Lots of good info here and thanks for everyone's response and time. I never imagined I would get this many ideas on how to scuff the tubes. Some are very interesting to read.
For those who are non-scuffers, everything I read when I first started making pens was that the tube needed to be scuffed up a bit. Sounds like maybe that's not 100% true. I also scuff the handle material on my knives before attaching the scales with a dremel. Between the brass pins and the epoxy I've only had one failure in almost 200 knives and the failure was due to abuse.
Thank you all for responding and giving me some great ideas.
I had enough blowouts early on in pen turning - from delicate blanks. Because of that, I started close scrutiny of what I was doing and why this happened for me. Several things were involved that others may have or may not have done. From that I started scuffing as a part of the solution, but now I don't usually do that.
Here are my observations:
How much adhesion area?
1. When observing the smooth glue adhesion on the inside of the blank that pulled away from the tube (aka blowout), I noticed how much glue was inside the blowout but not in contact with the tube. This can be deducted by the smoothness in the contact areas, and the ripple in the non-contact area. (Its Obvious) This told me that I was not getting full or in some cases even 50% of contact with the glue between the tube and inside of the blank.
This was especially true of CA - medium to thick. Then I started using epoxy. Still on occasion, I had blowouts. ON the Epoxy, I noticed again how much or little adhesion area I had. Usually 50%. This didn't make sense to me as I loaded the inside of the blank with epoxy and wiped the tube with epoxy, and placed putty inside the tube to prevent epoxy from getting inside the tube. When inserting the tube and twisting, that did not give as much area contact as I thought it should. The Resulting occasional blowouts (mostly weak burl wood) revealed that overloading with epoxy did not guarantee full area contact between the tube and blank with epoxy. Too many mini-caverns.
Polyurethane solved the area adhesion:
2. I finally solved the above issue by doing what many pen turners do not want to do. I started using polyurethane glue - meaning
overnight wait as poly foams and expands. The area contact either increased or the poly glue adhesion was far superior - probably both. (New users beware, poly - as it expands can and will push the tube out if you don't add something to prevent it from sliding out as the glue expands.)
Back to blowouts and CA/Epoxy lack of adhesion.
3. Why do people like Don (aka its Virgil) not scuff and have great success Probably several reason or possibilities.
a. Don has been turning for ages. Experience (sharp tools) and technique (feel). Long time turners have developed a feel for sharpness, wood grain type and cut and make adjustments. In turning, they do not put the pressure on the tool and let the tool do the cutting with minimal pressure - called "feel". It is pressure from dull tools and the high speeds that pen turners often turn.
Carbide tools are sharp. Inserts are sharp but they are NOT as sharp as a finely tuned HSS blade. I can feel the difference. This minute' bit of extra pressure from dull blades or even sharp carbide that is not as sharp as honed HSS will work against the forces that keep a burl or segmented blank together.
PLUS: Speed.
I noticed shortly after joining IAP that a few bowl turners coming here (as they started making pens), chastised pen turners for turning too fast. After all, bowl turners turned in the 200 - 1000 RPM max. (BTW - I read an article last year of some bowl turners criticizing the new lathes with digital readouts - as not necessary. - The point being that what one starts with is what they see as the norm). Back to the high RPM, higher RPM places much more stress on weak burls where there is not glue in spaces in contact between the wood and the tube. So - less sharp blade, higher forces (RPM) make for more blowouts, (but in some instance too slow can do the same.)
b. Environment:
Does your tubes have a minuscule of film on it?
Do you ever get in the car and notice how clear the sky is, or the scenery? Then at certain angles you notice a very slight haze or film on the inside of the windshield? Haze and film develops in the kitchen cabinets too, on long unused plates, cups and glasses. This happens - in the shop too. A minuscule amount of haze or film that is unseeable can be just enough at high RPM and too much pressure to cause a blowout even in areas that have full contact. Do you keep your tubes in a pouch or out of the ambient air? A minuscule film can weaken adhesion contact points.
c. Time: waiting is patience, sharpening, feel, instinct. Rushing to get through - causes weak areas to reveal themselves. Old long time turners (no disrespect meant) in general are more into the journey rather than wanting to get to the end result. These experienced turners feel or have instincts in which they treat one blank different than the other one. They have a feel for when the tool is sharp and when it is microscopically getting duller, and back off.
4. What scuffing does:
Scuffing Causes more adhesion points, but that alone does not fill the spaces. I wipe tubes with a clear cloth or drag it once or twice with a scuffing pad. As John T said (and others) it doesn't take but a second or two. Now as to a clean tube having good adhesion, Different forms of CA are or were used to stick rear view mirrors onto slick glass and some stayed on 50+ years. That alone says that Scuffing is not necessarily necessary on slick(smooth) objects. What is necessary: 1. Clean, 2. ALWAYS sharp tools, 3. "feel", 4. understanding the forces of speed and strength/weakness of the wood. If you ignore any of these, then learn to use polyurethane adhesive. :biggrin:
Eagle, who was a member here long ago (he passed away several years ago), taught me to learn to "read" a blank, especially segmented blanks and be observant as to each individual blank's need - inn order to keep it intact as I turned. I used to wind string around a segmented blank and CA the dickens out for it to hold it together. (Eagle did this). Today, gauze does the same thing as string, and a lot easier.
Experienced turners do a lot of these things instinctively. There is no ONE thing that is a cure all, but disregarding any ONE of those suggestions with the lack of experience can cause disaster.
The one easier way: Polyurethane Glue + Time, otherwise, a combination of several things mentioned above!