Sanding marks in acrylic

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chris99210

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Sep 4, 2008
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I'm having a hard time getting rid of sanding marks (micro scratches) in acrylics, especially dark colored acrylics. These are very fine circular scratches that can only be seen in just the right angle and light. I use a roughing gouge to round the blank and finish off with a skew. I usually have a good, smooth final surface and start dry sanding with 400 or 600 grit; I always sand lengthwise with the lathe off with those grits. I then use wet MM to 12000 and use a plastic polish. I don't sand lengthwise with the MM.

What am I doing wrong or not doing, and how do I get rid of those blasted circular scratches? :confused: To most people they aren't noticeable but I can see them. I've tried slow speed on the sanding (my lathe only slows to 500 RPM) and fast up to 2500 RPM with no difference. I always wipe the blank with a damp cloth between all sanding steps. I've tried spending a lot of time sanding lengthwise assuming that that was the problem, but I can't get an improvement. :befuddled:

Anybody have advice?

Thanks,
Chris
 
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Is the cloth 100% cotton?

What are applying the plastic polish with? After you apply the plastic polish, do you polish the barrel lengthwise before you wipe the polish off?

The annular marking is one reason I like to use a buffing wheel with plastic polish (white diamond?) on it for my final step. After that step I try to be careful about not touching it again with a paper towel, but use only cotton cloth for subsequent polishing and wiping.
 
If you are using a skew to final shape then throw away those 400 and 600 grit sandpaper. You should not need it. Start right with the micromesh. That is what I do. When using a 400 grit paper the scratch pattern is so deep it takes alot to get them out with the subsequent grits. Also when sanding do not sand in a straight pattern when the lathe is spinning. Constantly move the paper sideways quickly. Just like applying a finish. These are my methods that have been working for me.
 
More analysis would help.

WHEN do you see the scratches?? You stop to sand in the other direction, are the scratches there? Are you introducing them while polishing or not eliminating them from the beginning. EITHER is possible.

Stop and inspect at various stages. Then, tackle the problem, once it is accurately identified.

My most recent scratches came from a "nose-tissue" (Not Kleenex brand) that I was using to put on polish while demoing at shows. Took a while to figure it out.
 
You may have set your standards too high. Handling a highly polished plastic or finish is a a problem because our skin is rough enough to scratch the surface. Even if you could show the customer a perfect scratch-free surface, it would no longer be that way the first time they picked it up to look at it.

My opinion is, and it is just an opinion, that there are three causes for those late blooming sanding scratches that show up on both hard finishes and plastics.

The more you sand, the more you have to sand. They are there from an earlier and coarser grit, but they were so fine that you couldn't see them until after the surface was polished enough to make them visible.

Your MicroMesh has been contaminated with transient dust from the shop. 12,000 MM is a 1-micron particle size. Most shop dust is larger than that and it can leave a visible scratch. It can also happen to 400 and 600 grit sandpapers.

If you use a plastic polish, what you use with it is important. HUT says to use a cotton cloth, and there is good reason for that - cotton is less abrasive than paper and less likely to have dirt in it than paper. Old diaper flannel that has been washed many times makes the best polishing cloth. It is soft and definitely clean. I use Brasso to polish plastic materials (only) because it does a better job for me than any of the commercial plastic polishes.
 
Thanks for all the great suggestions guys...it gives me some areas to look at. A couple of more data points:

  • I can't see the scratches until after I get the final polish to a mirror finish. I'm not sure if they are there from sanding with 400 or 600 grit, but without the high gloss finish they don't show up.
  • I use Hut plastic polish with 100% cotton cloth (from the CSUSA 2 pound bag).
  • I've tried Novus polish with the Novus "paper" polishing cloth that they sell/recommend without any better results.
  • I bought a new set of MM for plastics but still had the scratches.
I'm going to skip the 400/600 grit dry sanding and go directly to wet sanding with MM and see what happens. I'll grab a magnifying glass to inspect for scratches at each step. I also have some Brasso and will try that instead of the commercial plastic polishes. Hopefully with all your ideas I can narrow down the timing of the introduction of the scratches and eliminate them at that step. If all else fails I'll just listen to my wife who says I'm being too picky. :wink:

