Saul KK

Hi, I'm looking at making my first bike frame, and would like to do a lugged cyclocross style frame. I work as a metal worker, so I have access to an oxy acetylene setup, and a fair amount of experience with general metal working.

As I understand it, lug angles can be manipulated 1 or 2° per side of listed angle, but after drawing up the frame I think I want in rattlecad, my lug angles would need to be manipulated by quite a bit at the ST/DT junction (by 3.3°), and the HT/DT junction (by 2.3°),

This issue seems to be caused by the longer fork (403mm axle to crown), and the fact that I want a BB drop of 70mm.

So I guess I'm just after any advice on modifying lugs, like could I cut around the socket, then bend it to desired angle, mig weld it back up and grind it all smooth?

Or is there any simpler way to work around this issue, like a redesign of the frame?

​​​​​​Any help would be much appreciated!

Also I've been looking at getting the parts from nova cycles, in particular the Columbus chromor road OS tubeset.

I've attached a PDF of the rattlecad drawing.

CliffordK

An option might be to go with seat tube and head tube lugs, but use a smooth bottom bracket shell, tig welded or fillet brazed.

duanedr 

Yes, the tall fork and relatively short front end are contributing. It's not clear what length stem you're using but for CX, shortening the stem and lengthening the top tube will give more stability and will help with the angles if you already have the materials and are determined to make them work. A better route would be use the design you want and find/make the parts. People do cut lugs and re-braze/weld. I don't know enough about MIG to say if that's the right approach or not.

For the drawing you have, the following options would get you pretty close:

In the drawing, it looks like a tapered DT - the RattleCAD default for the Road template is tapered 31.8-34.9 for some reason .
If you are using a DT with a 34.9 BB end, you could use the LB09N (34.9x31.7x30/17 Oval 57x64x7° ) . This shell introduces other issues like the 31.7 seattube which limits your lug and seatpost selections. If you are using a tapered DT, please let me know the source.

If using a straight 31.8 DT you could use W106B- (31.8DT, 28.6ST, 30x17 OvalChainstaysNo guides orcut-outs 57.4 x 64.8 x 7°). If this works, it will leave you with more options relative to other materials. 31.8DT/HT lugs are plentiful as are 28.6 ST/TT lugs.

I actually think for a cross bike, the 30x17 chainstays would give better clearance than what appears to be the Round Oval Round ones in your drawing.

These options would minimize the blacksmithing you'll need to do. Both of those are from Ceeway.

To change the tube dimensions, double click on the tube in the 2nd tab in RattleCAD (Frame Details) and enter the tube dimensions correctly. It will help later in your miters and other measurements.

Saul KK

Thanks for the responses. I would prefer to not have to fillet braze the BB as I don't have much experience with fillets.

I hadn't seen the lugs from ceeway before, but that w106b one looks like it could work well.

Apologies, I didn't pay any attention to the tube diameters in the rattlecad drawing, I will fix that up. I plan on using the Columbus chromor OS tubeset with 36mm HT.

Bit confused about CS dimensions, is a 30 X 16mm CS the same as a 24mm oval CS?

Thanks for your help!

Saul KK

Also looking at the ceeway site, I noticed I can buy my rod and flux from there. I'm thinking of getting the SIF silver solder no 43 55% and the SIF silver solder flux for all the lug joints, and getting the SIF bronze no 101 and the Cycle Design LFB bronze flux paste for brazing on cantilever bosses and such. Do they sound like the right flux rod combos?

Edit: system 48 flux and rod sounds like it can do lugs and small fillets suitable for cantilever bosses, according the the info on ceeway. Anyone have experience with this?

​​​​​​Thanks

fietsbob

bulge formed & sheet steel lugs, brazed, offer more bendability , stainless, cast, silbraze , near nil.

make your own lugs? Tig with regular steel filler wire can be fillet brazed over for aesthetics.
to sleeve over your frame tubing,

Brian25

I have built some lugged frames. I can tell you that I really do not see any problem(s)as far as severity that would stop you from using stock lugs. I have built a few 46 cm road frames with stock lugs where the top tube was tilted down way, way, way more than your pictured frame.

JohnDThompson 

Bulge-formed shells and lugs are easier to manipulate than cast ones. Often, you can just insert the tubes into the shell and use them as levers to bend the sockets to a different angle.

Looking at your drawing, you'll want to close the angle between the seat a down tubes. If you can't bend the sockets enough to get the angle you need, you can cut a slot in the crotch between the sockets and bend a little further to close the angle more. Fill what's left of the slot with brass when you braze the tubes in place.

Saul KK

Thanks for all the info and suggestions. I've found a combination of BB and lugs from ceeway that fit all my angles within 1°, so I think I'll go with them. Sounds like much less work than heavily modifying, or making my own lugs. Sent an email off to ceeway, so now just hoping they have what i want in stock. Thanks