# bad plastic for threading??



## watch_art (Mar 20, 2012)

Well, I turned two sections, and the same thing on both.  Several cracks on the threaded bit of this plastic:
Bear Tooth Woods - Invisavue UA-01 Black Pen Blank

Is this stuff just not good for threading?

Here's one of my sections...


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## watch_art (Mar 20, 2012)

here's the back end.


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## SDB777 (Mar 21, 2012)

I think your turning the inside threads firtst, correct?  Then screwing in something to 'support' the blank while turning the outside threads?

Maybe the 'support' is too large and once the material is removed on the outside, it's just enough to allow it to crack....




This is just a guess....cuase I really haven't seen your set-up.





Scott


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## watch_art (Mar 21, 2012)

It's really frustrating b/c I'm doing the same things with this as I do with the smaller sections and I haven't had any cracks like this.  I've squished a bunch of super glue in the cracks and will chase the threads to see how it does.  Ugh...


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## leehljp (Mar 21, 2012)

Another way of saying what Scott said - is that it is better to thread the outside first, put some kind of a support cap on it, and then thread the inside.

Different PR has different characteristics so the technique and sequence of threading become VERY important.

I have not done this, only reading the different posts on this as I intend to start doing the kit-less in the near future. (I hope I got it correct.) There was another thread on this very subject just a few days ago.


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## watch_art (Mar 21, 2012)

IT's not PR though - it's acrylic.  I'll go ahead and do the support collar though - for the next section (making three of these).

Thanks


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## leehljp (Mar 21, 2012)

watch_art said:


> IT's not PR though - it's acrylic.
> Thanks



OK, that doesn't make any difference in the results - because from what I have read, PR or acrylic act the same in threading. The "sequence" is what is important at this point.


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## Dan_F (Mar 21, 2012)

I've net tried threading this material, but I do know that as even though it seems relatively soft, it dulls my skew pretty fast, so it might be harder on taps and dies too. Might not be the best material for sections, and I'd be even more leery of using the triple starts on it for bodies for that reason.

Dan


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## watch_art (Mar 21, 2012)

Thanks.  Just using single start threading....
I'll probably end up making black sections from acrylic.  Dernit.


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## soligen (Mar 21, 2012)

I tried this marterial too and it is not near as friendly as the regular acrylics. My results were similar to yours. I used up the 2 blanks I bought and never tried it again.

It is more opaque than normal acylic. To do this, I think they have to add more pigment, which affects the workability of the material. I've also struggled with black acrylic, which is more opaque than the normal arcylics. My conclusion is that more pigment means less workability


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## watch_art (Mar 21, 2012)

Hmmm.... interesting.  THanks!  Guess I'll avoid this stuff in the future then.  Black delrin or even black ebonite would be the way to go I guess?



Source for black delrin?


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## Texatdurango (Mar 21, 2012)

watch_art said:


> Well, I turned two sections, and the same thing on both.  Several cracks on the threaded bit of this plastic:
> Bear Tooth Woods - Invisavue UA-01 Black Pen Blank
> 
> Is this stuff just not good for threading?



In my opinion, Alumilite, being polyurethane, is by far the best material for making sections.  Compared to the more brittle plastics, acrylics, and whatever else they are called, the polyurethane is more forgiving in that it will give more before it cracks.  I think it was Curtis who tossed an acrylic pen and an alumilite pen up in the air, one breaking, the other bouncing!  That pretty sums up the difference.

I've made and sold dozens upon dozens of pens with Alumilite sections and haven't heard any complaints but have received several positive comments about the feel.

To me, Ebonite has a soft warm "grippy" feel, acrylic has a hard cold "slippery" feel and Alumilite falls in-between.

*On Edit:*  I just saw your last post and I would NOT use delrin, it is way too soft and while it is nice to work with, the customers will scratch and mar it to pieces!


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## soligen (Mar 21, 2012)

George,

Do you use the black alumilite, or add pigment to the clear?


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## watch_art (Mar 21, 2012)

Alumilite huh?  Thanks!  I do like that stuff quite a bit.  Very easy to work with.  I also saw the video of throwing the alumilite and acrylic (or PR?).  Very cool.


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## Texatdurango (Mar 21, 2012)

soligen said:


> George,
> 
> Do you use the black alumilite, or add pigment to the clear?


I use the clear and have been adding Alumilite black dye but just last night realized I had a big jar of carbon black PearlEx pigment so I cast a few blanks.  I'll see how they turn and polish before commenting further on them.


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## Robert111 (Mar 28, 2012)

leehljp said:


> Another way of saying what Scott said - is that it is better to thread the outside first, put some kind of a support cap on it, and then thread the inside.
> 
> Different PR has different characteristics so the technique and sequence of threading become VERY important.
> 
> I have not done this, only reading the different posts on this as I intend to start doing the kit-less in the near future. (I hope I got it correct.) There was another thread on this very subject just a few days ago.



+1
I too find threading then supporting the cap threads on the barrel FIRST works best.


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