Chris
 
I will join the fray; On acrylics, always use MM wet. Use MM with the lathe on, then use the MM lengthwise with the lathe off. Afterward, wipe the blank with a water soaked cotton rag. Wipe off the MM after each use and hand wash it occasionally.
After I started doing this my surface finish improved markedly.

Hope this helps...
 
Not all plastic polishes are equal. My last application is with mcguires "platix". I cant see any scratches on the dark acrylics. After using Mcguires and then going to Hut plastic polish I can see right away the loss of shine and minute scratches. I wet sand to 12000 and do a two step plastic polish which ends with Mcguires. My neighbor who is a retired tool and die maker gave me some diamond paste but I cant tell the difference from that and Mcguires.
Hope this helps.
 
This works for me.. I always wet sand plastics... I start with the lowest grit on the MM, then go through each grit. I have all of my MM pads (I use the little 2 x 2 pads from PSI - I'm assuming they are MM) in a cool whip tub that's about half full of water.... I set the tube directly under the blank, (I put a cloth under the tub to protect the ways). I run the lathe at whatever turning speed I'm working at.. usually about 1800 - 2000 rpms. I use the water in the tub to rinse the blank between each grit, then dry with a soft paper towel and polish with a plastic polish.
 
jttheclockman said:
If you are using a skew to final shape then throw away those 400 and 600 grit sandpaper. You should not need it. Start right with the micromesh. That is what I do. When using a 400 grit paper the scratch pattern is so deep it takes alot to get them out with the subsequent grits. Also when sanding do not sand in a straight pattern when the lathe is spinning. Constantly move the paper sideways quickly. Just like applying a finish. These are my methods that have been working for me.
Click to expand...
I have to say that I tried that out tonight, (I was a hold the paper still and s l o w l y move it across the blank person) and I got a 100 percent better finish. No scratches (especially around the ends). What was going to be just quick slimline kit reshaped like a (sorta) euro out of yellowwood came out so perfect that I'm going to order a black Ti kit for it.

Good tip, and it makes a lot of sense. I've also found that if I cut my lathe speed back down to it's lowest setting (around 650 or so) I get better results. I think it's because of the slower cutting action, and the back and forth becomes more effective at lower speeds.

Steve
My Problem... My Standards Exceed My Skills.
My Solution... Stop Wearing My Glasses.
 
try adding just a drop of dish soap to your water.....it tends to make it a slight more 'slippery' (old trick)
after i wet sand through the MM, both with the lathe runninng and then stopped and sanding lengthwise....i wipe it clean with a 't-shirt- rag from a box i bought at Lowe's
i have a t shirt rag for applying polish and another very clean one that i use when buffing afterwards....all on the lathe

imight ought to try some plastix
 
Beware of magnification. With enough magnification, even the smoothest and glossiest of finishes will look like a dirt road after a long hot summer.
 
RussFairfield said:
You may have set your standards too high. Handling a highly polished plastic or finish is a a problem because our skin is rough enough to scratch the surface. Even if you could show the customer a perfect scratch-free surface, it would no longer be that way the first time they picked it up to look at it.

My opinion is, and it is just an opinion, that there are three causes for those late blooming sanding scratches that show up on both hard finishes and plastics.

The more you sand, the more you have to sand. They are there from an earlier and coarser grit, but they were so fine that you couldn't see them until after the surface was polished enough to make them visible.

Your MicroMesh has been contaminated with transient dust from the shop. 12,000 MM is a 1-micron particle size. Most shop dust is larger than that and it can leave a visible scratch. It can also happen to 400 and 600 grit sandpapers.

