Turning Segementation help

[sgimbel]

Hi all, I've made some segmented parts (aluminum & plastic) and they are always blowing up at the end of getting it to size. I'm using Cocobolo wood, thick CA glue for tubes, turning at 1250 rpm (should it be faster/slower) using extremely light cuts with a woodchuck (not using the corner of the bit) turning between centers. Preturning the blanks round on the disk sander after the tubes are in then being very generous with thin CA before putting them on the lathe.

I get within about an 1/8" of finish and the blow up. I could sand them down but 1/8" is a lot of sanding, especially on Cocobolo, and heat generation.

I need help. Different turning speed? different tool? different glue?
heeeeeeeeeeeeeeeelp!

 

[paintspill]

i find faster is better. seems if its slow there is an opportunity for the tip to grab. i'm not familiar with the woodchuck so i am no help there but i do use a skew for troublesome woods.

 

[ed4copies]

Sounds like you need to be very generous with the thin CA more often.

With metal in the blank, stop frequently to reapply thin CA. WHERE the metal is does make a difference in how to approach, and yes, for me the speed would be higher, but I would be using a skew, which does not hit the blank as "squarely" as the carbon edge tools.

And be certain your socks don't match--one orange, one yellow seems best.

 

[HoratioHornblower]

Well, I will do my best to offer thoughts with what little experience I have. I would check to make sure that you are making the aluminum fairly rough with sandpaper, and that the kerf of your blade is fairly close to the thickness of your metal. I use a 28 tpi scroll saw blade from Lowes, and that seems to match pretty close to my .01 sheet metal. I turn faster than you at about 3200 and that seems to work for me. Also, I'm not sure so I would wait to hear a more experienced voice on this, but you might wait a bit longer to let the CA dry if you haven't been waiting too long. I let my medium dry for 5-10 minutes and that seems to work for me. My 2 cents.

David

 

[firewhatfire]

they are spot on, turn faster, stop and glue as needed and light cuts. I use a woodchuck also and that is how I di it. Scuffing the aluminum before gluing does help also.

 

[sgimbel]

I scuffed up the aluminum with 220 grit. I only apply thin CA once, maybe twice so I'll start doing that more often and I'll kick the speed up a bunch. Thanks for the help. Anything else I can do? Ed I sit in a wheelchair so I don't wear socks/SHOES unless it's under 50 degrees LOL.

 

[leehljp]

I have not had any blowouts with segments and have done quite a few. I do turn it at high speed. And if it is wood that I know that is easy to blow out, I stop and soak with thin CA often, turn a little off, and soak some more.

On the metal part, I use a modified scraper (scraper than is not square at the end but slightly angled across) and I keep my sharpener close by. I do not hesitate to spend about 5 to 10 minutes sharpening and honing it and testing to see if it matches my expectations before beginning a segment. I look at the scraper edge under a magnifying glass too. The point is that I don't attempt it until I have prepared the scraper for that specific job.

Then I take minute' amounts off. My goal is not the last 1/8 inch but .2 to .4 mm at a time. Then hone the chisel, repeat. I also do this over one segment joint at a time, not the whole pen. After reducing one segment about 1 or 2 mm, I hone and move to another segment and do it. I use calipers to see how close I am getting to the final size. And then I turn the rest of the pen to match the segment joints. Usually, when I am within .5 to 1 mm of final size on the segmented joints, I will start doing the whole blank from end to end

As you can tell, this will take a longer time, but the results are worth it. Others, I am sure will probably do it differently, but this has been my method.

Added in: I use the TBC and also used Epoxy or rubberized epoxy or CA. If I have time to set the segments the day before, I use use gorilla glue because it will fill all the space. Lots of time sections that do not have glue completely filled will let go. Most blowouts that I have had, I could tell there were voids / air space between the tube and blank where the blowout occurred.

Like you, on delicate blanks, I have sanded down rather than risk blowouts. It does take time to do it that way! On my favorite pen seen here and the blank make up seen here - do not allow for sanding, because sanding will cause the solder to smear terribly. The finished pen had NO sanding on the blank, only on the CA finish. It was turned down smooth using the chisel that I described above.

 

[glycerine]

Use some two part epoxy for the glue up, or either the "rubberized" CA glue. That will give a little more so when the aluminum expands from the heat, the bond won't break (at least not as easily).

 

[IPD_Mr]

Scott - turn for a little bit taking very light cuts as you go. Stop and apply CA, like you would for a finish being generous with it. Put on enough that you need to take a couple of passes to get it off. Make sure your tools are sharp. Once you get the CA off to where you are taking material off again, touch up your tools so they are good and sharp. Repeat the process until you get to the size you want. Remember that it only has to get to 165 degrees for the CA to fail.

 

[sbarton22]

I had the same problems about a week ago. I found I wasn't letting the CA cure long enough. Once I gave it more time to dry, I was golden.