scratches in acrylic blanks

Signed-In Members Don't See This Ad
B

barrysj

Member
Joined
Oct 2, 2009
Messages
125
Location
woodbridge va
I'm having a hell of a time getting small scratches out of acrylic blanks. After shaping and a final sand with 600 grit sand paper, I move to micro mesh. After going through all the pads with water (about 30 seconds on the most course then about 20 seconds on subsequent finer grits) I have fine scratches in the final reveal. I then go back to the coursest grit I believe I need with out further scratching and then bring it down again. I'm making progress but it's taking me a long time to go through this process over and over. Should I just stay at the most course grit until almost all scratches are gone? Thanks for any help.
 
Signed-In Members Don't See This Ad
when I have scratches after the mm, I go over again. most of the time they come out after the second sanding. Be careful not to sand too hard.
 
are you sanding lengthwise with the lathe stopped after each grit to remove
the circular rings? and clean the blank with a clean towel between grits?
Stop and dry the blank between grits too, look for non-uniform scratches from the last, coarser grit. Then is the time to back up a grit or two, not at the end.:)
 
johnnycnc said:
are you sanding lengthwise with the lathe stopped after each grit to remove
the circular rings? and clean the blank with a clean towel between grits?
Stop and dry the blank between grits too, look for non-uniform scratches from the last, coarser grit. Then is the time to back up a grit or two, not at the end.:)
Click to expand...

I have been using Johns method above and "knock on wood" I have had great success. My latest turnings include black onyx (that typically shows all scratches & swirls). They look great using this method as well.

By the way John, I appreciate your FAST shipping on my order! I am now spoiled with my dead center and TBC....
 
O.k. I think I understand on the non-uniform scratches, took me a second to think it through, what about the uniform scratches? I swear I sat on the lathe for 10 minutes with the finest MM to get the small uniform scratches out and couldn't. Will plastic polish fill these scratches in or just tough it out for another 30 minutes on the lathe ? Side question...Should I use plastic polish prior to using BLO/CA finish anyway? Thanks for the quick help...I'm finishing a swirl burl blank and love how it came out so much...just want to go the last 10 yards and finish it.
 
I would not use plastic polish until after the CA is applied. You want the plastic polish to polish all the synthetic materials at once, and it might have a weird affect on the unfinished wood if you use it before the CA.

Add a little dish soap to your wet sanding water. Use a light touch and alot of back and forth motion. Use the SLOWEST setting on your lathe. clean the barrell frequently, spend a little more time with each grit, especially the early grits, stop the lathe and sand the length between grits, and use plastic polish and super soft lint free cloth. WAIT 5 MINUTES. Let the blank completely cool before you handle it.

All of these things together i think will cure your problems. Hope that helps.
 
On acrylics & PR, I do finishing cuts with a skew and wet sand 400g, 600g and 1200grit (wiping any residue after each grit). Next I polish with Novus #3 and Novus #2 and this seems to remove any scratches. The sanding/polishing process only takes a couple of minutes.

To wet sand: I dip the wet-or-dry sandpaper in a glass of water.
 
Thanks all! I'm going to slow the lathe down a bit, I think I was spinning too fast to allow the course grits to do their work...
 
Seems like every thread about removing scratches covers everything but the REAL problem itself, and that is NOT to put the scratches there to begin with! You can sit with 12,000 micro mesh all day and you are not going to remove scratches put there by 240 grit sandpaper!

I don't know about everyone else but when we finish turning a blank, especially an acrylic blank, is starting to sand with a handful of rocks really necessary. Why not try a simple test. The next time you finish turning a blank with a gouge or skew, have a close look at the blank BEFORE sanding. Then start with your usual grit then have another close look. If there are more scratches than before you started.... QUIT putting the scratches in!
 
I kinda disagree with that. I do agree that if you dont need 400 then dont use it, but the purpose of sanding by definition is to gradually make the scratches smaller. With that in mind, their has to be scratches to make smaller.

I can turn a blank to size, and scratch free without sanding at all. It is nowhere near as pretty as a well sanded piece of material. So to me, that rules out the scratch free hypothesis.

Not trying to be a butthead, just trying to help!
 
