:50 PM

There are several grit specifications, and most manufacturers don't tell you which one they use. I have those testors sanding films, and the finest is 6oo grit. But it is way finer than 3M 600 grit. Go figure. Micromesh uses a different spec, too.

Here are a couple of conversion charts I find informative.

https://www.fine-tools.com/G10019.html

 

https://www.sisweb.com/micromesh/conversion.htm

  • Member since
    August 2007
  • From: back country of SO-CAL, at the birth place of Naval Aviation
Posted by DUSTER on Saturday, May 15, 2021 11:35 PM

OK, I think I grit it now Propeller

Steve

Building the perfect model---just not quite yet  Confused

  • Member since
    October 2019
  • From: New Braunfels, Texas
Posted by Tanker-Builder on Sunday, May 16, 2021 7:56 AM

Hi;

     It's been my expeerience.That 600 grit (Wet-or-Dry ) is okay for models when you are doing Pre-Primer work. Afterards you want to use the grits recommended by other modelers. 600 that I use is fine for a real auto. It's just bout equal to 320 on a model.

      Besides in most cases you don't dry sand a model anyway. If you do the dust from the primer will get in every inaccessable place it can hide. Then watch out when you think you have a clean body. Tooth-Brushes and such don't get it all! 

  • Member since
    July 2019
  • From: Vancouver, British Columbia
Posted by Bobstamp on Sunday, May 16, 2021 10:53 AM

Perhaps my biggest foible in model building is overzealous filing/sanding. More than once I've badly scratched models through vigorous effort with sandpaper or files that seemed right for the job but turned out to be too coarse. This thread provides the best advice I've read. But I don't understand Eaglecash867's comment that said, "...polishing many times completely eliminates the need for any kind of filler because it completely eliminates gaps in most cases."

How does that work? Gaps must be filled, but how does polishing fill them? I assume, perhaps incorrectly, that sanding even with extremely fine sandpaper or polishing compound would inevitably produce dust or"glop" (wet dust) which wouldn't tend to stick in gaps.

Bob

On the bench: 1/500 Revell S.S. Hope, being built as the hospital ship U.S.S. Repose; Academy 1/72 F-86F Sabre, and a diorama to illustrate the crash of a Beech T-34B Mentor which I survived in 1962 (I'm using Minicraft's 1/48 model of the Mentor). 

  • Member since
    April 2020
Posted by Eaglecash867 on Sunday, May 16, 2021 12:10 PM

Bobstamp
But I don't understand Eaglecash867's comment that said, "...polishing many times completely eliminates the need for any kind of filler because it completely eliminates gaps in most cases." How does that work? Gaps must be filled, but how does polishing fill them? I assume, perhaps incorrectly, that sanding even with extremely fine sandpaper or polishing compound would inevitably produce dust or"glop" (wet dust) which wouldn't tend to stick in gaps.

Sorry Bob.  My post assumes that the two parts have been joined together the way that I join them together.  I work an inch or two at a time, tapping Tamiya Extra Thin cement to the joint, holding it open with just a tiny gap between the parts for about 20 seconds, then pressing it together to form a fairly even bead of melted plastic along the seam...checking/adjusting alignment of panel lines, etc. while the plastic is still soft.  After waiting at least 24 hours after the last section of a joint is completed, I carefully remove most of that bead of plastic with a #11 blade, and then the sanding and polishing begins (usually done under running water when the situation allows).  At the end of that process, fillers usually aren't even necessary as the two halves of plastic are completely welded together.  When I do have an occasional gap or depression that needs to be filled, I just use Gorilla Super Glue with the blue cap.  I dab a tiny amount of that into the gap or depression (which is easy to see in the right light after the plastic is polished with the 12000 MicroMesh), let that cure for at least 24 hours, scribble on and around the cured super glue with a black Sharpie, and then carefully wet sand/polish just that area until just after all of the black Sharpie is gone from the model.  Quick check under bright light to make sure the gap is gone (which it is about 95% of the time), then primer and paint.  I realize it sounds like a long, complicated process, but it beats the hell out of the old fill, sand, repeat process we are all too familiar with and eliminates all of the green dust all over the place.

"You can have my illegal fireworks when you pry them from my cold, dead fingers...which are...over there somewhere."

