Boxford 9" Lathe Half Nut Arms with Printed Threads

thingiverse

Replacement half nut arms with printed threads for a South Bend or Boxford (or Hercus) lathe with imperial leadscrew (3/4"-8 ACME) - requires drilling (2x for each arm) and making a small metal dowel to press into one of the holes. DESIGN CAVEATS: These require additional steps outside of 3D printing. I designed these to temporarily replace the worn out half nut arms on my Boxford 9" lathe, which shares an identical powerfeed apron to the South Bend and Hercus lathes. I printed it at 100% infill at .1mm with PLA+. I don't expect this to permanently replace the arms but printed these as I made iterations to confirm the fit and finish for making them out of steel (with a separate insert for the threads, not shown in the designs). However, I am surprised how well they worked as I was able to continue single point cutting threads with no additional hassle. I do not know how long they will last in a gritty oily environment. I am a complete amateur with 3D modelling, so although I included my Fusion 360 model, do not expect it to be a work of art. For 3D printing, I omitted the through-holes in the 3D model and added small dimples for hole and drillbit alignment. The pivot bolt is approximately a 1/2" diameter hole but please accurately measure your own. On my steel half nuts I bored them on a small mill for a perfect fit; on the 3D printed ones I drilled it with a 1/2" bit and it was slightly too snug but did work. For the small hole with a dowel, expect to turn down appropriate round bar to size. My dowels were around 0.312" to fit snugly into the cammed lever, and protruded approximately 0.220" out of the arm. I drilled into the divot of the 3D print with a smaller drillbit and used a minitorch to heat the round bar to create an interference press-fit. I have a drafting drawing I can upload that I used in my steel replacements if anyone is interested. These worked well for me, but also please note that everyone's threading dial will be clocked differently - if your threading dial does not line up anymore, there is an adjustment for it that is easy to find online. Thanks!