Spindle-to-shaft speed ratio (parameter #33) - and failed attempt at rigid tapping

Parameter #33 (motor to spindle drive ratio):

The vee belt drive between the motor and the spindle isn't 1:1 on The Shiz. For some reason, the motor pulley is slightly smaller than the spindle pulley. So currently when I ask for 1000 rpm, I actually get something less than that, by about 10-15% at a guess. So let's measure the typical ratio now that I have a spindle encoder. Then enter this as the value of parameter #33.

Using the drive dogs on the spindle nose, I can set the initial angular position of the spindle (with a large set square resting against the head casting), then note the encoder reading. If I then run the spindle at a slow speed for a large number of revolutions and return the spindle to the same angular position with the set square, I can calculate the actual drive ratio with reasonable precision - bearing in mind that a vee belt drive won't be deadly consistent of course. The actual ratio must surely vary with load and wear.

Sequence of events:

1. Set initial spindle angular position.
2. Note down encoder count
3. Rotate the spindle 50 times (I couldn't be arsed to count to 100 and it'll never be that precise or repeatable.
4. Set the spindle angular position again.
5. Re-read the encoder count.
6. Work out the incremental count from the encoder and divide by the encoder's counts per rev (CPR). That's how many turns the motor / encoder actually made for 50 turns of the spindle. 
7. Divide the number of turns of the motor by the number of turns of the spindle (50).
8. (Repeat to provide sanity check).
9. Enter the resulting ratio into parameter #33

Here are the numbers I noted. The value of parameter #33 is 1.1274. I know, I know, quoting 5 significant figures is taking the piss but I couldn't bring myself to round it off any further.

NB: Note that in the notes above, parameter #36 should actually be 17, not 16. Failing to increment "Bit 1" from 0 to 1 will result in rigid tapping not being enabled. 

Try to set up rigid tapping (RT):

There are several "Technical Bulletins" that address rigid tapping:

• TB083 - rigid tapping guidelines
• TB123 - rigid tapping setup
• TB175 - troubleshooting

Parameter #36:

And there seem to be a number of parameters that need to be set for the RT process to work. Initially, I struggled to enable the RT feature. Unless you do so, the options for the tapping cycles in the conversational environment only allow for floating or (self) reversing tapping heads. Finally I realised that I'd set up parameter #36 incorrectly. This is one of those "bit" words, where you can combine several options by adding together their individual bit values. So I wanted to set bit 4 (ie value 16) to enable rigid tapping with "encoder is on motor". But I also needed to change bit 0 (ie value 1) to enable RT in the first place. So that meant Parameter 36 needed to be set to 17, not 16. Doh.

That was despite having set most of the parameters I could see that related to RT, this was the missing step. But despite this, the g code that was posted by the "Intercon" conversational environment seemed to lack basic stuff like enabling the spindle. I must read up on how to use it some time....

Testing it out:

So I wrote a simple file to generate an RT operation. The basic G code is "G84", something like this:

G84 X0 Y0 Q1.25 Z-10

...and of course, I got an error message, something about "509 option not enabled". 

Which is a bit annoying, given that I paid for the full milk option, so there are no further options I could enable. WTF?

I'm not the first to have this issue. Hope there's a simple fix - watch this space...


Update (5th April):

It seems Centroid screwed up. The "Digitising" version (and "Pro" by the sounds of it) seem to shipping with the RT feature disabled. 

Just wanted to inform you that the Rigid Tapping feature was accidentally overlooked in the Digitizing Bundle package and will be resolved with the next software release which is coming out shortly. Thanks and I apologize for any inconvenience this may have caused.

Bugger. Obviously somebody had a bit of finger trouble. They are promising this will be fixed on the next update. In other words, no quick fix - that's another issue I will have to park on the shelf and leave for another day. Grrrr.....