CNC 4th Axis using Harmonic Drive and Angle Plates

grabcad

This is a low cost (~$600) DIY 4th axis design which maximizes precision by using off the shelf precision ground cast iron angle plates. Cast iron also have the benefit of being a great vibration dampener.The design is made for a Tormach 1100 bed specifications, and the height fits their "tall" tailstock.I wanted a beefy 4th axis that had no backlash. The strain wave gearboxes used on 6 axis robot arms appear perfect for this application, but they exceptionally stiff in torsion. To increase the stiffness, I went with a larger "32" size Harmonic Drive gearbox. (2x the stiffness of a "25" size, and 4x the stiffness of a "20" size) Used units are around $300.For the frame, I wanted to minimize the cost and maximize the precision. I found a 10" x 10" angle plate for $130. The ribs in my angle plate were narrower than in the model I downloaded from Shars, so this design will work with narrower 160mm spaced rib models of plate as well (but you'll have to deep bore some clearance.)With the 50:1 reduction gearbox and a 2:1 reduction pulley this machine will produce 20,000 steps per rotation or 0.018deg per step. At maximum speed this machine will produce around 10rpm at the chuck.Total mass for this machine is ~36kg or ~79lbs.Harmonic Drive shg-32-50-2uh"32" size, 50:1 gear reduction4.5kg mass(Ebay or new from a distributor)Nema 34 Stepper Motor (8.5Nm)5.5kg mass(Any source)5M 50T timing pulleyhttps://www.amazon.com/dp/B0BGF3M7G55M 25T timing pulleyhttps://www.amazon.com/dp/B09BFB8KK9365T 5M timing belthttps://www.amazon.com/dp/B09KBN4NF110"x10" plain angle plate23.85kg massGood price at cme-tools.comTwo 2"x2" plaint angle plates0.78kg masshttps://www.amazon.com/dp/B00N40Y5T0