If you use a plastic polish, what you use with it is important. HUT says to use a cotton cloth, and there is good reason for that - cotton is less abrasive than paper and less likely to have dirt in it than paper. Old diaper flannel that has been washed many times makes the best polishing cloth. It is soft and definitely clean. I use Brasso to polish plastic materials (only) because it does a better job for me than any of the commercial plastic polishes.
Click to expand...

Russ if I'm sanding to 800 grit and then using Hut's plastic polish will there be a "naked eye" difference if I sand through the same grit and use Brasso?
 
Are you guys using straight 'tap' water? Ever consider the hardness of the water? Depending on your location......lots of dissolved minerals! Try distilled water.........may help!


Barney
 
mick said:
Russ if I'm sanding to 800 grit and then using Hut's plastic polish will there be a "naked eye" difference if I sand through the same grit and use Brasso?
Click to expand...

There is a difference to me. But, I would suggest sanding to 1200 or 1500 instead of stopping at 800. The jump from 800 to the smaller grit in whatever polish you are using is a big one.
 
I would echo Randy's advice ("Always use MM wet. Use MM with the lathe on, then use the MM lengthwise with the lathe off. Afterward, wipe the blank with a water soaked cotton rag. Wipe off the MM after each use and hand wash it occasionally.").

I keep a tub of fresh water near the lathe and rinse each grit of MM before and after I use it on the acrylic. I used to use plastic polish as the last step, after the 12,000 MM, but noticed the same light scratches you described. I may not have had the best rag to apply the polish or the polish was too abrasive (despite being made for this purpose), but once I stopped using it, I was much happier with the final product. Having said that, darker acrylics ARE way less forgiving and the lightest scratches reveal themselves much faster (and sometimes only AFTER the pen is entirely assembled!).
 
I have tried expeimenting with different plastic polishes and have noticed some are more abrasive than others. Mcguires "PLASTIX" seems to polish one step past 12000 mm. That is where I stop.
 
I have been working with plastics for years now. I found that after wet sanding you use a buffing compound then polish there are no scratches. Crazy as it sounds I use a metal buffing compound and it works great. Wood Craft carries it. Its called ZAM.
 
This works!

CHICAGOHAND said:
I have tried expeimenting with different plastic polishes and have noticed some are more abrasive than others. Mcguires "PLASTIX" seems to polish one step past 12000 mm. That is where I stop.
Click to expand...
That's what I do, too -- no HUT, just Plast-X. You can go swimming in the finish, even on dark acrylics.
 
I read all the posting and i always had a difficult time finishing acrylic pens. I use the acrylic sanding kit from the WTC, I finally tried wet sanding it with the micromesh sanding kit. It turned out awesome, a mirror finish. I just wanted to say thanks for all the great postings, with out reading what everyone wrote my acrylic pens would still have a poor finish. =)

Thanks Guys!!
 
These are all great sounding ideas. I have one other suggestion: I spend a good deal of time (wet) sanding (with dish soap) using a 1500 MM strip from a sheet, not the pad. That usually knocks out all but the deepest hidden scratches. Then once I'm done with the Micromesh (1500-12,000), I hit the blank very aggressively with Novus Three heavy scratch remover. Three coats and lots of it. Take a little time, especially near the ends since that's where those scratches show up the most often-at least for me.
 
Sanding Marks in Acxrylic

After turning the acrylic blank, I sand to 800 grit, then micromesh to 12000 grit. I clkean the blank regularily between every 4 grit changes. Fianlly I apply Novus 3 for the removal of course scratches and Novus 2 for fine scratch removal. The first time I tried it, I thought I was seeing magic!!! It really is magical as you see the Shine that comes out of the blank after Novus 3. It gets even better with the Novus 2.

I buy mine at a local video game dealer. They use it to remove scratches from pinball gam,es and video games before they go back out into the market. I normally pay 8.00 for a huge bottle that lasts a year or more.

Dan Heine
 
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