Wow, its amazing what can be done with old iron these day. Thats turning out to be a very capable machine. Im wonder how the accuracy and repeatability is?
Jim
Wow, its amazing what can be done with old iron these day. Thats turning out to be a very capable machine. Im wonder how the accuracy and repeatability is?
Jim
I have use a ground tube to check - so far so good. it seems to trip consistantly within .0001. I have actually been checking axis acuracy with it. it seems the ball screws are a little off. about .00017" per inch. with sound pretty common. But the touch probe has been great for checking scaling against guage blocks.
sam
Hi Sam,
I just got my K&T out of storage over the weekend. I have a couple of other projects to finish before I start. Looks like this is going to be time consuming! I hope mine turns out as nice as yours!:banana:
Brandon
I would love to have one of those in the corner of my garage..
sam
Been a few since I have posted in here... Been busy machining
The old control compinsated the spindle for temp. The spindle extends about 11 inches from the ways so it grows about .0024" over 30 degree temp change. I found this info from one of the emc developers..
Improved Analog & Digital Interface with Arduino
The uno interface is a userspace component so it isn't realtime. Temp change happens relevively slow - so I am not worried about timing.
I bought an arduino uno and have been playing with it. The spindle already has a thermister in it that the old control used. I hooked that into one of the uno's analog inputs and have been tracking the volt/expansion. The line came out pretty close to linear so I am going to use a simple scale component into a offset component in emc to automatically offset the z axis proportional to the temp.
I hope to finish that up this week.
Other than than the K&T has been running very well.
sam
Crappy Video of the temp comp
[ame=http://www.youtube.com/watch?v=h-CdFd2Zakc]Emc2 - Using temperature to compinsate Z axis for spinlde growth. - YouTube[/ame]
sorry (but it works!)
sam
That's pretty cool. With temp sensors so cheap, it's tempting to do that on all axes... Nice work!
Here is a bit of a technical explanation of how it was done. (I had posted on another site)
The old control used the spindle temp to offset the z axis. The spindle extends past the ways around 11 inches so from cold to hot is can 'grow' around .003". I had found myself 'tweeking' programs when running from cold to hot to compensate. Well I got sick of that pretty quick and the temp sensor was still in the spindle (thermistor) so I hooked that into an arduino and am using that to offset Z autmatically. So far so good - no more thinking I tracked the voltage vs temp vs growth and it turned out to be linear. Yay.
So I just scaled and offset the voltage signal from the arduino and sent that through a few components - It goes in to a mux2 so that I don't apply the offset while the machine is homing.. Then through a limit3 component that limits its velocity, acceleration, min and max so if something goes wonky it doesn't send the axis into the limits. From there it goes through the offset component. This offsets the output and feedback from emc so that in effect - motion doesn't know that the Z axis is being adjusted. It sort of happens between emc motion control and the hardware. (In emc's the hardware abstraction layer (hal))
Still running great... Walk around