Replacing a Loose 9mm Filter Tenon on a Dunhill Cumberland 4102F

A loose tenon is a fairly common occurrence in the pipe world. Many little things can alter the fit of the tenon over time. For example, removing the stem while the pipe is still hot can compress the tenon, wear and tear can erode the surface of the tenon or the mortise or both, or, as is the case with today’s pipe, the tenon can be slightly too small from the get-go.

According to the pipe’s steward, the stem on his 2021 Dunhill Cumberland 4102F had been slightly loose from the start, but the fit had gotten progressively worse over time. When the pipe arrived on the bench, the stem was barely able to hold on to the stummel, making the pipe both awkward and potentially dangerous to smoke (can you imagine dropping a lit bowl on your lap?).

As you can see in this initial series of images, the pipe was in overall excellent condition when it came into the shop, showing signs of light use and careful maintenance.

The smooth underside of the pipe is stamped “4102F” over “9^MM“, followed by “Alfred” over” The White Spot” over “Dunhill”.

The final stamp on the shank reads “Cumberland” over “Made in England 21”. Taking the stamps altogether, we know that this is a Dunhill “The White Spot” Group 4, Tapered Stem, Bent pipe with 9mm filter, dressed in the Cumberland finish and made in 2021.

With the background info out of the way, I began taking a closer look at the troublesome stem tenon. This pic shows light but uneven wear on the 9mm filter tenon. The wear marks are concentrated near the stem face, which indicate that this small section of tenon is doing all the work to hold the stem in the shank.

The tenon is clearly not made of the same Acrylic Cumberland as the stem proper, and for good reason. Acrylic becomes very brittle when drilled out to the tolerances required for a 9mm filter. Fitting a Delrin tenon into the stem face is much more effective here, as it is a very strong yet slightly flexible material that won’t crack or distort during the heat of a smoking session.

The down side of Delrin is that it really cannot be expanded or bulked up using the techniques one might employ on a Vulcanite tenon. The only option to correct the fit of this stem is to remove the factory tenon and replace it with a new tenon made slightly larger in diameter to fit snugly in the shank mortise.

To get the ball rolling on this repair, I used sandpaper wrapped around a dowel to quickly remove a light buildup of carbon cake from the chamber. Pipe cleaners, cotton swabs and 99% isopropyl alcohol made short work of the small amount of tars and debris built up in the pipe’s shank and airway.

The rim had a thin smear of carbon residue covering the surface – not thick enough to be called cake, but if left there it would soon become so. A cotton swab wetted with good old saliva dissolved the smear without damaging the finish underneath.

With the stummel sorted, I moved on to the stem. To remove the original tenon, I warmed the end of the stem gently over the heat gun to break the glue joint holding the tenon into the stem face. When the glue let go, I pulled the old tenon out easily with a small pair of pliers. In this shot, you can see the end of the rod used to inset the famous Dunhill White Spot in the stem’s upper surface.

The original tenon apparently sat in front of the protruding white rod, providing a gap in which collected a small amount of tars. It’s a tiny quality control issue, but one I would also correct when installing the new tenon. A quick buzz with a cutting burr in my Dremel removed the excess white rod. To ensure a good glue bond, I cleaned the mortise and airway with more pipe cleaners, cotton swabs and alcohol.

Then I was ready to start making the new tenon. Taking a few measurements from the original tenon, I cut a section of 1/2″ Delrin rod to length and turned it in the lathe, first making a facing pass to square off the end of the rod before drilling a preliminary airway all the way through the Delrin to create a basic tube.

I could then turn the stem end of the rod to fit the mortise in the stem face. A quick test fit provided a good fit with a tiny bit of play to allow room for epoxy.

Flipping the proto-tenon around in the lathe chuck, I then turned the other end to fit snugly in the shank mortise. This time, I left the fit ever so sightly tight as the Delrin would give a little after being drilled to the final 9mm filter diameter.

Filters are identified by their nominal size, much like lumber. Anyone who has bought a 2×4 at the lumber yard knows (or quickly finds out) that the actual dimensions are 1-1/2″ x 3-1/2″. Similarly, a 9mm pipe filter can vary anywhere from about 8.2mm to 8.7mm in diameter. It’s a tiny difference, but it’s enough to make some filters fit tightly or not at all, while others are loose in the tenon.

To address this variation in filter sizes, I requested that the owner of this handsome pipe include a sample of his favourite 9mm filter. I could then drill the tenon to optimize the fit for the brand of filter to be used. These pics show the final drilling and a test fit of the sample filter.

The keen-eyed among you will have spotted the ring of Delrin remaining in the middle of the new tenon in the pic above. This is deliberate, as Dunhill traditionally cuts their tenons with a tiny angle where the tenon meets the stem face. The slope of the angle fits neatly inside the countersink of the tenon in the shank for a gap-free seal.

Cutting this tiny angle is a bit of a challenge as it is barely more than a millimetre tall, but I think details matter, so I set my cutting tool at the correct angle and depth to very carefully nip the leading edge of the squared off ring around the tenon to create the necessary sloped section.

There is a little tidying up to be done on the new tenon, but this pic shows the new shop-made tenon above the factory Dunhill tenon. Not bad at all. I don’t have a knurling tool to create the hashmarks on the stem end of the tenon, so I used a needle file and coarse sandpaper to rough up the tenon in preparation for glue-up.

For a seamless finish, I added some black dye to the two-part epoxy used to glue the tenon into the stem before applying the epoxy to both the inner surface of the mortise and the outer surface of the tenon. I slipped the parts together and assembled the pipe. After carefully aligning the stem with the shank, I clamped the pipe upright in a padded vise to let gravity assist in keeping the stem face flat against the shank. A wrap of masking tape ensured the stem would stay lined up properly overnight while the epoxy cured.

When I came back to the pipe the next day, I removed the tape and twisted the stem out of the shank. I chased the filter pocket with a drill bit turned by hand to remove any excess epoxy and ensure that the airway was fully open. Then I could take the finished pipe to the buffer for a shine and wax.

The finished pipe looks, well, exactly like a Dunhill White Spot Cumberland Bent Billiard, as it should. Recreating the original factory tenon in every detail (except its final outer diameter) was a fun technical exercise for me and a necessary improvement for the pipe. The stem now fits snugly in the shank, and the pipe steward’s preferred 9mm filters do not slide around inside the tenon.

This hasn’t been the most dramatic repair I’ve posted to the blog, but it does illustrate the importance of getting the details right. The result is a beautiful Dunhill Cumberland its steward can enjoy without worry for many years to come.

Thanks for joining me for another pipe repair project. Until next time, Happy Piping! Here’s the finished pipe.