Shrinkage problem??

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jimskio

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I turned a couple of pens over the last two days and have had this problem on both.

I bought a couple of acrylic blanks that I turned and finished with no problem. But when I took them off the lathe I noticed the tube was sticking out of the blank maybe around .020 of an inch or so. I thought the first one the tube shifted or something and didn't pay too much attention to it. But when the second one did the same thing I payed a little more attention. The tube was sticking out of BOTH ends of the blank. So is this due to the blank getting too hot and then shrinking? I trimmed the tube and had no problems putting the pen together. I was wondering if anyone else has ever seen this.

jimskio
 
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Could also be the tube expanding from the heat instead of the acrylic shrinking... but I've never really noticed that issue on any of mine.
By the way, I was relieved to see that you were talking about pens. From the subject, I was a little afraid to click on the post!!
 
You all had me worried for a minute. I thought you might be talking about the effects of a cold swimming pool. :eek::biggrin:
 
I don't see how you could get that much heat to shrink or expand the tube or acrylic. If you do, somethings not right. Tools sharp? Pressing too hard with sanding paper?

Are your blanks square to the tubes before putting on the mandrel? Do your bushings look ok? No grooves ect?

Only time I have seen acrylic shrink is just after they get poured and still in the mold.

Acrylic will crack when very thin and you apply too much heat/pressure on tubes.

Are the tubes really secured to the blank? I have seen the ca/epoxy come lose during turning and let the blank slide when turning, this could allow the ends to get turned down
 
I thought I had it until you said 'both ends'.
CA will soften with heat, allowing the blank or tube to move.
But I've never seen or heard of the acrylic shrinking from both
ends like that, nor have i hear of a tube expanding like that.
I'm stumped..
 
Hmmmm

Penl8the said:
Haha Seinfeld - Season 5 Episodes 21 (The Hamptons)

http://www.imdb.com/title/tt0697707/quotes

Not that there's anything wrong with it.

IPD_Mr said:
You all had me worried for a minute. I thought you might be talking about the effects of a cold swimming pool. :eek::biggrin:
Click to expand...
Click to expand...

Gee, I thought it was referring to how the basket of blueberries always seems to have less in it when you get home than when you left the store.

Or, how T-shirts that are too long when you buy them are too short after going through the clothes dryer.
 
I too have seen the tube be a bit longer than blank after turning on some plastics. Can't explain it. I just mount some sand paper on a piece of wood with double face tape. Carefully deck it flush by hand with a few strokes.
 
If the tube was not glued in securely , it may have moved when the second end was milled , leaving the blank shorter than the tube . It is possible to not notice this , and proceed with turning . During turning the blank can move on the tube , and when done , both ends of the tube may be exposed .
 
Acrylic Acetate does shrink over time but, I haven't seen it come off the lathe that way.

I've had several AA pens that have sat unused for a year or more and the tube is sticking out both ends just slightly but, noticable. It dries out just like opal does and shrinks. If it is used, the oils from your hands keep it moistened.
 
Check the drill bit that you use against the tube, and use the approiate bit, not the one the Mfg. recommends.

On smaller pens ( i.e. slims, comforts, et. al), there is so little material left around the tube that when the PR, even alumalite, and even worse with AA and IA, that the heat of simply turning causes thes materials to shrink.

I have found that if you make the hole so tight between the tube and the blank that it "just" dry fits, this problems goes away. IF you use a 7mm bit and the hole is a sloppy fit, as the CA expands and contracts during the turning process it moves the acrylics with it.

Additionally, you may want to consider carbide cutters for alternative materials. IMHO, HSS builds up WAY too much heat to be useful with acrylics.
 
If the pen mill were the culprit, you would see the tube sticking out the ends BEFORE you ever put it on the lathe. That requires JUST INSPECTING the blank before turning.

The problem is not really the acrylic shrinking, (although it does shrink somewaht throughout its life time), but instead the movement of CA glue when heat is applied.
To demonstrate this, you could take a soldering iron, heat the end of a skew chisel, and then hold the skew to the end on CA glued acrylic blank. You can actually see it pull the blank away from the heat. DAMHIKT.....and DAMNED, we really need a bowling alley here!

With slims, there is as much glue as acrylic left with a sloppy drilled blank.... it's fun to watch.
 
