[Alex, Daniel]

A bushing for a Newport 100 thread per inch (tpi) AJS screw is made of brass and therefore cannot be used to hold (and be held by) stainless steel because it thermally contracts when the dewer cools down (this part will be around 40 K). This has been experimentally seen by Alex. Instead of brass, Alex and I think we should use a 304 stainless steel or copper 101. The advantage to using stainless steel for the bushing is the identical thermal contraction to parts around it. Stainless steel 304 is cheap and fairly easy to machine compared to other alloys. The disadvantage of stainless steel is cold/vacuum welding to the surrounding parts, so copper is a good alternative with a nearly identical thermal contraction. Copper contracts 0.322% from room temperature to 40 K compared to stainless steel's 0.296%; brass is 0.380%. Beryllium copper contracts at 0.315% but is much more expensive than (nearly) pure copper, so we chose copper. All data from here, appendix A6.4

To test the fit and the G-Code, I made the bushing out of aluminum, except the threads because we are waiting on the tap. I also used a slightly oversized drill because we are waiting on the correct drill size. Attached are the SolidWorks CAD/CAM file and G-Code file.

The part I made looks good. I tweaked the G-Code from what I ran to what is attached to account for some issues with the cut and changing the material. Changing the material may require me to change the spindle speed, cutter feed rate, and depth of cut.

Alex has also enquired about Thorlabs or Newport making the bushing, but I doubt it would be quick and affordable.