Tandem Tom

When frames are built are the seat tubes "always" reamed as a matter of course? Or are they reamed to accommodate a specific size seatpost?
Thanks!

wsteve464

The seat posts are a set id. They are reamed to clean up the inside of the seat tube after brazing/welding. Some people want a larger id seat tube and a 27.2 mm seat post so they will build with an oversized seat tube and put an aluminum sleeve inside to fit a 27.2 mm seat post, no reaming required. Others want the tube id to match the seat post so reaming will be require. Reaming a seat tube is only for clean up. The tubing that is designed for seat tubes have walls that are only .7-.8 mm thick so not a lot of material to ream away.

Nessism

I built a frame with a double butted seat tube one time and wound up reaming off a little extra material so a standard 27.2mm seat post would fit (would have had to go 27.0 otherwise.) Normally reaming is just to clean up distortion but not always.

Andrew R Stewart 

No, not all bikes are made with the care to ream a seat tube after construction (and not every shop can do this preassembly step either). Of course if a post fits well and stays tight then who cares whether the ST was or wasn't reamed. But the vast majority of bikes you will read about here, those made by a caring hand, will have had some sort of consideration for best post fit. Be that reaming, sleeved, honing or some other step.

Before material removal is done it pays to really understand what is going on, why it is present, whether the frame can tolerate enough removal to fix the problem and which type of repair is the best choice. Cutting tools are really cool and sometimes sadly cruel depending on how they are used. Andy

JohnDThompson 

Seat tubes are prone to distortion from the heat during brazing. Heat causes the tube to expand (lengthen) slightly, and at the temperature needed for brazing (particularly with brass), the tube gets quite soft, so the expanding top tube pushes into the seat tube and distorts it. Careful reaming removes the distorted material so the seat post can fit. I prefer to use a straight or helical blade reamer, as this will preferentially material from the "high" spots; a brake hone is a much cheaper tool for this purpose, but will remove material from the entire circumference of the tube, not just the high spots. Seat tubes are thin enough at the top, so I prefer not to remove any more material than is strictly necessary.

Tandem Tom

Thanks for your replies!!

Andrew R Stewart 

To add to John's good advice- A reamer cuts off chip/swarf amounts of ID, at the high spots first. A hone grinds off smaller grits from more of the ID's overall circumference. Somewhat different tools for overlapping goals. Andy

duanedr 

HA! I recently replaced a seattube that I tried reaming with an adjustable reamer and messed up. Cruel...