Trouble with long barrel Part II

[harik.raif]

Hi, this is my second issue turning a long barrel for a pentel mechanical pencil. As I mentioned before I purchased a nice step drill bit and mandrel. Once I do get a blank drilled, I put it on the mandrel, rough it down ( with a 5/8" bowl gauge, you might think is crazy but works pretty well ), then when I'm getting pretty close to the end it blows out a chunk. I'm not getting a perceptible catch. I'm taking a pretty fine cut, no more than a 32nd. I'm turning at about 3k rpm. and I'm using a sharp skew. This is pretty frustrating. Just like with the drilling I blew out 3 blanks this way. So I lost 4 blanks drilling then lost 3 more turning leaving just one pencil left. I will probably destroy that one too. I'm just trying to figure out how.
Anyway, any thoughts/help would be appreciated.

 

[Curly]

Cross grain wood is inherently weaker than long grain wood and because there is no support from a glued in brass tube it will be even more difficult to cut. Out of curiosity are you successful turning one from long grain hardwood, not necessarily anything exotic?

 

[NJturner]

I might suggest that you may need to help the wood a bit in dealing with the length and pressure of the cut. The wood is getting stressed from both the pressure of the cut and the stress of the actual spinning in the lathe - meaning that any stress fractures or weaknesses in the wood get greatly magnified and ultimately fail. If the wood was stabilized, you minimize some of this risk, but it can still happen. Since you are not stabilizing the wood, I might suggest really soaking the entire length of the wood with thin CA, then let it dry naturally for an hour or two. Reapply the CA. Let dry again - do not use accelerator at any point, because you are trying to get the CA to be absorbed into the wood to harden and strengthen it. Once you have basically hardened the whole blank with CA, then remount and turn. I suggest also dropping your speed roughly in half for the bulk of the turning. You want to do this because the wood has variations in hardness as you pass through the blank. When your cutting a soft spot in the blank, then hit a harder spot, you stress the entire blank - and the faster your turning, the stress of these slight variations is again magnified. Adding the CA helps create a more uniform resistance, as well as increased blank strength.

I'd stick with a really sharp skew at say 1500 after the CA treatment and see what happens. Go to higher speed at the very end prior to sanding if at all.

 

[harik.raif]

Curly, great pic. Yes I have successfully turned these zebra wood blanks before, frankly I think I did better the first time.
NJTurner, this thought was just occurring to me. I use Glu Boost to finish the pens/pencils. It's pretty darn expensive and I don't think I want to be soaking a bunch of wood I'm gonna turn off. But what if I get it down to say with in 1/8 of finished. It never breaks at this point. Then I soak I apply the this stuff generously. Hopefully that would soak in and create some internal strength. It may also soak in and create a permanent bond between wood and mandrel.
I can hear folks saying now, take it off the mandrel first fool! But I find that, probably because of my drilling problems from the other post the mandrel is pretty hard to get in and once the blank is thinner it might not survive the process. Plus it could create some obstruction inside the tube.
Ok, stream of consciousness, I know I'm sorry. So how about this. As it approaches final size, I add a good coat of thin, keep turning, if I go through all the glue I add more till I'm pretty much done. I wonder if this is going to screw up my finish because I wont be really sanding the wood before it becomes a plastic.
Anyway, good stuff. Sorry for the rambling. Too much coffee
Raif

 

[mick]

Cross grain wood is inherently weaker than long grain wood and because there is no support from a glued in brass tube it will be even more difficult to cut. Out of curiosity are you successful turning one from long grain hardwood, not necessarily anything exotic?

Zebrawood, it's also very brittle and has to be drilled SLOWLY with very sharp bits.

 

[mick]

I don't own a stepped bit but have on occasion drilled the larger hole down to the point of the step and then switch to the smaller sized bit. Worked so far. Will also work the opposite way. Drill the smaller hole all the way through then drill the larger hole to the proper depth. This way the smaller hooke acts as a pilot hole.

 

[Mr Vic]

Drizzle Thin CA down the inside and let dry. This will add some internal strength. You may need to ream it out a little with your drill bit by hand.

 

[Bats]

Drizzle Thin CA down the inside and let dry. This will add some internal strength. You may need to ream it out a little with your drill bit by hand.

By hand or under power, I'd think would do about the same thing (assuming the drilling is being done on the full-size, pre-turned blank), so long as you don't let the bit get hot enough to start melting the glue. Or am I overlooking something?

