nun

A friend has a Bianch Volpe frame that's been converted to a city bike. The saddle is pretty low already, but she wants it a bit lower. The seat post is a laprade type, 350mm long

https://sheldonbrown.com/harris/seatposts.html

I went to lower the seat post and it's bottoming out somewhere. It comes out ok. Could it be that there's a small bulge at the top
of the seatpost where the saddle clamp is pressed in, or it's hitting something inside the seat tube, maybe the top bottle mount. If it's the latter it's easy to take an inch off the bottom, but I'm interested to see if anyone has encountered a similar issue.

2manybikes

It's probably the bottle cage bolt flange. If that bike has them. You could look in there with a flashlight.

nun

I bet that's it. I'm taking a tape measure and a pipe cutter over there tonight. The frame is a 52cm
so with most of the 35cm of the seat post inside the tube it's probably hitting the flange.

fietsbob

One other possibility, the top of the seat tube was bored out,
from a thicker wall tube, frame would likely be Aluminum ,

and the end of that bored out section has a shoulder,
the seat post is meeting that shoulder.

Chombi

Cut it short as needed. I wouldn't stress too much about cutting an SR Laprade seatpost as they are plentiful, not expensive and very easy to find. You should take off the burrs bevel the cut end a little on a belt sander after cutting so it can be inserted easily into the seat tube.

Chombi

nun

I'm going to use a plumber's tube cutter as it gives a nice clean cut with very few burrs to be filed off.

DannoXYZ 

It will take you forever with a pipe-cutter. May take a very long time given the 5mm wall-thickness of the SR posts. Perhaps start it with the pipe-cutter to create a beveled mark as a guide. Then hacksaw right on the lower side of the mark.

ColonelJLloyd 

^
I agree. I don't think pipe cutters are made for cutting aluminum alloys like those of which seat posts are made. I've had quick success with a new hacksaw blade, a cheap miter box and some steel wool for the burrs.

dabac

I don't think so. Maybe it's a tad slower than a hacksaw, but we're still talking minutes. That's a fine price for no burrs, a straight cut and a nice slope to the leading edge. I use mine at every chance I get.

Grand Bois

That works well. My pipecutter won't cut deep enough for a seatpost, but it's great for handlebars.

DannoXYZ 

Yeah, I use it on Thomson or American Classic posts. Just not on SR ones. Takes all of 30-seconds with a hacksaw.

silver_ghost

For real. The post in question is made of very soft aluminum but the walls are real thick.

nun

I should have read the proceeding 5 or so posts....Yes that wall is really thick and it took me 15 mins and a couple of blisters to get through it with a pipe cutter. The cut was very clean, but man was it tough. Next time I'll use the pipe cutter to make a guide groove and finish it off with a hacksaw.

The issue was the bottle cage mount flange. Anyway it's all good now and the seat has been lowered by a cm or so.