Wood cracking observations/questions

[Jhecht]

Hello. New member/lurker here that is just getting back into making a few pens. I like ebony and burls and am a bit paranoid about cracks, which seem to be a fairly common concern and point of discussion here. I've never had a pen develop cracks over time, but have had a few crack when pressing parts — which prompted me to a few thoughts (always dangerous):

1. I have seen discussion of brass tubes being a potential cause of problems, in that the metal may not change but the wood does. Makes sense but on the other hand the fit between the tubes and drilled holes in the blanks tends to be relaxed in most cases. Pressing in the parts, however, by definition and of necessity would seem to create a great deal of pressure on the tubes and blanks — significantly aggravating the potential for problems, either during assembly or leaving even less room for movement of the wood over time. So the hypothesis/question would be whether it is not so much the use of metal tubes, but rather the use of pressed parts, that is the bigger culprit in splitting/cracking issues. If so, would that argue for more frequent use of slip fit and gluing parts (i.e. by sanding down the pressed parts or tubes), instead of pressing? The downside of more work and the inability to later disassemble the pens might be outweighed by a significantly lower risk of cracks. Maybe this point is obvious, and I have seen reference to people sanding and gluing parts for this reason, I just wonder if there is a case for this to be more common given the large number of concerns with splitting of certain woods.

2. I wonder in this regard if kitless or semi kitless pens like the Apollo might have an inherent advantage in this regard, to the extent they are using only glued parts as opposed to pressed (and regardless of whether any tubes are used for support). It would be interesting to know if makers using only glued parts (with kitless or otherwise) experience fewer issues with cracks in split-prone woods like ebony over time.

Anyway, sorry for the long post and ramblings. Would be interested in any observations by the experts here. Seems like loads of great information on every possible topic here btw. Thanks.

 

[Todd in PA]

I've often wondered why the makers of pen kits even use compression fittings on thin pen barrels. Why not just size the parts to be slip fit and change the instructions to use glue. The industry standard seems to be press in parts.

 

[monophoto]

I probably don't have as much experience as some others here, but I can share a few thoughts based on observation of some of the pens currently residing on my desk.

The fact that wood can expand or shrink over time, especially with changes in temperature and humidity, is a factor. We are dealing with fairly small pieces of wood, so the amount of possible movement is quite small., but brass tubes don't change significantly, and the fact that wood is glued over tubes means that expansion or contraction of the wood can cause cracks. The fact that the holes we drill in blanks are larger than the tubes is not it self a source of problem - any excess space tends to be filled with glue (or at least should be - that's a subject for a different conversation). I'm a fan of the more resilient glues such as epoxy and polyurethane - I don't have any proof, but intuition says that using those glues tends to reduce the tendency of wood to crack because it is resilient and can move with the wood. By contrast, adhesives such as CA that cure to form a hard, brittle plastic, may be less forgiving. It would be interesting to see some tests of this theory.

Jhecht suggests that pressing parts together causes the brass tube to expand microscopically, increasing the stress on the wood. My 'every day travel' stylus reinforces that notion - there is a minute crack at the end of the blank where the finial was pressed into the tube. That crack is only a couple of milimeters long, and doesn't proceed past the end of the component inside the brass tube, so I think it's pretty safe to assume that assembling the stylus expanded the tube very slightly.

But I think there are other factors that enter this issue - one is the nature of the wood. Some woods expand/contract more than others. Straight grain woods tend to resist cracking better than burls. And the thickness and design of the turning is a major factor - a pen that is slightly 'fatter' in the middle of the turning, tapering to the end, will be less likely to crack than a pen that has a uniformly thin layer of wood glued to a brass tube.

 

[jttheclockman]

JHecht (sorry do not have a name) but welcome to the forum and look forward to seeing your work and continue with discussions such as this. Your point is well founded and Louie, as he always does covered the topic well. I will chime in with my thoughts and some are just repeating words. When working with pen kits as opposed to kitless pens you will notice a few things. Kitless pens are 99% made from non wood products such as metals and plastics so they can be easily threaded. If wood is used it usually is not threaded and a piece of plastic or metal is glued in its place to accept threads. Being wood expands and contracts it would be difficult to keep caps working well as other parts too. Those that make kitless can address this better and correct me if wrong. Also most parts are made by hand when working with kitless.

This is going to be a long reply. That is the first thing. next is the use of compression fit on components in kit pens. This has become a product standard and I am only surmising but because it is the easiest way to build a kit and gluing in parts can become very messy and problematic in case they need to be disassembled as you mentioned. Most adhesives do not play well when gluing in coated metals. Any adhesive that got on platings can destroy the plating as we see with CA. So pressing of parts is a better way around this and a universal method. Over time adhesives dry out and can become dislodged and other problems arise.

