This week I started to turn the main OD of the tube.
leading up to this week I have turned the OD of the tube to 7.4in along its entire length and turned its ID to its final dimension of 5.66in along its entire length. The ID had to be turned in 2 setups (as the boring bar was only 6in (half the length of the tube). This resulted in an imperfect transition between the halves along with different surface finishes. The ID difference is under 3 thousands of an inch (I am unsure on the exact dimension in the middle do to a lack of proper measurement tooling). This should definitely be fine with the designs safety factor >3x.
I begin isolating the end flange this week. I am doing this by feeding in reverse towards the end of the flange and stopping .2in from the final dimension. This will allow me to turn the more complex fillet on the flange and achieve a better finish once I have clearance. Right now I am stair stepping towards the end to give clearance for the tool holder and the side of the insert.
Due to this process I have to swap tools from a right-handed insert to a left-handed one to flatten out the stair step. My current process consists of stepping down at the angle of the non-cutting section of the insert down to the depth of each cut before feeding it until the flange. After I run out of room for passes, I switch tools and flatten out the steps. This gives clearance to go deeper with the next set of passes.
I am doing the OD of the tube in 2in sections so that I have the support of the thicker portion of the tube while working on the further forward sections of the tube. I turned the first section of the tube down to 6.5in. The final dimension for this section is 6.3in.
After the first section is complete, I will no longer have to stair step as the first section will be the clearance for later ones.
The fillet on the flange should be made using a button insert, however we are broke and we don’t have any, so I am going to grind my own radius tool.
After all 5 tube sections are roughed in, I will pull the tube mostly out of the chuck leaving only the flange in it, install the steady rest and do full length finishing passes before using the radius tool to add the radii.
