driving the knee......revisited

[fast89]

Well, been a while since i posted. Man have i been busy making parts with my j-head. I've got a 2550oz stepper on the knee moving at a snails pace of 15ipm. I've decided i need to do something about it. I refuse to use the quill as the z axis. I just don't like 5" of travel. I'm more of a 7++inch guy.hehehe. I just mounted two 250lb gas springs under the knee and that was definatly an improvement (30ipm now). I would really like some type of adjustable air assist. I've even thought of adding a counterweight off the back of the ram. I found this video on youtube, this is what i want.

You Tube

You Tube

Anyone added an air assist under the knee?

[pixburghenat]

Slick!

Really smooth.

Do you have an auto oil or drip to the dovetail?


Scott

[protman16]

Guys,

Your looking at a video of my machine doing a peck drill cycle. Currently the max rapid rate is 135ipm but I have plans to increase this to 500ipm.

[pixburghenat]

protman16,

Still Slick! :-)
Sorry, I must have skipped over reading the post at the end.

...I thought it was zipping for 15 ipm.

auto oil the knee dovetail?

Scott

Originally Posted by protman16 Guys, Your looking at a video of my machine doing a peck drill cycle. Currently the max rapid rate is 135ipm but I have plans to increase this to 500ipm.

[protman16]

Scott,

Currently I use a normal lube pump on the knee. It supplies all the ways and screws with lube.

I do have plans to upgrade to an auto oiler.

[fast89]

Boy, the internet sure makes the world a small place.lol. That is the kind of z axis i'm after. Can you give some details of the air assist. I assume you converted it to a ballscrew, what size? What kind of servo torque are you running? It looks like it works quite well, are you happy with it?

[protman16]

The air assist basically acts as a counter wieght but without adding mass to the machine.

The ballsrcew for the knee is the same size screw that is used on any other axis of the machine.

As far as servo torque goes I don't have any info for you. The reason is that the motor used is a surplus unit that did not have any valuse printed on it. I think a good rule of thumb would use at least the same size motor you would use on the X and Y axis'

It does work well and has been in operation for 3 years with no issues so far.

[fast89]

Did you drive the screw thru the original bevel gears or make a new mount and drive the screw directly? Do you have a pic of the air cylinder size and location?

[fast89]

Just a quick update, i mounted the 250lb gas springs and now put a servo on the knee. Initially, the servo couldn't even move the knee. (270oz continuous, 850oz peak). Now it moves it at 60ipm no problem, i had it as high as 90ipm. It wouldn't do 100ipm though, can you blame it, that's alot of weight. I might try a little more gas spring under the knee. It's definatley time for a ballscrew and maybe getting rid of the bevel gears.

[blackbeard52]

The air assist basically acts as a counter wieght but without adding mass to the machine.

protoman16
more info more more..........hehehe

i mounted the 250lb gas springs and now put a servo on the knee

fast89
Now you know not to install things around here without complete instructions

I have a request to help do a simular mod to a smaller bench mill head to reduce the mass...

Bob

[chevdrgtrk]

Protman16,
I have my pneumatic cylinders already, and was thinking about using a self bleeding regulator, I was just wondering what you used to bleed off the pressure? It seemed like yours bled off WAY faster than my reg could.

[protman16]

Originally Posted by chevdrgtrk Protman16, I have my pneumatic cylinders already, and was thinking about using a self bleeding regulator, I was just wondering what you used to bleed off the pressure? It seemed like yours bled off WAY faster than my reg could.

Thats the problem. You can't use a regulator.