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uute
11-20-2003, 05:01 AM
Not to stir the pot, but just to get it right. (My best attempts are parallel to .002-.005, square to .010-.020, starting with crooked, ugly scrap.) So I ask:

In the Lathe,

Using Evans method,

is sequence:

clean Top Face,
flip, set fresh cut tight to chuck face,
clean Bottom Face - should have parl Faces.

NOW, to cut 1st Side, do I chuck block excentric, shimming to reference rod for square?

Then repeat flip for 2nd Side.
Reference (on 2 surfaces)and flip for Ends?

Did I miss something?

Are square jaws (jaw 90* to chuck face) required/assumed in this setup? (It appears my chuck jaws grip tighter towards the outside - revese bellmouth like, so don't seem to be good reference for 90*)

Small mind - Big subject. : )

uute

PS no throwing those cubes at me, Please!

[This message has been edited by uute (edited 11-20-2003).]

winchman
11-20-2003, 09:37 AM
I started with a rough sawn block of mahogany about 2 1/8" on each side. Using the three-jaw chuck, I faced the first side. I turned the block 90* and used the machinist square to get side one square to the face of the chuck for facing the second side.

I turned the block 90* again, and used the square to get the two finished faces square to the face of the chuck for facing the third side.

With three mutually perpendicular sides finished, the rest was just a matter of making certain the block was tight against the face of the chuck while cutting to the other three sides to size. The carriage stop helps with this part.

I checked all twelve edges with the square, and can see no light under the blade on any side of the 2" cube. That's close enough for me.

Roger

[This message has been edited by winchman (edited 11-20-2003).]

11-20-2003, 01:00 PM
One thing to be careful of is chucks do wear. Their jaw clamping surfaces are seldom square with the plane of rotation.

Exaggerating the wear on the jaws clamping surfaces and the wear of the jaws in the T-slots in the chuck and you get a shape that if exaggerated 1000 times might have the appearance of the bell of a trumpet.

By the way, this is a job for a four jaw. It's more universal in its grip and holds odd shapes much better with less jaw effort.

Evan
11-20-2003, 01:02 PM
uute,

That sounds like the way I did it. I use my four jaw chuck and hold the work between a couple of beefy parallels clamped in the jaws. The parallels have nice smooth flat faces so the chuck jaws don't matter much. The parallels align both with the work and the chuck face, not the jaws which might be out a bit.

[This message has been edited by Evan (edited 11-20-2003).]

uute
11-20-2003, 03:10 PM
Thanks Again, Guys !! : )

uute

winchman
11-20-2003, 04:03 PM
I used the three-jaw because the angled areas at the end of the jaws have a fairly large smooth surfaces, and those surfaces on adjacent jaws are parallel. I figured that was less likely to mar the soft wood than using the four-jaw. If I had been working metal, I certainly would have switched chucks.

Roger

wierdscience
11-20-2003, 11:20 PM
A note on why people use flood coolant on lathes-when you chuck a workpiece in the chuck you apply pressure and stress the chuck,when you then turn the part without coolant and it gets hot and expands you increase that same stress,since most chucks have cast iron or semisteel bodies they are easy to stretch into the "reverse bellmouth"condition as mentioned above.