I don't have/couldn't find/haven't used step drills for these, and I don't know what the diameter is offhand - is it possible to glue in a 7mm tube for extra support?

I ask because I used a rather different process for mine - which I later discovered was basically what Don Ward had already documented (except that I used a bit of steel round stock in a metal lathe instead of turning down a soft brass finial on a wood lathe), which made for a much stronger barrel. The big drawback is that it didn't allow for tapering the barrel quite to the diameter of the nib (the base of the nib being exactly 7mm, so the wood had to be left a little proud to avoid exposing the brass) - I don't know whether the method you're using makes that it more practical.


-Bats

 

[Mr Vic]

I suggest doing it by hand to avoid any issues of heat build up causing the drill to get stuck. Ultimately the individuals choice.

 

[Bats]

I suggest doing it by hand to avoid any issues of heat build up causing the drill to get stuck. Ultimately the individuals choice.

Makes sense. I was thinking I'd probably just run it on the drill press around 300rpm, but it occurred to me later that "low speeds" was a big selling point on this press, and a lot of them won't go that low. Using a hand drill might be even better, since it could be run at an I'm-reaming-this-by-hand pace without the actual I'm-reaming-this-by-handness.

(or, better still, use a hand reamer... but who ever has a hand reamer lying around in the right size?)

-Bats

 

[NJturner]

Curly, great pic. Yes I have successfully turned these zebra wood blanks before, frankly I think I did better the first time.
NJTurner, this thought was just occurring to me. I use Glu Boost to finish the pens/pencils. It's pretty darn expensive and I don't think I want to be soaking a bunch of wood I'm gonna turn off. But what if I get it down to say with in 1/8 of finished. It never breaks at this point. Then I soak I apply the this stuff generously. Hopefully that would soak in and create some internal strength. It may also soak in and create a permanent bond between wood and mandrel.
I can hear folks saying now, take it off the mandrel first fool! But I find that, probably because of my drilling problems from the other post the mandrel is pretty hard to get in and once the blank is thinner it might not survive the process. Plus it could create some obstruction inside the tube.
Ok, stream of consciousness, I know I'm sorry. So how about this. As it approaches final size, I add a good coat of thin, keep turning, if I go through all the glue I add more till I'm pretty much done. I wonder if this is going to screw up my finish because I wont be really sanding the wood before it becomes a plastic.
Anyway, good stuff. Sorry for the rambling. Too much coffee
Raif

Raif - I hear you on the cost of the CA and GluBoost. Just bought my first bottle of GluBoost, and it was a bit pricey. A few other people have mentioned also putting some thin CA down the drilled hole in the center of the blank. I think doing that before starting, and then turning down the blank somewhat before getting to the thin stuff to apply CA to the outside, might just get you there. You can clean the inside of the tube with a thin file or a brass circular tube brush if you are afraid to use the drill bit to clean it up. Just be gentle.

As for cost - 4 busted blanks vs the cost of the CA? I'm thinking the CA might just be cheaper in the long run.....

 

[its_virgil]

Hi, this is my second issue turning a long barrel for a pentel mechanical pencil. As I mentioned before I purchased a nice step drill bit and mandrel. Once I do get a blank drilled, I put it on the mandrel, rough it down ( with a 5/8" bowl gauge, you might think is crazy but works pretty well ), then when I'm getting pretty close to the end it blows out a chunk. I'm not getting a perceptible catch. I'm taking a pretty fine cut, no more than a 32nd. I'm turning at about 3k rpm. and I'm using a sharp skew. This is pretty frustrating. Just like with the drilling I blew out 3 blanks this way. So I lost 4 blanks drilling then lost 3 more turning leaving just one pencil left. I will probably destroy that one too. I'm just trying to figure out how.
Anyway, any thoughts/help would be appreciated.

Maybe this will help...a unique way to make the pentel conversion.

