I’m working on a JK Special for a Gentleman back east and I thought it might be fun for you to see a single lugged joint at each of it’s major steps. I’ve chosen to feature the headtube/downtube lug and I think the photos give a good idea of what is happening.
The first photo shows the lug with the tubes installed and all of it fitted into the jig. This step is to check fit of the lug to the tubes and the angle between those tubes. I usually need to dry fit the lug a few times to check the fit as it’s being adjusted.
The following photo shows the lug all covered with brazing flux. The flux is an acid paste that, when heated turns into a glassy and smooth thick honey like liquid. The flux cleans the metal so the silver will flow properly and makes a barrier so that the metal isn’t exposed to oxygen during the brazing process.
The next photo shows the lug right after it was tacked together. ‘Tacking’ is simply put a number of small spots of braze in the edge of the lug to hold the joint together so the frame can be removed from the jig to be brazed in a free floating work stand.
The following photo shows the joint right after it was brazed and it still hot. The flux is a glassy coating over the entire surface and if you look closely you can see the silver shining through it. After the joint has cooled to room temperature it is soaked in a hot water solution to remove the flux which is water soluble.
Next up is a photo of the joint after the flux has been soaked off. You can plainly see the silver and where it has ‘wetted out’ onto the downtube. The downtube (and top tube) of the JKS is stainless and you can see how the silver wets out on the stainless differently than is does on the non-stainless head tube.
This last photo shows the joint after it has been cleaned and sanded. The sanding is done by hand and accomplishes two things. The first is that it smoothes out the rough parts of the cast lug. The sanding also removes any extra silver from the area so it will look smooth and clean under paint. The last step is to give the area a quick polish. The polishing will highlight any imperfections that would be hard to see otherwise and that would show through under the paint.
As you can see there are a good number of steps with each joint and while none of them takes all that long to do they all add up to a very full day. Today I did this process on the entire front triangle as well as adding the braze-ons, machining and checking the alignment. A pretty full day.
Tomorrow I add the rear end of the frame to this finished front.
Thanks for reading,