Lathe Dogs

All good reasons to turn between centers.
Be wary of using a chuck to hold the work in combination with a TS centre, the work tends to walk in the chuck.
 
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All good reasons to turn between centers.
Be wary of using a chuck to hold the work in combination with a TS centre, the work tend to walk in the chuck.

Toz, Can you tell me more about that--sorry I'm not following
 
When held in the chuck, as the workpiece rotates, any eccentricity in the holding of the work in the chuck jaws is exacerbated by the work being held centred at the TS end. So as the work rotates it tends to "rock" in the chuck jaws and "walk" around, becoming loose and marring the surface.
Hope I didnt make that more confusing than it sounds.............

Cheers Phil
 
Phil has explained it well. A common chuck is not expected to hold the work perfectly aligned with the TS. Any run out will increase as distance from the chuck increases. Stick a TS centre into the end of the work and either the work bends or the chuck slips or both. Rotating the spindle has the effect of rocking the work in the chuck under these conditions. Slippage can be very slight but repeated slippage on one side then the other is commonly referred to as 'walking'.
 
When held in the chuck, as the workpiece rotates, any eccentricity in the holding of the work in the chuck jaws is exacerbated by the work being held centred at the TS end. So as the work rotates it tends to "rock" in the chuck jaws and "walk" around, becoming loose and marring the surface.
Hope I didnt make that more confusing than it sounds.............

Cheers Phil


I tend to hang the part out long and center drill it in place if I'm going to use the tail stock center. As you say if you drill it close to the chuck then pull it out you can get issues with any bend in the stock or imperfect centering of the chuck.

Stuart
 
Stuart, Not necessarily ideal. If the stickout is long then any eccentricity can be exaggerated at the unsupported end. In a perfect world you could centre drill to perfection, but in the real world the free end of the stock is "whipping" around an eliptical orbit.
If it needs accuracy then keep it short in the chuck, "knock" it square and central in the chuck, measuring with a dial indicator, then centre drill. Then extend to length and support the free end.

Cheers Phil
 
Stuart, Not necessarily ideal. If the stickout is long then any eccentricity can be exaggerated at the unsupported end. In a perfect world you could centre drill to perfection, but in the real world the free end of the stock is "whipping" around an eliptical orbit.
If it needs accuracy then keep it short in the chuck, "knock" it square and central in the chuck, measuring with a dial indicator, then centre drill. Then extend to length and support the free end.

Cheers Phil

That tom's techniques on youtube has a video showing what i'm thinking of. If the work piece is whipping to much to be safe you can start it up with the center drill in contact with the work which will suport it (i use a biger center drill if it's extended a long way) If you have a fixed steady that would be a good time to use it.

Stuart

whopps nearly forgot vid link :)

 
Perhaps whipping wasnt the best word to use. I didnt mean it literally, (hence the "") but a long workpiece wont rotate on its axis concentrically at the unsupported end.
....If the work piece is whipping to much to be safe you can start it up with the center drill in contact with the work which will suport it....
If you engage the drill whilst the work is stationary how can you know that you are on centre? The workpiece could have sagged. If you are applying pressure without the work rotating then you could easily cause the drill point to "skate" across the surface and be off-centre.
.....As you say if you drill it close to the chuck then pull it out you can get issues with any bend in the stock or imperfect centering of the chuck.
Any issue with bent stock or imperfect centering will only be greatly exaggerated by turning with it extended further out

cheers Phil
 
Hoping to hear more opinions, about this video that stupoty just posted. I saw that video some time ago, and am not sure what to think about "Tom's Technique" on center drilling. With my limited experience, however, I can't say whether he is right or wrong here, So lets here from all you experienced guys!!! Thanks, JR49

EDIT, 12bolts, you posted as I was typing. You made three good points, but, for the novices like me, you didn't say what the correct procedure would be. I did once have the problem the Tom described in his video. When I was done with a 6" part that I had center drilled up close to the chuck, and I removed the tailstock center, the part wobbled at that end. So, looking for answers. TIA, JR49
 
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