Why is this happening all of the sudden?

[xCykax]

I noticed this issue a little bit on the blank i turned before this one, and so i sharpened my carbide insert. I haven't changed anything intentionally in my technique, and i'm currently using a square carbide insert. Can anyone tell me why this might be happening?

 

[xCykax]

Edit: I used a 600 grit trend diamond sharpening stone with matching brand lap fluid.


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[magpens]

First of all, of what material is the blank made ?

I have used carbide cutters for quite a few years. . I always use round cutters.

When you say you use a "square" cutter, is it actually perfectly square or is it "squarish" with the edges having a quite large radius ?

I would think that a perfectly square cutter would present some challenges that could give you results like you show ... catching due to the cutter edge being not exactly parallel to the blank surface.

Speed of turning could be an issue also.

I would recommend a round cutter, and a speed of about 700 RPM.

 

[johncrane]

could be your tool rest placement, is it set back too far and too low, looks like the blank is very brittle you need very light cuts

 

[Richard92]

Looks like an acrylic blank to me. I have had this happen when I have moved along the piece to fast. Slowed my movement along the piece and less cot depth and then no problem.
I was using a round carbide at the time.

 

[KenB259]

Looks like Inlace Acrylester blank I literally hate that stuff.


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[keithbyrd]

As Mal said above - perfect sq cutter is difficult. But you can put a tilt on it 45 degrees and let it slice across the blank. II use large radius cutters. Also John said tool rest placement - be sure you are cutting at the right height and keep your rest close to the blank. I turn mine as fast as the lathe will go - 3500 and take lighter cuts.

 

[Humongous]

Looks like polyester resin, chips if you look at it funny. Light cuts and as Keith says above tilt the carbide and use like a skew. I have had success using a square carbide on these blanks using the 45 degree method. Be patient, don't rush! It will take a while to turn these but you will be rewarded with a very nice piece. Polyester polishes to a brilliant shine.

 

[turnit2020]

Best suggestion is to use an R2 cutter. The other suggestion is a negative rake R2 cutter and turn at 2300 to 2600 RPM. Magpens has suggested using the round cutters. That may work for some. I have been using R2 cutters since 2011 with good results. I work the ends first and then work the center down in stages. Some acrylics are chipper than others and this must be one as well. KenB259 suggests the blank may be inlace Acrylester. That type is the most brittle of the acrylics. But since you had the same problem on the preceding blank I believe the solution may well be to change to an R2 or negative Rake R2 cutter and run the speed up to 2300 to 2500 RPM with light cuts. Re-sharpening carbide cutters can work but will not solve a problem on a brittle blank such as yours. Hope these suggestions solve your problem.
Turncrazy43

 

[xCykax]

Thank you all so much for your input! I ordered an R2 insert sometime last week and it should be arriving relatively soon. The blank I was using was just a standard acrylic acetate blank for those who were wondering.

 

[egnald]

Wow, that certainly looks like a brittle blank. I have often had chips like that but only one or two. The solution for me has been to use a round negative rake carbide cutter and by taking very light passes. (The other recommendations are also very valid -- tool rest height and distance, etc.) For brittle blanks like Inlace I also stop turning with the blank proud of the bushings and rely on sanding to do the final sizing. I start with 150 backed with a flat "shiny side" of a pen blank to keep it flat, then go to standard sanding through the grits up to 800 before micromesh and polish.

Good luck in developing a technique that works the best for you.

Regards,
Dave

 

[jttheclockman]

Dave hit the answer. The blank is brittle. This can be from to much hardener added whoever made the blank. Not everyone is a so called blank maker like they think they are. But that is my guess. I still would use a round carbide to get close to shape and finish with sharp skew to bring it home. Every blank can be turned. Just need to understand and read the blank. good luck.

 

[RobS]

If you want to save this, I would switch to a negative rake scraper, or negative rake carbide.

 

[PaulWitmer]

Use a round cutter taking light cuts and you virtually eliminate any of the gouges in the blank you see. Ensure your tool rest is close to the piece. I've turned many acrylic blanks and have been able to get away from the chipping you see following this technique. I've not tried the negative rake cutting heads yet as I've not really needed them as of yet.
Paul

 

[Chasper]

I think I know that blank, looks like flames on a black background, not a difficult to turn blank. It could be that in sharpening your carbide cutter you made it duller. A good new 600 grit diamond sharpening stone is too rough for a carbide cutter. If you have one that has been worn down by a few years of use it would probably work better.

I don't normally use carbide on resin blanks, I use HSS for resin, but I have seen chipping somewhat like what you have when I tried carbide. I would try to finish the blank with a sharp skew.

 

[its_virgil]

AA or acrylic acetate is not a necessarily difficult material to turn. Maybe you just got a blank from a bad casting. I have turned lots of acrylic acetate and never had one chip like that. I use a skew for all pen blank materials...no matter what the material. Love my skews. increase your lathe speed and give it a try. I really can't help with carbide...not a carbide user.
Do a good turn daily!
Don

 

[bsshog40]

I'm with the others on a brittle blank. I don't care how dull my tool is, it has never destroyed a blank like that.

 

[howsitwork]

I found a HSS roughing gouge presented so the edge is giving a skew type cut works for me. The extra weight of the roughing gouge and it's size dampens any tendency to vibrate. Have you also checked your set up for rigidity as any movement of the blank might cause vibration and chatter leading to the chipping out you can see?

cant comment on carbide as not used but I also stand by a sharp skew used both as a skew and as a VERY gently presented scraper works for me.

 

[qquake]

I've had chipping like that, but never the entire blank. It's makes a helluva noise when it happens, and I always stop. Usually, I'm able to finish it by taking lighter cuts, as long as the chipping isn't too deep. Like others, that looks like a brittle blank to me. Rhino, polyester resin, inlace acrylester, or some such. Acrylic acetate is softer, and rarely chips like that, at least for me. I'm famous for being too aggressive, for trying to take too much material with each cut. That usually gets me in trouble. Lately I've been using a 15mm square carbide cutter with a 2" radius. But I've started holding the cutter at a 45 degree angle to the blank, instead of straight on. This produces a "shearing" cut, which is giving me better results.

 

[howsitwork]

I've had chipping like that, but never the entire blank. It's makes a helluva noise when it happens, and I always stop. Usually, I'm able to finish it by taking lighter cuts, as long as the chipping isn't too deep. Like others, that looks like a brittle blank to me. Rhino, polyester resin, inlace acrylester, or some such. Acrylic acetate is softer, and rarely chips like that, at least for me. I'm famous for being too aggressive, for trying to take too much material with each cut. That usually gets me in trouble. Lately I've been using a 15mm square carbide cutter with a 2" radius. But I've started holding the cutter at a 45 degree angle to the blank, instead of straight on. This produces a "shearing" cut, which is giving me better results.

nice clear answer with good photos to illustrate it ! thanks

 

[robutacion]

And if everything else fails, you can always get the job done with the "Flap disc system".

Cheers
George