Tandem Tom

My adjustable teamer arrived today. Now a question.
How do I set it to get a 27.2mm seatpost setting? Do I creep up on the final measurement? Do I use calipers?
An inquiring mind wants to know!

N2deep

Start by using it smaller than your desired diameter and adjust it a few thousands at a time, measure the cut and adjust until you get the desired hole. You could measure the reamer but remember thar the hole it makes will be slightly larger than the reamer. This method ensures that your taking metal off the entire circumference or target area and not in a local location. Driving a reamer by hand will also make the hole slightly oblong so be careful

dabac

I simply use a set of calipers.
Creep up or not depends on how much material I need to remove.
If it’s a shallow cut, I’ll usually try to go straight for the target value and hasn’t had any issues overshooting.
But maybe mine are slightly dull.
If there’s more material to be removed, it’ll usually go smoother in stages.

Andrew R Stewart 

Use the seat post as a go/no go gage as you creep up on the final size. But my view is to remove only as much material as needed to best fit the post, not to result in a specific dimension. Andy

guy153

Half a turn half a turn half a turn onwards. I would use an actual seatpost to measure the fit rather than relying on calipers.

dsaul

+1 on using a seatpost as a guide. I have a 27.2 post on my bench that is used only for checking seat tubes when reaming them.

J.Higgins 

As a retired machinist, I wholeheartedly endorse the "creep up on it" method. Using lots of cutting oil and taking smaller bites will help keep your reamer sharper longer. For what its worth, I have never liked expanding reamers for anything other than a little cleanup. I realize that buying dedicated 27.2 reamers will cause you to make a decision whether to ream your seat tube or put food on the table that week. Also, I will disclaim that I am not a framebuilder, but I have almost six decades of machinist experience, if that's a qualifier.

Tandem Tom

Sneaking up it is!
And I will 7se a seatpost to check.
Thanks