Chatter on Our Okuma LU45

When you get a vibration in a tool holder, it can fret. And what fretting is, is micro welds between the tool holder due to high frequency vibrations, in this case your post and the tool holder for you tool bit.

I usually see this in VMC, where for example you have a BT40 tool holder, when changing manually, one cleans both the BT tool holder (what holds the BT tool) and the BT tool holder itself. Once it starts fretting onto the BT tool itself it can spread to other holders, and it gets progressively worse.

BUT, I never saw it in this type of case. and it does not look like fretting.

Actual problem may not show up where is noticeable. You could start with this, I would question to see if there are any types of micro cracks or defects in your post that holds your tool holder.

p911

The same "fretting" comes back even with a new tool holder extension. If the tool holder extension has micro-cracks, I believe that it is still a result of the process, and not a defect that causes the fretting itself. However, there could be an issue with the tool pocket in the turret, as this same #8 tool pocket has been used for all roughing for every part since the machines were new at our sister company. A good test might be to change to a different pocket that has not been used yet, with all new hardware and see if the problem comes back.

Hi,

possibilities of chatter origin:

a. too flexible clamping of tool - likely as the fretting shows indication of lengthwise movement. Try some soft layer (soft aluminum or copper foil or flakes or powder) below your tool and make sure that the clamping is symmetrical: upper and lower clamping parts should have the same areas match to the tool. Else you will have bending in the tool shaft and bigger bending movements.

b. backlash in spindles and guide-ways: take a measurement at standstill and if possible in operation. Rework if possible, check with heavy pre-load by spring or other force (pneumatic) to minimise movements by backlash.

c. Position of tool cutting edge above "zero": to check with axial planing and adjusting if necessary

d. torsional or bending deformation of cutting tool shaft that has a component that is amplifying an existing depth of cut. Change the shaft of the cutting tool to another cross section that is extended to above the cutting edge as far as to below and locate the cutting edge at the neutral of bending or torsion.

e. often but not expected in your situation: too flexible tool and machine.

Have success and please post experimental results.

RHABE

Make sure you have the tool extension as short as possible then check for chatter. Most likely cause is tool is cutting off center. Check alignment of turrent. If OK then look at the ways. Good Luck.

JGA Michigan

We had Okuma in to re-align the machine and I have reviewed the report they left, the machine is in alignment and cutting on center.

Okuma reported that Coolant nozzles were not directed to the tool tip, there is extreme tool wear on the roughing inserts, Axis and spindle loads are normal, SFM is 590 and feed is .018,

they, (Okuma) redirected the coolant nozzles and increased the SFM to 700, this reduced the wear on the inserts, but the chatter remains.

thoughts anyone??

laby

We run Okuma lathes here as well and run seperate programs for each diameter. I don't think running one program for diameters ranging from 4 to 6 inches is wise as there will be quite a diference in surface feet per second at the cuting tool. Given the fact that some of your parts run OK the machine is less likely to be the culprit.

Start with a new tool holder and tool bar, save your original program to run the other parts with and create a new program with diferent feeds, speeds and cutting depths for this size of material. I,m sure someone out there should be able to furnish you with feed tables for this type of material.

Our Okumas are older models, but are still capable of containing at least 20 programs in their internal memory.

Good Luck