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Discussion Starter · #1 · (Edited)
For my first frame what do you guys think my goal be for alignment should be?

Right now my seat tube is out of spec by about 1.6mm. My measurement is repeatable to + / - 0.2mm. I am taking the measurement at the end of the 20" seat tube with the bike held in my jig using steel cones on the BB.

 

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Get it straighter.

Is it just tacked, or have you finished the joint? Best to check this several times - once before tacking, once after tacking, and once after joining, and adjust each time as needed.

It is easy (just pull on the darn thing) to get it much closer than ~1.5mm out if it's too late to fix the miter.

All that said, it will probably ride just fine as is, so whether or not to mess with it is your call.

-Walt
 

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Discussion Starter · #3 ·
Thanks Walt!

The miter was REALLY good on this one. It did not hold water but it would stop paper and was in just about perfect alignment.

I checked after tacking and then flexed the tacks till it was dead on. After welding was complete it was about 2mm off. Later I did an extra pass with the TIG on one side to try to bring it back but it moved a bit more and is now 1.65mm off in the other direction. My extra pass must have moved the tube about 3.6mm.

I am thinking about doing mini pass a little with the TIG to try to pull the tube over and get it to be under 1mm.

BTW, what would be typical of a professional builders final alignment for this area?
 

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febikes said:
Thanks Walt!

The miter was REALLY good on this one. It did not hold water but it would stop paper and was in just about perfect alignment.

I checked after tacking and then flexed the tacks till it was dead on. After welding was complete it was about 2mm off. Later I did an extra pass with the TIG on one side to try to bring it back but it moved a bit more and is now 1.65mm off in the other direction. My extra pass must have moved the tube about 3.6mm.

I am thinking about doing mini pass a little with the TIG to try to pull the tube over and get it to be under 1mm.

BTW, what would be typical of a professional builders final alignment for this area?
IMO you are better off cold setting it at this point that re-welding it.
 

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I love this subject......because it is just that....subject.

I have dug around regarding alignment and have received many responses, and many 'no responses' on what is straight.

Without going into great detail, the 'average/norm/generally accepted' rule of thumb is roughly .039 in any single dimension and/or the same is adding up all measurements.

1.6mm isn't a deal killer as I have measured many off the shelf bikes from the big boys that were past your amount.

Type of bike factors here as does ability of the rider, etc.

If you aren't using an accurate reference and your measuring skills/procedure isn't up to snuff, you will have a difficult time establishing repeatability, and thus accuracy.

Good job-
 

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first frame?
basically finish the build for practice. dont worry about alignment, but be aware of what it out of alignment and roughly how far out. build it up, ride it a little, see how it fits and handles. then throw it out/cut it up and start on the second one.
 

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Nobody really talks about absolute frame alignment because there is no way for a hard and fast number.

I think you have done quite well. Push it a bit and see where it goes. Cold setting is preferable to additional welding at this point.

Some things to take into consideration. First and foremost the frame can only be as straight as the least accurate thing making it up. For example if you are shooting for sub 1mm but your tube has a bow in it that is 2mm than you can't build straighter than 2mm using traditional alignment methods.

So if you oriented any bow in the plane of the frame and know how out of round your tubing is I usually shoot for sub 1mm over the length of the frame BUT....it depends on the distance at which you are measuring it. i.e. 1mm over 650mm is a lot straighter than 1mm over 450mm. My general goal is sub 1mm on a standard sized frame. 1mm or less HT twist over 18 inches and .5 for the rear end.

Many frames are far more than this and ride wonderfully. I have seen horrifically aligned frames that even seasoned riders loved so in the end unless it is terrible it seems to have little effect on ride quality.
 

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Discussion Starter · #9 ·
Thanks everyone!

I did a touch up weld bead on one side of the seat tube BB. When the weld cooled, I re-checked alignment and am now at 1.2mm. I am going to leave it and then check it again when the frame is complete. I also did some touch up beads to bring the rear end into line and it is now 1.5mm away from "perfect".

For measurement, I am using my jig and a bit of care. I can take the frame in and out of the jig and get numbers that are .3mm repeatable. To arrive at 1.2mm as my "official" reading what i did is take 5 readings from each side of the frame (flipping the frame upside down in the jig for the far side). I then threw out the farthest outlier before averaging the results to arrive at what I feel is a reasonably accurate result. I did the same thing for the chain stays with measurement to the center of the dummy axle.

I have not done any measurement on other frames so I don't really know what industry average is. It is still a question that I am looking to answer.

The next step is is to weld on the seat stays.
 
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