We as pen makers over the years with plenty of practice develop ways around problems that arise with different materials used as well as different kits used. With each form of pen making and materials used comes with its own do's and dont's and it is up to us to work around them. That is the challenge of making a hand made item such as pens. To address your concerns of wood cracks it is one that unfortunately you are fighting with Mother Nature. All woods will move both ways. Many woods are just more inherent to form cracks than others. With experience you can avoid those woods or you can do your best to help not cause them. Sometimes it is a losing battle. But a few ways to avoid cracks is to seal the wood and work with well dried materials. If you start with dried woods and seal them the chances of outside moisture is reduced. When I say seal I mean both inside and out. Many people do not seal a blank after it is drilled on the inside but a thin coat of CA can do this and that is what I do. Seal the ends when sanding and finishing and not just the outside. We are often left with a thin piece of wood after it is turned down to dimensions needed. Any pressure put on those edges from either pressing in components on a wrong angle or just too tight will add tension to that thin wood. We try to avoid by the obvious. Pressing straight in and if need be file the inside of the tube to get more of a slip fit. Sometimes the kit parts come with more plating than others and there is no way of knowing till too late. But check before pressing in and take appropriate steps. The other thing is many kits give you drill bit sizes to match the kit but that is not gospel. Have a good set od drill bits in both metric and English is handy. You can step up one or 2 sizes larger to give some breathing room between tube and blank. This will not hurt but need to be aware how much material you have to work with for final product. Again experience works well here. Finally the adhesive you use. If you use CA that dries brittle and the wood movement can not happen. If you use polyurethane or epoxy which I always do then that stays flexible and just gives you another tool to fight that cracking you refer to.

There is nothing wrong with filing out the inside of tubes when needed to make a slip fit. I suggest using either red or blue loctite when gluing in parts. Many of these things come up as we make hand made pens and with experience we learn ways around them. Then there is the tried and true method to avoid cracks is to not use wood as a blank. Good luck.

 

[jrista]

I don't have any answers for you... All I can say is, I have the same question:

"Why aren't pen kit parts slip fit?"

I have not had many wood pens crack, but I have had other materials, including buffalo horn and trustone (and its cheaper alternatives) crack. I'm a fan of the trustone stuff, and I was quite dismayed when I first started turning it that many blanks cracked due to compression fit parts. I have particularly had this problem with the Triton pen kit...which I absolutely love, but wow, something about its design, it seems highly prone to cracking blanks (these pens are the only ones I've had wood blanks crack with.)

I'd be all for a complete shift to slip fit, away from compression fit, to avoid any risk here.

 

[jttheclockman]

I don't have any answers for you... All I can say is, I have the same question:

"Why aren't pen kit parts slip fit?"

I have not had many wood pens crack, but I have had other materials, including buffalo horn and trustone (and its cheaper alternatives) crack. I'm a fan of the trustone stuff, and I was quite dismayed when I first started turning it that many blanks cracked due to compression fit parts. I have particularly had this problem with the Triton pen kit...which I absolutely love, but wow, something about its design, it seems highly prone to cracking blanks (these pens are the only ones I've had wood blanks crack with.)

I'd be all for a complete shift to slip fit, away from compression fit, to avoid any risk here.

My question to you is how do you do that? Parts would fall off. Not all platings are the same. Even kits made from Dayacom are pressed in and they to me are the leaders in pen kit world. As I said what a mess it would be to have to glue parts in. The problem is in the wood world. If you look basically it is us pen makers who make wooden pens. You rarely see wood pens being made by the big name brands. Twist pens would have to be done away with. If some of the things I mentioned were followed by pen makers who use wood I bet there would be less cracking. But again a 2X4 can crack and develop hairline cracks. Stabilizing might be an answer for woods that are prone if they can even be stabilized. I actually think the pressing of components is ingenious way of assembly.

Now with that said I would like to see pen kits with smaller tubes. To me there is no reason for caps to be as large as they are. Even barrels can be made thinner. What this does gives more meat on blanks to combat such problems. Of course the down side of this is a weight thing . But with many of these gaudy looking pen kits today they could go on a diet easily. Just more fuel for the thought process.

