Tag Archives: inserting a Delrin tenon

Replacing a tenon in a stem with a minimum of tools


Last evening I was looking at the lone pipe bowl in my refurbishing box and decided I wanted to do something with it. I wasn’t sure if I would refinish it or rusticate it with the new tool Chris sent me. Either way though, it needed a new stem. I went through my can of stems and found that I did not have any that would fit the shank without a lot of work. I did have one with a broken tenon that was the right diameter for this pipe. I looked at it for a while and then found a Delrin tenon that I had on the work table. The tenon was the right size for the shank! The stem was the right diameter for the shank. Now all I had to do was wed the two of them and I would have my new stem.

I have drilled out broken stems in the past and inserted a new tenon. I have used a tap and then screwed in a threaded tenon that I purchased from Pipe Makers Emporium. Either way it was work that I did by hand. By hand means that I do not have a drill press, I do not have a vise to hold the stem. I have my two hands and a cordless drill. This takes steady and slow work to keep all the angles straight and get things properly aligned. It is one of those processes that will either work really well or not at all. There is no in between. You cannot redrill a crooked hole to straighten it out without making it too large to fit the piece. So really the fact of the matter is that it all comes down to whether I can drill the stem out straight!

To begin the process I needed to square up the end of the stem and remove the broken pieces of the tenon that still remained. The end needed to be flat and even for the drilling. I sanded down the end of the stem flush using a sanding board (like the one used when topping a bowl). In the photo below you can see that the end of the stem has a divot out of it due to the breakage. I did not worry too much about that as the drilling would take most of that area out of the equation. I only worked on flattening out the rest of the stem. When finished I pressed it against the end of the shank to see if it was a flush fit or if there were any high spots. The fit was perfect. Now it was ready for drilling.
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I took out my cordless drill and found that the battery was dead. I put the battery on the charger and sat thinking for a bit about how to best drill out the stem. I measured the diameter of the new tenon and found that it was 15/16 inches. To make sure I did not crack the stem or break it in the process I would drill it out in stages. I would mark the depth on each drill bit I used with a piece of tape so that I would not over drill or under drill the depth of the hole. I used the tenon as the measure for this. The tenon I had came with a slight lip on it so I would need to countersink the end of the stem once the hole was drilled in order to accommodate the lip.

I decided to try something different this time and not wait for the battery to charge. I stood the drill on my desk, inserted the drill bit and hand turned the stem onto the drill bit. I started with the 11/64 inch bit which was slightly larger than the airway in the stem. I turned the stem onto the stationary bit to the depth that I had marked on the drill bit. I lined up the stem and the angles making sure the line was straight and the hole stayed centered throughout the process. I worked my way through 7 bit sizes up to the 17/64 inch bit. Each time I turned the stem onto the bit in increments and cleaned out the hole with a dental pick. I continued to turn it on and off the bit until the drilling was smooth before moving onto the next sized bit.
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I found that when I got to the larger sized bits from 19/64, 5/16, 21/64 inches it was hard to turn them on by hand. I could get them started but they quickly bound up on the bit and I could not turn them further. I turned them back and forth but it was not working well. I put the battery back on the drill and drilled the stem using a very slow speed. It worked well. When I had finished drilling it with the 5/16 inch bit the tenon pressure fit very nicely in the hole. There was not enough room for epoxy to be applied and still fit in the hole, so I drilled it with the 21/64 bit to give it the amount of room for the epoxy. To countersink the end of the stem I used a slightly larger drill bit and then a sharp knife to bevel the inner edge to accept the ridge on the tenon.
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In the morning the tenon was firmly in place and dry. I cleaned the face with a dental pick and removed the excess epoxy from the stem. I pushed the stem into the shank of the pipe to see the fit. This was the final test. Did things align properly? Did I get the angle square and straight? Would there be a gap in the stem and shank joint? In case you are wondering I have had all of those issues in the past and had to do a lot of adjustments to get a clean fit. But this time things worked well. The fit was perfect and the alignment was absolutely correct. The pipe now had a new stem and it was time to make a decision on what to do with the finish of the bowl. That will be another story however. The photo below shows the fit of the stem and the shank. I am very pleased with the fit.
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I sanded the stem and the shank to get a smooth transition between the stem and shank. I wanted the fit to be seamless so it took some sanding with 220 grit sandpaper followed by a sanding sponge to fine tune the fit. Here is the pipe as it stands now. Later today I will rework the bowl and finish the entire stem. But for the purpose of this post the tenon replacement and fit of the stem to the shank is complete.
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