[mendez]

Hello,

I'm using a 4 jaw chuck with a 10mm stainless steel rod, and I'm trying to drill a straight/true hole with a drill bit (cobalt). I used a center, fluid oil and multiple drill bits (from small to larger diam) to reach my inside diameter dimension. The hole is end up offcenter.

I tried with a softer material (aluminum) but I still get the same problem.

Does anyone know how can I correct this?

Thanks for the help,
Jose

[DALEK]

How deep? What diameter? It's only the first drill that matters. All the others will follow this. If the hole is in the centre and right through, you could start with a 12 mm bar and turn the outside of the bar between centres after you have drilled it.
Guaranteed concentric hole.

[Superman]

Is your 10mm rod running true in the 4 jaw before you start any machining?.... no... then hole will not be in the centre.

Is the hole diameter the same as the drill diameter ?... no.... tailstock not on centre or drill is not sharpened correctly.

HSS drills may cut better then cobalt on the softer stainless steels as they retain a sharper edge... but need to be kept sharp.
Don't force the tool too hard, on break through, make sure you go slower and the area is kept cool

[mendez]

How deep? What diameter? It's only the first drill that matters. All the others will follow this. If the hole is in the centre and right through, you could start with a 12 mm bar and turn the outside of the bar between centres after you have drilled it.
Guaranteed concentric hole.

Thanks for your reply.

How Deep? 20mm (a little less than 1in) and the Smallest diameter I use I believe is 1/8

As for using a 12mm bar and turning it after I drill the hole, I tried with aluminum....here were my steps:

Had like a 14mm stock, and turned to 10mm and THEN drill the hole. Still out of center (the back face looked more off-center than the front face)

[mendez]

Is your 10mm rod running true in the 4 jaw before you start any machining?.... no... then hole will not be in the centre.

Is the hole diameter the same as the drill diameter ?... no.... tailstock not on centre or drill is not sharpened correctly.

HSS drills may cut better then cobalt on the softer stainless steels as they retain a sharper edge... but need to be kept sharp.
Don't force the tool too hard, on break through, make sure you go slower and the area is kept cool

Thanks for your reply. Yes, the 10mm run true before machining.

Now, this is a good point because I notice that the hole is slightly bigger than the drill bit. How do I check if the tail stock is on center ? I have one of those TAILSTOCK ALIGNMENT BAR from Edge Technology and it seems to be OK.

I want to fix this; but if I need a machinist to make me two of this parts; how much will this type of job cost?

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Attachment 416212

Here is the picture of the part

[deadlykitten]

hello mendez, there are some alignment requirements, for a lathe, so to drill on center :

... spindle low tir ( simple dial indicator )
... chuck ( free chuck ) low tir ( simple dial indicator )
... chuck clamping low tirr ( simple dial indicator on a cilindrical stock clamped inside the chuck )
... S axis paralel to Z axis ( turning something inside the chuck, and check it to be cilindrical)
... S axis coaxial with the tool station ( coax ); this coaxiality test is good to be done on :
...... toolholder ( once in a while, so to check machine alignment )
...... sleeve
...... tool ( machine setup, preparation, whenever needed )
... tool station is rigid during cutting ( 2 dials, at 90*, on the tool during cutting )

is this ok ? do you need more details ? kindlly