Crack/Blowout Repair?

[Fibonacci]

I apologize if this is in the library somewhere, but I couldn't find it.

How do people deal with cracks and blowout in a blank?

I have been doing one of two things about blowout:

1. Cut back the blown out part and put a contrasting piece of wood on that end of the blank. This has given me mixed results. I most cases, the thin part on the end either ends up blowing out itself, or I get a small gap where they meet.

2. Sand the tube down past the blowout and modify the hardware to make it fit. This only works on some kinds of pens (I have had it work for slimline and cigar), but tends to give better overall results.

For cracks, I have tried drizzling glue into the crack and letting it dry before continuing, but that has resulted in a blowout every time that I have done it. On one that cracked during assembly, I was able to glue it and add a CA finish to cover it. That worked well, but the item was fully turned before I added the glue.

 

[76winger]

On most of the few that I've had, have been minor enough that It didn't go all the way to the tube and I was able to continue turning and just go slower and take very thin cuts each pass until I had id cleaned up. Of the two or three that's gone clear to the tube, I've usually ended up turning it all down the to tube and putting a new piece on it.

Filling cracks and gaps with CA has thus far worked VERY good for me and I've never had any problem turning blanks that I've done this on. I first saturate it a couple times with thin, so it soaks into any bark or soft areas. Then I fill the remaining gap with thick.

Maybe my success in this area is because I cut down and turn using light slicing passes with a skew, whereas a lot people I see use a gouge and go at it more aggressively. In either case, try to make sure the angle of attack of your cutting edge is performing a slicing action rather than a tearing action.

 

[monophoto]

Each failure has to be dealt with individually because they are all different.

If you detect the problem before it explodes on you, you can soak a cracked blank in thin CA. The CA will be drawn into the crack. Work gently when turning the blank, and if the crack appears to get larger as you take off the outside layers of wood, soak it again.

If the piece comes off in one chunk, you may be able to simply glue it back on using some CA (medium may work better in this case).

If the blank explodes, then you can do things like adding a bit of contrasting wood, or adding some kind of filler. I've used ground coffee, and some people use ground stone in a contrasting color.

 

[azamiryou]

1. Cut back the blown out part and put a contrasting piece of wood on that end of the blank. This has given me mixed results. I most cases, the thin part on the end either ends up blowing out itself, or I get a small gap where they meet.

We call this an "oops band". It's almost as common as blowouts.

I've never had the contrasting band blow out. I can only surmise that you're either not using enough glue, or not giving it time to fully cure. Or you're cutting too aggressively or with dull tools, which could have caused the original blowout as well.

I'm not sure what you mean by a gap - is it all the way around, or just on one side? If it's all the way around, then I would guess your shoulder is not perfectly flat - use a parting tool to make sure you've got a clean shoulder at 90 degrees to the tube. If the blank is near its final size, you could even undercut it a little bit.

If the gap is just on one side, then either the blank or (more likely) the contrasting wood surface isn't perpendicular to the drilled hole. Use a parting tool to clean up the blank. The contrasting band has to be squared up just like a blank; insert a spare tube to hold it for this operation.

For cracks, I have tried drizzling glue into the crack and letting it dry before continuing, but that has resulted in a blowout every time that I have done it. On one that cracked during assembly, I was able to glue it and add a CA finish to cover it. That worked well, but the item was fully turned before I added the glue.

I echo others' responses here - use thin CA, let it soak in, and give it time to cure. If you're still having trouble after that, tools or technique are likely the culprit.

 

[Fibonacci]

1. Cut back the blown out part and put a contrasting piece of wood on that end of the blank. This has given me mixed results. I most cases, the thin part on the end either ends up blowing out itself, or I get a small gap where they meet.

We call this an "oops band". It's almost as common as blowouts.

I've never had the contrasting band blow out. I can only surmise that you're either not using enough glue, or not giving it time to fully cure. Or you're cutting too aggressively or with dull tools, which could have caused the original blowout as well.

I'm not sure what you mean by a gap - is it all the way around, or just on one side? If it's all the way around, then I would guess your shoulder is not perfectly flat - use a parting tool to make sure you've got a clean shoulder at 90 degrees to the tube. If the blank is near its final size, you could even undercut it a little bit.

If the gap is just on one side, then either the blank or (more likely) the contrasting wood surface isn't perpendicular to the drilled hole. Use a parting tool to clean up the blank. The contrasting band has to be squared up just like a blank; insert a spare tube to hold it for this operation.

The gap is all the way round. The shoulder not being square makes sense.

Almost all of my blowouts are with my large gouge, even when it is freshly sharpened. I have been thinking about putting more angle on it, as my small gouge works much better and has a much larger angle. I would think that it should be shallower than the small one to take advantage of the thicker metal, but I don't know enough about the theory of lathe tools yet.

 

[Fibonacci]

I added a bit more angle to the large gouge tonight. That made all the difference in the world. The chips were really flying then.

Which begs the question: If I had to reshape the tool, does that indicate that my technique is totally out of whack and in need of correction?

 

[azamiryou]

If I had to reshape the tool, does that indicate that my technique is totally out of whack and in need of correction?

Maybe. The angle of the tool to the work is related to the bevel, so a different bevel means a different angle. The way I learned - and it seems to work pretty well - is ABC: anchor, bevel, cut. First, get the tool solidly on the tool rest. Second, bring the tool to the work so the bevel is riding the work. Third, raise the handle (lower the tip) of the tool just until it starts to cut.

I'm sure there are other techniques, but this (and sharp tools) works very well for me. I don't get many blowouts, and when I do, it's because I was getting impatient and aggressive.