Reaming a piston cylinder

In order to have a perfectly fitting piston and cylinder pair, it's necessary to have an accurately drilled cylinder.  When I tried drilling before, I was unable to get the accuracy needed for smooth motion.  The inside of the cylinder changed diameter and had internal ridges that the piston would get caught on.

The usual solution to the problem is to drill an undersized hole (bearing in mind that a typical drill bit will drill slightly larger than its stated size) and then ream it to the correct size.  This requires a reamer, which can be made as needed.  This is the first such reamer I made -- loosely inspired by this page -- it's passable, but not perfect.

To start, I turned the reamer body from a 1/4" steel rod to precisely the size I wanted to have the cylinder bore.  In this case, I turned it to a diameter of 0.19" -- just 2.5 thousandths larger than 3/16". 

One roughly turned, I polished it with several grades of carbide sandpaper, finishing with 1200 grit and parted it off.

Then, I ground about half of the diameter away on the griding wheel and beveled the leading edge. 

This came out much more messy than I intended, but after cleaning up on an oilstone, the edge was sharp.  I heat treated the reamer tip and left it dead hard. I never got the rest of the reamer hot enough to harden it.

Here's the cylinder after drilling with an 11/64" bit.

Here is the reamer in action, cutting about 1/16" at a time before needing the chips (rather a fine powder) to be cleared.

After reaming, I turned a piston to fit. 

I cleaned both the piston and cylinder in isopropyl alcohol to remove chips.  The piston slides smoothly and is a quite close fit. 

A little clock oil improves the action, and you can feel a small amount of compression as the piston moves in.  If the piston is pushed in quickly and then withdrawn, the end of the piston is slightly warm.  Not hot enough to be used as a fire piston (it should be longer, so more compression occurs), but still enough to indicate that the fit is close.