Aluminum shaft chatter

[Andy S]

I am trying to make an aluminum shaft out of 1.25 stock, shaft portion finishes at .860 and is about 10 inches long. When turning .01 finish pass, starts chattering about 1 inch from tailstock untill about 3 inches from end of shaft. Tried 3000 rpm, 1500, .005 feed and still chatters. not shure what im doing wrong. Tail stock pressure is about 90psi. Any Ideas??

[Geof]

Look in your manual for spindle speed variation. Haas allows you to program a cyclic change in rpm to help stop chatter arisingDo a search on cnczone for 'spindle speed variation'. You will get several threads and posts that mention it.

[il_performante]

Cyclic change sounds great, but you could just change to a much thinner, pointy tool.

M.F.

[tooldude328]

I belive the Spindle speed variation is a M38 command

[Geof]

Tes it is M38. I found my copy of the lathe manual, here is the part about Spindle Speed Variation;

M38 Spindle Speed Variation On / M39 Spindle Speed Variation Off Spindle Speed Variation (SSV) allows the operator to specify a range within which the spindle speed will continuously vary. This is helpful in suppressing tool chatter, which can lead to undesirable part fi nish and/or damage the to cutting tool. The control will vary the spindle speed based on Settings 165 and 166. For example, in order to vary spindle speed +/- 50 RPM from its current commanded speed with a duty cycle of 3 seconds, set Setting 165 to 50 and Setting 166 to 30. Using these settings, the following program will vary the spindle speed between 950 and 1050 RPM after the M38 command.

O0010;
S1000 M3
G4 P3.
M38 (SSV ON)
G4 P60.
M39 (SSV OFF)
G4 P5.
M30

The spindle speed will continuously vary with a duty cycle of 3 seconds until an M39 command is found. At that point the machine will come back to its commanded speed and the SSV mode will be turned off. A program stop command such as M30 or pressing the Reset button also turns SSV Off. If the RPM swing is larger than the commanded speed value, any negative RPM values (below zero) will translate into an equivalent positive value. The spindle, however, will not be allowed to go below 10 RPM when SSV mode is active. Constant Surface Speed: When Constant Surface Speed (G96) is activated (which will calculate spindle speed) the M38 command will alter that value using Settings 165 and 166. Threading Operations: G92, G76 and G32 will allow the spindle speed to vary in SSV mode. This is not recommended due to possible thread lead errors caused by mismatched acceleration of the spindle and the Z-axis.

Tapping cycles: G84, G184, G194, G195 and G196 will be executed at their commanded speed and SSV will not be applied.

[gizmo_454]

You might try a larger depth of cut. I find it helps with that. At least it does with unsupported cuts.

I have turned things to 6x diameter in length before with our SL-10, which does not have a tailstock. I find that the tool is not loaded enough when taking shallower depths of cut like that. Ideally, you should be cutting enough material per side to have the full nose radius of the tool in the cut, if not more. For the 0.016" radius tools that I run, I like to leave between 0.040 and 0.050" per side for a finish pass. I do know that is not always possible though.

Good luck!

Mike

[Andy S]

Thanks for the help i got the part made today. using the ssv and made multiple roughing and finish passes cutting 1.25" length at a time and overlapping cuts .050. it worked however seemed unnessary to have to do that. I was only doing a .01 finish cut with a .032 rad cutter, i will try a heaver cut next time. One question? say you make a .040 finish cut and the part is still like .005 big will you be able to make a small cut without chatter?

[gizmo_454]

I have not been successful with that kind of length to diameter ratio. I am not saying it's not possible. Just that I haven't found a way yet.

It may be possible if you can find a tool with a small enough radius to be fully engaged. See, the problem is, with a 0.0025" DOC with a 0.032" radius tool, most of the pressure tends to push the bar away and cause chatter. If the radius of the tool is fully engaged, most of the pressure is pushing towards the chuck helping to reduce the chatter.

Again, good luck!

Mike