Spindle? deflection

You can make a reasonable estimation using one of these calculators. The real buttock-clenching moments come during parting, when we are busy rubbing our stomachs and turning round 3 times with the toolpost upside down at the rear of the machine. These are the circumstances under which we see tools visibly moving due to backlash, spring etc and also when they tend to fail. From what I can see, the forces under these circumstances will be of the order of 10s of kg (100s of N).

It was in order to be reasonably scientific about this that I gave some thought to how you would apply a controlled load to the tool and measure its deflection in an accurate and repeatable fashion. Of course, the forces need to be applied and measured in the correct direction(s), ideally horizontally and vertically.

Murray

Murray,

I have seen these and they are available for sale (peanuts) without having to get all the rest of the scale assy if you go looking. The RS amps are about £40-50 I think but they are very stable and as I mentioned, will support multiple modes of operation. Perhaps outside the budget for messing about but it you go to the trouble of making a sensing system as you modelled, it might be a shame if it is let down by flaky sensors?

I usually (always) employ at least two arrays normal to each other (they often come in that configuration to save space and agro glueing two close by) to compensate for thermal effects - always an issue with resistive strain gauges.

It also requires a lot of thought implementing them in any system that measures in more than one plane as you have to take account of any coupling of forces to ensure you are measuring what you actually want.... again, another one of those "how hard can it be" jobs!

Mark

I can't remember if it was Wookey Hole or Cheddar but I was once asked to leave the caves after jumping up and down on a steel footbridge. I wanted to amuse my kids by making it bounce but the woman behind me had a panic attack...

Thanks for an excellent reason for never going clothes shopping again. It's obviously not safe if the floor moves.

Dave

I have one from an old scale that uses beams like an old analogue scale with a single strain gauge.

I keep meaning to fire it up as there are zero and span pots on the board I should be able to make it do something useful (although if I can get one pre-calibrated for £1...)