# MTB Tandem build thread



## Erichimedes (Jul 30, 2010)

Hey all,
I just wanted to share some photos of today, it's starting to feel like this project is really happening! It's actually recognizable as a bike.

Things have gone reasonably well. The learning curve mostly seems to be that I'm taking forever to do pretty simple stuff. I'm having fun though! The welding has been harder than I was expecting. I'll probably focus more on tube cleaning from now on.

These are all taken where I work, at Andrews Design Works, also known as King Cage. He's letting me use the shop this weekend, best boss in the world.













































I think my next move is to do some preliminary alignment. Get things in the right neighborhood. Although it's pretty straight as is. Then weld in my lateral in the back there. Then it's bottle bosses, cable guides, and a real alignment. Then next week I'll start on the chainstays.

I love making stuff


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## Walt (Jan 23, 2004)

Looking great!

What is your alignment plan? At this stage, it's going to be nigh-impossible to really move anything around much. 

Then again, it's a tandem, so it could be crooked as a pretzel and it wouldn't matter. 

-Walt


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## Erichimedes (Jul 30, 2010)

Walt said:


> Then again, it's a tandem, so it could be crooked as a pretzel and it wouldn't matter.


Ha! I'm glad to hear that. That being said, it's really already as straight as I could wish. I just would like the HT to be in plane with the rest of the bike. The thought was to bolt the headtube down to the Bridgeport table, vertically, and use the digi-level on the seat tubes to get them vertical. Or at least 90 degrees from the table.

A quick check with string from the HT to the stoker ST, measuring the distance from both sides of the captain ST, it's only out about a 1/4 of a mm or so. And conveniently, it's further out on the side I plan to put my cable guides on


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## Walt (Jan 23, 2004)

You will find that the kind of manipulation you're talking about needs to happen before the stoker and captain seat tubes are attached to each other. Actually preferably before the captain toptube is in as well. Once the whole thing is together it's very hard to make it move with tube diameters this big.

IMO if you are off by under, say, 5mm in either direction, call it good. HT twist is the only thing that can really cause a problem for a tandem, and even there, it would have to be pretty extreme. Putting a ton of force on it to try to make it straighter is only going to do damage (mostly to wherever you're clamping it, but in extreme cases also to the tubes). .5mm is less than the margin of error even if you've got an alignment table just due to BB shell irregularities. Leave it.

-Walt


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## Erichimedes (Jul 30, 2010)

Interesting. I guess that makes sense. I was originally planning on doing some alignment after putting the boom and down tubes in, but decided against it. Now I think perhaps I should have gone that way. It sounds like the best way for a frame with these kind of tubes to be straight is for the jig to be straight to begin with.

I'll check the headtube today and see how far out it is. It fit back into the jig very easily after finish welding, some I'm hopeful that it's straight. As for the rest of the frame, I'm more than happy with it as is.

Thanks for the info Walt, I appreciate it.



Walt said:


> You will find that the kind of manipulation you're talking about needs to happen before the stoker and captain seat tubes are attached to each other. Actually preferably before the captain toptube is in as well. Once the whole thing is together it's very hard to make it move with tube diameters this big.
> 
> IMO if you are off by under, say, 5mm in either direction, call it good. HT twist is the only thing that can really cause a problem for a tandem, and even there, it would have to be pretty extreme. Putting a ton of force on it to try to make it straighter is only going to do damage (mostly to wherever you're clamping it, but in extreme cases also to the tubes). .5mm is less than the margin of error even if you've got an alignment table just due to BB shell irregularities. Leave it.
> 
> -Walt


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## Walt (Jan 23, 2004)

Yeah, unless your jig is wicked off, you should be more than good. Some string and a true wheel will give you all the data you need, really. 

I find it humorous to see people hovering over dial indicators on their .0001" from flat alignment tables. How flat is the face of your BB shell? Even being very generous about the accuracy of a hand tool that is indexing from threads that *also* aren't very straight once it's welded up, it's not going to be better than +/- .005". Translate that out from the 19mm radius BB shell to the head tube (call it 700mm from the BB shell) and you're talking like .2" or ~5mm! Even with an amazing facing tool that gets you to .001", you've still got a mm or so of fudge factor. 

-Walt


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## Erichimedes (Jul 30, 2010)

Yeah, it makes sense. Reading the "the tell all NO HOLDS BARRED alignment thread" over on Velocipede Salon really helped me relax. My favorite: The alignment table isn't going to be riding the bike."

Got the lateral, water bottle bosses, and cable guides on today. Left my camera at the shop though, so I'll put some more pics up tomorrow.