I think that sanding is to get an even surface and whatever grit you start with puts that grit scratches on the piece. So the next grit must remove (all )the scratches uniformly left before and the next grit must remove all scratches that one before left and so on and so on. Somewhere you are leaving scratches that the next step is not removing. What are your grits ? Example you would'nt skip from 320 to 600, the 600 would take to long to take out the 320 if if could.
NO --plastic polish will not fill ,it is a polish or liquid sand paper. good stuff
EEE also has polishing compounds in it.
 
Texatdurango said:
Seems like every thread about removing scratches covers everything but the REAL problem itself, and that is NOT to put the scratches there to begin with! You can sit with 12,000 micro mesh all day and you are not going to remove scratches put there by 240 grit sandpaper!

I don't know about everyone else but when we finish turning a blank, especially an acrylic blank, is starting to sand with a handful of rocks really necessary. Why not try a simple test. The next time you finish turning a blank with a gouge or skew, have a close look at the blank BEFORE sanding. Then start with your usual grit then have another close look. If there are more scratches than before you started.... QUIT putting the scratches in!
Click to expand...

I agree with George 100%.

In the past year I have revised my basic method to eliminate as much sanding as possible. I haven't used anything below 400 in a couple of years cause it puts in too much and deep scratches. In my opinion, if it takes 280 or 320 to bring it down, the deep scratches that those put in makes a case another few seconds with the skew or scraper.

Even when my CA finish builds up and I have a bad moment of ridges or waves, I don't go below 400 and often start with 600. Any ridges or waves - I get out with my scraper.

Can you turn anything good without sanding? Click here to see Brian's pens that were turned without sanding on the wood and segments. Click on the picts to increase the size to get a closer look.

And here for a pen that would not be possible if sanding were requited. (No sandpaper or MM touched that wood, only the scraper.) Some people have trouble getting the sanding dust from metal segments off of the wood and the best way is to turn it to size with a skew or scraper so that sanding is not needed. It can be done and has been done.

I am not suggesting to do away with sanding, only that starting with too course causes more problems that just have to be overcome.
 
Last edited:
I had a long talk with the master (Ed) and still have problems with scratches. I get bummed about it since I enjoy turning "plastics" more then wood but will not sell a pen with even tiny scratches in it. I am going to reread this entire thread and see if I can figure out what I am doing wrong.
 
If you're using acrylic, then go with the plastic polish. I usually apply the hut plastic polish 2 or 3 times and get a glassy smooth finish. If you still see very fine scratches, then do it again. This will also get metals super shiny if you're segmenting...
 
barrysj said:
After going through all the pads with water (about 30 seconds on the most course then about 20 seconds on subsequent finer grits) I have fine scratches in the final reveal. I then go back to the coursest grit I believe I need with out further scratching and then bring it down again. I'm making progress but it's taking me a long time to go through this process over and over. Should I just stay at the most course grit until almost all scratches are gone? Thanks for any help.
Click to expand...

When I had first started, I was producing OK (in my mind) finding there was a better way. If you do your first 3-4 grits for 30 seconds, and subsequent grits at 20 seconds, are you allowing those grits to do their job? And as stated, slow down. It's better and easier to spend a little time the first time than "go back to the coursest grit". Yes, we all seem to get in a hurry to see that fantastic blank.

Just my .02, YMMV
 
I will say this once again:

I doubt you are using acrylic. While some blanks are labeled with "acrylic" names, please try to be specific, as each kind has different challenges. If you do them all exactly the same, you will get different results.

GENERALLY: Sand to 600 or 1000 grit, then MM (all grits), then plastic polish should work. On softer resins, it may not be perfect.

Since there are people here selling those resins, I will let THEM address how to make it best. With OUR products, the above procedure should give you excellent results.

IF IT DOES NOT!!! Stop the lathe after each sanding and SEE what has happened. Do you have ONE pad of MM that has a defect? Is you plastic polish rag, actually still large pieces of wood, instead of cotton? Identify WHEN the scratches occur, THEN you can fix.
 
Ed is hitting on something VERY important ,yet mostly overlooked (IMHO)

There is often debris in the sandpaper, micromesh, polishing cloth etc. This debris
will scratch. Often, it is the next lowest grit that you just sanded with, since it may
be difficult to see how well you cleaned after sanding with each grit.

Sand with 400, move on to 600 and now your 600 grit paper is full of 400 grit dust.
The 400 grit dust will still leave a 400 grit scratch pattern even when you use 600.

