Thin wall aluminum--chatter

[jeff]

I have a square box about 1.2 deep with .050" thick walls.

I've been using 1/2" dia 3 flute "osg blizzard" style endmills but they like to chatter on the finish pass especially when brand new.

These 3 fluters have a 45 degree helix, would a 2 flute with a 30 degree helix be a better choice to eliminate the chatter?

I've played around with amount of stock to leave for finish pass, right now it's at .010"

 

edit: 

it's 6061 T6 aluminum... .can't change material.

[EX-wccprogrammer]

How are you holding the part?  I have made vacuum assist vise jaws in the past that have eliminated chatter on thin-walled parts.  Maybe you can stabilize the walls with something like that?

[jeff]

It's 1-1/2 thick material, holding onto .100" in soft jaws.

It's basically a rectangular part inside and out with a .05 wall. the floor is also .05 thick

[djstedman]

Personally I have had a lot of luck in reducing chatter by going to a 2 flute as you suggested in your post, also it probably wouldn't hurt to go down to .005 for finish.

 

Switching to a 3/8 with enough flute length might help some too since it will create less tool pressure.

 

One thing to keep in mind is you want to make sure that the roughing pass isn't leaving a lot of chatter either, if the existing finish has a lot of chatter in it, it can induce chatter in the finish tool.

 

On particularly problematic chatter in the past I have even gone so far as to use three passes taking off .005 each pass to get to finish to keep from pushing the material and to keep chatter down.

[Tim Johnson]

Rough 0.200" deep then finish pass all the way to the floor. A 30°/35° end mill is a plus.

[jeff]

Rough 0.200" deep then finish pass all the way to the floor. A 30°/35° end mill is a plus.

 

This would make the cycle time too long, we do thousands of these parts a year.

I will tell the boss to get the slower helix endmills to try out, thanks!

[jeff]

Personally I have had a lot of luck in reducing chatter by going to a 2 flute as you suggested in your post, also it probably wouldn't hurt to go down to .005 for finish.

 

Switching to a 3/8 with enough flute length might help some too since it will create less tool pressure.

 

One thing to keep in mind is you want to make sure that the roughing pass isn't leaving a lot of chatter either, if the existing finish has a lot of chatter in it, it can induce chatter in the finish tool.

 

On particularly problematic chatter in the past I have even gone so far as to use three passes taking off .005 each pass to get to finish to keep from pushing the material and to keep chatter down.

This is what I've tried as of today and it seems to be working, but only on endmills that are not brand new. 

New ones are too sharp and chatter like crazy.

[crazy^millman]

Might try using a Slower RPM or a Higher Feed Rate. Those are the 2 things working against you in any chatter prone applications. Sometimes running the part with a slower RPM seems crazy, but making the best quality part possible is also just as important as how fast you make it. I told someone speeding up some bad looking parts not to long along. All you accomplished was making a terd faster.

 

I am all about getting it done fast, but sometimes need to think outside the box. I would go up to a 5 to 6 flute endmill for finishing. The bigger core on the endmill will also help eliminate chatter and make up for the slower rpm if you need to use it. Since it is a finish pass should not have to worry about loading up the endmill with chips.

[Guest]

I've always stagger stepped think wall parts. Depth pass 1, Rough and finish Outside/Inside, Rough and finish Inside/Outside, rinse and repeat. I had better luck with 3 and 5 flutes than 2. How I determine which goes first is what needs the better surface finish.

[Mr. M]

If you can, leave more finish stock (like .2) and ramp down at size making one pass at depth. That seemed to work good for the thin walled box type stuff I used to do.

[elbro]

That is a thin wall for that distance. What about a variable helix cutter?

[Mr. M]

 

New ones are too sharp and chatter like crazy.

Are they uncoated? Coated endmills might help. They are a little duller so it would have a similar effect

[RonC.]

You could try leaving .025 to .05 on wall and ramp cut to finish.. done this many time in the pass.... just my 2 cent worth.. :-)

[The Cathedral]

This is what I've tried as of today and it seems to be working, but only on endmills that are not brand new. 

New ones are too sharp and chatter like crazy.

 

Have you ever tried an endmill from Ultra Tool? They are very nice endmills, and you can get them with a pre-honed edge so they are already "broken in." Look 'em up. 

[jeff]

Thanks everyone for the suggestions, I have changed my operation order a little bit and finishing the outer before I do the inside. 

Seems to be working out better!

[Newbeeee™]

Seco Hemi cutters work well for this - 2flute and slow taper. Old style router looking but they haul.

[dstryr]

You have to 2 op this part anyways right? Redo your process. Do the back side first / profile the outside. Flip it over, hold it 1.150 dp pocket (i.e. walls supported) in soft jaws and then do the inside pocket.

[scooke4073]

This may sound counter-intuitive but put as many flutes into the cut as possible....just leave .001-.002 on the walls and hit it with a 7 fluter.  Odd number of flutes tend to have better harmonics.

 

Variable helix is also a good option.

[jeff]

You have to 2 op this part anyways right? Redo your process. Do the back side first / profile the outside. Flip it over, hold it 1.150 dp pocket (i.e. walls supported) in soft jaws and then do the inside pocket.

 

I can't do it this way, there are feet and a step at the bottom that prevent a good holding, and the aggressive cutting we do would rip the part out of the jaws even if they were 1.15 deep.

This is how we first tried processing the job and it wasn't pretty.  

[dstryr]

I can't do it this way, there are feet and a step at the bottom that prevent a good holding, and the aggressive cutting we do would rip the part out of the jaws even if they were 1.15 deep.

This is how we first tried processing the job and it wasn't pretty.  

Okay so then you are stuck with rough / finish levels.

30-35* helix / 4 flute tool for aluminum will help as well. 

 

If it was me I would just finish the walls as I went down or ramp them with a 3/8 35* helix endmill.

[dstryr]

It's 1-1/2 thick material, holding onto .100" in soft jaws.

It's basically a rectangular part inside and out with a .05 wall. the floor is also .05 thick

 

How does holding it .100 deep in soft jaws work but holding it 1.150 deep not work? Show a picture of the part?

[jeff]

Here is an approximate model of the part

[Tim Johnson]

Face and machine the perimeter of the part minus the "inside" section from the bottom side as a first process. For the second process,flip the part gripping as deep as possible on the two flat sides and pocket out the inside at normal speeds/feeds, then machine the two sides at the reduced speeds/feeds needed for a good finish.

[dstryr]

Here is an approximate model of the part

Machine the part from the back side. Cut the one wall with a keyway cutter. Flip over, relieve the one jaw so you can hold as deep as possible and not have to worry about that step. Piece of cake.