Turning Question

[jbolt]

I have a question for those of you who do or have done machine work as a career.

I'm working on a prototype part for a friend. It is an aluminum wheel 7" dia x 4" wide. All cross sections are .2" including the hub and central web. After squaring up the ends and rough turning the OD I bored the hub for the axle. The wheel will be spun up to 6k rpm so the final turning is being done on a precision ground mandrel so everything is as concentric as possible. The majority of the pocket material was removed on a CNC mill to within .05" for final turning on the lathe.

The trickiest part has been the internal fillets which are .25 radius. All I had on hand was some HSS tool blanks so I ground a form tool from a 1/2" square tool blank. With a 2" stick out I am getting a lot of chatter unless I plunge hard but that is difficult to control. Additionally when the tool bites into the material it pulls away from the backlash in the carriage even with some drag on the carriage lock.

My question are:

What tool would you use for the fillets?

Tips for controlling tool bite?

If all turning was done on a manual lathe, what tool would you use for roughing out the pockets?

Photo of the part with one side and final OD completed. The fillets are acceptable for a prototype for testing but not for a finished product. (FYI the red tape is helping contain 4 lbs of plumbers putty packed into the opposite cavity to dampen the harmonics otherwise the part was un-turntable.)

 

[T Bredehoft]

If you could CNC the radius you would have what you need with a single point tool. This doesn't answer your question, but the logic of it willhelp. You need to profile a .25 radius with a tool point of .03 or so. Otherwise you'll get chatter.

 

[bakrch]

You have a CNC mill available?

Mount the part in the CNC mill spindle, boring bar in the vise .... presto you have a CNC lathe. Just edit a lathe post-processor to spit out radial X values (or simply program it by hand).

Set Y0 to tool centerline. Z0 is controlled via G43 tool height offset.

 

[jbolt]

If you could CNC the radius you would have what you need with a single point tool. This doesn't answer your question, but the logic of it willhelp. You need to profile a .25 radius with a tool point of .03 or so. Otherwise you'll get chatter.

I get where you are going. I'd bet I could get away with a larger tool point. Have to think about it.

 

[jbolt]

You have a CNC mill available?

Mount the part in the CNC mill spindle, boring bar in the vise .... presto you have a CNC lathe. Just edit a lathe post-processor to spit out radial X values (or simply program it by hand).

Set Y0 to tool centerline. Z0 is controlled via G43 tool height offset.

Interesting idea but the setup would not be rigid enough.

 

[bakrch]

Interesting idea but the setup would not be rigid enough.

Then I think you might be stuck forming it little by little.

You can also rig up a makeshift tracer, but I would not attempt it on a lathe that didn't have some sort of feed stop.

 

[Cadillac]

I just got done with something similar all on the lathe. 5.5 OD 2.5 thick material pocket is 2” deep center hole .625 center section is 1”. All material was taken out with a .375 boring bar at some length I forgot how long but I used .250 hss blanks and supported the stick out from below the bar. Maybe try raising the cutter at touch to do the outer radius to avoid the dig in.