It's actually a completely custom design since I had to design and retrofit it to the existing rotary table after some testing results. I can show more details in a future video. It's fairly simple, uses two x-rings and an aluminum piston with a large bore, with a stack of spring washers to unclamp when there is zero air pressure. The piston acts on a custom stainless steel brake rotor supported by an inner web flexure that allows axial movement but with very little angular rotation. The brake rotor contacts mountain bike brake pads directly affixed to the c-axis spindle.
@@CNCWerks That's awesome, that sounds like a really neat design. I'd definitely be interested in a video on that design too. Was an "off-the-shelf" rotor/disc/caliper setup written off just because of space/rotational freedom constraints?
@@drivenba I couldn't really find a brake with zero backlash for the size and design constraints I had. I also had access to a machine shop and waterjet, so I could produce most of the components fairly cheaply, with a bit of my own time. If I didn't have access to a shop, I think I would have found something from this company - Nexen - www.nexengroup.com/rotary-motion-control/precision-brakes/shaft-brakes and adapted it to fit my existing design
I like your use of the harmonic drives, did you purchase them through Aliexpress or similar? I have seen some reasonable priced ones on Aliexpress but wasnt sure of the quality.
I ended up getting both on Ebay. I would probably recommend buying them on Ebay, I was able to get authentic reducers from Harmonic Drive (HDS). Also makes getting spare/replacement part easier I think. The SHF-40 was salvaged from a robotic arm, and the main support crossed roller bearing was completely worn (seller didnt tell me) but I was able to buy the replacement off Alibaba.
Really cool project! Your leadscrew looks nicer than the rolled chinese ones on Amazon, do you mind sharing where you found it? Itd be really cool to see more details into your design and more info on the project!
Thanks! The ballscrew is still a rolled 5mm pitch x 25mm diameter screw, but purchased off Ebay (seller was econvenience1986). They can offer customizations and other items. I've also had pretty good luck with Maxtenso Motion Store on AliExpress (where I got my servo motor mounts and angular contact ballscrew bearing supports). I haven't had a chance to evaluate/measure the linear accuracy or backlash of the screw yet, but I did pair it with a DFU2505 pre-assembled dual ball nut to reduce the backlash. There is a bit of eccentricity/runout in the ballscrew shaft itself
Do you have enough stalling torque in the servos and enough rigidity considering belt driven to machine something in 5 axis considering the cutting forces acting on the part in this configuration? I mean with tens or hundreds of N cutting force acting on a part on the 5-axis table/fixture I see big torque applied to the motors and not sure it can hold the position. This will manifest in bad surface finish and lack of precision. Am I wrong?
You're right. I generally only plan on 5-axis machining non-ferrous metals, plastics and waxes, etc. I haven't completed all of the testing on the torsional stiffness of each rotary axis yet. I don't have plans for machining many ferrous metals. I could do it as a 4th axis with a indexing table, and not simultaneous. The table axis (c-axis) does have an internal pneumatic brake that is capable of resisting ~100Nm of torque. I designed a brake for this axis since the harmonic drive and spindle connection is via toothed belt. However, on the large tilting axis, the harmonic drive is directly coupled to the structure and output and the belt drive is after the gear reduction. In this set-up the belt forces are very low, there is a 100:1 ratio greaing prior to the load. From mfg datasheets, the HDS SHF-40-100 has a back-driving torque of 134Nm, and the torsional stiffness of harmonic drives increase as the torsional load increases, due to the elasticity of the flexspline and increase in tooth contact.
@@CNCWerks Sounds good. Thanks for taking the time to explain. I'm planning myself to build a 5-axis and I was wondering what should I use to have the stiffness resolved
@@car9167 No problem at all. I would really look for used industrial harmonic drives or cyclodal drives. Typically used in the elbow joints of multi-axis industrial robots. They come up on ebay and other sites pretty often. Crossed roller bearings are also a good option too. I had to replace the CR bearing on the SHF-40 unit since it was worn and lost its preload, found a supplier on Alibaba.
Nice Job! 👍
Awesome! Go ahead!
Could you share what pneumatic brake you're using?
It's actually a completely custom design since I had to design and retrofit it to the existing rotary table after some testing results. I can show more details in a future video.
