Gas Springs on Knee

[thosj]

I've done some searching and can't find what gas springs folks are using on BP/clone knees to take some of the weight off when CNCing the knee. Anyone know what to use? And roughly where to mount them?

[HimyKabibble]

Originally Posted by thosj I've done some searching and can't find what gas springs folks are using on BP/clone knees to take some of the weight off when CNCing the knee. Anyone know what to use? And roughly where to mount them?

I used two of the longest 200# gas springs from McMaster Carr. I mounted them close to the base, to keep them out of the way, but most people seem to put them in the middle of the knee. I"m not sure it really makes a lot of difference. With the springs, it now takes less torque at the motor to move the knee up than down!

You can just barely see one of the springs in the attached picture.

Regards,
Ray L.

[thosj]

OK, cool, thanks. I was just thinking out loud that I'd put them out a ways just because it seems it would take some of the cantilever off!! That's a lot of weight hanging out there!!

As an aside, how does your CNC'd knee work? I was thinking about doing Z on the quill, but I may do the knee first just to get the long travel part first. Do you use the acme screw, or did you put a ball screw on the knee?

[HimyKabibble]

Originally Posted by thosj OK, cool, thanks. I was just thinking out loud that I'd put them out a ways just because it seems it would take some of the cantilever off!! That's a lot of weight hanging out there!! As an aside, how does your CNC'd knee work? I was thinking about doing Z on the quill, but I may do the knee first just to get the long travel part first. Do you use the acme screw, or did you put a ball screw on the knee?

The knee works well, just not real fast - 75 IPM. Accuracy is very good, though. I'm working (slowly) on adding a quill drive, modeled after the Elrod. I left the leadscrew and bevel gears on the knee, and added a 4.8:1 belt reducer to the 850 oz-in servo.

Regards,
Ray L.

[thosj]

Thanks, Ray. I ordered two gas springs from McMaster!

I'd like to keep in touch on your quill drive. I have the Elrod patent thing printed out and I think I might be able to design something like it, but a lot of figuring and hoping you get it right. The patent documentation, I'm sure, is left as obscure as possible to keep guys like us from copying it. I'd sure like the ability to disconnect and use the hand quill lever. I am just starting my conversion, ball screws in X/Y, design/build X/Y brackets and drives next, build power supply control box, get all that working, so I have a ways to go. I'm retired, but it's still hard to find the huge blocks of time required to do this. I DO have a part time job at a local university machine shop, so I have another set of machine tools just like at home to use to build if mine's down. Good luck on the quill drive and if you wouldn't mind sharing, I'd love to hear/see how it's going.

[HimyKabibble]

Originally Posted by thosj Thanks, Ray. I ordered two gas springs from McMaster! I'd like to keep in touch on your quill drive. I have the Elrod patent thing printed out and I think I might be able to design something like it, but a lot of figuring and hoping you get it right. The patent documentation, I'm sure, is left as obscure as possible to keep guys like us from copying it. I'd sure like the ability to disconnect and use the hand quill lever. I am just starting my conversion, ball screws in X/Y, design/build X/Y brackets and drives next, build power supply control box, get all that working, so I have a ways to go. I'm retired, but it's still hard to find the huge blocks of time required to do this. I DO have a part time job at a local university machine shop, so I have another set of machine tools just like at home to use to build if mine's down. Good luck on the quill drive and if you wouldn't mind sharing, I'd love to hear/see how it's going.

I'll certainly make a post with some pictures when I get it done. I don't expect it to be very difficult, just time-consuming. I'd forget about the manual operation - it just complicates the design, and could introduce backlash. And, you'll probably never really use it....

Regards,
Ray L.

[thosj]

Ray, on your knee drive. Is all that stuff bolted up to the three M6 bolts that originally held the shaft in? All I have are those three with no other flat surface to mount anything else to, unlike Y. I was thinking of making it 6 bolts just for redundancy's sake!! Seems hanging all that on 3 M6 bolts is a bit much!

What's in the box behind your belt housing/motor mount? I was designing mine closer to the machine, and thinking about down and left slightly to get room for the motor on the back side, out of human knee's way. I have my Y designed that way, 30 deg. down and right so the motor is in along the knee behind the bracket stuff. I'm trying to maintain use of handles!!

What servo motors? They look like my Kelings. What encoders?

I'm new to this and the electrical part has me scared stiff. I'm building everything, way more time than money, including the box. No one local to help me, so I'm hoping I can figure it out on my own or with help here on CNCZone! I feel so stoopid on the electrical stuff sometimes I wonder if I've finally bitten off more than I can chew. One step at a time, I guess.