Moisture, Movement, and Finishing

I like to make fountain pens for myself, and I thought I'd branch out and make one from wood rather than metal as I have done in the past. This one also marks my first 100% self-made pen as well, the nib, feed, body, etc. all made by me.

The main issue I had was with the body. I had adapted a design that I've used successfully on metal pens before, a delrin sleeve to hold the ink out of contact with the body, with a modest press fit to keep the sleeve in place when the nib and feed need to be removed for filling.

That's the background, now on to the problem. The wood is from a 1-2" diameter branch of an American elm tree (I think, there's a possibility that it's slippery elm, I can't tell) which has been drying bark on for 18 months. I cut it to a size I was happy with, fitted the body, and finished with Tung oil. To expedite the polymerization process, I dropped it in the lab oven to hold it at 90°F and lots of air exchange. Two coats, 3-5 days apart each, no noticeable scent left from wiping the pen after the second coat.

Once I was satisfied with it, I went to press in the sleeve and found the hard way that my body had shrunk! I measured it after the fact to find that I was actually asking for almost 0.008" of press fit, which is outrageous for a 1/2" pen diameter.



After a bit of searching, I found this thread here which makes me a bit leery of doing a plastic-sleeve-pressed-in wood body at all, but there was some talk about sealing the wood at a particular moisture content to prevent this type of thing.

So, do any of you think it's possible? Is it just going to crack later as the years and seasons go by? Tung oil is supposed to have good waterproofing properties, will it be sufficient to stop moisture migration? Could it possibly make a wood body watertight enough to hold ink directly?

My first choice would be to try again with the elm branch, but I also have some hard maple which I think would make an attractive pen if that's more likely to be a success.

I don't know much about pen making, but can you dry the blank first, then bore it? Or dry it, pressure stabilize it with epoxy then bore it?

I have made a lot of wood pens and pencils from kits. The kit is the metal mechanism with two brass cylinders. The wood blocks (1/2" x 1/2" square by 2" long) for
the pen body are bored out lengthwise and the cylinders are coated with super glue and inserted into the blocks. Then the cylinders are inserted onto a metal shaft
and the blocks are turned round. Even with glue holding the wood, some would crack like your picture. If wood is going to move it's going to move no matter what.

Your branch wood did not fully dry out. Maybe if you drill a smaller pilot through your block and then let it dry. Bore it to size when fully dry.
Other people have used PEG on wet wood which I never tried.

If you look at the wood body hole and it changed from circular to oval then its the drying thing. A general rule is 1" thickness per year when air drying. Who wants to wait
that long.

Gonna be a little guessing about the moisture level, but I’d bake it in an oven as a roughed out blank and then seal it with epoxy resin all around. Finish machining and recoat with epoxy.

So get it real dry and stabilize with epoxy in and out then work it.

So the thought is that Tung oil isn't going to hack it for moisture control? I'd prefer not to use epoxy since I like the way Tung oil finish still has a natural feel to it. I just took a look at the body again, looks like it has stayed at its smaller size but I don't recall exactly what it got down to. Still a fair bit below .500 like it was when I finished it in the air-dried condition. It has been at least a couple weeks since I busted it, so maybe Tung oil is good enough to keep it stable and I won't need epoxy after all, but I wanted to know if anyone here could answer definitively on that without me needing to go through another round of cap/body making.

If I understand your post correctly you are turning down from the intact branch rather than turning a split piece of it?

If so, that will be much more prone to cracking due to radial stresses. Only way that will work is to dry it more and then stabilize it with some kind or resin. Tung oil won't do the job.

Another thought would be to let it crack, fill the crack with clear resin with additives such as pulverized mother of pearl to make it interesting and then re-drill for a brass tube as per normal practice.

A resin finish looks more natural if you dull the gloss with pumice.

If it shrank after machining it obviously got drier. When you say it was drying for 18 months, was that outside or indoors? It just won't get dry enuf outside, needs to be in a heated space, unless you live in the desert.

The simplest solution, as suggested above is to stick it in the oven before you machine it. If it's dry to begin with, it won't matter what kind of finish you use.

I checked the wood shrinkulator calculator on the woodweb site and it can help you understand the rate of shrinkage vs moisture content. The calculator doesn't go below 1" wide so I used the 1" dimension and split the calculated number in half.

For American Elm, the shrinkage rate for a 1/2" blank should be around 0.0100 using initial MC of 13% and final MC of 7%. I think this is a typical swing from air dried to kiln dried. Your location could affect the percentages to some degree.

As mentioned, tung oil will do little to inhibit the movement. The blank hasn't stabilized because of the tung oil, it's "stabilized" because it's most likely being kept in an environment with the same ambient MC.

As pointed out already, moisture is your problem. To be honest, any wood is the problem as it is all going to move and 99% of time it does exactly what your piece did. I make wood duck calls for a living so have dealt with this for many decades.

First thing is starting with dried wood, I only use kiln dried anymore as it’s the only way to get any consistency for my selected species and use.

