I'm not sure if this is the best way to do this, but I don't mind sharing what I've figured out.
I took Tink's vessel class last August and was struggling with handles for a
long time afterwards. I think I finally have them figured out though ...
In the photo below I've marked the four connection points to help with the
explanation.
I originally tried using Peter's tweezers to help locate the dots, but found
that they didn't work for me as the tweezers don't guarantee that your
contact points are 180 degrees apart.
So, here's what I've been doing...
I first place a dot of glass along the rim where I want one of the handles
to be:
Then, holding the mandrel horizontally, I rotate it 180 degrees so the dot (red) is on the opposite side. I rotate the mandrel slightly in my fingers back and forth so that the dot (red) appears on the opposite side on the top and on the bottom. I usually roll it back and forth like this several times and stop it "in the middle". In other words, I stop it when it seems to me that the dot is directly on the other side of the mandrel and is out of view.
At this point, I place the second dot (yellow) on the rim at the spot that is in the direct line of sight to the other bead. I hope this makes sense...
So, now I have the "red" and "yellow" dots. I then hold the mandrel level and place another dot (blue) directly in line on the horizontal with the "red" dot. The same is done for the other side, though on the other side, you need to make sure that you make the dot not only on the horizontal with the yellow dot, but also the same distance away.
Once I have all four dots, I rotate the mandrel and look at all four dots to see if the distances look even.
If the distances are off, sometimes you can heat the dot and
push it a short distance ( I use the razor blade tool to push it from the bottom, but if you do this, you need to make sure that once you get the dot to the right spot you should reheat it and press it a bit to make sure you don't end up with an empty space under the handle connection.)
Once I'm sure all the dots are in the right spots, I give them some heat to make sure hey are well adhered to the vessel.
Next, I heat a rod so that I have a bead of glass molten, wait for it to cool off a bit, touch it to one of the dots ("red") and stretch it to the other dot ("blue") making sure that it's straight so that the empty space remains between the vessel and handle. I wait for it to solidify and do the same on the opposite side.
Once both handles are on, I heat one side of a handle just enough so that the original dot (e.g. "blue") melts in with the new handle glass. (I don't know why, but I usually do the non-rim side first...)
I then do the same thing for the other side of the handle ("red" side). Repeat for the other handle.
Finally, I melt the handle and pull it to shape. I bought a graphite hex reamer, but actually prefer
to use a tool I made which is simply a 1/4 inch graphite rod, sharpened with a pencil sharpener
and wrapped with masking tape for a handle.
Regardless, what you use, you probably need to play with the handle to get it to the right shape and to get the handles to match. Sometimes you may need to add or remove glass from the handles to get them even.
Often, I find that when I shape the handles, I'll end up with more glass on the bottom "blue" of the handle than the top "red" or vice versa. When this is the case, I usually heat the handle and use my fine tweezers to pull some of the glass from the thick area to the thin area. Sometimes the tweezers will stick. If so, just wait them out until they release from the glass.
Final Handles
Also, don't forgot to check the view from the top to see if the handles are even. Occasionally, I get to this step only to find that the handles don't line up. Most of the time, you can heat them gently and push them into alignment. Sometimes there's nothing to be done but to remove one or both handles and redo them.
I would show a picture of the final vessel except that it cracked while taking the last few pictures ( I was taking them myself and had the vessel out of the flame too long)
Hope this helps.
edz