How to Sleeve Cracked Barrel Threads

(This page published June 1, 2017)

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Introduction

There are few things about pen collecting that are so disappointing as finding a great pen, one that you really want, in perfect condition except for a tiny flaw like a hairline crack in the barrel threads (or where there would be threads if the pen had a screw-on cap). The mottled hard rubber “Huracan” pen shown above was one such pen; the virtually invisible crack in its barrel threads did not impair the appearance of the pen, but I was unwilling to use it because of the risk that the crack would grow under stress as the pen was used. In most cases, it’s possible to repair a crack of this nature, and the repair is equally effective with celluloid or hard rubber. You can’t make the pen perfect again, but you can certainly make it usable and, quite probably, collectible. This article shows how to repair the cracked barrel by fabricating and installing a brass sleeve to reinforce the barrel.

Tools Required

• Machinist’s lathe (tabletop size is fine), with self-centering three- or four-jaw chuck, an ordinary facing chisel, and a cutoff tool
• Machinist’s drill set, ANSI N^os 1 to 60 and letters A to Z (or metric drills in the sizes you will need)
• Vernier, dial, or digital caliper to measure inside and outside diameters
• X-acto knife with new (or nearly new) N^o 11 blade

Supplies Required

• Thinwall brass hobby tubing in a range of sizes (see text)
• Micro-Mesh buff stick, pink/white/gray or black/white/gray (2400/4000/12000 grit)
• 1500- or 2000-grit wet/dry sandpaper
• Blue painter’s tape
• Two-part epoxy glue
• Fusing solvent if working on a celluloid pen (see text)

Restored and ready for a sac, here are the parts of the pen:

Taking Measurements

In order to make a sleeve that will fit in the barrel, you need to know the inside diameter of the barrel. First, measure the barrel’s ID using your caliper.

Note Measuring an inside diameter (ID) is difficult. You can usually improve your accuracy by making the measurement several times and calculating the average of your measurements. I recommend this practice.

Then, as a check on your accuracy, measure the outside diameter of the section where it fits into the barrel. For the pen shown here, the barrel’s ID measured 0.299" (7.59 mm). The section’s OD was 0.300" (7.62 mm), indicating that the barrel measurement was sufficiently accurate to use. You might come up with a slight difference, as I did; there is sometimes crud in the barrel — or on the section — that you don’t see, and some calipers are more accurate than others (and some people have more difficulty making accurate measurements).

Note I have found that the accuracy of calipers is an instance of “you get what you pay for.” Cheap digital calipers from bargain tool outlets like Harbor Freight are good for many things, but when you require repeatable accuracy, you have to pay for it. I use professional-grade Mitutoyo machinists’ dial calipers, which will last a lifetime and do not require wasteful disposable batteries.

You also need to know how far the section extends into the barrel. This distance does not include the sac nipple; measure only the part of the section that mates with the inside surface of the barrel. On the Huracan pen, this part of the section was " (7.54 mm) in length. (Absolute precision is not important, but the closer you can easily get, the better.)

Tubing, and the Choice of the Right Size

In the list of supplies, I specify brass tubing. You can use aluminum tubing instead of brass, but the amount is so small, and brass works so well, that I do not think it worth the slight cost saving. If made of brass, the sleeve will weigh only about half a gram. (The one for the Huracan pen weighed 0.46 g.)

Thinwall tubing has a wall thickness of 0.014" (0.356 mm) and comes in steps of " (0.794 mm) in outside diameter, with ODs from " (1.59 mm) to " (16.7 mm). Once you know the inside diameter of the pen’s barrel, choose the tubing size that is closest to that diameter but not smaller. For the Huracan pen, " thinwall tubing, with an outside diameter 0.3125" (7.94 mm), is almost perfect.

Making the Sleeve

WARNING Do not get the idea that you should drill out the barrel to fit the tube, rather than the other way around. That is a sure way to disaster, as the cracked area is virtually certain to split or chip during the drilling operation. Flying chunks of hard rubber or celluloid can cut you or even put out an eye.

Before you make the sleeve, make certain that the inside of the barrel is clean, with no adhesives, dirt, or other foreign matter for at least as far in as the length of the crack. You need to expose a fresh, non-oxidized rubber surface to ensure that the epoxy will stick, and the best way to do this is to sand the surface with 1500- or 2000-grit sandpaper wrapped around something that will allow it to fit easily into the barrel, such as a paintbrush handle, dental pick handle, length of brass tubing, or X-acto knife handle (with the blade removed!).

CAUTION When you sand the interior of the barrel, you must be careful not to extend the crack by squeezing, stretching, or otherwise distorting the barrel. Wrapping blue painter’s tape fairly tightly around the barrel is a good precaution.

Chuck the tubing in the lathe with the length of the finished sleeve plus about 1/4" (8 mm) exposed. If the exposed end is rough, face it to produce an end that is flat and true. Find a drill that will fit as closely as possible into the tubing. Chuck the tubing into the tailstock with its shank end exposed, and slip the drill into the tubing’s open end to act as a mandrel. The drill shank should go in at least 1/2" (13 mm) so that it will provide a backing for when you cut the sleeve loose with the cutoff tool. Now lock the tailstock down.