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Check your pen mill if your using one, these sometimes leave a protruding edge especially if it is and interchangeable one when your doing the 7 mm's.
Curt
 
not the pen mill

I have used a pen mill on these blanks, as well as others, and these are the only blanks this happened to. I would have noticed the tube protruding before I turned the blanks. Thanks for all of the ideas guys!

jimskio
 
Had this exact phenomenon happening several times with wood pens: the tube is exposed on both ends. The last one was yesterday with an Artist Sketch. The first times this occurred, I also concluded (somewhat sceptically for I inspect my blanks before sanding) that the pen mill was responsible for this. But the last time I noticed that the blank heated while sanding.
My thougth after this: if heat is the cause, the tube protruding could also occur during the finishing process with CA glue.
Conclusion: avoid too much heat.
 
What size tube was it? 7MM? I had a similar problem and found out it was my pen mill head. There was just enough clearance between the 7mm pilot and the head for the tube to go into the void. Every 7mm blank I squared off with this head left a little bit of tube sticking out the ends.
 
15/32" for the Artist Sketch.
If I had a problem with the pen mill head, I presume I should have a tube protrusion issue with every blank, at least with the same tube diameter.

From the last batch I checked another (finished) Artist Sketch: no problem. I also checked some Statesman (not finished yet) lower tubes which also need a 15/32" drill bit: no problem.
But on this specific Masur Birch blank (glued with Gorilla glue and finished with CA) the tube is protrudring on both ends...
 
I have read and also replied to this thread. It seems that people are getting protruding tubes on their turned blanks, and it appears that the pen mill doesn't seem to be causing the problem on some of these.
Critical thinking needs to be brought into the discussion.
1: what is being done differently on the blanks that have this problem compared to the ones that don't
2: is it possible to get an acrylic blank hot enough to cause shrinking.
3: is it possible to shrink an acrylic blank at all
4: if you get the blank hot would you see other problems before something like shrinkage
5: eliminat known causes of this problem, like the pen mill

just my thoughts
Curt
 
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Ok I just had another idea, is it possible for the bushings to be squeezed in so hard that it compresses the acrylic?
Curt
 
Attached is a picture of the protruding tube on the Masur Birch / Artist Sketch blank.
 

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jimskio said:
I have used a pen mill on these blanks, as well as others, and these are the only blanks this happened to. I would have noticed the tube protruding before I turned the blanks. Thanks for all of the ideas guys!

jimskio
Click to expand...

Jim; On 7mm brass tubes & blanks I have seen the brass deform and get between the cutter and pilot of the pen mill. The result is the brass sticks out beyond the tube. I prefer a sanding jig for trimming blanks for this reason.
 
NewLondon88 said:
That seems like a lot of shrink .. was the wood wet when it was
turned?
Click to expand...

A lot of shrink indeed. I checked some Masur Birch blanks from the same batch: 8-10% humidity. The fact is that birch is very sensitive. More precisely, if the blank did really shrink from heat, produced by sanding or finishing; that is if such a phenomenon is possible, birch is one of the woods more prone to this shrinkage.

randyrls said:
jimskio said:
I have used a pen mill on these blanks, as well as others, and these are the only blanks this happened to. I would have noticed the tube protruding before I turned the blanks. Thanks for all of the ideas guys!

jimskio
Click to expand...

Jim; On 7mm brass tubes & blanks I have seen the brass deform and get between the cutter and pilot of the pen mill. The result is the brass sticks out beyond the tube. I prefer a sanding jig for trimming blanks for this reason.
Click to expand...

I've also seen the brass deform on 7mm tubes. But nothing to do with the picture above. Furthermore, another Artist Sketch tube (with a Maïdu blank) from the same batch was just fine. Also, no problem with other similar tubes (different mechanisms but same diameter) like Statesmen or Emperor lower tubes.
As for the pilot mill head cause, is it possible such a shrinkage could go unnoticed?
1° All of us stop milling when the brass tube is flush with the wood;
2° Assuming the protruding tube appeared during the milling process I'd rather had stopped instead of persisting;
3° Assuming again that I incidentally insisted. Who can imagine I only did notice this kind of tube protrusion (on both ends!) right after finishing the blank?
 
same blank, same problem

I had this problem on Sierra tubes. I turned another over the weekend, same exact blank, and it did it again. I turned quite a few of the same kit, different blanks, and this one particular blank is the only one I had problems with. Guess I will have to keep this in mind next time I order blanks. These blanks were NOT from Exotics.

jimskio
 
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