Spindle synchronized motion with gear

Hello Community,

I have a customer machine here with a servo driven spindle with 2 gear stages.
There is a TTL encoder on the spindle with a, b and a index pulse.

I want to use the encoder on the spindle motor to provide spindle synchronous movement, which is normally no problem, but the gear is providing me headache....

I can easily multiply the encoder scale according to the current gearstage, but the index pulse will come on every full revolution of the motor, which is not a full revolution of the spindle because of the gear.
I think the index pulse is important to be there on a full revolution for spindle synchronized movements.

Can somebody tell me how to solve that problem ?

I have already thought of a comp that will trigger the a fake index on every full revolution of the spindle, but I'm not quite sure whether this works.

I don't worry about the backlash in the gear because it is nearly nothing and doesn't matter at all.

Thank you guys!


Greets Rene

add a index sensor somewhere outside of the gear train - like a prox switch.
use the AB from encoder and the index from the added sensor.
Just another idea

Chris M

I just thought about that, but my customer is far away...

Just for confirming, can I use a fake index ?

I would do it like so:

First index Signal will be real index and the following will be emulated by a comp according to the gearstage.

perhaps something along these lines
forum.linuxcnc.org/forum/10-advanced-con...e-index-enable#64338

Okay, now I understand it!

The index pulse is used to place the thread cutter on the spindle in the right position, so if you cut a thread miltiple times you will be in the exact same path.

I don't have a index that comes once on a turn so I cannot say whether the position of the thread cutter is right.It is like having multiple reference switches so you don't know where you are.

My customer does only need spindle synchronized motion to cut threads without special toolholders on its mill, so this is no problem!

It would be a problem on a lathe with multupass threads or milling threads with a special tool.

I think I can use the normal index pulse as it is only used once. And it does not matter where.

Am I right ?


Greets Rene

It depends... the index is not used just once but at the start of every threading pass

If your index happens at a integer multiple of spindle turns (say every 2 or 3 spindle turns), it would work
if not, it will not work because the threading passes will start at different angular positions of the spindle

@PCW: Yes I totally agree. But in my case it doesn't happen on a integer multiple.

But this is no problem for the way my customer wants to use it.
For him it is only important that the z-axis is geared to the spindle no matter of the starting index.


Greets Rene

Yes Andy you are right.

Orientation is not needed, as you mentioned, if it would be needed there musst be a sensor.