Aaaargh!! What the heck am I doing wrong?

[Mullanphy]

I've been turning wood for a few years and decided to turn my hand to pens. Wooden pens I'm doing OK with, but most of my non-wood blanks (store bought acrylics and self-made epoxy resin) explode on the mandrel.

Sometimes I see
the adhesive separated from the brass tube
the adhesive separated from the blank
So many small gouges in the blank the cutter (standard HSS chisels and carbide tipped) just takes a big bite and spits it back at me

I've tried speeds from 800-2000 rpm
I've used both HSS chisels and the new-fangled carbide tools, or a combination of both
My tools are sharp
I used thick CA as well as 5 minute epoxy - I let every tube sit at least 24 hours so the adhesive will cure completely.
Tubes are sanded with 220 grit
Drilled holes in non-wood blanks are rinsed in water and let dry

Light, moderate, or heavy pressure seems to obtain the same results - another tube/blank good as a bad example.

What the heck am I doing wrong?

 

[KenB259]

Well it's really hard to say. Since you've been turning awhile, you must have learned correct tool technique. Speeds for pens is pretty much wide open except for drilling, if you drill on the lathe. People will tell you the type of glue matters even though lots of people here use all types and all have successes as well as failures. Heavy tool pressure is never a good idea. Maybe find a pen turned near you and observe or maybe a pen turning class. Don't give up, you'll get there.

 

[egnald]

Hmm - I'm sure this must be very frustrating for you.

I have no way to tell how brittle your self-made blanks are, but the rules of thumb that I learned regarding 2-part resins at the place I worked are:

1) Make sure the resin and hardener are getting mixed thoroughly - it is important to scrape the sides and bottom of your mixing cup during the process to make sure the materials are very well blended.

2) The ratio of resin to hardener is also a critical parameter. Some of the materials we used could be measured simply by volume, but others had to be measured by weight as the volume was not concise enough.

3) The temperature of the resin and the hardener along with the room temperature needs to be in the right limit - usually too cold is the problem. We kept our storage and mixing room between 21 and 24 degrees C.

4) We monitored the humidity but did not control it. Frequently the problems with our coatings would coincide with higher than average humidity - anyway humidity would frequently get the blame. Make sure anything you are adding to the resin or anything you are casting in the resin do not have a high water content i.e. water based pigments or wood that has not dried out thoroughly enough.

As far as purchased pen blanks go - based on my experience:

Acrylic Acrylester blanks are on the extreme end of brittleness as far as purchased blanks go. It usually takes extreme caution and ultra sharp tools to keep them from chipping or blowing out. I personally avoid them; however, they do make very beautiful pens. When I do turn Acrylester I use negative rake cutters and take very light passes.

Rhino Plastic blanks can also be brittle, but not so much in the extreme. I still use very sharp tools, make very light passes, and often use negative rake cutters. They polish very well.

On the other end of the brittleness spectrum you should find Alumilite blanks. In my experience, the commercial Alumilite blanks are the least brittle and usually cut like a dream. Non commercially produced Alumilite blanks (or Craft Made blanks as I call them) may hot have the same brittleness consistency as commercially produced - because of the reasons stated at the top of the post.

I have used both CA and Epoxy successfully for gluing the tubes into plastic blanks. I have blown blanks up and blown out the exit side when drilling them - usually because I have been impatient and drilled too fast without letting both the bit and blank cool down. A "peck at it" approach has worked the best for me. Heat is the enemy when drilling and cutting plastics.

I don't know if anything I have offered will help, and I hope you are able to figure out a process for working with plastic blanks as they can produce some very attractive pens.

Regards,
Dave

 

[wolf creek knives]

Not to worry and practice makes perfect. My first Acrylic experience was very similar to yours. I was picking small pieces of Acrylic out of my hair, beard and the shirt I was wearing. It was a mess. Then I talked with my mentor, Chuck, and he gave me some great advice that I'm still using today. First off, I use a two part Epoxy (T-88) that is super strong. I plug the ends of my tubes with Playdo and apply the Epoxy to both the tube and the inside of the blank. Turn it while inserting the tube then set it aside and wait for 24 hours. I now have a set of Carbide turning tool but mainly use the tip that is the circle. Take your time, nice slow easy passes will produce long ribbons but more importantly the blanks shouldn't blow up on you. The picture below is from the same blank I turned the first time, the picture is probably my tenth Acrylic pen and I think it turned out pretty good. Best of luck and there's plenty of great advice from turners with a ton more experience than I'll ever have.

Note: The knife was part of the donation but I wanted to show you the pen.

 

[Mullanphy]

Being the Newb on the block, I'm not sure what the etiquette here is, so I'm giving each response a thumbs up instead of replying to each response.

Some food for thought so far, and I appreciate each post. I especially like the idea of some face time with someone more experienced than I am, and I have just the guy who might help.

Another issue pointed out is speed - not of the spinning blank, but of the operator. I do tend to get in a hurry far too often. Something to look at.

 

[Mullanphy]

Not to worry and practice makes perfect. My first Acrylic experience was very similar to yours. I was picking small pieces of Acrylic out of my hair, beard and the shirt I was wearing. It was a mess. Then I talked with my mentor, Chuck, and he gave me some great advice that I'm still using today. First off, I use a two part Epoxy (T-88) that is super strong. I plug the ends of my tubes with Playdo and apply the Epoxy to both the tube and the inside of the blank. Turn it while inserting the tube then set it aside and wait for 24 hours. I now have a set of Carbide turning tool but mainly use the tip that is the circle. Take your time, nice slow easy passes will produce long ribbons but more importantly the blanks shouldn't blow up on you. The picture below is from the same blank I turned the first time, the picture is probably my tenth Acrylic pen and I think it turned out pretty good. Best of luck and there's plenty of great advice from turners with a ton more experience than I'll ever have.

Note: The knife was part of the donation but I wanted to show you the pen.

View attachment 303966

Nicely done pen! (Hope that's not too exuberant )

 

[wolf creek knives]

Being the Newb on the block, I'm not sure what the etiquette here is, so I'm giving each response a thumbs up instead of replying to each response.

Some food for thought so far, and I appreciate each post. I especially like the idea of some face time with someone more experienced than I am, and I have just the guy who might help.

Another issue pointed out is speed - not of the spinning blank, but of the operator. I do tend to get in a hurry far too often. Something to look at.

Thumbs are great. That way we know you've read our responses. Thanks for the compliment.

 

[leehljp]

1. The vast majority of bowl turners coming to pen making turn too slow initially. There have been two other turners recently with a very similar problem as you. When the math is applied to pens 3/4" in diameter vs a 12 inch bowl, 3/4" at 3000 rpm is slower and less stressful than the outer edges of a 12 inch bowl at 600 rpm. Now imagine this part - Trying to turn a 12 inch bowl at 50 rpm, - it would catch on the chisel and throw it across the room. Faster speeds prevent this and make for smoother cuts.

Both recent problems with acrylic were solved by cranking the speed up to around 3000 rpm.

2. CA, thin, medium or thick, or Epoxy, or Gorilla Clear will get air bubbles and do just as you mentioned. Polyurethane (expanding kind) Gorilla Glue does not leave pockets that cause what you experienced.

Poly requires about 18 - 20 hours to cure well but it hold everywhere.
BEWARE of two problems with poly glue:
1. you need to put tape on both ends after gluing and inserting the tube - to keep the expanding poly from pushing the tube out. Doesn't happen often but when does, there is no saving the blank

2. In case you are not familiar with it - Poly does not come off easily, wear gloves.