Gallery, Projects and General > How do I??

How do I measure a spindle taper?

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AdeV:
I'm getting fed up with the runout in my chucks, it's impossible to get anything even remotely re-centred, and even if you do the chances are it's at a funny angle, so whilst I can work fine so long as everything can be done without having to turn the workpiece around, as soon as one needs to reverse a part to finish off the backside, it's all out of true.

I'm 99.9% sure the problem is a worn out chuck - all my chucks are second hand at best, and quite bashed about & worn, so it's not entirely surprising they're past their best. The final solution will be to buy a new chuck.... but that'll have to wait a few weeks until I can raise sufficient spare funds.

So - in the meantime, I'm pretty sure the spindle taper is an MT5: I've got an MT5 to MT4 sleeve, and MT4 to MT3, and my ER32 collet chuck has an MT3 arbor on it. Put them all together, and I should have a super true-running chuck  :thumbup:

Er, no chance. Seems the spindle isn't MT5 after all. So.... question is.... how do I measure the taper? Given that it's deep into the spindle, which is only a couple of inches across at best..?

seadog:
I would use two DTIs. One to measure longitudinally and the second to measure radially.

Set one square against the plate and the second bearing onto the start of the taper. Advance say one or two inches and take the readings. You can then easily calculate the taper per foot and look in tables to find which taper that corresponds to.

AdeV:
Presumably the DTI which goes up the spout (so to speak) has to be a finger type? The problem being I've only got little ones of that style, send them an inch up the bore and I'm not sure i'm even going to be able to read the dial.... Also, wouldn't it need to be dead nuts on centre to read accurately?

I had wondered (earlier today, long after I wrote that message) whether I could use my telescoping bore gauges:



Send into the bore, lock, extract, read; return it to the bore, advance one inch (or two, or whatever), lock, read. The hard bit of course, being to return the gauge to the exact same point between readings... which I think I can do by throwing together a tool holder for my QCTP.

seadog:
Yes, it would need to be a finger type. I've an old Starrett plunger type that has a lever arrangement so would be capable of going in an inch or so. It definitely has to be bang on centre.

The problem with the telescopic gauge is that the contact area won't be along the axis of measurement.

Rethink - maybe that won'k matter, the error will be the same since the contact point willstill be the same at any point on the taper. It may just work, but you'll need to clamp the gauge bang on centre and will still need an accurate way to measure the depth.

AdeV:
Centre height is easy enough for me to manage - I can use a dead centre in the tailstock to sort that; has to be eyeball, but I'm assuming that once I'm pretty close to the taper, the numbers will suggest what it really is (e.g. if it's 4.007" per foot, one can be reasonably sure it's actually 4" per foot... for example).

I don't need to be cock-on the centre of the taper (so long as I'm on centre height), as the arms of the gauge can expand independently, so as long as they're contacting on centre height, the reading should be good.

I'll use the compound slide to measure my inch, it's got a decently graduated dial, and about 6" of travel.

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