Pentel™ Pencil Conversion

Pentel pencils, especially the P205, P207 and the P209 are very popular with accountants and engineers. The step bit made making these conversions much easier. But in the December 2012 issue of Woodturning Design magazine had an article by my...

www.penturners.org

Do a good turn daily!
Don

 

[harik.raif]

Wow! That is a great idea! And the article also has a description of a clip jig for getting the clip on there! I was going to post a question on how the heck to do that! So that's a double win.
On a side note does anyone have any idea what pen would go well with one of these pencils as a set? Maybe I should post that as a separate thread.
Thanks!
R

 

[harik.raif]

OK, I'm done with it. Between the drilling problems and the blow out problems ( although I suspect that is largely do to the zebra wood ) I can't take it any more. its_virgil posted an article on how to do this with 7mm tubes and that's just what i'm going to have to do. FWIW I drilled some more blanks, then poured thin CA down the hole. It immediately started bleeding through to outside of the blank. Then I cleared out the tube with the drill bit. This seemed to remove much of the glue. In any case I still had blow outs and when looking at the inside from the view point of the break it did not look like there was any ca anywhere, despite the fact that it was quite well dosed. I suspect different wood would be easier to use. But now it's the dang principle of the thing. I'm going with a machined slimline clip insert or whatever that piece is. I tried making one last night and it seems like it's not that difficult. I actually didn't drill the holes, just machined of the sort of mushroom part. I"ll probably cursing the heavens when it comes time to drill. But at lease the wood will be epoxied to to a tube.
One last point in favor of this technique, besides all the reduced "infrastructure" is that it will be easier to turn a pen that will look good with the pencil given they will both have the same inside diameter.
Thanks for all the help, and I'll keep you posted on the success of this final technique.
Raif

 

[PatrickR]

I looked at the first thread about this and don't recal you specifying what you were drilling. This looks like cross or diagonal pieces. That alone will make your failure rate very high. I have seen the tube pentel write up and it will give you a pencil with the pentel mechanism but it will be substantially bigger and heavier.
if you are inclined try your process with a piece of plastic to see how it goes. That will show you how much of the problem is due to grain. You may just need to change wood types to get acceptable results.
I just drilled a 9/64 hole through a 7" piece of snakewood that is centered at both ends. it is doable but with crosscut wood your failure rate will be very high.

 

[PatrickR]

^ Correction - 19/64

 

[Bats]

I have seen the tube pentel write up and it will give you a pencil with the pentel mechanism but it will be substantially bigger and heavier.

Maybe not as substantially as you'd expect. The 7mm tube does mean a slightly larger hole (the mechanism itself, at the widest end, could squeeze down a ~6.3mm hole), but the added rigidity also means you can turn down the wood far thinner than if it were unsupported, which is likely to balance out.

The tube itself definitely does add some extra weight - about 4g (useless factoid: 7mm tubes weight about 1g/in)- which could be seen as substantial compared to the basic (plastic) pencil's 9g. I don't have a tubeless version to compare it to, though, and the finished one I have handy is both fatter than necessary (there was some figure I wanted to preserve) and stabilized, both of which are going to add some chonk - it tips the scales at 15.8g. I like my pens/pencils a little on the heavy side, though - and the stock p205 is awfully light - so that suits me fine.

The one point where I think the tube version may have a significant drawback is by the tip. The nib is about 6.7mm (.2637") where it meets the 7mm tube's 6.8mm (.2677" - and yeah, 7mm tubes aren't actually 7mm dia), meaning even if you turn it down to the bare brass you won't get a perfect transition - and once you add enough wood to keep it from chipping off the end of the tube, you'll be able to see the difference. This may or may not be a problem with the tubeless variety, too (which would explain why so many examples have an exaggerated lump at the nib end), I don't know.

 

[leehljp]

There have been times when I got to a certain point in size that I took 220 or 320 sand paper and worked it down to size with that. I rarely use sandpaper now but on an occasion, I will in delicate situations. CA it well and then do a clean up with very light touches of a scraper.

BTW, I have made a custom made pen successfully and then the next 6 or 7 were disasters! It happens.

 

[Bats]

There have been times when I got to a certain point in size that I took 220 or 320 sand paper and worked it down to size with that.

Ahhh, the 220 grit gouge! My favorite chisel for detail work!

I rarely use sandpaper now but on an occasion, I will in delicate situations. CA it well and then do a clean up with very light touches of a scraper.

I managed to do it with carbide and a light touch (and then sanding back the barrel length to remove the bit where I'd shaved through to the brass) and took the wood down to just a hair over 7mm (I just mic'd it as around 7.05mm), but there's just no getting around the fact that the brass is wider than the base of the nib. It's probably possible to hybridize the two methods - using a tube to strengthen most of the length and then a step drill for the very tip - but I didn't play with it, since my goal at the time was to be lazy and avoid the finicky drilling.

BTW, I have made a custom made pen successfully and then the next 6 or 7 were disasters! It happens.

Bah - that's nothing! I'm so good I can make 6 or 7 disasters without even making a custom pen!