  • Member since
    July 2019
  • From: Vancouver, British Columbia
Posted by Bobstamp on Sunday, May 16, 2021 12:43 PM

@Eaglecash867: Thank you for that excellent explanation, which not only answered my question but showed me a better way to join parts with super-thin styrene cement. I've always had trouble joining larger parts because the glue often evaporates before I'm able to bring the two parts into contact. That's especially problematic with aircraft fuselages and wings, and even with small-scale ships' hulls and decks.

Bob

On the bench: 1/500 Revell S.S. Hope, being built as the hospital ship U.S.S. Repose; Academy 1/72 F-86F Sabre, and a diorama to illustrate the crash of a Beech T-34B Mentor which I survived in 1962 (I'm using Minicraft's 1/48 model of the Mentor). 

  • Member since
    April 2020
Posted by Eaglecash867 on Sunday, May 16, 2021 1:10 PM

No problem, Bob.  The gap between the parts when you apply the cement is usually going to be about the width of the thickness of a sheet of paper.  It keeps the cement from evaporating too quickly and gives it time to do its job.  Much more effective than having the parts firmly together when the cement is applied.  That method doesn't get enough cement into the joint to completely fuse the plastic together.  You'll also find that even poorly fitting fuselage halves will come together with no gaps because doing things in small sections slowly builds structural support for the subsequent sections and allows you to carefully twist and flex things into shape.  I don't even use clamps most of the time.

I primarily build planes and helicopters, and putting fuselage halves and wing halves together used to be the bain of my existence.  I HATED that part and always struggled to get a good result.  I'd finally get everything filled, primed, and painted (and the seams still showed in the right light), drop the model or not set it down gently enough, and the place where it wasn't quite glued together would make a cracking sound and I'd end up with a giant crack in everything.  Ever since I learned this method of cementing things from a YouTube channel based in Singapore called "Sprue Cutters", I no longer dread putting the fuselage and wings together.

"You can have my illegal fireworks when you pry them from my cold, dead fingers...which are...over there somewhere."

  • Member since
    November 2005
  • From: Formerly Bryan, now Arlington, Texas
Posted by CapnMac82 on Sunday, May 16, 2021 5:25 PM

In all fairness to OP, it's good to remember that for sanding wood, "coarse grit" is down to 80 or so.  And they make floor sanding grits of 40 & 60.

Most of te bowl turners stop around 800 grit, as it's hard to see much change with 1000 grit wen used on wood.

Tose polising metal, like knife makers, will often hand sand to 1000 grit--if more often in a carborundum grit than an aluminum one.  Tey move to paste abrasives after that, typically.

We in plastic have been blessed with a selection of clear acrylic polishing compounds that can run up into the 3200 range which can give optically pure clear finishes.

I remember when the marvel of the hobby was coating clear parts with Future.

  • Member since
    July 2019
  • From: Vancouver, British Columbia
Posted by Bobstamp on Sunday, May 16, 2021 7:08 PM

Would Tamiya Limonene Cement Extra Thin cement qualify as a one that works by capillary action? I have that on hand, while "extra thin" cements are out of stock, at least from the company that I usually buy from.

Bob

On the bench: 1/500 Revell S.S. Hope, being built as the hospital ship U.S.S. Repose; Academy 1/72 F-86F Sabre, and a diorama to illustrate the crash of a Beech T-34B Mentor which I survived in 1962 (I'm using Minicraft's 1/48 model of the Mentor). 

  • Member since
    April 2020
Posted by Eaglecash867 on Sunday, May 16, 2021 7:14 PM

Bobstamp

Would Tamiya Limonene Cement Extra Thin cement qualify as a one that works by capillary action? I have that on hand, while "extra thin" cements are out of stock, at least from the company that I usually buy from.

Bob

 

Not sure if that would work the same way.  Sprue Brothers has the regular Tamiya Extra Thin in stock though.

"You can have my illegal fireworks when you pry them from my cold, dead fingers...which are...over there somewhere."

  • Member since
    July 2019
  • From: Vancouver, British Columbia
Posted by Bobstamp on Sunday, May 16, 2021 7:50 PM

The only difference between Tamiya Limonene Extra-thin cement and Tamiya Extra Thin seems to be the "Lemon" additive.

Bob

On the bench: 1/500 Revell S.S. Hope, being built as the hospital ship U.S.S. Repose; Academy 1/72 F-86F Sabre, and a diorama to illustrate the crash of a Beech T-34B Mentor which I survived in 1962 (I'm using Minicraft's 1/48 model of the Mentor). 

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