I would suggest starting with properly dried pieces of wood and after drilling your holes, wipe the end grain with shellac and set aside for a few days to a few weeks (depends on when the movement subsides). When the holes have stabilized, you can then ream (by hand) with a chucking reamer back to the correct hole diameter. Note, your reamer may need to be a thou or two over nominal.

At this point you can install on mandrel and turn away with a lot less worry about hole shrinkage.

Tip, you might hit the pieces every day or two with the reamer in lieu of waiting till the end as it’s easier to shave a thou or two off at a time instead of .008” at once.

I hope some of this made sense!

Murf


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You can still finish with tung oil after using epoxy. I like the look and feel of tung oil a lot. You can have a sealed piece os wood and your choice of finish.

Thanks for all the input. I would be totally happy if the pen could simply live in the same building indefinitely, so if I can make that work with a dry, rough cut, stabilize, finish cut, tung oil process and get something that won't split I would be very pleased. I also think it would improve my chances to leave the liner a bit loose and glue it in rather than try for a press fit, since even a single percent MC is going to be enough to either remove the press or split the finished pen if it's pressed in.

What's odd is that the wood has in fact been in the same building where I was doing the work and plan to keep the finished product, for those 18 months. Maybe it didn't dry out all the way with the bark still on?

The big mistake I made before. Thinking that coating a piece of wood in tung oil or some other type sealing finish is going to keep the wood from moving.
You can't displace water in a wood cell, you can only surround the cells with sealer. Maybe it helps a little but I'm not sure if the movement is just slowed down
or reduced. My 7' x 4" table moves every season and it is covered in tung oil.

This is why we have laminated impregnated wood products. To get as close to those might be to vacuum bag impregnate the roughed out blank. It would not be super expensive given the small size of your parts.

You took 'air dried' wood and 'kiln dried' it

kiln dry it first, as mentioned

Hi Pete. I'm in the wood business. Lots of good advice from others in this thread.

Wood is hygroscopic, which means that it will move as it absorbs and releases moisture. Typically in a modern climate controlled home it will equalize to around 8% moisture content (MC). In a non-humidity controlled environment, it will typically vary between 10% - 15% depending upon your geographic location.

Oil finishes typically harden "in the wood", and not "on the wood". To harden on the surface, you either need to use a film finish (varnish, poly, or for pens cynoacrylic (CA) is very popular), or you need to use an additive called "Japan Dryer" in your oil.

Your pen blank shrunk because it lost moisture after milling. Moisture in wood cells falls into two categories - free water and bound water. Think of an egg.... the yolk and egg white represent the free water, and whatever moisture is contained within the eggshell represents the bound water. Wood movement only occurs when there are changes to the percentage of bound water.

What many pen turners will do is they will rough out their blank somewhat oversize, dry fully it on a low power setting in a microwave oven, and then soak it in a stabilizing agent such as pentacryl or CA, and then complete the dimensioning and finishing. Fully stabilized in CA, you won't get any absorption of the tung oil, but the CA will provide a very durable finish.

You could also fully dry the roughed in blank in a microwave, then soak it in tung oil, and then finish turning it. Be sure to allow it 24 hours or more for the tung oil to cure after soaking. I like to thin my initial coats of pure tung oil with 50% d-limonene - a citrus based solvent. Turpentine is another good alternative. the 50% thinning will encourage greater depth penetration of the tung oil.

Best of success to you with your project.

Scott

Cactus juice (google) is popular with cue makers, for stabilizing burl wood, spalted woods, and wood that would normally be too soft for a cue butt. I never tried it, but am tempted for a burl.
Sometime after a lot of other more pressing projects.

For any "stabilizing" method to be successful, the substrate wood has to be bone dry to start with.

People have mentioned epoxy saturation.
Back when i was still making wooden totes for metal handplanes, i tried several experiments to vacuum impregnate them.
Never found WEST to penetrate much more than it does merely painted on. IOW, "barely". At virtually net size with all but the final sanding required, it seems to add a modicum of useful "stabilization" to wood fibers. After sanding that, i count on a saturation coat of very thin shellac. Sand that after full dry. Then soak with penofin until it bores me, and finish with wax. Honestly, half of finish methods like this one mentioned is superstition.

Some cue makers who are finish challenged and don't mind challenging their lungs and remaining few brain cells, use cyanoacrylic glue finishes. Brilliant, under glass effect, but it is not really durable in the sense that it is brittle, can crack, & dents pop it easily. OTOH it is probably safer than linear polyurethane clearcoats.....

Shellac alone, with wax on top, makes a spectacular finish, but you might have to refresh it occasionally. My cues last for years & stay bright, but other peoples hand chemistry can be different to the point of softening lacquer or sometimes shellac.

smt

Can you make a narrower diameter metal pen, that gets a wooden sleeve? You could allow clearance for shrinkage.

thermite, are you a southpaw? explains everything.