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## Eric Malcolm (Dec 18, 2011)

Many, many years ago at the LBS where I learned about the cycle trade in general, we had a frame come in that needed a HT 'tweek' after a crash. To address the twist, we put a bar of steel that neatly fitted the HT and clamped it down. Gave it a pull at the BB shell to rid the frame of its twist. It suddenly caved in at the thin butted section. It looked like the effect of holding an empty aluminium can that you hold in each hand and twist. Amazing wrinkles. Ok on a job that insurance paid for, and replaced, sad if, on a new build, it goes wrong.....

Eric


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## Feldybikes (Feb 17, 2004)

Walt said:


> Then again, it's a tandem, so it could be crooked as a pretzel and it wouldn't matter.


True dat.

My rule of thumb for my bikes is that once it's straight enough for me to ride no-handed without noticeably leaning to one side, then any straighter is pretty much irrelevant. Of course, I sell to no one, so I guess that gets taken with a grain of salt. That said, since one never rides no-handed on a tandem (unless one's stoker is a Cirque du Soleil performer), I s'pose this metric gets loosened quite a bit for a tandem.


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## Blaster1200 (Feb 20, 2004)

Looking great!

As you saw in my tandem build thread, I had to do a little twisting to the down tube. I don't remember the True Temper model number but it was the BMX 1.5" 1/.9/1. My head tube was fractions of a degree off from being parallel with the seat tubes, which were as parallel as I could measure. The muffler tube expander worked great for holding the front eccentric BB to my truck hitch. It took all the leverage I could get (note long tubes in the picture) just to get a little twist out of it. With the front top tube in place, no way was I going to bend it.


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## Erichimedes (Jul 30, 2010)

Yeah, I think it's pretty clear I'm not going to be aligning it any more at this point. Sorry if I didn't make that apparent. As far as I can tell, the head tube is off by about one tenth of a degree, according to the best of my abilities to measure it. I feel ok about it. If we ride it and I feel like there's a noticeable issue, maybe I'll revisit it.

My first post was a little rushed, and I just wanted to get some pictures out there. I feel like I should have told a little more story about this build.

This is the result of my girlfriend and I deciding to ride the Great Divide Route next fall on a tandem mountain bike. We ride quite our Ibis road tandem quite a bit, and have been wanting to check out a tandem MTB for a while. After quite a bit of research and thought, I decided that what I (we) wanted just wasn't out there in a production bike. We wanted Steel, 120mm fork corrected, sizes that fit us both well, and 74 degree seat tubes. Steel for obvious reasons, 120mm because I feel like the best fork options out there only go down to 120, and steep seat tubes because we both (aw, we're cute right?) have back problems related to cycling that have been kept under control with steeper seat tube angles.

The design process went pretty well. I started with a full size drawing, and then at night while (not) falling asleep I'd remember some detail I'd overlooked, and go back the next day and factor it in. After a lot of erasing and 2 more drawings, I was really happy with the geometry I'd come up with.

While this was happening, my boss and I were chipping away at building the jig. We settled on the beam design for it's ease of construction, extreme flexibility, and relatively low cost. I also realized that the beam is keeping in tradition with Durango framebuilding, as Yetis were built on beams here. In fact, this jig has a little piece of a Yeti frame jig in it!

I started construction with some seat tubes. Two standard 9/6/9 butted frame tubes were cut in half, and some thicker walled 4130 was machined so the bottom would press fit and be welded to the top of them. Some rolling, marking, and witch-wanding later, I had a surprisingly straight result. The small remaining tilt was lined up in line with the frame, and mitered and welded to the bottom brackets. I then put them on the Bridgeport table and did my best to get them straight.

Loading the jig and mitering and fitting the tubes was nothing out of the ordinary. Just a ton of fun, and a lot of learning for me, with a little guidance from my boss. I tacked everything up, and welded the tops and bottoms of everything I could reach while it was still in the jig. Then put it in a bike stand and finished what you see in the first pictures.

I'll admit that for some reason I though I would be able to align it after finish welding. I guess that was just something that go lost in translation, but I seem to have gotten really lucky there. We'll see I guess!

I got the lateral, some cable guides and bottle cage bosses (also leftovers from the yeti factory) in yesterday:



























Sorry for the crazy long post. Shorter next time.


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## Walt (Jan 23, 2004)

1/10 of a degree is nothing to worry about. You're golden.

Alignment is 90% good miters and 10% good weld sequence, in my experience. In rare cases you can fix things a little after the fact but with mountain bike size tubing, realistically you are stuck with what you're stuck with once the front end is all together.

