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How do I avoid building warped frame?

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How do I avoid building warped frame?

Old 08-05-18, 11:01 PM
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How do I avoid building warped frame?

Hello! This is my first post in this sub-forum so please excuse my ignorance if this topic is already discussed. I have a few frame ideas that could fit my needs like a glove and I have the resources to build one or two or even a thousand frames but I often see that average joes like me end up having warped frames although not by much, e.g. rear wheel is off by a few mm. I think this is because of the welding heat, correct me if I'm wrong. I would like to know how do I avoid this problem?
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Old 08-06-18, 06:19 AM
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Unfortunately this isn’t a question that can be adequately answered in a post. It goes to the heart of how a frame is made and what equipment is used. The problem is that the heat of a flame distorts whatever it is brazing. Steps have to be taken to counteract those forces. Here is a story to illustrate the issues when Reynolds 1st came out with its heat treated 753 tubing in the late 70’s. Unlike its cousin 531, it could not be bent much into alignment. The old methods many classic builders used with simple tooling and brass brazing wouldn’t work. To avoid having builders make a mess of their new flagship tubing Reynolds required making an entire frame to be sent to them for testing before they were allowed to buy it. That didn’t go well for many builders.

In 1977 I visited Reynolds in Birmingham and talked to Terry Bill one of the managers. He told me that up to that time every American had failed the test and only 5 European companies had passed. To put this into perspective, Americans had just started to build frames in the early 70’s (following the bike boom around 1970). Probably every one that had sent in a test that cost them a decent amount to apply and didn’t pass wanted to know the same thing you are now asking.

This is self serving to say but one of the primary reasons to take a frame building class from a knowledgable teacher are to get answers to your question. One of my class objectives is for every student to leave with a frame built to within 1mm of alignment tolerance. Class instruction involves the sequence a frame is put together, what flame pattern is used on each joint and what equipment is required to hold and check whatever is being brazed. That is a lot of information.
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Old 08-06-18, 07:19 AM
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Doug gives good advice, as usual. To more directly answer the question, the first question to ask yourself is how you are going to measure to see if the frame is straight or not. As far as procedure goes, the frame should not be constrained during the joining process. My procedure goes like this: tack (or pin) the frame in a fixture. Frame is taken off and measured on a granite table. Before I got the granite table, I used the bed of my milling machine. If everything is straight, fully join the frame. If it's not straight, do something about it before fully joining the frame. When the frame is joined, check again to see if it's still straight or if needs to be cut into pieces. I have seen a video of a builder using witch wanding to align a frame. I'm not convinced that is a permanent fix, but I have used it successfully on chainstays. Witch wanding is heating the side of the tube that you want to be shorter. Don't have to get it too hot and it will shrink.

Joining is done in a bike repair stand. Be careful not to squish the tubes.

I suspect that European builders passed the 753 test while Americans didn't because at the time Americans built fully in their fixtures. Europeans were much more likely to build outside of a fixture. Or else do a lot of pre-heating. And also, the European motto was "kill it with fire."
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Old 08-07-18, 08:52 AM
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I was taught early on that the evenness of the heat (the whole joint up to temp if possible) and the duration of the heat were two real biggies to insure that your brazing isn't adding warping stresses. Still to this day these are my pitfalls. The before brazing set up has it's contribution to warping. A tube miter that's off center will press more on one side of the other tube. When heated this pressure can cause the joint to slip a bit sideways. Without a doubt the most important tool I have is my flat surface. Next up is possibly the bench vice (Rapid 125 for most frame work) or the bike stand (Park w/ big steel base). My jig (HJ Universal) really only speeds up the fit up/mitering and speeds up the tacking steps. (When I first got it I built two frames with brazing fully in the jig, the frames weren't very straight until the flat surface was applied).

It's interesting to hear of the Reynolds 753 stories from different old time builders. Each has there take on the testing of their/others' frame test, or non test. I have heard of some who just ordered the two frame tube sets and never sent one in for testing. Andy
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Old 08-07-18, 07:48 PM
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there was a mini test set later in the process. I think Reynolds just wanted to sell tubes and didn't want to be in the position to tell someone they wouldn't take their money. I never got certified because I didn't want to spend the money. I am not sure I regret that now. Anyone can buy better tubes from any number of suppliers.
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Old 08-07-18, 11:03 PM
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Somewhere in my desk is a check made out in British pounds to Reynolds dated '77 or so to buy a set of sample tubes to be made into a complete frame for testing. I didn't send it in because just then I got a couple of Raleigh 753 frames with cracked chain stays in for repair. They hadn't gotten the hardening/thickness right. I didn't want to take the risk of making a frame and having something break that wasn't my fault. Eventually they figured out how to make chain stays that didn't break and only required a simple short tubes brazed into a BB shell test. Since Reynolds had a distributorship in nearby Chicago I wanted access to their entire line and submitted and passed that simple requirement.

Having visited many English builders in the 70's it was obvious why Reynolds needed to have a complete frame test. In order to make money at a price their customers could afford they had to make a frame a day and couldn't afford expensive tooling. That is not a recipe for high quality. Reynolds 531 could be bent while 753 couldn't be much. Even as high school teacher with a master's degree in education I made less than $10,000 a year and still was a lot richer than a typical British worker in 1975. Frames usually cost less than $150.

About that same time Tange came out with their high quality Prestige line that was also thin walled heat treated tubing. They didn't require any test to buy and I"m sure Reynolds change in testing policy was in response to this competition.
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