Sphere on lathe

[jorgepease]

I need to cut a .5 ball out of rod and leave a .125 shank. When I draw the cam drawing, I notice that no tool will leave the ball smooth because of the angle. The material will be aluminum or delrin.

I was thinking I could make a second pass with something like a halfround cutter as used by routers to smooth it out completely.

How can I do this, I only have a lathemaster benchtop lathe and it will be cnc'd

[CNCRim]

I don't think it will be a big problem since you have CAM system and you also have CNC, so my suggest to you is a neutral cutoff tool will be a nice application for you.

[jorgepease]

Didn't try that one,

Thanks

[tobyaxis]

Originally Posted by jorgepease I need to cut a .5 ball out of rod and leave a .125 shank. When I draw the cam drawing, I notice that no tool will leave the ball smooth because of the angle. The material will be aluminum or delrin. I was thinking I could make a second pass with something like a halfround cutter as used by routers to smooth it out completely. How can I do this, I only have a lathemaster benchtop lathe and it will be cnc'd

Something like this?

[miljnor]

The downside with a form tool is the chatter will be huge if you use a half round ( or even a quarter round) on an 1/8 inch shank.

[jorgepease]

Yep, that's what it will look like. Actually there will be a sphere on the other end of the shank as well.

The part that is confusing to me is that Bobcad (which I am learning) asks you to define the point of the tool. So If I define the leading edge I can cut the leading edge of the sphere but the tail end is going to be jog'd to compensate for the tool width or radius.

The only way I see it would work would be to cut one half the sphere with one (leading)edge of the tool and then have the program do a finish pass in the other direction using the other edge of the tool.

Is that right?

As far as the chatter, I figured that might be an issue.

[tobyaxis]

Originally Posted by jorgepease Yep, that's what it will look like. Actually there will be a sphere on the other end of the shank as well. The part that is confusing to me is that Bobcad (which I am learning) asks you to define the point of the tool. So If I define the leading edge I can cut the leading edge of the sphere but the tail end is going to be jog'd to compensate for the tool width or radius. The only way I see it would work would be to cut one half the sphere with one (leading)edge of the tool and then have the program do a finish pass in the other direction using the other edge of the tool. Is that right? As far as the chatter, I figured that might be an issue.

This is a good example of a CNC Swiss Screw Machine part. I have bored .05 diameter 2" deep and turned parts like this holding +-.0001. This is cake work for a Swiss. Yes it is BobCAD V21 they have a Forum http://216.117.147.20/bobcadsupport/forums/

There is a way to make this part on a Lathe but it will require a special ground groove tool and holder with a specific method of cutting. If you would like PM me and I'll help you with it.

[Geof]

Originally Posted by jorgepease .....Actually there will be a sphere on the other end of the shank as well......The only way I see it would work would be to cut one half the sphere with one (leading)edge of the tool and then have the program do a finish pass in the other direction using the other edge of the tool....As far as the chatter, I figured that might be an issue.

We make a part that is similar but bigger. With a 1/2" ball and 1/8" stem you may have serious problems with chatter. Also for the ball on the other end you will need a second chucking. I have done a sketch showing the sequence I would use. The tools are Iscar brand with a .008" nose radius, you need a left and right hand because it is not possible to use a single tool for the full sphere. The first three steps in the sequence are from bar stock. To minimize chatter the first ball is finished before the stem is turned.

Doing these in Delrin will be a real challenge because it is so flexible; brass would be my choice but aluminum is probably okay. What accuracy are you aiming for? Because the spheres have to be done using two tools and a second chucking for the second ball it might be tricky getting better than +/-0.0005".

[tobyaxis]

Nice graph Geof. I couldn't get a clear method in posting this type of chart. This is the same and I think the only way to do this on a regular chucking lathe. I wonder if a special solid brass "Emergency" 5C Collet can be machined for the second operation. Didn't get the chance to try that.

I had the luxury of doing parts like this on a Swiss 99% of the time and only did this on a Regular Lathe once in 321SS. What a PITA Mean part, very mean. LOL, lots of polishing too.

BTW: There is a new BCC user site here http://cadcamtrainer.com/forums/index.php

And Sorins Training Videos for BCC here
http://www.cadcamtrainer.com/index.html

[jorgepease]

Geof

Great illustration

Tolerance is not so tight +- .005, I am more concerned with automating most of the steps.

Brass is an option.

[Geof]

Originally Posted by jorgepease Geof Great illustration Tolerance is not so tight +- .005, I am more concerned with automating most of the steps. Brass is an option.

How many are you making? The first three operations and part-off would be done using a collet chuck with a bar feeder. The last operation could be done as I suggest using custom jaws although I would probably make a three piece sleeve to use a collet chuck. However, for doing thousands I would do the last operation in a VMC with a fixture that could hold many parts. Actually it would be two fixtures so one is loading while the other is running.

I am prompted to ask what are these for? They look like something that is pasrt of an articulating holder; each sphere being held in a clamp. I have a camera mount that has two balls on the end of a stem almost identical to these. If this is the case you don't need a full sphere, the end of the sphere opposite the stem can be flat without altering the function. This change would mean you could part them off finished from bar stock.

[jorgepease]

Originally Posted by Geof How many are you making?

Runs would be around 150 pcs. If it gets into the thousands, the job will be contracted out.

The last operation could be done as I suggest using custom jaws although I would probably make a three piece sleeve to use a collet chuck.

Couldn't you just feed the bar a bit further when cutting the other side of the ball closest to the chuck?

I would do the last operation in a VMC with a fixture that could hold many parts. Actually it would be two fixtures so one is loading while the other is running.

I have considered this, it's a good idea.

I am prompted to ask what are these for? They look like something that is pasrt of an articulating holder; each sphere being held in a clamp. I have a camera mount that has two balls on the end of a stem almost identical to these. If this is the case you don't need a full sphere, the end of the sphere opposite the stem can be flat without altering the function. This change would mean you could part them off finished from bar stock.

These are barbells for baby chickens ...

Just kidding. These are friction ball joints for a photo light. At this time we have allot of options available to us including just buying the ball from a ball mfg. and boring holes to press fit stems. That is probably the fastest cheapest way in the long run. Also the ball is not clamped with a knob but by a bushing in back preloaded with belville washers.
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Edited

I am in the middle of converting a manual lathe to CNC. I ditched the compound slide and want to create a custom tool holder. If I can do that, and if I can cut in both directions, then this is what I had in mind, what do you think? I would cut one side of the ball with L then the other side in other direction with R flipped over on other side of piece