General Machining Question:

[rhino]

HI ALL.

MY BOSS JUST GOT A NEW JOB (CAN'T TELL YOU MUCH ABOUT IT) BUT WHAT I CAN TELL YOU IS THAT THE PART REQUIRES A SPIRAL GROOVE/COARSE THREAD. THE RADIUS OF THIS GROOVE IS R4.5MM (OR 9MM DIA.) WITH A 18MM PITCH AND 4.5mm/5mm (APPROX. DEEP). THE MATERIAL IS 300mmx260mm (CS1020) STEEL HOLLOW BAR AND THE LENGTH OF THE THREAD IS APPROX. 500mm LONG. I AM CONSIDERING GRIPPING THIS JOB FROM THE I.D. AND MACHINING COMPLETE (AS THE I.D. DOES NOT HAVE TO BE MACHINED). HOW SHOULD I TACKLE THIS OPERATION? I AM DOING THIS JOB IN A CNC. I'D THOUGHT ID ASK YOU GUYS FIRST AS I KNOW I WOULD RUN INTO PROBLEMS WITH CHATTER WITH SUCH A THIN WALL THICKNESS. HAS ANYONE DONE A JOB LIKE THIS IN THE PAST, I KNOW I NEED TO USE THE TAILSTOCK, BUT WE DON'T HAVE A PIPE CENTER BIG ENOUGH (MIGHT HAVE TO MAKE OUR OWN YET).

ANY HELP WOULD BE BL**DY APPRECIATED. THANKYOU.

P.S. I WILL LET YOU GUYS KNOW HOW I GET ON.

RHINO.

[One of Many]

A couple of issues I would address at first glance.

The ID of this material may not be round. If there is any TIR callout between the ID/OD, this could force you to machine the inside just to grip it either on a mandrel or otherwise to control it. Same goes for the OD before cutting the groove.

Why a 4.5mm radius helical groove? As if this were for a ball screw function, then grinding may be in order.

Knowing its intended purpose might help in regard to how critical the end result will be and so direct the process of manufacture. Any heat treat, like case hardening could also influence portions of the process.

If I read your dimensions correctly, 30mm wall thickness is not thin is it? Chatter should not be a problem, but might be reduced if you rough the groove with a smaller radius tool, then finish it to spec with the majority of the finish material removed from the leading edge.

DC

[Geof]

What is the total length and do you have available length and a big enough chuck to grip the OD? If you are working with a big enough and rigid enough machine I would suggest you consider making a plug for the ID and grip the OD. Your wall thickness is not thin in itself but compared to the OD it is thin enough that I think you will get serious distortion gripping ID or OD in a three jaw chuck tight enough to drive against the load from the grooving tool.

If you can plug it, grip the OD really well and support the far end on a good sturdy pipe center you may be able to do the groove full width in a single cycle. What you really need is an Oil Country Lathe; monstrous spindle bore and torque you wouldn't believe.

[rhino]

i'll let you guys in on a secret: its a winch drum, it has been machined complete before on a manual lathe by gripping on the I.D. i'd thought i give it a go in the cnc as the machine is big enough, it will turn a diameter of 1m, has a 36" (3ft) 4-JAW chuck to hold my work, and has a MASSIVE toolpost so the machine is definitely rigid enough.

the O.D. has to be machined anyway, and i will be gripping with the 4-JAW chuck I metioned above.

QUOTED BY: ONE OF MANY
If I read your dimensions correctly, 30mm wall thickness is not thin is it? Chatter should not be a problem, but might be reduced if you rough the groove with a smaller radius tool, then finish it to spec with the majority of the finish material removed from the leading edge.

good idea, but i don't think i can do that in my cnc(might have to research the manual a bit more).

sorry geof, the part has 2 spigots at either end about 15-20mm wide

once again thankyou for your replies. and i hope this helps you guys out.

[One of Many]

You should be able to set the 2 cutters with a slight offset in your settings. Set the finish cutters Z-zero true to the end of the part and the X-Diameter at true diameter. Set the roughing cutter +.02 in both Z and X. At least set Z +.02 since you have basic control of the programmed X during the threading cycle verses the sync in the Z position. Point being to get the roughing radius at a larger pitch diameter slightly to the right, within the finishing cut.

If this has spigots welded into the ends. Take advantage of them if you can. If anything else, they will prevent gripping distortion.

DC

[rhino]

re: ONE OF MANY:

the spigots are to be machined in the material - nothing welded.

[rhino]

sorry folks, the boss contracted the job out to someone else.