Tips for Preventing Splits
in Pen Barrels

You can easily prevent
splits in your pen barrels using these techniques

One of the more frustrating things a new turner can experience is having one of their pen tubes split, either during turning/sanding or during final assembly.

While this can be an aggravating problem, it's also one that can be easily prevented by taking a close look at your turning and assembly protocols. Here are a few tips to help make sure your turning protocols are optimized for the best chance of success.


Pen Barrels: Blank Preparation Concerns

Pen blanks need to fully reach equilibrium moisture content (EMC) before turning. Most pen blanks that are sold by turning suppliers do not give any indication of how dry the blanks actually are, or even when they were first cut. I've met many turners that thought their pen blanks were "dry," only to find out that they were still quite wet when they begin to cut and drill the blanks.

This is further complicated by the fact that many woodturning suppliers list their turning stock as "partially seasoned." This can be confusing to new woodturners who think that the wood they just purchased is ready to go, when in fact it may need several weeks, or even a few months before it's dry enough to use. For me, it has either reached EMC, or it's still green – there is no middle ground.

If you use a pen blank that has not fully reached EMC, the subsequent drying of the blank, either during turning or after assembly of the pen, can easily cause the pen barrels to split. To prevent this, I always date and mark pen blanks when I receive them from a supplier, or when resawing them on the bandsaw from thicker billets.

This date is my "first cut" date and lets me know how long the blank has been laying around in the studio drying. Since I don't know when a supplier may have cut the blank, I just use the date of receipt as the first cut date. This gives me an extra measure of protection when working with purchased blanks, which is a good thing.

I also wait a minimum of one year before using any pen blank, unless it's a man-made composite. This "aging" period helps to insure that the blank has reached EMC and is ready to turn on the lathe. Many exotic timbers dry very slowly, especially if they're stored in garages or sheds without any heating or air-conditioning. Although my studio is air-conditioned and heated, I still use the one-year rule for pen blanks.


Pen Barrels: Drilling Concerns

Many exotic timbers are very susceptible to heat checking, either during drilling or sanding. Therefore, you should always try to minimize any heat buildup during the drilling process when drilling your pen blanks. One good way to do this is to adopt a "fluid-pulsed" drilling technique that helps to cool the bit and keep the flutes clear of shavings and sawdust.

To watch a 90-second video of the fluid pulsed drilling technique, click here.

Using a fluid pulsed drilling technique helps to cool the bit and clear the flute of shavings

If the blank is overheated during drilling either by using a dull drill bit, or by continuing to drill when the flutes are impacted with shavings, you can cause microscopic hairline fissures to form inside the drilled hole in the pen blank. As the pen blank cools, these fissures can increase in length and width. To prevent this, always use sharp drill bits when drilling your pen blanks and frequently clear any impacted shavings from the flutes.

Another concern is drilling at too high a speed. As you drill your pen blank, the rotation of the drill bit inside the hole causes friction. This friction generates heat. The heat is transferred into the drill bit and the walls of the drilled hole. If your drilling speed is too high, the heat generated can be significant and you can develop heat checking inside the pen blank. When the pen blank is later turned and finished, these checks can migrate to the surface of the pen barrels, resulting in a visible crack.

Sharply pointed brad
point drill bits are not recommended for drilling blanks

Most of my pen blanks are drilled at 650 RPM using bullet pointed bits, or parabolic bits. I also use brad pointed bits on occasion with some materials. When drilling a lot of blanks, I setup an air hose to blow cool air across the drill bit and down into the hole to help reduce heat buildup.

This is not necessary when you're drilling a few pen blanks, but it sure helps when you've got a stack of 50 or 100 blanks to drill.

Bullet point drill bits are recommended for most drilling applications into endgrain exotics. Notice the small bullet point on the tip of the bit

Parabolic high-speed drill bits. The flutes are specially designed to allow faster chip extraction


Pen Barrels: Sanding and Finishing Concerns

Heat checking can also be produced when sanding your writing pen barrels. This is exacerbated if you use your abrasives too long. As abrasives wear, they begin to burnish more than they cut, which increases the heat generated. Overly aggressive sanding (pushing too hard) can also cause excessive heat.

Excessive heat during sanding can cause microscopic fissures to form on the outside of the pen barrels. As the barrel subsequently cools these can open up, increasing in length and width. To help eliminate any heat buildup, shoot a bit of cold air from a compressor onto the surface of the pen barrel between each abrasive grit change.

I would also encourage you to cut your abrasives into thin strips and use them only once, then throw them away. Reusing abrasives is a false economy, pure and simple. You should always use abrasives like someone else has to pay for them and they have really deep pockets.

You can also slow the lathe down to 500 RPM or so when sanding and this will help to reduce any heat buildup. If you sand at high speeds, you need to allow the blank to free-spin a bit between each grit change, or direct cool air streams onto the barrel from a compressor when sanding.

Full-size sheets of abrasive can be easily cut into strips for working on small projects

Remember, when your pen is turned down to the bushings, very little wood is left around the brass tube. On slim line pens, it's less than 1/16" on an inch. It does not take too much heat to overheat that small amount of wood. Even on larger pens like the Cigar and Gentlemen style pens, the amount of wood left around the brass tube is quite small. Heat is your enemy, but it can be controlled very easily with simple counter measures that anyone can employ.


