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View Full Version : chatter -- whats it telling me??



Tony
04-18-2003, 04:31 PM
hello all.
being relatively new to this i'd appreciate some insight on the world of chip-making..

let me start off stating that i know tool-chatter is bad. i know its bad because its ugly. nothing ugly can be good (aside from, say, flamecutting)

i've got a Machinery's handbook and i love it. i try to figure out all my speeds/feeds and use them when i can (ie, my machines allow me the right settings/ranges)

sometimes i get great cuts, sometimes i dont.

so, on tool chatter:
1. when i drill a hole and the bottom isn't shiney, when its got radial chatter marks.. what is this supposed to tell me??
2. when the cutter in my lathe leaves chatter marks on my workpiece, whats its trying to tell me? (esp chatter in threads!)
3. when my endmill leaves ugly chatter marks on the side of a pocket.. what am i doing wrong?

thanks!
-knucklehead

rklopp
04-18-2003, 04:53 PM
For #1, slow it down & feed it harder to force the drill's torsional springiness to one direction rather than letting it oscillate.

For #2, get better support on the work, like less overhang, use tailstock, steady, or follow rest. Try higher feed rate to force springiness to one side. Use less nose radius. In general, minimize cutting edge contact with work. Be sure to have enough trailing edge clearance. Use shallower depth of cut. Slow down spindle. Back up thin-walled pieces with low-melting alloy.

For #3, don't dwell in the pocket. Plunge cut the corners first, then finish the straight sides of a rectangular pocket. Minimize the amount of workpiece in contact with the endmill. (Along the sides of a pocket you essentially have line contact, but in a corner, the workpiece wraps 90 degrees around the cutter.)

Joel
04-18-2003, 05:14 PM
Do you realize you are insulting most of the people on this BBS, (especially Thrud!)by stating that nothing ugly can be good?!

darryl
04-18-2003, 05:37 PM
For #1, could also be uneven length of lips on drill bit. #2, many things, also look at all areas of play, including lack of rigidity in cutter mounting, and height of cutting edge, in the case of lathe.

ibewgypsie
04-18-2003, 06:21 PM
Massive weight dampens harmonics. Cadillacs ride better than toyota's. Harmonics have various sources. My old chinese milling machine would not cut at 1/100th of the speed of my current bridgeport cause of the weight diffrence. (probably some of the other reasons too)rigidity? tool flex, slide tolerance?
My first machine used a powered x-y slide and a gear pulley on the downfeed for a 100 dollar drill press. It worked great drilling pcbs, not so on cutting, it was just too light.

BC21OSH
04-18-2003, 07:18 PM
Item #2

I've found that using Tap Matic or Rapid Tap makes threading much smoother, cuts down on chatter and drag/tearing when cutting threads.

I used the nasty stuff before the new regs. I haven't used any of the new friendly stuff.

This assuming that the tool and setup is proper.

Bernard

bspooh
04-18-2003, 10:01 PM
I think RKLOPP said it all....

Just remember chatter is largely due to deflection of the workpiece on lathes, and deflection of the cutters on the mills...

My old foreman used to say "chatter doesn't matter"

brent

Oso
04-18-2003, 11:08 PM
At the risk of stating the obvious, make sure gibs are tight, and as a check, try oiling the crosslide and compound.

Sometimes oil will damp out chatter. Besides they probably need some.

Don't stick the compound way out, try to keep the cutter near the pivot.

As a last resort, buy an Axelson or a Springfield :-)

Tony
04-19-2003, 05:10 AM
thanks for all the tips.
despite my feed/speed rates and cutting
tools i think you hit it all on the head
with the ridigity issue.

most of my equipment is relatively light
and i (we) work it probably much harder than
it was intended to work.

the equipment is well-maintained .. everything is pretty tight... in fact, most of the time, i have to overtighten the ways to get nice clean work done.

maybe its time to upgrade the equipment.

i have a more specific question.. regarding chatter and my "precision" boring head in the mill.. i'll post as a different topic.

thanks again
-knucklehead

darryl
04-19-2003, 05:55 PM
I'm intrigued by your having to overtighten the ways to get good results. I'm not too sure what you mean by that, but it sure sounds like the cutting edge is too high. Maybe for some reason the carriage doesn't sit flat on the ways, and you're having to 'squish' it down?

nheng
04-19-2003, 08:37 PM
I had chatter in my small Maximat lathe recently. Tightened gibs and anything that could be tightened to no avail. Finally checked the spindle bearings. A quick spin on the chuck by hand and it would keep spinning for a number of revolutions. Adjusted the preload for about 1 revolution on a quick snap of the chuck and my chatter was gone.
Den

Oso
04-19-2003, 09:49 PM
Sounds like wear on the bed. If loose enough to travel full length it is too loose at area of most use, hence over-tightening means making it too tight to travel full length?

Interpretation right or wrong?

[This message has been edited by Oso (edited 04-19-2003).]