Thursday, January 19, 2012

Building a mountain bike Coconino style post #2

Picking up where I left off the front triangle is all tacked together, and it's time to check the alignment before I attach the chain stays.

The head tube is off by this much.

......And, the top of the seat tube by this much.

I know my miters are sound, and my bowing has been marked and taken into consideration so I know it's just a matter of (usually) that I simply tack heavier with my left hand - I tack from my chair of course, so I tack with both hands. Sometimes it's spot on from the get-go, but it's no big deal, and I'll make it fine with out bending or cold setting the tubes. Read on.

See all the arrows on the frame in sharpie? (you may have to click on the image) they are where I will place additional tacks to "pull" the frame into near perfect alignment.

The size of the tack, it's location, the amount of filler applied and how hot you make the tack all influence the amount of pull the tack will have on the structure.

I have done really nice tight clean fabrication so I know it "wants" to be straight, I just have to accommodate it to let it be proper.

Like these two tacks I'm going to lay, which have great pulling power - careful!

Click on the picture and you can see the tacks.

And, amazingly enough (I love this aspect) it's all nice & straight.

Everyone has their own ideas and sequences for alignment, some theory and some factual, it's best to find a repeatable sequence which allows you repeatable results.

Waiting for that to cool I have cleaned up the chain stays a bit, it's easier before you tack them on. Again - clean everywhere you will be joining inside and out with 80 grit and 91% alcohol.

See where this is going? the inside tacks are where the chain stays go, and the vent holes are being drilled.

I have one tack - the one you can see - holding on the left chain stay, it's always a few file strokes shorter every time due to the deflection from mitering both stays at the same time in my Anvil chain stay fixture in which the dropouts were brazed as well. Then, you match the right stay to the left and check the clearances for the chain rings and tire and then tack both stays on good and solid at 12:00, 6:00, 3:00 and 9:00.

Checking to make sure the dropouts are parallel to each other - good to go!

......And, making sure that the center of the hub is centered to the BB shell and the rest of the frame. good to go.

making sure everything is all good and that the tire, the rings and the disc all clear.

That's it for now, I was assembling bikes until 9PM last night so I may not go out into the shop today but it's back at it tomorrow with seat stays. Thanks for reading! - Steve.


Cyclebound said...

Thanks for putting these together. It is definitely an artform and a honed skill to put out quality. Although I probably won't ever make a frame I do know that sweat and most likely blood and some tears were shed creating my Coconino. I like riding all of my bikes but I am proud of that one.

Anonymous said...

Love the detailed progress pics!
Gives all us non-frame builders a great appreciation of the skill and attention to detail that go into your creations.

FTMN said...

Thank you!!! I've been doing research on framebuilding for the last couple months, and these last two posts have been GREATLY educational. Both the words and the pics do an awesome job of showing the process... definitely one of the best resources I have found on the web. I hope you continue the series!

Thanks again!

steve garro said...

More on the way - my computer went down!
- Steve.