Spindle encoder

[andrewbishop66]

Hi All

Perhaps I might ask for some suggestions I have a Kondia mill similar to a bridge port with a cnc conversion running for about 10 years now I have a spindle rpm output 1 pulse per rpm but would like to add ridged tapping

Problem is it has a power drawbar so I cant mount a encoder on the spindle

is it acceptable to mount the encoder on the motor or are there other options for encoders ie reflective pickup type

any ideas welcomed

Thanks andrew

[cncdrive]

It is not a problem where the encoder is mounted, I mean for the A and B channels which counts the position,
but if the machine has different changable gearing in the spindle-head then you will always have to change the encoder resolution settings to fit the actually selected gearing and therefor the encoder counts per spindle turn.

And it is a problem if the index channel is behind a gearing, it must be on the spindle with 1:1 direct connection, because the index is used to get the absolute position angle information and if it is behind a gearing then the motion controller can't syncronise the threads and taps to the index, because it will happen on different angles of the spindle and not once at the same angle at every rotation, so that is a problem.

[Derek]

I have a mini timing belt running from a timing gear on the drawbar to a timing gear driving an encoder 1:1.

I can snap a picture tomorrow if you like.

[cncdrive]

Hi Derek,

Would be really great if you could post a picture of that, because we are also about to build 3 identical CNC mills for a customer company and my collegue is currently scretching his head about how exactly to install the encoder, because the machines will be mainly used for rigid tapping. We have some ideas, but maybe your solution is even better.

[Derek]

No Problem.

It's a little crude and changes the index point every time you change a tool since it is part of the draw bar. But it works reliably and that's what counts. The index issue would only be a problem if you needed to go back and re-tap holes after you have removed the tool.

Derek

[Derek]

Well I woke up with a clearer head this morning and it dawned on me that my rig will only work with Fixed quills. Both my mills use the knee for the axis and the quills are locked in place.

On a regular mill couldn't you leverage the existing gearing that normally drives the Z feed for the encoder and an optical on the spindle for the index?

Just a thought.

[cncdrive]

Hi Derek,

This is the base machine we converting: http://www.dolphincadcam.hu/IMG/HBM/HBM ... rofi_1.jpg
We converted a few of these over the years, but these 3 will be the first ones where we will have to install rigid tapping.
The machine is a medium sized one with about 320kgs weight and it has ISO30 tool holder and manually adjustable (levers) gearing in the spindle head.

[Derek]

This is the base machine we converting

What is that a key chain or a mill:)

This first picture is on my Alliant with the ATC. Just in December alone it tapped 8000 holes. It's the original encoder I hooked up when you had me testing the tapping so that's how long it's been in use. It's still the original belt.



The next pics are the one from the Bridgeport. It's not on the machine at the moment as I'm doing a large upgrade. I have a custom length drawbar and a sleeve that it runs through. I bored out the timing pulley to fit over it.



The encoder mount is machined from Type1 PVC but could be any material. The pulley is on a shaft with flanged bearings and set screw collars. Really simple.





I have a 3D file that I can make available if anyone wants it but it's all pretty basic.

Derek

[andrewbishop66]

Thanks every one for the suggestions

My options are quite limited as the machine has 8 speeds going from 40 rpm to 3000 rpm using 4 step pullys and a back gear
at the moment speed pickup is taken off the back gear spindle which is ok for the top 4 speeds but for the lower 4 its wrong I think there is a worm drive off the quill which i might be able to use originally it was used for auto feed of the z until i converted the machine

In fact just been out and checked mounting no problem but because its worm drive backlash is about .5 of a degree
and second problem is 26 rotations of the spindle = 1 rotation of my encoder

so even a 1000 count is going to be only 38.xxx per revolution

Should I go for a higher resolution

Thanks andrew

[Derek]

I'm using a Bridgeport head as an example but it should apply to any drawbar style machine. Could you machine a ring that presses into the shaft that drives the step pulley.

I found this picture on the webs.


If you look at the drawbar you will see the shaft I'm talking about. On my mill it's 1.025" ID. There is enough space between the .75" nut and the 1.025" bore for a .075" wall ring to press into it and still clear the draw bar nut. The ring would protrude above the upper bearing far enough to attach a timing pulley to it.

I'd be looking in that direction if it was me.