Polishing cloths, buffing wheels .. these things love to collect dust. Is the dust really
sawdust or flaked off sanding grit? Is it wood shavings? Is it airborne particles of
acrylic or CA?

Using fresh sandpaper helps, but it won't eliminate scratching if you don't wipe down
the wood after each grit. Micromesh (especially wet) loves to hang onto grit.. and it
gets ground right back into your surface.
 
For the record, I had to sand off a CA gone bad finish on the blank. Went to the finest grit possible that still removed the CA. I've gotten the scratches down a bit finer but starting with the most course MM and going down, but still sanding with MM...two hours later...can't get the super fine scratches out. I know with wood, covering a scratched blank with ca finish gets you a shiny blank with scratches. With the acrylic, will the CA/BLO seal into the scratches and hide the fine scratches?
 
When I sand acrylics, I go from the skew right to 400 grit wet, then all the MM wet, then platic polish with small pieces of old receiving blankets. During the sanding I have a large tub of water beside the lathe that I continuously dip the sandpaper and MM in to remove build-up. Seems to work for me!
 
Sorry, this may sound harsh.

barrysj said:
For the record, I had to sand off a CA gone bad finish on the blank. Went to the finest grit possible that still removed the CA. I've gotten the scratches down a bit finer but starting with the most course MM and going down, but still sanding with MM...two hours later...can't get the super fine scratches out. I know with wood, covering a scratched blank with ca finish gets you a shiny blank with scratches. With the acrylic, will the CA/BLO seal into the scratches and hide the fine scratches?
Click to expand...

When you buy a car, do you run out and get CA to cover all the plastic surfaces? No, so we consider plastic pretty durable. WHY cover it with CA??? (Sorry Monty).

IF you are laminating wood and resin, it creates difficulties. But, if you are using a simple "plastic of some kind" blank, the CA should be put away after the tubes are inserted.
 
Sorry, my fault for not being totally clear....I'm finishing a worthless wood burl type blank that has alluminite in it. I got it clean and ready for a BLO/CA finish and proceeded to get a non-uniform finish ....tried using BLO then CA because CA alone for me only worked half the time (got the dreaded cloudiness). So I tried BLO first then CA. Finish came out a bit dull then got real non-uniform the further I went. So I sanded the blank down again. That's where the scratches came in. I finally got them all out ( I think there was some debris in my MM so cleaned it really well). Started all over with the BLO/CA and I'm back at square one with some shiny spots and some dull spots. I look forward to reading more replies on the "how repeatable is you finish" thread from Curtis et al. And I'm thick skinned....just looking for the truth....

Thanks again for all the replies.

Steve
 
Steve .. I think for worthless wood, you'd want to soak the wood in thin CA, not try
to finish it, but just soak it. Then sand to a uniform finish before applying your CA
finish. The CA soaking will firm up the wood so it is closer in consistency to the Alumilite.
The BLO will just get in the way and stop the CA from penetrating the wood.
Once you have that uniform coating, you can apply your CA as a finish on top of that.
The BLO might still get in the way, as the resin won't absorb any and the wood
might still take in some of it. That could give you inconsistent results.

At least this is how it's working in my head..
 
Using MM is a waste of time on any plastic finish.

Use a skew or scraper or whatever tool your comfotable with and get the blank level on the final cut. Then use 400 wet with the lathe around 1800 rpm. Stop the lathe and sand lengthwise until all the radial scratches are gone. All you should see is the scratches the length of the barrel. Now go to 600 wet and spin it at 1800 rpm until all the scratches are gone from the lengthwise sanding of the previous grit. When that is accomplished, stop the lathe and sand lengthwise again, just as with the previous grit.

Now, if you are not familiar with buffing, I suggest starting with the Tripoli. I always go straight to the White Rouge. You need to do a cut stroke around the radius, then a cut stroke and color stroke the length of the barrel. Do this with both the Tripoli and the WR using different wheels for each. This will give the best possible shine and final finish in the least amount of time to boot.

This is not all the specifics of the process, but it will get you started. There is quite a bit to buffing properly and would take me forever to explain it all. Just use a light touch (let the compound do the work, not the wheel) and avoid a catch, since if you find the the barrel, it will no longer be intact. It's much harder to remove those scratches.

If you have any specific questions, just pm me.
 
You must log in or register to reply here.
Back
Top Bottom