Lathe stock flip - how to set parts up?

[pmurdock]

So I've got a little question regarding accurately cutting a part. I have a piece of 6" long x 1" diameter aluminum bar that needs threading on both sides. So a lathe stock flip will be necessary - but my question is how to ensure that the length of the piece says at 6"

1st Setup - face it, then perform operations (no cut off operations since the stock is already at length??)

2nd Setup - flip the stock, then face it (perhaps I can skip this step if I used a cut off tool?? ie stock was cut to a larger size to begin with) and perform operations


So on the 2nd setup it needs to be accurately setup in the Z direction. What is the best way to do this? a rotating stock stop? or just bringing in a tool on the face until it skims and then back off by 0.001"? use a sheet of paper? Unfortunately I don't have a probing tool on this lathe.

[PBMW]

Uh....
Collet stop?

[Mazaholic]

I couldn't give you any good advice without knowing what kind of spindle is on your lathe.
Thru hole spindle? if so,how large is the thru hole?i have retrofited thru hole spindles with an adjustable stop.
How long are the jaws on your lathe?
Do you possibly have soft jaws long enough that you could bore to accomidate the part and leave a wall in the back of the jaws?
There are many options,but without knowing what you have to work with,it's just a best guess.

[pmurdock]

Thanks for the tips.. It's a 5C collet closer that pulls back the workpiece. So if I put something into the collet and hit it against a stop the collet closer will pull the piece back. I don't think it pulls the collet back the same everytime either (it moves back about 1/8"). Do I need to ditch this collet? I've seen some of the reverse collet closers that push to close the collet and thus allow the piece to stay in place (ie if pressed against a stock stop)

If a new collet closer isn't in the cards then taking a skimming cut is the next best thing?

It has a 3" spindle bore through hole. So plenty of room.

PBMW - doing a bit of research it looks like the collet stop is perhaps the trick. Thanks for the tip! so much to learn!

[pmurdock]

Another interesting thing of note. I was looking at the collet chucks specs.

http://www.ats-s.com/products/workho.../pullback.aspx

Turns out the machine came with this and it's description says it all:

Universal Pull Back Features
Cost-effective solution when part length is not a concern
Ideal for 1st operation and slug work
Direct mount to the machine tool

So... when part length is not a concern eh???? geez..

[Mazaholic]

Many thru bore machines have tapped holes in the back for bar feeders,different chucking cylinders ...ect
You can make a flange that will bolt to the back (make sure it bolts to the spinning part) also make sure there is room for any moving parts when the chuck clamps and unclamps.
A hole in the middle of the flange for a rod and a stop on the other end of the rod.
Holes at different intervals and a hole thru the side of the flange that you can put a locking clevis pin in.
I'm not a draftsman but maybe you get the idea.
I would'nt get rid of the collet chuck,they are very usefull,but i would look into getting a three jaw.

Also you can thread the rod at one foot intervals so that it screws together,that way you never have much more then one foot sticking out the back.

[SeymourDumore]

Actually, when part length is of a concern, you must hold the OD to be clamped withing tighter tolerances.
By calculation, the 5C collet will have a 3 to 1 ratio. IOW .001 change in the diameter will result in a .003 change in length.
In reality it's more like .001-.002 in a typical setup.
So if your length tolerance is .005, keeping the OD consistant within .002 will do the trick no problem.

[gizmo_454]

What kind of length tolerance are you playing with? I use both 5C and 16C in the "pullback" style chuck. Not a problem. Just as SeymourDumore said, you just have to hold the OD of the part to a tighter tolerance if you want the length to be closer. There has only been one part that I was making that I couldn't hold the length tolerance using this type of setup and it's tolerance was +/-0.0002". I was able to hold it with the 3 jaw chuck. I just don't like using that thing. I worry every time it is on the machine that one of my drills is going to come up missing.

Also, you didn't say if you had a barfeed on the machine or not. I have successfully used our Servo 300 as a stop for some longer shaft work before. Of course the OAL tolerance was +/- 1/64". But it still worked well for what we needed.

Gizmo

[fizzissist]

I'd be tempted to use a collet stop or internal spindle stop. Create 2programs, one for each end. Do the 1st op with the 1st program, flip the part, change to the second program and touch off the end to set the Z, and run it. The Z might change each time, it might not, depending on your part's consistency.

Otherwise I'd just face it to length on the 2nd op.

I've done this often on a chucker and it has worked fine for me, holding +/-.005 easily. On my Mazak I can have the program automatically shift back and forth between programs. Don't know if it's a PITA on the Haas or not...

[gizmo_454]

Originally Posted by fizzissist On my Mazak I can have the program automatically shift back and forth between programs. Don't know if it's a PITA on the Haas or not...

When I do this on our SL-10, I just unite the 2 programs. Use 2 different work offsets. Write the program for one end, put in an M00, then write the program for the other end using the second offset. If both ends are the same, you could even use a subroutine or subprogram. That way you don't even have to write it twice!

Basically, chuck the part and start the cycle. When the machine finishes the first end and finds M00, it will stop. Open the door, unchuck the part, flip it, chuck it again, close the door and start it up again. When it hits M30 at the end, the program resets and the part is complete in one run.

Have fun!!

Gizmo

[djr76]

Here is a few collet stops I made to accommodate longer parts. Mine are for 16c collets, but I'm sure you can make something similar. For the extra long stop, I use a spindle liner to support the overhung load of the stop in the spindle bore. The long one screws right into the back of the collet and I use loc-tight to keep it from getting loose.

Note: The blue anodized one is a bought tool but made a similar longer design

http://img169.imageshack.us/img169/8077/p6210046sn4.jpg
http://img364.imageshack.us/img364/3280/p6210047vy0.jpg
http://img364.imageshack.us/img364/7586/p6210048ug9.jpg