Rigid Tapping Help

This will probably turn in to a new thread in the right section....

So the encoder is working and technically tapping works, but I don't have enough torque without back gear. Apparently the previous owner/builder didn't get far with rigid tapping, or at least not anything big enough to need gears so the machine is not set up to tap (or really do anything cnc) in back gear.

Brainstorming a bit and reading some threads here, I'm thinking of a couple solutions

1) Could I put a micro switch on the back gear lever - when in gear and the switch is tripped, apply a reduction scale to the encoder and reverse the spindle (M4?)? I'm researching exactly what the 2J head reduction is, but it seems like it would be simple and would work. As a temporary solution, I could just do a manual switch to tell it that it's in gear.

2) Ditch the rotary encoder and do the gear encoder referenced on pico-system's site. From what I understand this can be challenging (but not impossible?) on a 2J due to the movement the gear makes to engage.

3) Go really hack and once I figure out the gear reduction in the head, apply that to the thread pitch in Fusion so Z moves properly relative to the reduced rotation speed. Not a long term solution but I could see it working in a pinch.


I feel like option 1 would be pretty easy to pull off. Any reason why I wouldn't want to go that direction?

Where is the encoder mounted at the moment?

On top of the the spindle, pre-gears.

Edit: This machine used QC30 tool holders, so no draw bar.

I think it is worth checking that that doesn't still run at true spindle speed. (If you haven't already). With a drawbar setup that is where the drawbar would be, and those always have to spin at full spindle speed.

No, it definitely does not match spindle speed when it's in back gear.

I'd have to dig up the assembly diagram to remember the exact configuration, but I know it's basically 1:1 direct when it's out of back gear. When you engage the gears, it disconnects the direct drive and runs it through the gear train.

As a quick example, I had a threaded program that ran a 400rpm out of back gear. In gear, it still showed 400 but the spindle was obviously spinning much, much slower.

NCPatrol wrote: In gear, it still showed 400 but the spindle was obviously spinning much, much slower.

What is "it" in this example?

It seems to me that the drawbar (on heads fitted with a drawbar) always spins at spindle speed, and if the encoder was connected to a drawbar-surrogate (which would be the easiest way to do it) then the encoder would always read true spindle position.

Dividing-down the encoder isn't usually an option as the index won't then happen once-per-rev.