Need Help with Composit Blank (Wood.Acrylic.Wood Sandwich)

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KarlSangree

KarlSangree

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Joined
Jan 11, 2022
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Location
Secane, PA
Let me preface this by saying that I am a machinist with some experience turning wood pens, but absolutely no experience with acrylics.

I am trying to make a "thin blue line" pen for an animal cruelty investigator buddy of mine. Here's what I've tried so far:
  1. Two pieces of mahogany on either side of a pen blank mold, then poured blue dyed MAX CLR resin to fill gap in the middle. Cured overnight at 60 psi in pressure pot.
  2. CA glue (Starbond medium) a 0.125" x 0.750" x 3" piece of blue acrylic between two 0.3125 x 0.750" x 3" pieces of mahogany. Clamped tight and let sit for 2 hours.
Both of the blanks looked awesome before turning. However, during turning, both blanks exploded towards the end when the blanks got a little thinner. I am guessing it's either my poor turning technique or I'm using the wrong tool. The 100% wood pens I've turned have all been exceptional, but these sandwich blanks have me a little frustrated. I am using the chisels that came with the lathe. They are a set of Penn State Industries Benjamine's Best Carbide. I'm using the one equipped with a (3/8"?) round carbide cutter. I'm turning at around 2,000 RPMs.

Any help for this acrylic newbie would be greatly appreciated.
 
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Used slow drying epoxy .. score the acrylic
turn using a live cutter
Laminate and then drill and dowel the pieces if you have to .
Thin blue line !
Do one slit and then use blue veneer .
 

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There are SpectraPly Thin Blue Line blanks out there, but I don't know who makes them. I have had the best luck with the Alumilite Thin Blue Line blanks from Turner's Warehouse. Alumilite turns just great! - Dave
 
If you are going to make your own, I second @farmer 's approach. Scuff up both sides (wood and acrylic), wipe down with acetone as some woods are oily and it can affect the bond, use 2 part epoxy and clamp but don't crank it super tight or you will squeeze out all of the epoxy.

Personally I use T88 epoxy from System Three. It takes a full 24 hours to cure but so far I haven't had any failures on pieces where I have used it.
 
Thanks all. I'll try your suggestions and let you know in a few days... as soon as the new T88 epoxy gets here. I think my biggest problem is the carbide button style chisel. I tried using a skew chisel and it was working great, albeit a little rough looking from my lack of experience. I went to clean up the marks from the skew with the carbide button and boom went the dynamite.

I'll try let and you know in a few days. The epoxy will be here tomorrow, and the T88 website says 72 hours full cure time.
 
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I tried the suggestions posted previously. I scored the acrylic, not too much clamping pressure and so on. Turned the blank entirely with a skew chisel instead of the carbide button. Not entirely happy with the colors but at least I was able to finish one. Still waiting for the T88.

Thanks everyone for the help!
 
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Not sure if this would help or hurt the situation, but 2000 rpm seems pretty slow. I think most of us turn close to as fast as our lathe will let us. I routinely turn at 3500rpm. Going faster and taking light cuts may reduce a "catch" which results in a blow out.

My 2 cents anyway.

PS - the finished pen turned out awesome.
 
KMCloonan said:
Not sure if this would help or hurt the situation, but 2000 rpm seems pretty slow. I think most of us turn close to as fast as our lathe will let us. I routinely turn at 3500rpm. Going faster and taking light cuts may reduce a "catch" which results in a blow out.

My 2 cents anyway.

PS - the finished pen turned out awesome.
Click to expand...
Wow! And here I was thinking 2000 RPM was too fast. Newbie mistake... too much time on the metal lathe spinning material at 400 RPM lol.

I am going to try again when I get the recommended (T88) epoxy and I'll try the higher RPMs at that time.
 
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