[erikjgreen]

Hey, all;

I'm working on an upgrade of the electronics on my Lagunmatic 250 CNC mill, and I'm adding an encoder (from a smaller 1 hp motor) to the 5 hp spindle motor, so I can do things like rigid tapping.

The mill head has a variable speed pulley with a V belt, in a similar mechanism to the bridgeport variable speed heads (or the Lagun FTV-2 mill, the manual for which is around on the net).

I'm wondering: How much backlash will the variable speed pulley system create? Will having the encoder on the spindle motor (instead of on the spindle itself) with the belts in between motor and spindle cause me severe accuracy problems?

I'm using a Hitachi WJ200 VFD, and the encoder is a differential quadrature type with 1024 cpr. I'm taking the encoder feedback into Linuxcnc, not into the VFD.

Anyone done something similar?

On a side note, since I removed the electromechanical brake on the spindle to fit the encoder, should I plan on replacing it with a magnetic brake or would the VFD's dynamic braking function do just as well?


Thanks,
Erik

[samco]

You need the encoder on the actual spindle. we shoe horned ours in (the 60's vintage original control didn't have one..)
K&T spindle encoder with collet unclamp/clamp - YouTube
this may be an option for you..
Adding a spindle encoder to a Bridgeport 1J head

As far as the dynamic braking on the vfd - depends on what you want. it probably will not stop it as fast as the brake - but depending on the rotational mass of the spindle drive train - it will probably be pretty quick.. We are just using the vfd braking for our hmc - it is pretty slow but our spindle gear train is pretty hefty..

Rigid peck tapping with emc2. (200rpm) - YouTube

sam

[erikjgreen]

I could maybe work something out using the spindle top, near where the air wrench is for the drawbar. I'd end up using a different encoder though.

I was thinking it might be easier to replace the varispeed pulley with one or two big timing pulleys and belts. That way backlash would be minimized. I don't need the pulleys for speed control with the VFD anyway.

I suppose I could do both... replacing the pulleys would give me a really nice location to install an encoder inside the head.

[erikjgreen]

Nice peck tapping video... what's that part for?

[samco]

It is a motor adaptor for some equipment we are working on.

I have to say - linuxcnc is awesome. I have had no issues with it doing something 'odd'.

sam

[DrDomino]

Long-shot since 2005. Erik, I also have a Lagunmatic 250 now retrofitted with a VFD. My variable speed head needs rebuilding and I am wondering what you did to yours? Did you replace the v-belt variable speed gearing with fixed pulleys?

[erikjgreen]

Long-shot since 2005. Erik, I also have a Lagunmatic 250 now retrofitted with a VFD. My variable speed head needs rebuilding and I am wondering what you did to yours? Did you replace the v-belt variable speed gearing with fixed pulleys?

I upgraded to a Milltronics VMC instead... for the Lagun, I've just been replacing the belt as needed, it acts as a shock absorber for when I do dumb things with it occasionally.

Erik