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Ewood42

Best free cutting endmill for unstable aluminum parts

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Have a part in a picture frame orientation that gets pretty thin out away from the frame cross sections between .11 and .06". 7050 AL. Need something free cutting that I can use to finish the last .03" to down to size, 63 finish. Not super tight on thickness, +/-.01", but having issues with chatter. Any suggestions?

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What I have done in the past is to leave more material, .100 or so on the floor post finish. If you start machining in the center of the pocket ramping to finished depth. Now start spiraling out with a radial engagement of 25% or less. The added material on the pocket floor will support the thin wall as you machine it. No skim cuts allowed, that would defeat the purpose. I hope this helps.

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I have also done this with Titanium. Use the extra stock to keep the rigidity adjacent to the cut for as long as possible.

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If you are having issues with chatter due to vibration you may be better off using a smaller tool and/or reducing your rpm.

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Can you look at a left hand endmill to force the part down and do it that way?

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I  second the thin wall approach. Leave the wall thick, finish with Stepdowns

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13 hours ago, 5th Axis CGI said:

Can you look at a left hand endmill to force the part down and do it that way?

The thinnest surfaces are not restrained in any way aside from being attached to the frame I'm leaving in the stock. I'm looking for something low helix, high positive rake, little/no corner radius. 

 

I'm thinking I might end up having to make a finish fixture, I'll see how that rev worked out tomorrow. Job is still in testing phase so I have a little time to screw with it still before we have to run them in production.

 

Cutting from top to bottom  in sections leaving .01" to finish and facing all the flats with a square endmill instead of the bull I was using (has radius in all corners). I think that alone will help immensely. I already had RPMs somewhat low, I think around 450 sfpm.

 

Did I mention It also has an obnoxious multi-axial curving flange hanging off the top supported by the very thin walled section?? That part actually came out fine on my first test part. Was just the chatter marred finish on all the thin stuff that failed. I may end up having to hand draw a bunch of wire to face it in the exact order I want it done, but that'll be an enormous pain in the butt since there's steps all over and I'll have to be constantly switching depths to work top-down.

 

 

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Single lip Onsrud?

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1 hour ago, Ewood42 said:

The thinnest surfaces are not restrained in any way aside from being attached to the frame I'm leaving in the stock. I'm looking for something low helix, high positive rake, little/no corner radius. 

 

I'm thinking I might end up having to make a finish fixture, I'll see how that rev worked out tomorrow. Job is still in testing phase so I have a little time to screw with it still before we have to run them in production.

 

Cutting from top to bottom  in sections leaving .01" to finish and facing all the flats with a square endmill instead of the bull I was using (has radius in all corners). I think that alone will help immensely. I already had RPMs somewhat low, I think around 450 sfpm.

 

Did I mention It also has an obnoxious multi-axial curving flange hanging off the top supported by the very thin walled section?? That part actually came out fine on my first test part. Was just the chatter marred finish on all the thin stuff that failed. I may end up having to hand draw a bunch of wire to face it in the exact order I want it done, but that'll be an enormous pain in the butt since there's steps all over and I'll have to be constantly switching depths to work top-down.

 

 

I would seriously look at the finish support fixture then and think about downward force. I learned about these types of tools years ago where the company I was working at was cutting plastic membranes down .003 think. The had a pie section support fixture for the underside and then machined the other side with the left hand tools forcing the material down and were able to machine them all day with no issue. I have used them on thin walled parts over the years and been very surprised how much I had to not fight things using them. Key is the supporting fixture. One or two off parts not worth it, but you start looking at 5-100 parts and then they start to make sense. 

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On 1/14/2020 at 6:00 PM, content creator said:

If you are having issues with chatter due to vibration you may be better off using a smaller tool and/or reducing your rpm.

Try this. I cut something the other day that had a .03 thickness and I used a 1/4" square endmill and lowered the SFM down a lot. Low as in 100-150 SFM. 

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On 1/15/2020 at 3:20 PM, civiceg said:

YG/1 Alu power is my go to.

Excellent choice.

But for thin wall and floors, the Seco Hemi is the best I've found because it has a nice sharp hook, but low helix, so it doesn't drag the material into the cutter

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Ended up going with a MB266 from Walter. Worked well. Actually took a .01" finish pass on that .06" floor and came out perfect. 

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