Negative rake

[CMC75]

I turned my first acrylic the other day and had a hard time making smooth finishing passes with the tool. Using EasyWood tool on an Inlace Acrylester. It came out really nice but I had to sand starting at 180 to make it smooth.

Would a Negative Rake do me better? My 10 year old son wants to turn acrylic, so this is also a question for make things easier for him as well. Thanks

 

[CMC75]

This is the finished piece. Other than a crack from a blowout while drilling it seems like it came out well. Any advice will greatly be appreciated.

 

[BHuij]

In theory, yes.

I have found my regular radiused square carbide cutter leaves quite a nice surface on synthetics if I simply tilt the handle up to present the cutting edge with a negative rake angle on my finishing passes.

 

[egnald]

I am a firm believer in negative rake, especially on the very brittle Inlace Acrylester material. The material is owned and produced by WoodTurningz. They blanks are cast using a polyester based resin, much like Reichhold PolyLite and they are usually heavily filled with pigments, powders, and other optical grade materials.

The manufacturer/s instruction sheet (link to it here) recommends only using carbide tools with Negative Rake Cutters to turn the material or by using a fingernail bowl gouge or a skew held to give a shear cut to slice the material from the blank. Sharp tools and light cuts to prevent chipping.

Rather than using carbide cutters that are specially ground to have a negative rake, and since I build my own tools, I have made tools that use standard, "flat" carbide cutters. The cutters are fastened to the tool at an angle so that they present a negative rake to the material when the handle of the tool is held flat on the tool rest.

Pens made with this material are usually quite stunning!

Dave

 

[JohnU]

Like said above, negative take will work very well on acrylics but it's not for removing lots of material at one time, It's for shallow and finishing cuts.

I would suggest starting your son on commercial acrylics and not acetate or anything that comes pre chipped. That material is usually very beautiful when turned but the resin is mixed to cure very hot and fast so it's chippy and not a good material to learn on.

 

[randyrls]

Synthetics don't turn quickly. You should get endless ribbons. Present a flat topped carbide bit below center. The further below center the more aggressive the cut and the more force you apply to the blank. Start the cut in the center of the blank and work your way to the ends. Chippy blanks get the corners sanded off on a 5" sanding disk on my lathe. Use the tool rest to support and steady your hands. Do half of the blank at a time. The idea is to remove that sharp corner.

 

[CMC75]

Lots of helpful advice from you guys. Thank you.

I would suggest starting your son on commercial acrylics

John are these all commercial type categories of blanks you speak of? Im still trying to understand all of the blank material. This is from exotic's website. Are the Resin blanks easy turning? There are 3 subcategories under resin?

 

[NJturner]

I am not a fan of teaching new turners on Acrylester as it is a difficult material to work with due to its tendency to chip, but a light touch and a negative rake tool will help. The resins you show above are all different chemical combinations of materials to create blanks. Each combination has its own special characteristics for the people who make the blank and the ultimate turner.

Alumilite is a brand name, whose different names of it's resin defines it chemistry. Most pen blank makers use Alumilite Clear Slow which is a Urethane resin while Alumilite Amazing Clear Cast is an epoxy, so be careful which you use or try. Urethane is normally easier to turn than epoxy, but the urethane tends to yellow faster with UV exposure. There are a number of other Urethane resins used by pen blank makers, like those from Thermoset which I sometimes use, which are less subject to UV damage.

Acrylic is typically harder and more brittle and is not usually a material home makers can use to produce blanks with as it's creation is more demanding. Acrylic is a bit tougher to turn similiar to Acrylester but the reward is it polishes really nicely.

Polyester resins are another potential resin used by pen blank makers, but its distinct odor when pouring makes it a tough one for home use. Polyester is also subject to chipping when turning, but it is a bit easier than Acrylester. There are a lot of blanks out there using polyester, especially when something like a playing card or other item is embedded into the blank as the polyester creates a very clear material when poured correctly allowing the embedded items to show nicely. Check out John U's feather blanks and you will know what I mean.

For newbie turners, I suggest Alumilite Clear Slow blanks, with a negative rake cutting edge to get the most dependable results until you develop good turning skills. One last one, new turners tend to turn cautiously at slow speeds - turn Alumilite at 2,000 RPM or higher to get a better finish and less tendency to chip. Drop the speed to sand. Have fun!!

Kevin

 

[CMC75]

For newbie turners, I suggest Alumilite Clear Slow blanks, with a negative rake cutting edge to get the most dependable results until you develop good turning skills. One last one, new turners tend to turn cautiously at slow speeds - turn Alumilite at 2,000 RPM or higher to get a better finish and less tendency to chip. Drop the speed to sand. Have fun!!

Thank you Kevin! This helps me so much. I have some Alumilite on order. The speed reference helps a lot. Whats nice is I can come back to my threads later because it creates saved information.

 

[bugradx2]

I'm a big fan of blanks made with alumilite's resin, they turn very easily. It's a great material for anyone to turn. I've turned some different acrylics that I've purchased from Exotic Blanks too. They all make great looking pens.

I generally don't turn any acrylics much anymore because I don't like the smell the blanks give off when I turn them. I will occasionally hear comments about a smell coming from upstairs too. I'm also pretty "terrible" because so many of the acrylics require me to paint the inside of the hole to make sure a user can't see the glue or tube. If I can save the step with something else I typically do that.

I'm not a production turner and when I sell pens it's typically after a discussion with the end user on what they're looking for the end design to be. It lets me get away with being choosy on materials that way.

As Kevin (@NJturner) says, polyester resin based blanks are used for (I think) many of the clear casts you'll see out there. To me, they are kind of between something like alumilite or an acrylic. I turn a ton of items with polyester resins each year because I like so many of the embedded items within blanks or something that is showing the subject under the resin like blanks with flags or playing cards.

For any of these materials, I would advise you keep a spare toothbrush or something similar to knock the shavings off the spindle of the lathe as you go. I would really recommend one of the Lathe Spindle Thread Covers that Exotic Blanks sells too. Not having a snarl of shavings around the headstock is an awesome thing. I turn a lot of "resin" based pens and that sucker hardly comes off my lathe anymore.

 

[CMC75]

For any of these materials, I would advise you keep a spare toothbrush or something similar to knock the shavings off the spindle of the lathe as you go. I would really recommend one of the Lathe Spindle Thread Covers that Exotic Blanks sells too. Not having a snarl of shavings around the headstock is an awesome thing. I turn a lot of "resin" based pens and that sucker hardly comes off my lathe anymore.

I have seen this cover while looking at websites and will keep that in mind. Thanks. I picked up some small nylon brushes at harbor freight, very handy and I use them often. I have thought about getting some of those compressed air cans( like for cleaning keyboards) to blow out dust around the machine. I have a big compressor but dont like to turn it on for just a blow off. I imagine the air in a can would be a good idea?