Problems turning "acrylic" pen blanks

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fxk3760

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Hello, I am brand new to this forum and have been trying to find threads that may answer my problem, but so far I can't. I am trying to turn a slim line pen with "acrylic material". I realize there are many types and am not sure what I have. I bought them at Woodcraft. I am using a pen mandrel with a live center mandrel saver. No matter how tight I make my tailstock, the material will stall as soon as I touch a tool to it. I am running the spindle at 2500 rpm. I am using carbide tooling. I have a square and round cutter. I also have the same in a negative rake. All of them do the same. I barely touch the material and the material stops but everything else continues to turn. I tried to sand the corners and that helped a little but not enough. If I tighten the tailstock too much, then the bushings start to deform. When it stalls out, it starts to melt the end of the blank. I had one blank get so warm that the tube came out. I use a sander to square the ends and I checked with a square and they look pretty square. I can turn wood with the same setup and I have no issues. Maybe a stall if I am too agressive, but other than that the wood turns great. About ready to give up on acrylic but there are so many beautiful pens that I want to keep trying. I watched You Tube videos and everything looks so easy. Please help. Thanks.
 
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Edgar

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I use that same setup & a square-R2 carbide tool, so perhaps it’s in your technique.

Carbide tools should be presented to the center line of the material with the tool held horizontally. At 2500 RPM, you should be able to round off the blank without being overly aggressive & stalling the blank.

Once the blank is round, I cant the tool so the cutter is presented to the material at a 30-40 degree angle, but the tool is still horizontal & cutting along the center line of the blank.
 

KenB259

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Hello, I am brand new to this forum and have been trying to find threads that may answer my problem, but so far I can't. I am trying to turn a slim line pen with "acrylic material". I realize there are many types and am not sure what I have. I bought them at Woodcraft. I am using a pen mandrel with a live center mandrel saver. No matter how tight I make my tailstock, the material will stall as soon as I touch a tool to it. I am running the spindle at 2500 rpm. I am using carbide tooling. I have a square and round cutter. I also have the same in a negative rake. All of them do the same. I barely touch the material and the material stops but everything else continues to turn. I tried to sand the corners and that helped a little but not enough. If I tighten the tailstock too much, then the bushings start to deform. When it stalls out, it starts to melt the end of the blank. I had one blank get so warm that the tube came out. I use a sander to square the ends and I checked with a square and they look pretty square. I can turn wood with the same setup and I have no issues. Maybe a stall if I am too agressive, but other than that the wood turns great. About ready to give up on acrylic but there are so many beautiful pens that I want to keep trying. I watched You Tube videos and everything looks so easy. Please help. Thanks.
Please show us a picture of a blank mounted and ready to turn.
 

leehljp

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What do you mean with this: "If I tighten the tailstock too much, then the bushings start to deform." What kind of bushings are you using? Nylon, or similar? You should be using metal bushings. IF they are deforming such as getting out of alignment under pressure, then you probably are not using the correct bushing with respect to the mandrel.

Another point makes it sound like the tube is not fully glued to the blank - that was just a thought/question.
 

fxk3760

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I double checked my setup and I am cutting on center. I was able to get the blanks somewhat rounded, but at this point they kept stalling. In Pic 1, you can see where it started to melt the blank. I am getting a lot of chipping as well. Pic 5 shows the deformed 7mm bushing from overtightening. One thought, I made all my tools and they are all 24" in length. Is this too long for turning small parts? Also, when I engage the tailstock, I move it to touch the bushing. Then I lock the tailstock down and move the quill in about a 1/4 turn and then lock it down. Thanks.
 

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Valleyboy

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Are you trimming the blanks first so that the ends of the tubes are completely flush with the end of the blanks? You can sand it down on a sander or use a barrel trimmer to do this. The bushings need to locate against the tube and the fact that the blank is melting in pic 1 seems to indicate that it’s locating against the end of the blank.
 

Edgar

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I agree with Valleyboy - it appears that you did not trim the ends of the blanks down to the tube. Friction caused the bushings to melt a circle down to the tube. As the blank melted, the tension was released & the blanks stalled. I think your problem will be solved by trimming the ends down to the tube. Just be sure not to over-trim and reduce the length of the tubes.
 

1080Wayne

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Agree with Valleyboy and Edgar , but in addition to that , the second picture looks like your square cutter is perfectly square , not radiused R2, as is best . A perfectly square cutter requires a higher skill level than I have .