 

[sorcerertd]

There's soooo many variables. You might get better feedback asking more specific questions about specific kits or materials when the time comes to make decisions. Here's some things to consider, though:

• What type of wood? (Some are notorious for cracking. Snakewood and Ebony are great examples.)
• How dry is the wood?
• Did you take your time drilling so that the bit would stay cool?
• How tight is the fit on the tube after you drill the blank out?
• If you are not using wood, is there a little room for the brass tube to expand without putting pressure on the blank material?
• What type of adhesive are you using? Does it set rock hard or have slight elasticity?
• What's the humidity like in your shop? How about where the pen will be stored or used? (We usually don't have much control over the latter, but it does matter)
• What is the quality of the pen kit and/or manufacturer's QA process? (I've had some that barely fit the tubes and a couple that were loose enough that I wasn't comfortable not gluing them in.)
• This is kind of a BIG deal: Make sure there is NO adhesive inside the tube before you press the parts in! Are you sure? Try running a bottle brush through the tube and look again before you press.

There are many other pen turners here with much more experience than myself. They can probably add to that list.

That being said, one thing is for certain. There's going to be duds, whether it was a manufacturing defect in the kit, a poor quality blank, or a bad decision in your process. It's a learning process. For me, mostly learning patience and caution. I've made what I thought were some nice pens, only to mess them up with stupid mistakes. Then again, sometimes that leads to a beautiful plan B.

 

[jrista]

My question to you is how do you do that? Parts would fall off. Not all platings are the same. Even kits made from Dayacom are pressed in and they to me are the leaders in pen kit world. As I said what a mess it would be to have to glue parts in. The problem is in the wood world. If you look basically it is us pen makers who make wooden pens. You rarely see wood pens being made by the big name brands. Twist pens would have to be done away with. If some of the things I mentioned were followed by pen makers who use wood I bet there would be less cracking. But again a 2X4 can crack and develop hairline cracks. Stabilizing might be an answer for woods that are prone if they can even be stabilized. I actually think the pressing of components is ingenious way of assembly.

Now with that said I would like to see pen kits with smaller tubes. To me there is no reason for caps to be as large as they are. Even barrels can be made thinner. What this does gives more meat on blanks to combat such problems. Of course the down side of this is a weight thing . But with many of these gaudy looking pen kits today they could go on a diet easily. Just more fuel for the thought process.

You seem to have missed that I said it was non-wood materials I had the most problems with. I have only had wood crack with a couple of Tritons. Usually its the resins that crack for me.

As for gluing parts in, I don't think that would be a mess. Once glued in, I don't see parts "falling off" all over the place. I have been filing down triton and similar git parts for a while now, to the point where they are slip fit, and haven't had any issues with parts falling off over the place. One of the nice things about a slip fit is you can try out the assembly, without having to worry about having to disassemble, nor all the risks associated with that. You can test your part fit and the seam of the part to the blank very easily with a slip fit, zero risk!! With compression fit, you can't see how well parts fit, nor trial fit to check seams, etc. unless you intend to fully assemble, then take the risks of disassembly (scratching, cracking, crushing blanks and tubes, etc.)

IMO there are a lot of benefits that could be had with slip-fit parts. And the glue thing is a red herring.

The one thing I do agree with is, tubes can certainly be smaller. I'm not sure weight is a huge issue with a lot of people, as many people seem to really like Cigars, which are actually exactly what you described: smaller tubes, beefier blank thickness, and a good deal heavier. Somehow, that heft and weight seems to appeal to a lot of people. Not everyone, but I haven't seen it be a huge issue either. I think a lot of the capped pens could certainly use smaller tubes and have a little more heft.

Would a thicker turned blank prevent cracking, though? I'm not sure...in fact, a very thin blank should actually have more flex, whereas a thick blank might not. For some harder resins, a thicker blank might make the cracking issue worse... I don't know for sure. Would be an interesting study for sure...but, one thing I do know: If parts were slip fit, it would never be a problem regardless!

 

[jttheclockman]

I did miss the part about non wood. Bone, antler and materials like that can be a pain as you said too. I just can not see them going to slip fit. That would be a huge investment in either retooling or using different tubes. Just see it as a messy deal. I believe in your case the best tool for you is what Ken mentioned not long ago and that is the tubing expander. https://www.penturners.org/threads/tube-expander.176341/ Probably the one factor you would have to contend with is the size of the drilled hole which may have to be increased.

 

[jrista]

I did miss the part about non wood. Bone, antler and materials like that can be a pain as you said too. I just can not see them going to slip fit. That would be a huge investment in either retooling or using different tubes. Just see it as a messy deal. I believe in your case the best tool for you is what Ken mentioned not long ago and that is the tubing expander. https://www.penturners.org/threads/tube-expander.176341/ Probably the one factor you would have to contend with is the size of the drilled hole which may have to be increased.

Oh, I don't see anything CHANGING.

I'm just sayin...slip fit has so many benefits.

 

[jttheclockman]

Oh, I don't see anything CHANGING.

I'm just sayin...slip fit has so many benefits.

In your eyes and in mine I see nightmares.