Pen Barrels: Assembly Concerns

Even if you've done everything right up to now, your pen barrels can develop cracks during assembly of the metal pen components. There can be several reasons for pen barrels cracking during assembly, including these:

1) The components may be inserted at a slight angle, instead of straight into the barrel. To prevent this, make sure you insert your components straight into the tubes. Any deviation from this can cause the component to be inserted at an angle, this in turn makes the brass tube over expand to accommodate the component which can crack the barrel. Pen assembly jigs help to insure you insert your components straight into the tube, so if you're having problems, consider purchasing or building your own assembly jig.

2) The pen component may be slightly oversize, causing the brass tube to over expand upon insertion, which breaks the thin wood around the tube. I have found that pen components can vary in size (several thousandths of an inch) from kit to kit. If this is the case, you may be splitting your pen barrels unknowingly, even if your insertion procedure is "spot on." The reason for this is due to the fact that pens utilize components that are press fit during assembly.

This means that whilst you are inserting the component, the brass tube must expand a tiny bit to accommodate the component. It's this slight expansion that holds the component in place through friction. If you have a bad batch of components that exceed normal size, when they are inserted into the pen barrel the subsequent expansion of the tube can be above the tolerance of the timber to expand without causing a split.


Calipers can be used to accurately measure variances in pen components

To prevent this, simply take a caliper and measure each component to within 1-1,000th of an inch. If you have some components that are more than a few thousandths oversize, you have a recipe for failure.

Some thicker body pen styles (like a European Style) can accept a greater size variance without problems because the pen barrels are much thicker when finished. Slim line twist pen barrels however, have only a few millimeters of wood thickness on the finished barrel, requiring a greater conformity to the specified optimal size.

Remember also, that most if not all of the writing pen components available now come from overseas and can suffer from quality control problems. That is why I always measure EACH component individually and reject any kits that do not fall into acceptable limits. At times, my reject rate has amounted to 10% or more of the kits I've received, so get in the habit of checking your pen kits when you receive them and return any that you feel are out of spec.

3) The interior of the tube may have excess glue inside, causing the inserted component to overstretch the brass tube. This can be a problem with new pen turners, or turners that sand the ends of their tubes square instead of using a pen mill. The advantage of using a pen mill is that it not only mills the outside of the blank square to the drilled axis, but it also cleans the interior of the pen tube of any excess glue or debris.

If any excess glue remains on the interior of the tube, it can easily cause your component to over expand the brass tube, causing the barrel to crack. Pen mills are relatively inexpensive and help to insure your pen components fit tight and snug against the wooden (or other materials) barrels.

This pen mill features interchangeable shafts to fit a variety of tubes

Diamond sharpening hones can be used to sharpen dull pen mill cutter heads

4) The brass tube ends may have burrs left over from the milling process, which causes the component to over expand the pen tube. This can happen if the cutter head on your pen mill has become dull. Since the steel cutters will eventually dull (like any other cutting edge will over time), you must periodically resharpen your pen mill cutter head. It's easy to tell when you need to resharpen your cutter head – instead of leaving a smooth and clean surface, the cutter head will tend to skip (creating a staggered stepped texture not unlike that produced with a chatter tool) and may even tear the endgrain.

Some timbers can be very abrasive as well, accelerating the frequency that the cutters need to be touched up. I use a small diamond hone to resharpen the cutters. Care must be taken when resharpening the edges on your pen mill's cutter head to insure that you resharpen each cutter at the same angle it was machined at. When honing the cutting edge with your diamond hone, keep the original angle, or your cutting performance will be diminished. A properly sharpened cutter will not produce burrs on the inside of the pen tube.

5) The pen component may be over pressed into the tube end. This can easily happen if you use an arbor press, or a large vice to insert your pen components. You want a good tight fit with the metal component and the wooden barrel, but if apply too much pressure during installation you can easily crack your pen barrel. This is a finesse procedure as it's difficult to describe when tight is "tight" enough. The main point to remember here is to only apply enough force to fully seat the component, anything more is counterproductive.

Pen presses can be used to accurately assemble writing pens

As with most everything in woodturning, when you experience a problem, take a close look at your procedures. The culprit may well be hiding somewhere in there and it can usually be easily corrected with a slight modification to your turning, finishing, or assembly protocols. If all else fails, seek the advice of other woodturners who may have had similar experiences and can help you get back on track.


Safety Note: Always follow all manufacturers safety instructions before working with your lathe, or any of the tools or products you may use. If you are unsure about any operation, obtain competent professional instruction before proceeding. Use and wear all necessary safety devices during turning and observe safe woodturning practices to prevent accident or injury.


Steven D. Russell is a professional studio woodturner, teacher and writer. He has written numerous articles for international woodturning magazines, which have been published in more than 78 countries around the world. Steve has demonstrated in numerous cities across the United States. His studio, Eurowood Werks, specializes in bowls, platters and hollow forms with unique visual and tactile treatments.

Steve is also the current and founding President of the Lone Star Woodturners Association, Inc., an AAW member chapter. The LSWA is a 501(c)3 non-profit educational organization dedicated to teaching and demonstrating the art and craft of woodturning.

Steve is also a featured writer for the Guild of Master Craftsman's "Woodturning" magazine, published in London England. Woodturning magazine is the world's leading magazine for woodturners. Look for his articles covering technical topics, or project based articles in an upcoming issue.