Chipping can be caused by being too aggressive with the tool . Tool length might enter into it , if it doesn`t feel comfortable with your personal geometry . Your tailstock/quill procedure is normal practice .
 

fxk3760

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I sand the blanks down, but possibly I am not sanding enough. I try to not sand into the tube. I will double check these. I did try the R2 cutter as well as a negative rake radius cutter. I begining to think I really need to make sure I am sanding enough. This is probably the issue. Thanks to everyone for your help. I have another set of blanks that I will drill out today and get set up to try again. I'll update soon.
 

Edgar

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When you square the ends of the blanks, you need to take the ends all the way down to the tube. When you’re done, the top of the tube should be flush with the end surface of the blank as shown in the attached photo. Try not to sand so much that it eats away at the tube, but you want to see a complete shiny brass circle at the surface of the blank.

The bushings need to press against that rim of the tube to work properly.

Definitely use an R2 cutter. Personally, I prefer smaller tools for small projects like pens, stoppers, ornaments, etc. My carbide tools for those projects are 12.5” overall length. I use full size tools (24”) for bowls & other large projects.But that’s just a personal preference, you can certainly use full size tools to turn small projects, but if you might try some smaller tools in the 12” to 18” range with 3/8” shanks to see how they compare for you.

There are some good tutorials in the Library and the Bushings & Tubes App on squaring blanks that might be helpful as well.

Keep us posted & don’t hesitate to ask more questions.
 

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fxk3760

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Great Success!!!. These are the blanks that were on my PIC 2 picture from my previous post. I used an R4 square cutter and once I got them round, I used a round cutter. I found a Kit Bushing & Tube Reference sheet that showed tube and bushing dimensions. I found that I was definitely not sanding enough. I measured the overall length of the blank and was oversized. I resanded and they cut like a hot knife through butter. Now the shape may not look ok but that part I am learning. It is always something simple that is overlooked that causes the most grief. I cannot thank everyone enough for your help. I was about to give up on these things. I know that there are a lot of different types of "acrylics" out there. Is there one type that is easiest to turn? Also, thanks Edgar for the information about the tutorials. I was looking but again I am new to this site and still trying to find my way. Thanks again!!!!!!
 

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Edgar

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Wonderful! I’m happy to hear that we were able to help you out.

There are lots of tutorials in the library to be sure. The ones on squaring with sanders are in the Tips, Tools, & Jigs section. They are also in the IAP Bushings & Tubes app if you have that (only for iPhone & iPad) at this time.

Here’s a link to one in the library.


An R4 cutter is probably best for pen turning. I use an R2 because it’s a good compromise between pen turning & other small projects like stoppers & ornaments where I want more detail in the profiles.

Here’s a link to some discussion on R2 vs R4:

Happy turning!
 

MPVic

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Excellent! Like Edgar said, don't hesitate to ask questions. And don't ever, EVER give up - there is such a huge knowledge base on IAP which always means there is someone, somewhere that has a solution to your problem. Happy turning!
 

1080Wayne

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Delighted that you are making progress , but a comment on your 7:57 post . I think you will achieve a smoother surface if you use the round cutter to get the blank round , then switch to the R4 , and use it as Edgar described in his first post .

Alumilite polyurethane is one of the easiest plastics to turn .
 
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Just to note that I am still very new my self. When sanding the blank ends when getting close with a light touch and look, when you touch up to the barrel you can see the brass get shiney and most the time I think I can here a change in the sanding tone. The folks on this site are just awesome helping out others learn. Just saying........
 

qquake

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Congratulations! Just a couple of tips. You should consider painting acrylic blanks before you glue in the tubes. I paint the holes, tubes, and color the epoxy. If you don't, the brass tube can show through after you polish the blanks.

I too use a carbide chisel, with 15mm cutters. You can use square cutters, or square cutters with a 2" or 4" radius on the edge. I use all three, but usually a radiused cutter. I use a "shearing" cut, with the cutter held at a 30-45 degree angle. This gives me my best results.

Do you use a barrel trimmer to square your blanks? I highly recommend them. I use the Ultra-Shear Pen Mill, and love it, but it's very expensive. There are cheaper ones.

I always "knock the corners off" acrylic blanks with my bandsaw before I turn them. This gives me a head start on turning them round.
 

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