Jim,
For the benefit of others on the list, a "Lap Seam" is a flaw in the metal, not a manufacturing process.
Lap seams usually develop when a billet of raw material is first formed from a square to a round shape or similar kind of manipulation.
It's frequently caused when a an outside surface is "folded" into the billet.
The outside surface can be covered with contaminants such as "mill scale", oxides and other impurities caused by the extreme heat used in the process. It can also result from manipulating the part when it's not hot enough to "weld" together and form a homogeneous solid.
What can start off as a microscopic layer or crack within the billet can create a lap seam flaw many feet long in a finished tube, pipe or bar.
Materials used in critical parts such as aerospace applications are frequently inspected using x-rays, magnetic flux or other non-destructive testing methods to look for lap seams and other defects.
The original Durifort, Vitus and Vitus 172 tubes were all made of seamed tubing. The 3 main tubes were DOM - Drawn Over Mandrels to provide the thin walls and butted ends in the tubes: both ends on the top and down tubes, bottom end only on the seat tubes.
Most seamed tubes are produced from low quality, low carbon steel which requires no further heat treatment after welding.
An alloy like 4130, Reynolds 531 and so on requires additional steps after welding, that's one reason they are usually made with the DOM seamless process.
Reynolds produced their low alloy "A Quality" tubing in both straight gage and butted versions. I thing that it was available seamed or seamless.
It's quite possible that during the mad rush of the Bike Boom, some Reynolds A Quality tubing or even the lower grade "B Quality" tubing found it's way into some better quality bike frames... ;-)
Hey! They're bikes, not Swiss watch movements!
Chas. Colerich Oakland, CA USA
Jim Merz wrote:
> The cost for material is not enough to make up for the many more steps to
> butt the tube. Seamless tubing is more expensive because it takes many more
> steps to make compared to seamed. True Temper is seamed, but the weld is
> done nicely and then drawn over a mandrel. This makes the bore smooth, you
> cannot see the weld normally. The properties are very similar to seamless. I
> believe the FAA requires airframe CrMo tubing to be seamless. In all my
> framebuilding experience I only had one frame fail beacause of defective
> tubing. A lap seam in a 531 down tube. They gave me a new tube! Normally I
> would inspect each tube before the frame was made, sometimes you could see
> lap seams.
>
> Jim Merz
> Big Sur Ca
>
> On Fri, Jun 25, 2010 at 8:27 AM, Don Wilson wrote:
>
>> Thank you, Norris, for your recollection of CAMUS tubing.
>>
>> As usual, your wealth of knowledge triggers another question.
>>
>> Did Reynolds innovation of double-butted tubing reduce the quantity of
>> steel used in each tube, and so lessen the raw material cost/unit (and per
>> unit shipping cost on both receiving steel and shipping tubes) of each tube?
>>
>> At their volumes, and economies of scale, even slight reductions in steel
>> required per tube could yield significant cost savings, especially if the
>> additional technology costs of double butting could be rather quickly
>> recovered.
>>
>> I know they charged more for DB tubes, but that would just have been all
>> the sweeter for Reynolds. Firms sometimes charge more, at least early on,
>> for "advances" (especially patented ones) that have been undertaken, largely
>> because they saved cost. Just curious if that were the case with Reynolds DB
>> tubing.
>>
>> Thanks in advance.
>>
>>
>> Don Wilson
>> Bandon, OR/Los Olivos CA USA