Using current as cutting force indicator?

[mitchejc]

Thanks Jonathan. Call it cheap thrills but I'm basically looking into some interesting little future enhancements to make to my router once I have it working to keep me occupied. I'll play around a little to see what the no load current looks like at different frequencies and take it from there. Until my spindle is actually cutting something, is there a safe way to put some load on to see what happens to that current output? The though had crossed my mind to put a thick glove on and gently apply pressure to the collet nut but I'm way too scared to be the first guy to try that :-)

Your plan of automatically varying the feed rate or spindle speed sounds like a very cool idea or maybe even just to do a estop when it figures out its about to break a certain size cutter or stall the spindle but I'll have to learn quite a bit more before I can join in on that fun :-)

[Jonathan]

I'll play around a little to see what the no load current looks like at different frequencies and take it from there.

If you're keen you could take several readings, graph them then use that as a look-up table or function to subtract from the on-load current in software, on an Arduino (or similar), then connect a display... In fact you could do it quite easily with an Arduino, current sensor and display:

http://www.ebay.co.uk/itm/New-Blue-I...item3f3eb02c30

http://www.ebay.co.uk/itm/Range-ACS7...item565bbee604

The though had crossed my mind to put a thick glove on and gently apply pressure to the collet nut but I'm way too scared to be the first guy to try that :-)

You wouldn't be the first ;)

[mitchejc]

Arduino. Yep those are very high on my list of things to toy with, just wasn't sure what I'd use it for but now I have a plan!

Sorry last stupid question. Using this approach with that sensor would I measure current on then single phase input side of the vfd or on the output side or does it even matter?

[Jonathan]

Output side - you want the line current. You could use the current sensor to measure the frequency of the current, then scale that to read spindle speed... just for fun.

[EddyCurrent]

The though had crossed my mind to put a thick glove on and gently apply pressure to the collet nut but I'm way too scared to be the first guy to try that :-)
)

With motors the general method was to jam a piece of 3 x 2 against the rotating shaft to act as a brake, you want it so the shaft is trying to pull the wood from you.

[mitchejc]

@Jonathan: Ok, thanks, that makes sense.

@Eddie: Thanks, I'll give that a go. My fingers is getting older so they so they don't grow back as quick as they used to :-)

Not sure but I think I read somewhere the peak torque of these 2.2kw watercooled spindles is something like 0.8nm. Does anybody have a rough idea what the torque curve for these looks like?