A problem I haven't had in a long time.

[Wood Butcher]

I have been making pens for about 15 years and thought I was past this. Yesterday I spent several hours gluing up laminated blanks using different burls , guitar pickguard and corian. I've done this a lot without any issues. In the past I have turned with a mandrel and bushings but a few months ago I went to turnimg between centers. Today I blew up three out of four that I worked with. I have noticed that when drilling on the lathe, I get some wobble of the bit and thus the hole os a little oversized, not much, just a little. After the blow-ups I examined the part still on the tube and saw that there were small gaps or voids where the thick CA didn't fill the gap. Should I go to epoxy for gluing in the tubes? Are any of you getting the wobble I mentioned? Am I maybe putting too much pressure on the live center when mounting the blank for turning? This is frustrating enough I needed to get out of the shop before I blow up all of the ones I put together. Any suggestions will be appreciated. Thanks
WB

 

[ldb2000]

I use epoxy now to glue all my tubes . I coat both the inside of the blank and the outside of the tube . You can do the same with thick CA to avoid the gaps . You might think that the polyurethane glues like Gorilla will fix this problem but it is a false sense of security . The foam that fills the gaps has NO structural strength , think of it like Styrofoam , not very strong .
As for the wobble , check your bits , I have only seen this on cheap bits . The cheap bit are very seldom perfectly straight .
One last thing , sharpen your tools . The main cause for blowing up blanks is having to press too hard to get the tool to cut .

 

[Dalecamino]

Bill, I got wobble when drilling on my press. And after I went to drilling on the lathe, I found out the hard way, that, I have to keep advancing the whole tool rest and, not just turn the crank. This made the difference for me. Sorry about the damaged blanks. Oh yeh, and use epoxy.

 

[IPD_Mrs]

We have used gorilla glue as well for when the tube has too loose of a fit. It has been a long time since I have watched you turn Bill. You do have an aggressive touch when doing demos and I know part of that is because of the time restraints. If that carries over to segments, it could be a part of the problem as well.

 

[ed4copies]

Bill,

In my shop, wobble was accepted, until I watched Tony (Hilltopper) do a demo of "bit sharpening". Now, it is VERY rare to see a hole that is bigger at the top.

SO, first suggestion--sharpen bits.

Suggestion 2: IF the hole is bigger at the top, and your blank is longer than you need, so you can cut the end off, instead of drilling through, go a little deeper and cut off some of the "top" of the blank where the hole is larger. (Of course, if you are doing a pen that has a grain match, this is a bit of a risk).

Yes, you can change the glue. But, if the hole is larger than it should be, when turning you will have less material left and a greater possibility of a "Cracked pen", either immediately or later.

FWIW!!!

 

[Wildman]

I have never had a glue failure using polyurethane glue. Have read the test that say not really good at gap filling and not water proof. Still never had a tube come out during curing or failure. Stopped using because always ends up hardening in container on me.

I like epoxy for all tube glue ups and like not having to wait 24 to turn.

 

[Wood Butcher]

Thanks for the input. Here's a little more info: I don't have the wobble if I use the drill press and I checked and found that the wobble is in the tailstock of my Jet mini. I lock down the tailstock then I tighten the quill lock until it will barely move when cranked to advance the bit. I think the bit is sharp, probably could always be sharper, but will have to invest in a Drill Dr. or something similiar. I tried pre-drilling with a bullet point bit several sizes smaller than the 27/64" used for the Sierra then swapping the bits and that seemed to help the problem. Oh, and drilling acrylic Acetate and Acrylester I don't have the issue. When I glue the tubes in I flood with thick CA but I will now switch to the epoxy, I just hate waiting overnight to turn. I do tend to "go at it" when under a time constraint but today I was litterly .003 to .005 from finishing taking really slow and fine cuts and heard that small whisper that says, "stop and use the skew or sandpaper" when POW parts and pieces were everywhere. Made me say "the word". I really do appreciate all of your helpful suggestions and the sharing of your experience, guess I need to rethink some of my habits and practices. I'm teaching a newbie tomorrow, hope I have all the messups out of the way or it will be a little more than embarrasing.
WB

 

[Dalecamino]

Bill, the 5 minute epoxy I get from Mike & Linda is good to go in 30 minutes. Get you some ! :biggrin:

 

[johnnycnc]

If you recently changed to turning between centers, there is one variable to consider.
If you are not using bushings, just centers, there is another thing to consider.
Having tried this, I have to wonder how much force it takes to crank that tailstock
tight enough to "drive" the blank to cut it without it slipping.
I never had enough luck or patience to give it a second thought, the blank always kept stalling, and I kept cranking things tighter and tighter.
And considering that the centers are wedge shaped, the mechanical slpitting forces are a factor I don't want in play on my blanks.
I'd guess you are forcing the centers in and "wedging" the blowouts as the blank gets thin.
The centers are a wedge, after all, if not positively stopped from progressing.
Just my random thoughts.

John