TURNING MANDREL

[Webster]

Some people think that a neck turning mandrel expands from heat and causes it to get too tight.

Below caliculation: A piece of steel .243" long heated 20F warmer. It expands 0.000013" longer or greater in diameteer. If the fit is tighter it must have to do with the case?

 

[M-61]

000013"

Interesting measurement

 

[D Coots]

Brass build up. Wrong speed cause problems. I do 48 at a time...no problems. Warm pumpkin before starting with warm tap water. 110.4567 degrees.

 

[Mulligan]

Brass build up. Wrong speed cause problems. I do 48 at a time...no problems. Warm pumpkin before starting with warm tap water. 110.4567 degrees.

Nearly choked laughing so hard. Now we need a whole new thread on the tools that can measure temperature 4 places right of the decimal.
CW

 

[BoydAllen]

I think that the easiest way to avoid mandrel heating is to have the correct match between expander mandrel and turning mandrel. Evidently there are a lot of guys out there who think that a wring on fit of the case neck on the turning mandrel is needed to turn accurate and consistent necks. With some attention to technique, it absolutely not. I have had a neck mic, that measures to .0001 for over a quarter century and I have measured most of the necks that I have turned, admittedly in small batches of 25 or less. As long as the cutter is cutting, it will keep the case pinned to the mandrel. I advance the cutter to the shoulder rapidly so that there is a lot of material left behind to keep the cutter engaged on the return trip, pause so that the cut on the shoulder is clean, and then come back to the case mouth very slowly, and I do not go back. While I have the case on the power adapter, I grab the neck with a wad of 0000 steel wool and spin the case for a second. Then I use my PMA trimmer, followed by chamfer and deburring tools, all with the case under power. I have an old Makita cordless drill that has an actual two speed gear box that I set on low speed and I do not squeeze the trigger all the way. RPM equals heat. Another thing that I have found is that if I expand all of my necks at one time and do not turn them right away, the next day or later their fit on the mandrel will be noticeably tighter, requiring me to expand them again that little bit to get the fit that I want. Typically my necks are on the same tenthousandth, and if they vary by more than .00005 I start looking for a cause. Since my speed and fit do not cause much heat, I have not had to cool my tool.

 

[Straightshooter1]

I think that the easiest way to avoid mandrel heating is to have the correct match between expander mandrel and turning mandrel. Evidently there are a lot of guys out there who think that a wring on fit of the case neck on the turning mandrel is needed to turn accurate and consistent necks. With some attention to technique, it absolutely not. I have had a neck mic, that measures to .0001 for over a quarter century and I have measured most of the necks that I have turned, admittedly in small batches of 25 or less. As long as the cutter is cutting, it will keep the case pinned to the mandrel. I advance the cutter to the shoulder rapidly so that there is a lot of material left behind to keep the cutter engaged on the return trip, pause so that the cut on the shoulder is clean, and then come back to the case mouth very slowly, and I do not go back. While I have the case on the power adapter, I grab the neck with a wad of 0000 steel wool and spin the case for a second. Then I use my PMA trimmer, followed by chamfer and deburring tools, all with the case under power. I have an old Makita cordless drill that has an actual two speed gear box that I set on low speed and I do not squeeze the trigger all the way. RPM equals heat. Another thing that I have found is that if I expand all of my necks at one time and do not turn them right away, the next day or later their fit on the mandrel will be noticeably tighter, requiring me to expand them again that little bit to get the fit that I want. Typically my necks are on the same tenthousandth, and if they vary by more than .00005 I start looking for a cause. Since my speed and fit do not cause much heat, I have not had to cool my tool.

You're process is almost identical to mine . . . even to using a Makita cordless drill.

Typically, heat is not an issue for me, except when my garage (where my reloading bench is) gets over 100°F in the summer days here is Arizona. I have a small frozen gel pack that I set my PMA trimmer on while switching out cases just to be sure the tool stays cool. It really works well, though I do try not to have to do this operation that time of year.

 

[Silo1616]

I believe Brass has a higher thermal expansion that most, perhaps all, steels. If heat was the issue, would not the neck fit on mandrel get looser not tighter?

I think Boyd nailed it when he said brass neck "spring back" was the culprit.