Chatter issues

[Jimmy Galto at SAR Engines]

I am machining an impeller in 6061 and cannot stop the tools from chattering. I have to hang out my tools 2.25 inches. The two tools in questions are a .250 ball and .375 ball. I have tried reducing and increasing spindle RPM and feed rate with no luck. My depth of cuts are .030 for the .375 cutter and .010 for the .250 cutter.

 

Any suggestions would be appreciated. Thanks.

[jeff]

Can you use an endmill with a larger shank?

Or do you need 2.25" of flute length?

[chris m]

I am assuming we're talking carbide, right? If not, then that would be the obvious first step.

 

How are the tools held [collet chuck, Weldon shank, etc]?

 

Are you sure that it is the tool that is vibrating and not the part? BIG difference in fixes, obviously.

[MLS]

+1 on Carbide. Also, I use the shortest flute length possible and go with solid shank for the stickout. Avoid 4 flute cutters totally in my experience.

[robk]

Sometimes carbide may be too "rigid". Might want to try HSS with AlTin coating. This may absorb some of the vibration. Make sure your speeds and feeds are good, and make sure you go "under" the chatter to get rid of it... In the past I have also wrapped up some rubber bands around my cutters to absorb some chatter

[Trevor Bailey]

What is the distance between blades? Have you maxed the "chucking" on the tool itself. you may want to try different control methods to be able to get a shorter length tool in between the blades. Is the chatter on finishing only or roughing and finishing?

[Zoober]

When doing impellers etc. We always try to use tapered ball endmills. You get much more rigidity.

 

+1 on rubber bands. And stuff Nerf footballs between the blades. Not too tightly tho, as you don't want to distort.

[Jimmy Galto at SAR Engines]

I'm am using carbide mills. They have .375 and .500 flute lengths with the rest being solid shank. The portion of the shank sticking out is reduced by .020 for clearance and does not rub the part while machining. The tools are chucked in standard end mill holders, obviously not ideal since clamping is from one side with a set screw.

 

Is there any reduction or increase in speed, feed or depth of cut you guys would recoommend? I will try the rubber bands, that is on thing I've never tried.

[Rick Henrickson 65]

with that light of cut it may be hard to load the tool enough to remove all the chatter.

Side lock endmill holders are not the ticket

What RPM do you have available and do you have any other holders available?

[Trevor Bailey]

Jimmy you have mail.

[Jimmy Galto at SAR Engines]

I have up to 12000 RPM. I can take deeper cuts if necessary for the roughing paths with the .375 tool but I'd like to keep a smaller step for the finish paths.

[TonyNanni@BNB]

are you producing the blades with a swarf cut using the side of the cutter or are you surface machining stepping down using the ball of the cutter?

[PeterM]

Another vibration dampening material that I have used is modeling clay, works pretty darn good too.

[Jimmy Galto at SAR Engines]

I am stepping down the blades to cut them. I have tried the rubber bands. That helped a little. I just received a collet style tool holder that I'll try to see if maybe it's how I'm holding the tool.

 

Thank for all the help so far.

[TonyNanni@BNB]

if you are stepping down can you change the angle to reduce the length of extension and try this cutter. I have had good luck with it. http://www.garrtool.com/viewitempublic.jsp?edp=14260

[TonyNanni@BNB]

if the blades are real thin try a smaller dia cutter maybe 4mm. Reduce the stepdown to aprox .006-.008 and go faster feed to make up the time. The shank is tappered so it is a strong tool. once the blades start to singing it is hard to shut them up.

[Chris Rizzo]

how many flutes is your cutter? I've found 3 fluters in aluminum to be the most chatter resistant.

[Jimmy Galto at SAR Engines]

Tony, I'll check out that tool.

 

The cutter I'm using is 3 flute.

 

Thanks

[Colin Gilchrist]

Jimmy,

 

Contact Sandvik and ask them about their vibration dampening holders. They are kind of expensive, but work like magic for jobs like this. They have a liquid/mechanical dampening system built into the holder itself. The other thing you might consider is vibration Tap testing (also called hammer testing) to find the ideal RPM/DOC range for your setup.

 

Try this...