Need help with long thin part in Swiss lathe

[Rk1989]

Dear All,

I have a part which is 10" long and has various step diameter across length stating Ø.190" up to 2.5" length then Ø.250" to 5.3" length after Ø.420" up to 7.8" length and lastly Ø.312" up to 10". raw material is Ø0.5" SS316, since it is a hard material I cannot cut in single pass with current tooling. and also the guide bush we have currently is only 1.5" long, so I cannot cut each step OD separately, because the step lengths are more then 2.5". currently I am turning the part 1" length then 1" again, like this I was able to complete the part. but the part has band step marks on OD at every one inch length because deformation or mismatch. to make things even worse the part has very close tolerance ranging from 0.0005" to 0.002". Although I have fairly good experience with swiss lathe, I have never machined the parts this long and thin. so if anyone has experience with similar parts in swiss lathe, help me out.

I tried with sub spindle holding the part on synchronization mode, the part still deforms after parting. and also since the part has multiple diameters, I am not able to support the entire part with sub spindle.

Hope someone helps me out, thanks in advance.

 

[TeachMePlease]

What is the material? What is the current tooling?

 

[FamilyTradition]

What model of machine are you running? This is a situation where pinch turning might help you out, if the machine has that capability.

 

[Ox]

Why can't you take it in one bite?
Material is slipping in the collet?

OK, why are you starting with 1/2" if the biggest D on the part is 5/16"?

Starting with 5/16" might solve your issues.
Is it just not currently available?
Or just not at the nice price?
(which is costing you WAY more in mfg costs)


-------------------

Think Snow Eh!
Ox

 

[FamilyTradition]

Ox, you might have misread the OP's post.

The last diameter is 5/16", but that is smaller than the largest dia. on this part, which is .420"

 

[Ox]

OH!
I (obviously) missed the .420!

I thought that it was git'n bigger as we went.
Kind'a like a swadge tool.

I don't see pinching it helping if he is having grip issues tho.
He says "too hard", but 316 isn't hard, so I'm guessing that the ground finish is slipping in the collet.
(not breaking the tool)
Depending on what type collet closer he has.
One of mine is spring op close, and I can't run ground pre-hard in it hardly at all.

My guess is that he will need to just polish with Scotchbrite afterwards to hide blend.

I can't imagine the hourly rate of burden for just being in Dubai.
Seems like a tough place to make a living in manufacturing?


--------------------

Think Snow Eh!
Ox

 

[Rk1989]

What is the material? What is the current tooling?

SS316- Heat treated to 44 HRC. I am currently turning with SECO DCMT11 insert R0.4 for Roughing and R0.2 for finishing.

 

[Rk1989]

Why can't you take it in one bite?
Material is slipping in the collet?

OK, why are you starting with 1/2" if the biggest D on the part is 5/16"?

Starting with 5/16" might solve your issues.
Is it just not currently available?
Or just not at the nice price?
(which is costing you WAY more in mfg costs)


-------------------

Think Snow Eh!
Ox

Currently we have Ø1/2" Rod only, we will receive Ø.430" Rod soon, so I thinking about taking in one cut then.
but with current half inch rod, I have not tried cutting in single pass, because the material is hard.

 

[Rk1989]

What model of machine are you running? This is a situation where pinch turning might help you out, if the machine has that capability.

KSI TCM 20S series Swiss machine, the machine does not have lower turret for pinch turning.

 

[Rk1989]

I am also thinking about finishing the part by doing facing method instead of turning, so I don't have to retract the bar, which will prevent the Bar slipping from guide bush. but I am not it will work or not.

 

[maguilera]

SS316- Heat treated to 44 HRC

316 is an austenitic SS and can’t be hardened by heat treatment but will harden when cold worked, also, 44 HRC is close to the maximum hardness this stainless steel can achieve through cold working.

I don’t have experience machining cold worked 316 SS, but would assume machinability is worse than on annealed 316 and probably different from a steel hardened by heat treatment.

Cheers