Chuck Problems or just chatter?

[pmurdock]

Been trying to turn a bar of aluminum down from 1.250 to 1.000 so I can use my 5C collet chuck to hold the piece.. I know I know why didn't I buy 1.0" bar to begin with.. hehe

Attached are some pictures of the results I'm getting.. Using kennametal inserts (CNGP) made for aluminum.. flooding with coolant.. 200 SFM, 0.005 in/rev, .005 DOC.. real gentle.. RPM comes out to about 600-700 RPM.

Is this type of cut impossible with the piece extended out as far as it is - I know a tailstock would likely be appropriate but my current tools are too short to use with the tailstock and it will take a week to get some longer tool holders.

So my question is - is this just plain old chatter due to flexing of the part? and is there a way to actually cut this bar as is (either through some combination of in/rev, SFM)?

[pmurdock]

Upon a little more research I happened upon an article mentioning the use of VNMG inserts as opposed the CNGP or CNMG.. Would that make that much of a difference? It's essentially a 35 deg insert or 85 degree insert.

Also - if you look at the end of the bar it looks smooth.. That was when I moved the piece near the mouth of the chuck. It turned it ok, so I'm sure it's a length issue.. At least I think it should cut smoothly albeit with a large taper.

cheers,
Paul

[little bubba]

If you can turn it close to the chuck, why are you cutting it out that far? I'm guessing you are trying to take down most of the length.

Sticking out that far, you are going to have a problem, there is just simply no way around it. A VNMG or Vwhatever won't help. You are using the correct insert, but you need to go with the smallest nose radius possible, keeps tool pressure down.

If I was trying to do that, I would try an .008 radius run .010 or .012 deep and feed maybe .003. This would try to push the material more in the Z towards the chuck and less in the X.

I've actually had 7/16 1018 sticking out 2-1/2 inches so 6X diameter or so actually deflect and spin up on top of the insert, so don't get too aggressive.

[pmurdock]

Here is an image with the tailstock in place.. I simply cannot extend the tool far enough to clear the tailstock and still reach the piece. What does one normally do in a situation like this?

Cheers,
Paul

[little bubba]

I missed that sentence in your original post, sorry, I just saw the huge hangout, and didn't see a tailstock.

The V*** insert is what you need running the tail stock. A 43* has a pretty good reach, getting to 1" diameter shouldn't be a problem. I've ground D series holders on the Z+ side to clear the tailstock also, may or may not work depending on your diameter and tailstock.

On edit if you have multiple tool holders, you can run part of the diameter toward the chuck, and run a seperate tool as if you are running a subspindle(back turning?) from chuck to tail stock, even if you have to flip your rotation. I hope that makes sense, flip a tool so it points to the tailstock, right hander facing up M4, left hander facing down M3.

[UZU-90]

Hi, just curious, what are you going to do in the 5c collet,does 1" surface finish matter? can you choke up on the 1.25 mat. turn 3" down to 1" then pull all the way out, use your tailstock and continue to turn starting at the 3". Or do a flip half and half, or is there something I am missing why you are trying to turn that length all at once just if it is just for grabbing in collet.

[pmurdock]

Originally Posted by UZU-90 Hi, just curious, what are you going to do in the 5c collet,does 1" surface finish matter? can you choke up on the 1.25 mat. turn 3" down to 1" then pull all the way out, use your tailstock and continue to turn starting at the 3". Or do a flip half and half, or is there something I am missing why you are trying to turn that length all at once just if it is just for grabbing in collet.

Well - it was more an exercise in learning to see what will or will not work.. I've given up on trying to extend a 1.125" Aluminum bar 6061 30" with a tailstock. The deflection was just too much. Taking it down to 15" inches worked much much better. I just have to realize there are some limitations.. Haas wants $7100 to add a steady rest. Is there really any job that can't be done without a steady rest without some other workaround?

cheers,
Paul

[UZU-90]

I see, good luck. I do agree with little bubba, the smaller the nose radius, and the 35* insert may be your best bet for chatter. and yes be careful, wouldn't want to make a fan.

Doug

[Oti]

Did you try turning the first 3-4", enough for turret clearance, then sticking the part out all the way and using the tailstock? Or making a center that is longer that will give you the turret clearance needed? I've used both methods before with success.

[pmurdock]

So I actually figured out the clearance issue. The CNC settings had a tailstock restriction zone which left about 1" clearance before it wouldn't let the ways move to avoid a crash into the tailstock. I shortened that clearance to about 1/8" and now the tool can cut as needed. For a CNC a clearance is a clearace right? whether it's 1" or .005".. hehe when it moves that close I can just feel my stomach drop as it' cutting a part.

cheers
Paul