This sets me back a week on the project. I'm going to cut another piece of stock, neck down a 3/8" to 1/2" section behind where the thread goes (the Ø20mm section) and mill flats on the last 1-1/2" to clamp in the chuck. I'll do four flats at 90º apart and for the first time, mount my 12" 4-jaw independent chuck so I can be sure that end is true. Now firmly clamped, I need to upgrade the threading tool.
I looked at what I'd threaded and saw a problem. It was clearly pushing and though chip control was perfect it wasn't cutting right. Checking the helix angle, a 1-1/4-5ACME has nearly 3º of lead angle. The standard lay-down holder accounts for 1 to 2 degrees of lead angle, so I need to get a YE4-2P or YE4-3P anvil for the holder. Since it's a borrowed holder, I'm just going to buy my own and get the additional anvil with it. That should make threading this MUCH easier, and make a high quality thread form.
I looked at what I'd threaded and saw a problem. It was clearly pushing and though chip control was perfect it wasn't cutting right. Checking the helix angle, a 1-1/4-5ACME has nearly 3º of lead angle. The standard lay-down holder accounts for 1 to 2 degrees of lead angle, so I need to get a YE4-2P or YE4-3P anvil for the holder. Since it's a borrowed holder, I'm just going to buy my own and get the additional anvil with it. That should make threading this MUCH easier, and make a high quality thread form.