I wanted lightweight bike with lower gears for cycling holidays and winter use. Rather than going for a mountain bike group set I thought I would try a Sram single ring road group, though I still have a healthy scepticism about it. Getting a low enough gear is not a problem with the 42 tooth inner sprocket but it does compromise the top gear because of the small front chainring. Even getting the parts was a problem as availability is sketchy and I have to thank Paul Hewitt Cycles for obtaining the components for me. However, I wanted to use caliper brakes and nobody, at present, makes a 130mm non disc rear hub to accommodate Sram’s XD cassette, which is needed to get a 10 tooth sprocket, so I have to settle for a 11 tooth.
As in the past I wanted to use an oversize tube set with Llewellyn lugs (this time the Crescendo XLS) and as before there isn’t really a stainless steel tube set from one manufacturer that will fit this lug set and suitable bottom bracket. Therefore I have used Reynolds 953 fork blades and top and down tube with Columbus XCR Head tube, Seat tube, Seat and Chain stays. Using BikeCad for the design I managed to get all the angles within 0.3 degrees of the actual lug angles which I usually have found satisfactory for assembly with minimal modification.
The only non-stainless part on the frame will be the steerer tube so I decided to seal the bottom end first.
This was done by turning a disc in the lathe then drilling three small holes in the bottom of the steerer to accept three little bits of stainless dowel pin upon which the disc sat to be brazed in with Sif No 2 brass. The dowels were knocked out afterwards. I was then able to turn the end of the steerer in the lathe.
I then discovered that the hollow fork crown was still exposed, a feature of the angled fork crown I used because I had to get straight 953 blades, due to the temporary unavailability of curved blades. The standard fork crown would not have this problem. So I had to fashion a sealing ring which was silver soldered in after I had assembled the forks with silver soldering.
Unfortunately after I had turned the end of the steerer down the sealing disc was probably too thin and it distorted when the sealing ring was added which does not look brilliant! I later on decided as an afterthought, after getting a particular set of mudguards, to fit a boss under the crown to attach said mudguards.
Of course if I had planned this properly I could have made this whole bit in one piece saving a lot of trouble!
I had intended to mitre up the whole frame before starting brazing but as I often have in the past I ended up brazing up the front triangle before starting on the rear (see later). This was after checking all the lugs for fit and filing and sanding them all, with the intention of mirror polishing all the lugs. After mitring the top tube I inserted a brass tube for brake cable routing.
Front triangle then silver brazed in the jig.
Chain stays inserted next, XCR being a better fit than 953, but still need squashing in the vice before mitring the ends to fit
It was only at this point I realised I should have mitred the chain and seat stays before brazing up the front triangle. This is because the crescendo seat lug I had not used before has integrated seat stay ports. Once you have brazed in the seat tube the ports are obviously sealed up, making a simple mitre (pushing the seat stay through the port, marking and cutting) a difficult one!
Also the ports are slightly off set laterally from the seat tube and I do not know of any mitre template program, BikeCad included, that will calculate this, so it was back to hand and eye. Before this I had to modify the upper end of the seat stays because XCR stays are only 16mm diameter, whereas the ports are 17mm.
They are designed to accept Columbus Life seat stays only, there being no 17mm stainless stays available. I used some over sized stainless tube and bored this out to 16mm.
This was followed by making a paper template using a simple computer drawing program and cutting the sleeves down so they could be made into a feature.
These were brazed onto the top end of the stays. As they are necessarily a loose fit I suspended them on an old brake cable threaded through a bit of scrap bar holding the cabe taught at the top with a mole wrench to stop them falling off.
I was then able to turn the sleeves down to 17mm on the lathe. Despite being only 0.5mm proud they still look OK.
I then cut one of the mitres by hand and eye (OK so I used the BikeCad nearly template and adjusted it to fit). I then used the tracing paper transfer technique to do the other side.
Now it is possible to braze in the chain stays, but not the rear dropouts, then insert the seat stays and rear dropouts and braze them all in last.
I decided to add a pannier boss to the brake bridge before fitting to accommodate a Tubus fly pannier rack. Also to tap a hole under the brake bridge to bolt in a mudguard.
Mitring the brake boss is easy, setting it in a vice at the appropriate angle using a 16mm mill in the milling machine.
Just have to mirror polish the lugs, bottom bracket and dropouts before sending for painting.
The plan is to paint the frame graphics in gold so I am making some polished brass bits to go on the frame, including a cable guide, cable boss and stem cap, spacers, plus threaded bolts and a cable adjuster.
Finished frame now off to be painted.
Picture does not really do it justice!