It's fairly simple, uses two x-rings and an aluminum piston with a large bore, with a stack of spring washers to unclamp when there is zero air pressure. The piston acts on a custom stainless steel brake rotor supported by an inner web flexure that allows axial movement but with very little angular rotation. The brake rotor contacts mountain bike brake pads directly affixed to the c-axis spindle.
@@CNCWerks That's awesome, that sounds like a really neat design. I'd definitely be interested in a video on that design too. Was an "off-the-shelf" rotor/disc/caliper setup written off just because of space/rotational freedom constraints?
@@drivenba I couldn't really find a brake with zero backlash for the size and design constraints I had. I also had access to a machine shop and waterjet, so I could produce most of the components fairly cheaply, with a bit of my own time. If I didn't have access to a shop, I think I would have found something from this company - Nexen - www.nexengroup.com/rotary-motion-control/precision-brakes/shaft-brakes and adapted it to fit my existing design
Would u share the cad files
You go Ninja!
I like your use of the harmonic drives, did you purchase them through Aliexpress or similar? I have seen some reasonable priced ones on Aliexpress but wasnt sure of the quality.
I ended up getting both on Ebay. I would probably recommend buying them on Ebay, I was able to get authentic reducers from Harmonic Drive (HDS). Also makes getting spare/replacement part easier I think. The SHF-40 was salvaged from a robotic arm, and the main support crossed roller bearing was completely worn (seller didnt tell me) but I was able to buy the replacement off Alibaba.
Really cool project! Your leadscrew looks nicer than the rolled chinese ones on Amazon, do you mind sharing where you found it?
Itd be really cool to see more details into your design and more info on the project!
Thanks! The ballscrew is still a rolled 5mm pitch x 25mm diameter screw, but purchased off Ebay (seller was econvenience1986). They can offer customizations and other items. I've also had pretty good luck with Maxtenso Motion Store on AliExpress (where I got my servo motor mounts and angular contact ballscrew bearing supports).
I haven't had a chance to evaluate/measure the linear accuracy or backlash of the screw yet, but I did pair it with a DFU2505 pre-assembled dual ball nut to reduce the backlash. There is a bit of eccentricity/runout in the ballscrew shaft itself
CNC Werks thats great, thanks for all the info! Ill be looking forward to the updates!
Do you have enough stalling torque in the servos and enough rigidity considering belt driven to machine something in 5 axis considering the cutting forces acting on the part in this configuration? I mean with tens or hundreds of N cutting force acting on a part on the 5-axis table/fixture I see big torque applied to the motors and not sure it can hold the position. This will manifest in bad surface finish and lack of precision. Am I wrong?
You're right. I generally only plan on 5-axis machining non-ferrous metals, plastics and waxes, etc. I haven't completed all of the testing on the torsional stiffness of each rotary axis yet. I don't have plans for machining many ferrous metals. I could do it as a 4th axis with a indexing table, and not simultaneous. The table axis (c-axis) does have an internal pneumatic brake that is capable of resisting ~100Nm of torque. I designed a brake for this axis since the harmonic drive and spindle connection is via toothed belt. However, on the large tilting axis, the harmonic drive is directly coupled to the structure and output and the belt drive is after the gear reduction. In this set-up the belt forces are very low, there is a 100:1 ratio greaing prior to the load. From mfg datasheets, the HDS SHF-40-100 has a back-driving torque of 134Nm, and the torsional stiffness of harmonic drives increase as the torsional load increases, due to the elasticity of the flexspline and increase in tooth contact.
@@CNCWerks Sounds good. Thanks for taking the time to explain. I'm planning myself to build a 5-axis and I was wondering what should I use to have the stiffness resolved
@@car9167 No problem at all. I would really look for used industrial harmonic drives or cyclodal drives. Typically used in the elbow joints of multi-axis industrial robots. They come up on ebay and other sites pretty often. Crossed roller bearings are also a good option too. I had to replace the CR bearing on the SHF-40 unit since it was worn and lost its preload, found a supplier on Alibaba.
@@car9167 some good content here th-cam.com/video/OU-bKb_KJBU/w-d-xo.html
@@car9167 this is a good source too th-cam.com/video/0MHSmU4-vsw/w-d-xo.html