Manonfire91
Plastic
- Joined
- Apr 1, 2020
Ok. So Ive been programming/machining for around 8 years now but until a year or 2 ago, been mainly running mills. We have an integrex (millturn) in the shop that the two older guys HATE programming because we do it EIA/ISO by hand. So I took it on and have been working with it for a while now. Its been a learning curve on the turning side, mainly learning how to turn at much much higher surface footage. I had only really run manual lathes before the integrex and never really ran fast. Ive got OD turning down pat and can get fantastic results. But when it comes to boring in steels (we do a LOT of 4130/4340 heat treated to 150-180kpsi 35-42rc roughly) i cant get bars to not chatter. Ever.
Currently I am running a driveshaft end (splined on 2.5" end and then it tapers up to a 4.118 journal with a 3.8" ID) made from a 4340 forging heat treated to 38-42rc. I am running the first setup. I have premachined a journal on the small end and am clamping in 3" machined steel soft jaws. The part is 8" overall in length roughly. So the big "bell end" is hanging out. Unfortunately, the spindle thru bore is only 2" so i am unable to fit part into spindle to shorten the stickout. I am drilling 1.5" dia with a carb spade drill about 4" deep. Then i am proceeding to rough out the id with a 1.25" A20-MCLNR boring bar using a CNMG431 insert. 1.25" is the largest bar the lower turret will fit. (On a side note, ive tried using some large insert drills to rough out the part, but given the length of the drill and the part reach, they instantly chatter and break inserts. Ive tried milling and plunge milling but they also destroyed inserts...) So i resorted to boring. Ive got deadlines to meet.
My question is in regards to general speeds and feeds when rough boring alloy steels that have been heat treated. Even in parts not hanging way out of the chuck i always get chatter in steel. Regardless of bar size. Carbide bars only run quiet at slow speeds. Ive also bought split sleeve adapters for the tool blocks to try and damp the vibration but they only help minimally. So i am roughing this steel with my cnmg431 at 200sfm (bar is extended 4.5" from tool block, no split sleeve as tool block is 1.25 ID) .05" radial doc, .01 ipr. The chatter is higher pitch and constant, but i can get about 4 parts before insert starts to break down. I noticed on my finishing bar (also a 1.25" bar but uses a vnmg or vpgr top notch insert) that it would chatter until i really crank up the sfm. At 500sfm, it runs like a wet dream, even with the knurled finish from the roughing bar. Babys bottom finish that shines. And Im scratching my head.
Do I need to crank up the sfm on my roughing bar? Does that increase tangential force and load the bar? Do i need a heavier doc? Higher feed? Ive tried up to .015ipr at .05 and it only worsens the chatter. Ibe tried increasing the speed by maybe 20-40% on the control but it worsens the noise. What do you experts do to quiet boring bars? Unfortunately this is a semi long run and i cant run 70sfm to quiet it. Aint nobody got time for dat! Its been recommended to us by a fellow shop that tunable bars are the way to go but the smallest i can find is 1.5 and quite expensive. Want to see if i can optimize this steel bar first. Should i run higher sfm with lighter doc and heavier feed?
Thanks in advance for any pointers. If i forgot to add any info, let me know and Ill correct.
Currently I am running a driveshaft end (splined on 2.5" end and then it tapers up to a 4.118 journal with a 3.8" ID) made from a 4340 forging heat treated to 38-42rc. I am running the first setup. I have premachined a journal on the small end and am clamping in 3" machined steel soft jaws. The part is 8" overall in length roughly. So the big "bell end" is hanging out. Unfortunately, the spindle thru bore is only 2" so i am unable to fit part into spindle to shorten the stickout. I am drilling 1.5" dia with a carb spade drill about 4" deep. Then i am proceeding to rough out the id with a 1.25" A20-MCLNR boring bar using a CNMG431 insert. 1.25" is the largest bar the lower turret will fit. (On a side note, ive tried using some large insert drills to rough out the part, but given the length of the drill and the part reach, they instantly chatter and break inserts. Ive tried milling and plunge milling but they also destroyed inserts...) So i resorted to boring. Ive got deadlines to meet.
My question is in regards to general speeds and feeds when rough boring alloy steels that have been heat treated. Even in parts not hanging way out of the chuck i always get chatter in steel. Regardless of bar size. Carbide bars only run quiet at slow speeds. Ive also bought split sleeve adapters for the tool blocks to try and damp the vibration but they only help minimally. So i am roughing this steel with my cnmg431 at 200sfm (bar is extended 4.5" from tool block, no split sleeve as tool block is 1.25 ID) .05" radial doc, .01 ipr. The chatter is higher pitch and constant, but i can get about 4 parts before insert starts to break down. I noticed on my finishing bar (also a 1.25" bar but uses a vnmg or vpgr top notch insert) that it would chatter until i really crank up the sfm. At 500sfm, it runs like a wet dream, even with the knurled finish from the roughing bar. Babys bottom finish that shines. And Im scratching my head.
Do I need to crank up the sfm on my roughing bar? Does that increase tangential force and load the bar? Do i need a heavier doc? Higher feed? Ive tried up to .015ipr at .05 and it only worsens the chatter. Ibe tried increasing the speed by maybe 20-40% on the control but it worsens the noise. What do you experts do to quiet boring bars? Unfortunately this is a semi long run and i cant run 70sfm to quiet it. Aint nobody got time for dat! Its been recommended to us by a fellow shop that tunable bars are the way to go but the smallest i can find is 1.5 and quite expensive. Want to see if i can optimize this steel bar first. Should i run higher sfm with lighter doc and heavier feed?
Thanks in advance for any pointers. If i forgot to add any info, let me know and Ill correct.