With the lathe running at about 360 RPM, adjust the cross-slide so that the chisel’s tip just touches the outer surface of the tubing. Then back the cross-slide off toward the tailstock. Advance the chisel crosswise by a very small step and test whether it cuts into the tubing. Repeat this action until you get a full cut all the way around the tubing. Measure the cut area to determine how far you will need to advance the chisel to cut the final diameter. Advance it part of that distance and use the leadscrew to cut an area somewhat longer than the finished sleeve is to be. The sleeve should be as long as the crack, plus a very small amount; for the Huracan, which had a crack only 3/16" (4.8 mm) long, I made the finished sleeve 1/4" (6.35 mm) long. Measure the diameter of the cut area, and cut again, taking a very small step. Lather, rinse, and repeat until the sleeve's OD is as close to the ID of the barrel as you can get it, but not even the slightest bit larger. There should be perhaps 0.0005" (0.0127 mm) of clearance to allow space for the epoxy. It’s a really good idea to back the tailstock away and test-fit the barrel onto the sleeve before cutting the sleeve free. If necessary, take the sleeve down another 0.0005" or so.

Note If you are working on a celluloid pen, I recommend that you fuse (solvent-weld) the crack before installing the sleeve. Do this work before you make the sleeve, as it might affect the final diameter to which you will turn the sleeve.

WARNING Fusing solvents are toxic. Use with adequate ventilation.

Set up the cutoff tool in the lathe, mark the point where you want to cut the tube, set the cutoff tool in the proper position, and cut the sleeve free.

Remove the drill from the tailstock chuck, bringing the sleeve with it. Use the drill as a convenient mandrel to hold the sleeve while you deburr both ends. (If you try to hold the sleeve in your fingers without a mandrel, you will most likely be making another sleeve after you crush the first one.) Here, I am using the white abrasive on a Micro-Mesh buff stick. As noted in the list of materials required, 1500- or 2000-grit wet/dry sandpaper will work as well.

Installing the Sleeve

Installing the sleeve is very simple. First, use the sandpaper to clean the interior surface of the barrel far enough down to accommodate the sleeve; for a 1/4" sleeve, 5/16" to 3/8" (7.9 to 9.5 mm) is good. Make sure that the surface is dry and free of sanding dust. (Epoxy will not stick to a wet or dusty surface.) Mix up a small batch of epoxy, coat the outside of the sleeve, and slip the sleeve into the end of the barrel, wiggling it a little back and forth as you go, to spread the epoxy around. Press the end of the barrel against your work surface to seat the sleeve fully and ensure that it’s true. Then go away and let the epoxy set. For five-minute epoxy, an hour is the minimum amount of time you should wait. For 12-minute epoxy, wait a correspondingly longer time.

When the epoxy has set, use your X-acto knife to form a small chamfer on the inner edge of the sleeve, so that the section will seat properly when you install it. If there is excess epoxy present (there is), cut it away, being careful not to nick the sleeve or the barrel.

Modifying the Section

With the sleeve in place, the opening in the barrel is smaller than it was originally. You can compute what the size of the opening “should” be by subtracting twice the wall thickness of the tubing from its original outside diameter. Nominally, the 5/16" tubing I used for the Huracan pen should have an ID of 0.285" (7.23 mm). Because my experience tells me that the tubing actually runs the tiniest bit large, I recommend that you actually measure the ID with your caliper. Once you know the actual ID of the sleeve, chuck the section up in the lathe.

If the pen has a screw cap, the section will probably have a table (the flared-out flat end adjacent to the nib, where the inner cap seals when the pen is capped), and you can chuck it into the lathe quite easily. Wrap two layers of blue painter’s tape around the section to protect its surface from the chuck jaws, applying just short of two full wraps. Fit it into the chuck, positioning the place where the tape layers overlap so that it is between jaws; this ensures that each jaw will clamp on two layers and thereby keep the section centered. Carefully tighten the chuck jaws, sliding the section in or out as needed until the chuck clamps both the table and the base of the section as shown in the following drawing. Note that for illustration the section in the drawing has a table:

(If the pen is a cone-cap model like the J. Harris pen pictured below, the section will not have a table. For this situation, wrap a narrow strip of the blue tape around the nib end of the section multiple times to build it up to very slightly more than the diameter of the base of the section, and then apply the two-layer wrap. When you clamp the section in the chuck, the tape will compress slightly to approximate the diameter of a table.)

Once you have the section chucked up, turn it down to the desired diameter, taking small steps (0.0005" at a time) and testing the section in the barrel after every cut.

CAUTION Taking extremely small steps and test-fitting the section repeatedly are imperative. If you cut too far, the section will be too small, and it will fit sloppily in the barrel. (It might even be so loose that it will fall out.) Do this right the first time because you don’t get a second chance.

CAUTION The sharp-eyed reader will notice that Richard did not use blue tape on the section in the photo above. Don’t be like Richard. Use the tape, or risk a permanent scratch or divot on the surface of the section.

Finishing Up

With both the barrel and the section modified, all that’s left is to install a sac on the section and assemble the pen.

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