Lug/BB Reshaping (changing angles)

[mxboy349]

Question on lug/bb reshaping. BB shell I purchased is a 60° x 62° x 7.5° (“Richie-issimo Series”). My design with the fork I am using will require the 62° to be more like 66°. Can the CS sockets be “reshaped” for this much of a difference? Bend the CS slightly to make up the difference? Am I crazy and I shouldn’t even be close to 66° for an angle of the CS? Am I way off base on anything? For my design I am just copying and existing frame that I ride with a slightly less “standover”. Attached is a pick of my design.

8263789839_a0fd91e510_z.jpg

[Pi Guy]

Assuming this is a standardish road bike your BB drop seems a bit small to me. Please keep in mind that I am only speaking from my limited experience (10 frames).

[Eric Estlund]

No comment on the design (I haven't clicked on it yet), but changing angles in lugs and shells is par for the course. Stick a piece of bar in there, grind away, hammer, etc. Make the parts work for you. Of course, some parts might need less "encouragement"- that's why there are so many great BB shells on the market. But don't be afraid to lean into it a bit.

[Andrew R Stewart]

The chain stay sockets can be bent a bunch. Do as much as you can prior to attaching any tube, if you screw up it's easier to start over with only the shell the loss.

I will comment on the design. Why so tall a BB height? Are you running 185mm arms? Pedals from a exercycle (which have a lot below the axle)? Will this be a fixed gear bike?

[Andrew R Stewart]

As I look more at the design i have more questions. Axle to race is 365mm- Is this correct? Is the tire diameter 688? If so then the fork height is really tight. If you are running long arms or have big feet or run fenders the front center is a bit tight (espically with the 33mm tires).

One of the reasons to build your own frame is to try out stuff no one else is building. But there's a reason that the manufactured bikes fall into such a narrow range of geometries... Andy.

[mxboy349]

Andy-Fork is off the shelf and it is 365mm Axle to race, I have measured it twice.. Don't have the skills to build a fork yet. I have the tire diameter drawn at 668 (700x23 tires). BB height is a "result" of the fork. From what I can tell the "off the shelf" fork is painting me in a corner with the rest of the frame geometry. Seems like I may have to play with the DT socket on the BB and the DT/HT socket to get the geometry in the norm.

[Eric Estlund]

Not sure why the fork is painting you in to a certain BB drop. Get the bike where you want/ need it, and make the parts work (or get parts that will).

(Edit- that read harsh to me; it isn't meant to be. Draw it out as you want it, and then assess the best plan of action.)

[mxboy349]

Not harsh at all Mr. Estlund. I think I understand now. Lugs and BB shell will need to be "massaged" to my needs. Thanks.

[suhacycles]

Yup, might work (and ride) better overall if you dropped the BB a little, make the ST-DT angle more like 59 and the CS-ST angle ends up closer to 65. HT-DT angle might end up being around 58-59 too but that's no biggie or live with a head angle around 72. Have fun... =)

[Andrew R Stewart]

Eric- Sorry but with my poor eyes and monitor it looked like 33mm tires were in the plans. hence my wondering about the fork height, and the vanishing clearance... I do agree with others. Make the frame parts fit your design and the design fit your needs.

BTW this is very close to the frame I'm building right now for myself. I'm making the fork to free myself of the industry narrow mindedness that manufactures seem to have about tire sizes and braze on options. Frame #830 is the thread link. Andy.

[Dave Anderson]

I agree with whats been said here, but thought I would throw in a couple of photos of how I adjust angles & such. See below (they also sometimes need some heat and a little "blacksmithing"). It's very common to have to tweak lug and bb shell angles. In fact it rare that I don't have to tweak several things when building a lugged bike. I also agree with whats been said about your BB height. It's pretty high...unless your maybe building a track bike that will actually be ridden on the track....and you shouldn't have any trouble using an RS BB shell with a more typical road bike BB height.

Dave

PS: When adjusting angles, go easy and check them as you go. Watch for and correct any ovalization or etc.

[mxboy349]

I completely understand now. I was under the assumption that the lugs would be “fixed”. Here is an updated design with the DT adjusted to 58°. Still playing with some of the measurements, but I now see how you have to “manipulate” lugs and BB shell to get the final geometry. I can also see why some people Fillet Braze/TIG weld.

8267927354_bc6d41d40a_z.jpg

Larger res pic here.

Mr. Anderson- thanks for the pics, worth a 1000 words. Is that solid stock for “cheaters” or tubing? Are they mitered so that it fits close?

[Dave Anderson]

Mr. Anderson- thanks for the pics, worth a 1000 words. Is that solid stock for “cheaters” or tubing? Are they mitered so that it fits close?

Yes...see below. I got these from Omar Khiel: Oasis Custom Cycles | Handmade Bicycles and Custom Wheels


DSCN4161.jpg

[ToddFarr]

^ Those are awesome! I def need to make me a set! Thanks for sharing. I may just use a heavy gauge tube though. Seems like a lot more material than I want to remove :)

[Cooper Cycles]

I like having BB cups threaded in when using brute force to manipulate the BB to prevent ovalizing...

Have Fun!
Travis

[mxboy349]

Made a "persuader" and it worked like a champ. All I had was a short piece of stock, but it was long enough to put a "cheater" bar on and get the job done. Thanks to all for the tips.

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[devlin]

I agree with whats been said here, but thought I would throw in a couple of photos of how I adjust angles & such. See below (they also sometimes need some heat and a little "blacksmithing"). It's very common to have to tweak lug and bb shell angles. In fact it rare that I don't have to tweak several things when building a lugged bike. I also agree with whats been said about your BB height. It's pretty high...unless your maybe building a track bike that will actually be ridden on the track....and you shouldn't have any trouble using an RS BB shell with a more typical road bike BB height.

Dave

PS: When adjusting angles, go easy and check them as you go. Watch for and correct any ovalization or etc.

Sorry about the thread revival but then it's about important skills and techniques. Dave's pictures above are perfect for my quandary at the moment. I have already had to start again on one DT/HT lug. Being a little distracted with life didn't allow me to think it out enough.

[Andrew R Stewart]

I'll add another bit too. When bending lug or BB sockets a bunch the internal gape start to build up on one side of the tube and the shore line gaps open up on the other side. The shore line can be tapped down with a hammer or bent down with an adjustable wrench but the inside gaps usually remain. This is when being able to flow bronze filler comes in to play. Bronze is far more able to fill the internal gaps and not loose strength or suffer internal voids/cracks. Andy.

[devlin]

Yes, I'm already thinking I'll do the HT lugs in bronze. I have a combination of a lowish BB and slightly taller fork for bigger tyres and fenders. I'm at around 59 deg for the DT/HT lug with the 72.5 HA. Lug is 60 deg and it won't sit well without a bit of new shape set into it.

[Andrew R Stewart]

I use to make "Terry" type bikes for my late wife. With the 520 ft rim and short TT the lower head angle would be around 66*-67*. Bending that lug at least 2* and more often 4*. Bronze was used always for those. Andy.