Looking fantastic and that's a great story, too. Can't think of a better reason to build your first frame/marriage destroyer! 
-Walt


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## Erichimedes (Jul 30, 2010)

*Chainstays*

Didn't get too much done this week. I've been tracking down parts for the build, as well as just being busy.

However, I did build a boxy sort of chainstay bending die:









































I didn't get a picture, but I did weld those 3 pieces of metal together.

I couldn't be happier with the result! The dimple gives me even more tire clearance, and looks great (imho).

Going on a river trip this weekend, but will probably get to fitting chainstays next week. I cannot _wait_ to ride this thing!


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## Erichimedes (Jul 30, 2010)

*Rear triangle progress; pic heavy*

Alright, finally have made some real progress on the rear triangle. Once I got the chainstays bent, I made a crude tube block for the narrow end and got it mitered up. I used the same setup to both jig up the chainstay/dropout weld, and to miter the stays. It ended up being a compound miter, in a pretty big way. That poor bottom bracket only has like 5mm of unwelded surface down at the bottom now.

I got crazy lucky that the dummy axle we made held the dropouts the _exact_ distance off the surface of the 80/20 at the correct angle and met the miter I made while the chainstays were clamped down to the 80/20. That's never going to happen again.

Tonight I got the seatstays mitered and fitted up. Tacked them in place, then worked on some bridges. Got those tacked in, and will hopefully finish weld the whole thing tomorrow morning.









































































I'm in the home stretch! Gonna ream some seat tubes tomorrow, and chase/face the BB and bring it to the bike shop to have the head tube reamed. Then the painting adventure. Whoo! Dang this has been fun!


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## Walt (Jan 23, 2004)

That is looking great! This is my favorite first-frame post in a long time, though I think your industry-insider status costs you a few cool DIY points. 

BTW, WTF can't I get King cages from BTI or QBP anymore?

-Walt


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## adarn (Aug 11, 2009)

Awesome!


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## Erichimedes (Jul 30, 2010)

Thanks! I'm having a ton of fun building this thing, and I can't wait to ride it!

Walt, we're always getting busier and keeping a distributor in the loop was getting tough. Give Ron a call and he'll get your order out next day or sooner.

I've now got a question: I've decided to get a cheap gravity-feed sandblasting gun from Harbor Freight. I will probably be rattle-canning the paint job. Does anyone who sandblasts have a recommendation on media? My first thought is Aluminum oxide, 120 grit.


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## Walt (Jan 23, 2004)

If you are rattlecanning, don't bother blasting, it's a waste of your time. The paint won't last long regardless. 

-Walt


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## Erichimedes (Jul 30, 2010)

So, I do have pictures of everything in between my last post and this one, but they ended up on other people's cameras. So I will post them eventually, but right now this is all I have:

























I'm thrilled with the color. The green is a little darker than it shows up in these photos. It got a little washed out in the direct sun.

The $19 harbor freight sand blaster did a pretty good job! My compressor was unable to keep up, but I ended up sandblasting just the difficult areas, i.e. tube junctions. I sanded the middle lengths of tube, and did a double full wipedown with acetone.

I decided to go with two part epoxy primer, with an acrylic urethane topcoat and clear coat. Two coats of everything. I went with Summit racing's paint because it was easy to order online, and didn't cost a mint. I got a 1mm tip HVLP touch up gun that got raving good reviews on amazon, and it turned out to be a great size for bikes. Brand new organic vapor cartridges for my respirator and I was on my way.

I got a few sags in the primer, one sag in the paint, and one small sag in the clearcoat. I'm still happy with it, and luckily we will destroy this paint job on our GDR trip. I still have much to learn, but honestly, I had more fun painting than I ever guessed I would! I'm chomping at the bit to paint another frame, and at this point I could paint another two bikes with what is left in the quart of paint I bought. I think in the future I will reduce the epoxy primer a little, and do lighter coats, and pay much closer attention to how and where the clearcoat goes on. I have to find a way to turn bikes I'm painting upside down. It just seems to reveal every spot I miss otherwise.

Time to build it up...


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## Feldybikes (Feb 17, 2004)

Rad.


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## Erichimedes (Jul 30, 2010)

I figured I'd post an update, although I don't have many pictures.

I finally got the tandem built up by Thanksgiving, and right about that time was when the snow started hitting us, HARD. We got three rides in before the snow completely socked the trails in, and just went for another ride yesterday.

