How To: Exhaust Pipe Nut
The fun part about restoring old machines is rebuilding or recreating items. That should be clarified a bit better: I think that it is fun to make replacement parts. Your mileage may vary. But the latest project in the shop, the 1913 Veloce, has given me a lot of opportunity to make parts. The nut that holds the exhaust pipe onto the cylinder head needed replacement, due to numerous abuses by previous owners who possessed hammers and screwdriver-chisels, but who didn’t have the correct wrench to fit the grooves in the nut. 99.75 years of moisture hadn’t been kind to the steel either.
As you can imagine, some parts for early machines are available from vendors, but many are not. I couldn’t find this one didn’t from the limited sources. But I already had a $3 bar of steel and all the necessary tooling, so I went about making one on a Tuesday afternoon.
This is Step 3: setting up to cut the six 3/16” grooves in the outer edge of the nut. Step 1-2 aren’t shown, but they were to turn the part to the correct outside diameter, drill a 1/2” hole in the center, and pressfit a 1/2” rod into the part. That rod was gripped in the spin indexer, which is a cheap and simple way to rotate a part by any number of degrees on a mill. You can get them for about $45 on sale from Enco, MSC, etc.
This photo shows the part, the spin indexer and the milling cutter. The part was held in the vice, one groove was cut to half depth, then the vice was opened. The indexer was indexed 60 degrees, and repeat. Another repeat set of cuts to the full groove depth and we were ready to get back on the lathe.
Step 4: bore for the internal threads. I use an end mill in the tool holder when boring a lot of material, it is more rigid and faster than using a boring bar. The paint pen marks on the part and chuck jaws are used to mark where it fit in the 4 jaw chuck.
Step 5: Cutting the threads. I have a new favorite tool, this ID threading tool holder. The carbide tool is formed to a 60 degree triangle, just like a male thread. There are three faces, so the tool can be removed and rotated if the cutting edge breaks. Previously I used carbide boring tools with a thread form ground into the tip, but they were fragile and more expensive than one of these 3x tools. This toolholder will pay for itself pretty quickly. I don’t recall the thread diameter, 1.9something inches with 24 tpi.
The exact thread diameter wasn’t terribly important to me, since I could check the fit with the mating part –in this case it was the cylinder head. Doing this makes threading jobs on the lathe go much smoother. Machining to a print showing the dimensions is great, but old parts can be tough to measure and draw, and ultimately all that I care about is the fit to the part, not if it was exactly a nominal dimension on a drawing print. The remaining steps aren’t shown, but they were to cut the part to length, face the cut side, and chamfer and then round over the external edge.
No more hammers and chisels to tighten and loosen the nut. This adjustable spanner wrench was a few bucks at a flea market 10 years ago. They are also for sale new from various tool vendors. This type has a flat end, there are also types with pin ends for that type of nuts.
Comparing the new and old nuts.
Now ready for deburring, polishing and nickel plating.
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