More grumblings about encoders and Centroid's rigid tapping - and some cockery

This is heading for the rocks. So far I've failed to find a simple solution to gear range selection (ongoing) and probing (try to use a probe and a tool setter together on the Acorn) and despite connecting up the encoder yesterday, it seems that rigid tapping is no closer.

The main bugger is that they only cater for encoders that are mounted directly on the spindle. And they seem to have designed(?) the rigid tapping software so that it requires a very high encoder count per pulse (CPP). The CPP for a 2 channel encoder is 4 times the pulse per rev (PPR), so my 2000PPR Omron clone is 8000 counts per rev. They are adamant that my 192 count signal, derived from the 48t spindle-mounted bull gear is way below the required minimum count. The index signal seems to be essential too, just to further complicate matters.

As you can see, there is bugger all space in there to get a toothed belt out to an external encoder. The large bull gear is the only accessible part that is directly splined to the spindle itself.

This is what I came up with back on 15th Jan this year. Worked nicely but it seems Centroid require significantly more CPRs.

Funny thing is that Steve Blackmore managed to achieve multi start rigid threading on his lathe with only a single slot encoder (see the bottom of this page). That was using the turning version of the very same Newker 990 controller I have just removed from my machine. Part of the reason for doing that was to achieve rigid tapping. What have I done???

Here's what Steve managed on his first trials:

I seem to have established beyond any doubt that Centroid can't support a motor mounted encoder and they seem equally adamant about the encoder count. I can't really believe that they act on each encoder count, given the likely thread time in the controller. I wonder if it's worth connecting up my gear tooth encoder through the differential line driver and seeing what happens. As a second line of attack, I wonder if it would be possible to increase the effective counts per rev by triggering a burst of pulses from each transition, to fool the controller into thinking that it was seeing a high count encoder signal. Sounds tricky, given that the phasing must remain correct so that it can deduce the direction of rotation.

Apparently that cock Elrod came up with a product (described as a "rigid tapping adaptor") that allows you to mount an encoder alongside the head of a Bridgeport and drive it with a toothed belt. As you might expect from the guy, he claims to have found something to patent in the process. Think about it - use a belt to drive an encoder from the spindle. Sounds like a patent worthy result to me. I used to joke that you could patent a glass of water in the US and it sounds as if I wasn't far off there. Take a look at the patent - 2 pulleys and an encoder. What a joker.