Final frame weight after paint, including dropouts: 10.75 lbs. About a pound less than the Powderkeg.

The final build ended up being:

-Cane Creek 40 headset
-RS Pike at 120mm travel - 45mm offset
-White industries 36h front hub laced to Velocity Cliffhanger rim
-Rohloff 36h laced to Velocity Cliffhanger rim
-Shimano UN55 square taper cartridge bottom brackets
-Shimano MT60 cranksets
-Thompson and Thudbuster seatposts
-BB7 brakes with 200mm rotors
-Easton Havoc carbon bar - front
-Easton aluminum bar - back
-Chunky Monkey 2.4 tires front and back

An unexpected but very welcome advantage of going with a 28.6 captain seatpost was that I have a huge selection of stoker stems at my disposal. The goofy 140mm stems from the 90's that no one wants anymore are a perfect fit.

I'm glad I obsessed over the geometry and tubing for so many weeks during the design process. This thing rides better than I ever could have hoped. It just feels so perfect when I jump on the saddle. Hayley is really happy with her fit, too. We notice very little flex in the frame, and I think the 71 head tube angle was also the right choice. It handles like I think it should. I'm really happy with how she turned out.

Just a couple pictures from yesterday:

















I might upload a couple more after our White Rim trip next week


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## Feldybikes (Feb 17, 2004)

Nice the geo works for both of you. I built a tandem awhile ago and used the then-available True Temper penta-butted tandem tubes. I made the front half the right size for me and the stoker cockpit as long as the tube would allow. Still too cramped for my wife. Guess I'll build a new one someday, but likely this one will start to get more use with a kid stoker crank soon.


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## Erichimedes (Jul 30, 2010)

Feldybikes said:


> Nice the geo works for both of you. I built a tandem awhile ago and used the then-available True Temper penta-butted tandem tubes. I made the front half the right size for me and the stoker cockpit as long as the tube would allow. Still too cramped for my wife. Guess I'll build a new one someday, but likely this one will start to get more use with a kid stoker crank soon.


Yeah, that makes sense actually. We have an Ibis road tandem that's a touch small for both of us, and my stoker doesn't like riding it nearly as much as the new rig. I went about as long as the butted tubes I was using would allow, and I'm glad I did, she's much more comfortable. We're not to the kid stage yet, but when we are I think the tandems will be perfect!

And a White rim picture just because:


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## shlammed (May 19, 2015)

Awesome build. The smiles tell all that's needed to tell about the bike.

This thread motivates me to build our new tandem up (albeit a road bike).
I built one for us last year and its great, but im doing some geo changes.


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## Rubberduckxi (Sep 10, 2015)

Really cool tandem you made!

Sorry for digging out this post, but I have a same kind of project in mind. My question is, what exact tubes are you taking for the specific spots? What kind of material, diameter and wall thickness? 
I have found a frame builder near my home, but he never has build a tandem but a lot of other interesting cycles. So I am wondering what I should choose. 
By the way, I would like to build a 29+ with rigid fork, and all should be brazed, nod welded...


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## Erichimedes (Jul 30, 2010)

Rubberduckxi said:


> Really cool tandem you made!
> 
> Sorry for digging out this post, but I have a same kind of project in mind. My question is, what exact tubes are you taking for the specific spots? What kind of material, diameter and wall thickness?
> I have found a frame builder near my home, but he never has build a tandem but a lot of other interesting cycles. So I am wondering what I should choose.
> By the way, I would like to build a 29+ with rigid fork, and all should be brazed, nod welded...


The tubeset was the trickiest part of this build. Very little info for me to go on. As it all worked out, I built a second tandem frame after this one that fixed all the little problems this one had. I tried to upload a picture here, but MTBR is not letting me. Just visit my website to see it.

Here's the updated tubeset that fixed the stiffness problem the first one (this green one) had.

-Down tube & boom tube: True Temper OX platinum 1.75" x 9/6/9
-Top tubes: Nova 1.5 x 8/5/8
-Lateral tube: Nova 1.375 x 8/5/8
-Chainstays: Nova Tandem 27mm oval
-Seatstays: Nova 19mm x .8
-Seat tubes: Nova 1.375 x 9/6/9 cut in half and collar welded to the top.

If I were to build a 29+ version, there are some specific changes I would make. Also, I updated the geometry. There are some pretty serious pitfalls you wouldn't think of if you haven't ridden an off-road tandem before. My second one turned out really great. Shoot me an email if you want to talk geometry.


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## dr.welby (Jan 6, 2004)

VariWall has has some nice big long tubes that would work well in tandem applications.


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