My frame #1, 29er.

[J_K]

Here's my first frame project.

First of all I would like to thank Kris from the 44 Bikes for the help with the jig!

Rattlecad drawing of the frame, 29er with shortish chain stays with offset seat tube. The front triangle is Reynolds 631 .9/.6/.9 with externally butted 32.7/33.1mm 30.9mm ID seat tube, Dedacciai 29er stays and Paragon dropouts.


Here's a couple of shots of the jig



Setting head tube bottom height


Mitered front triangle





Next job is to braze all the braze-ons and then to weld the front triangle and chainstays.

TT .9 butt lengths are pretty short and I would like to know if there's any problems with brazing cable guides to butt transition area?

Not sure yet how I will do the chain stay miters, I have plans for the jig but it will not be ready for this frame. Most likely I have to file them but I'm little bit concerned about how they will turn out without the templates.

[woutlaw]

Sweet! Looking forward to watching the progress.

A 29er looks like a fun thing tackle.

[David Tollefson]

I'm curious, if any one cares to comment, about the long front/short rear and fairly high (seeming) trail, and potential weight distribution on the bike... Handling? Just asking for experience for those who've ridden such geometry.

[Bingomck]

This is great. Looking forward to more progress pics as they come!

[Filly-fuzz]

Loving the jig.

Looking forward to the progress!

[Willie1]

I'm curious, if any one cares to comment, about the long front/short rear and fairly high (seeming) trail, and potential weight distribution on the bike... Handling? Just asking for experience for those who've ridden such geometry.

This is the current fashion in MTBs. Long, low and slack makes for great descending, but they are more of a chore pedaling back up.

[steve garro]

This is the current fashion in MTBs.

Kinda "loopy" on the steep uphills, too........

- Garro

[J_K]

I have no idea how it will ride, but I like my bikes with short wheelbase and short rearend. If I don't like it I will build another frame, actually I will build another frame anyway.
My riding does not contain steep uphills as they're non existent over here. We'll see how it works out. I would prefer to build it with curved seat tube but I don't have bender available or access to suitable bender. I'm open to any info about the ridability of the shortish chainstays.

Kris from 44 Bikes has nice blog post about the chainstay lengths here


Anyone could give me some advice about this? TT .9 butt lengths are pretty short, seat tube end has only about 30mm of full .9 butt and in the front there's about 70mm left of the .9 butt. I would like to know if there's any problems with brazing cable guides to butt transition area?

[shiggy]

This is the current fashion in MTBs. Long, low and slack makes for great descending, but they are more of a chore pedaling back up.

Depending on your view of "great." IME the descending is great if you do not have to turn or hold a narrow line. And it compromises the handling on the flats as well as the climbs. Except for the stays we called this type of geometry relaxed or sluggish when it went out of style in the mid-late '80s. Now it is called aggressive, likely because you have to ride very aggressively to get the bike to do anything.

OK, end of retro grouch rant.

BTW I do not consider 70.5 HTA to be very slack for a 29er, though I would want more fork offset (48-50mm) to reduce the trail a bit.

[Willie1]

Depending on your view of "great." IME the descending is great if you do not have to turn or hold a narrow line. And it compromises the handling on the flats as well as the climbs. Except for the stays we called this type of geometry relaxed or sluggish when it went out of style in the mid-late '80s. Now it is called aggressive, likely because you have to ride very aggressively to get the bike to do anything.

OK, end of retro grouch rant.





BTW I do not consider 70.5 HTA to be very slack for a 29er, though I would want more fork offset (48-50mm) to reduce the trail a bit.

The low and slack geometry is inspired by the "north shore" designs, where trail bikes have 67-65 deg HAs and super short chainstays. I didn't actually look at the numbers in the drawing, I was just responding to the long front, short rear, trail question. HA is just one variable amongst many. Looking at the drawing, the BB height is a bit high for the "long and low" feel, and the HA is steep. Its like 1/2 of the design is north shore, and the other half is more traditional. It'll be interesting to see how this combination rides.

[J_K]

I made little progress today.
Downtube is tacked and top of the DT-HT joint is also welded as it was easier to weld it before toptube is tacked.
I decided to weld the cable guides, because I didn't want to mess them with my poor brazing skills, not that my welding is any better. I'm happy with the result, I tried to keep most of the heat input on the cable guide to not cook the tube. I used ER312 1mm filler wire.

[J_K]

The front triangle is now fully tacked and partly welded. I enjoy the process!

The DT fully welded to the BB

I had to improvise little bit to keep the seattube in place, in the future I will add tubeholder there.

[steve garro]

I had braze ons on the side like that once.
The rear one cut into your inner thigh, and you could (somehow?) get a killer gash to the patella from the front one.
YRMV.
- Garro.

[J_K]

I had braze ons on the side like that once.
The rear one cut into your inner thigh, and you could (somehow?) get a killer gash to the patella from the front one.
YRMV.
- Garro.

I realized that when I had them welded, but I can't correct them anymore.

[Andrew R Stewart]

Take this as a learning step and make things right to the ability you can. Grind off the stops, sand clean and smooth and braze on a new set. This frame is for yourself anyways. Andy.

[shand]

Take this as a learning step and make things right to the ability you can. Grind off the stops, sand clean and smooth and braze on a new set. This frame is for yourself anyways. Andy.

this ^^^

[J_K]

Take this as a learning step and make things right to the ability you can. Grind off the stops, sand clean and smooth and braze on a new set. This frame is for yourself anyways. Andy.

this ^^^

After thinking of it last night and after your comments I decided to grind the guides off. Not exactly what I wanted to do, but I had no choice as they were in really bad position.
I cut them off with the dremel and then filed and sanded them down. I'm quite pleased with the outcome.

[roburrito]

Why is the seattube welded to the downtube and not the bottom bracket shell?

[J_K]

Why is the seattube welded to the downtube and not the bottom bracket shell?

Offset for the tire clearance with the shortish chainstays, I don't have a tube bender, so offsetting the seattube was easiest option.

[bellman]

Why is the seattube welded to the downtube and not the bottom bracket shell?

It's for tire clearance. When i looked at the STA and the CS length I wondered how the OP was going to pull it off. The route he's chosen to go in my mind is fine having done it before with great success. His execution of it is first rate as well. Bending, smashing or otherwise finessing seattubes to get them just right for tire clearance can be a mental mire hole when it comes to maintaining STA. I think 29r's are a lot trickier to make work then people give them credit for. Sometimes there's just not enough room.

Great looking project all around.
for me though i would add 3/4 of a degree to the HT to bring the front end back a little and add a cm or better to the back end to make up for it but thats what first, second, third.........tenth bikes are for, getting it just right for yourself. Who knows, maybe it will be the best bike he's ever ridden, i hope it is!!

jake