Author Topic: Leveling Denford lathe - has no levelling screws?  (Read 15060 times)

Offline DavidA

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Re: Leveling Denford lathe - has no levelling screws?
« Reply #25 on: December 19, 2015, 02:09:39 PM »
Phil,

Yes, I remember well the last discussion we had.

My point is that you are starting out with a built in error, no matter how small.

If you are bolting something to the dished faceplate, then either the job has to bend or the faceplate does until the faces touch.  A fifteen thou dip in the middle of a 12" plate really is a lot.

I just can't see the doing in doing it.

Each to his own; of course.

Dave.

Offline philf

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Re: Leveling Denford lathe - has no levelling screws?
« Reply #26 on: December 19, 2015, 02:30:19 PM »
Hi David,

It's not 15 thou - it's 0.015mm - just over 1/2 a thou.

It's incredibly difficult and therefore very expensive to get it exactly right. Convex is an absolute no-no because you'd never get a flat object bigger than the radius to sit in a stable position.

With your 1/2" thick bar the out of squareness would be a maximum of around 0.0004mm.

Phil.
Phil Fern
Location: Marple, Cheshire

Offline Pete.

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Re: Leveling Denford lathe - has no levelling screws?
« Reply #27 on: December 20, 2015, 05:14:22 AM »
You could easily  scrape a faceplate flat or with a much smaller dish than quoted above.

Bear in mind that a 300mm faceplate probably runs out more than the quoted figure above and will almost certainly distort more when you clamp an irregular shaped object to it.

Offline DavidA

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Re: Leveling Denford lathe - has no levelling screws?
« Reply #28 on: December 20, 2015, 06:31:11 AM »
Phil,

You're right.  My apologies for that. I'm used to equating three places of decimals to Imperial. I didn't take into account the 300 mm next to it.

Dave

Offline Alan Haisley

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Re: Leveling Denford lathe - has no levelling screws?
« Reply #29 on: December 20, 2015, 11:49:37 AM »
You could easily  scrape a faceplate flat or with a much smaller dish than quoted above.

Bear in mind that a 300mm faceplate probably runs out more than the quoted figure above and will almost certainly distort more when you clamp an irregular shaped object to it.
True, but the concern is what a lathe will do in facing off a piece of work. It could be a faceplate or it could be a surface of a properly held piece. The idea is that since we can't get the lathe to machine perfectly flat we may as well go for a slight concave which provides a more useful surface.

Offline loply

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Re: Leveling Denford lathe - has no levelling screws?
« Reply #30 on: December 20, 2015, 01:43:02 PM »
Hi folks,

I'm concious of the chuck jaws - I think the issue is that if the chuck isn't very good the workpiece can deflect a bit and (at long stickouts) you can get uneven turning.

Because the taper appears to be completely linear though I think that's unlikely to be the case here, especially given I was only taking small cuts. I am going to re-run the test using the 4 jaw at some point before I take the head off just to be sure though.

Luckily the head on these lathes is just bolted on to a flat section of bed, so no need to rescrape anything (unless it's vertical misalignment!). I will simply put a bar in the chuck, loosen the head up, then 'push' the bar using the cross slide to make the requisite realignment, then tighten back up. Shouldn't be a big deal I don't think.

Cheers,
Rich