Acrylic Acetate...Major Problems...help

[Herb G]

I turned only my second AA pen today, only to find out it is full of small cracks & crevices when I got it sanded down.
I turned it as close as I could to the bushings, then sanded it the rest of the way. The blank is now pretty much translucent, and it is full of cracks going in the direction of turning.
It almost looks like it sat in the hot Sun too long. Could it be stress cracks, or the blank got too hot, or what exactly?

If I could take a decent pic, I would.
Thanks for any help or a place to start looking for the problem.

 

[MikeinSC]

If it's running in the same direction that you were turning, it's likely to be sanding marks. Especially if you used a coarse grit paper such as 80,120,220.
What grit sandpaper did you use?

 

[magpens]

Most likely sanding marks, as Mike said. . I really doubt the AA would crack without you experiencing a blow out during turning.

I would suggest that you try sanding lengthwise with the lathe off and turning the spindle by hand a little bit at a time as you sand. . I would use 180 grit for this.

 

[MikeinSC]

I would start at a higher grit than 180. I would think that too much material could be removed too quickly and still have a good chance at having deep cuts.

 

[magpens]

You are probably right, Mike .... 220/240 might be a better starting grit.

 

[Herb G]

If it's running in the same direction that you were turning, it's likely to be sanding marks. Especially if you used a coarse grit paper such as 80,120,220.
What grit sandpaper did you use?

I used 80 grit at first, then moved up to 600. I did not sand inline with the blank between grits though.

Most likely sanding marks, as Mike said. . I really doubt the AA would crack without you experiencing a blow out during turning.

I would suggest that you try sanding lengthwise with the lathe off and turning the spindle by hand a little bit at a time as you sand. . I would use 180 grit for this.

Yeah, I forgot this step. Still getting back in the hang of turning again.
The mind ain't what it used to be. I will give it a try & see what happens.

Thanks for the help guys.

 

[Herb G]

You are probably right, Mike .... 220/240 might be a better starting grit.

Well, I used 320 grit inline with the blank, & I got the scratches out.
The blank has major flaws in it from when they made it though.
There are fine imperfections in it from when it was poured that show up big time when it's buffed out to a shine.
I won't be using this blank for anything, but it's a reminder that no plastic blank is perfect.
Thanks again for the help.

 

[MikeinSC]

Are you able to get any pictures of it?
When I started turning, I hated acrylic blanks. Now, I make a living with it. I used to think the stuff had lots of issues too but I learned it was myself. Granted, I have come across some that have problems built in but that is very uncommon.

 

[gtriever]

Herb, I've found that that the quality of the sandpaper makes a huge difference. When I first started I was using the "turners packs" that everybody sells. After switching over to 3M, I discovered that I could start at a higher grit and get much better results. Now I start with 150-180 if I need to remove a lot of material, or 320 if I don't.

I don't do any inline sanding until I get to 400, and usually that's the only time. After 400, a light sanding from 600 - 1000, 1500, and 2000 gives me a silky smooth finish. Micromesh after that only if you think it needs it for the look you're going for.

I highly recommend 3M. This is one time not to be "thrifty".

 

[Woodchipper]

Food for thought, gtriever.

 

[magpens]

Yes, "sandpaper" quality matters. . I never use what woodworkers use. . Always what autobody guys use, which is not much more expensive either, and it is much more consistent in quality.

I have never had any manufacturer's problems with Acrylic Acetate blanks (AA) of the manner that you describe. . I have been using them for 8 years. . You do have to bear in mind that they don't like heat, so you have to drill slowly and back out often. . I use carbide cutting tools, also at relatively low speeds of around 800 - 1000 RPM, unless I am making extremely light cuts, in which case I will up the speed to 1500.

 

[Bernski69]

I had issues like this before until I bought a sand kit with all of the grits at Lee valley. I start out low grit and go to 8000 grit or even more. I use polish to get that shine in. It's not perfect under a microscope but looks ok .


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[gtriever]

Yes, "sandpaper" quality matters. . I never use what woodworkers use. . Always what autobody guys use, which is not much more expensive either, and it is much more consistent in quality...

Yep, I get my 3M paper from the Auto Body guys as well. My local store also has a very good selection of Mirka (Abranet) products.

 

[More4dan]

I've always sanded length wise every other grit. I start with 120 only if there are grooves from turning. If not, 220 then 320 then 500. Then micromesh 1500-10000 also alternating directions between every grit. Final polish on my buffer with pink rouge. Each higher grit has to remove all the previous grit scratches, very hard to do without changing directions as you sand. Learned this in polishing out knife blades and handles.


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[randyrls]

One other technique that helps eliminate splitting out the end of the blank:
1. Cut the blank longer than needed.
2. Drill the blank from the center outward just to the length of the tube.
3. Trim off the outside un-drilled end to length + 1/16" (1mm)

 

[Beautys_Beast]

Okay, maybe I am doing something wrong... Why are people sanding with such low grits? I understand using lower grits on wood, but not on acrylic.

I VERY seldomly sand acrylic dry. I NEVER sand acrylic blanks, with any grit lower than 600, and if I do, I use 3m 600 wet, that I have adhered to an old micro mesh pad. I just don't see the need to sand it more than that. The skew leaves the blank perfectly smooth. More often than not, after turning, I go right to the first sanding pad, at 1500 grit.

I no longer use purchased micro mesh pads, but instead buy quality cloth backed waterproof sand paper and adhere it to old pads with fabric glue. They come in packs from 1500 to 7000. I purchase 12k cloth backed micro mesh sand paper separate, and do the same thing. They last as long as the pads you can buy, and for what it cost to buy a set of 2 pads, I can make about 20 sets. I use a sharpie to write the grit in the middle, as they are all the same color. It never comes off.

As for splitting on the ends. I always ensure that I barrel cut (square off) my blanks right up to the brass tube. I have found that if you leave any extra, when its turned down thin on the end, the pressure from the bushing will cause it to either split, or bubble.

 

[MikeinSC]

I start with 320 Festool padded sandpaper to knock down any tooling marks. Then 400,600, 1,000 wet sandpaper, then through micromesh. Then it goes to a buff and polish.

I've got no worries when a person picks up a pen at a show and goes over it with a loupe. And that happens.

We've all developed a process to go through to get our pens to the result we're looking for. Yes, some steps aren't always needed but if it works, then it works.

 

[Herb G]

Well, a follow up, if I may.
I was sitting at my desk this morning with the blank in front of me.
I had not touched it at any time, but I heard a *CRACK*
& looked down to see the blank had delaminated itself from the brass tube.
It split along the length & peeled back like a banana.

I picked up the blank & most of the acrylic fell off the outside of the tube.
I painted the tube & let it dry for 24 hours. I glued the tube in the blank with 2 part epoxy & let it dry for 24 hours before I turned it.

My guess is that this blank had too much catalyst added to it & it dried way too fast, or it was poured in layers & it did not bond well.

Either way, the blank itself was definitely defective.
This is the blank I'm talking about & where I bought it from.
Acrylic Green and Swirl Pen Blank | Rockler Woodworking and Hardware

 

[magpens]

Most bizarre !

 

[Beautys_Beast]

I agree with Mag, that IS bizarre.

 

[Wood Butcher]

Take it back.



or tannerite
WB

 

[Herb G]

Take it back.
or tannerite
WB

I like the tannerite idea. But I live in a residential area, so that's out.

I was thinking of strapping it to a large bottle rocket & launching it at New years.