Ball end mill in steel?

[Black Forest]

I need to make half round groves in steel with a 6mm round end mill. So the final depth will be 3mm I suppose. The grove will be in a 30mm round shaft. My question is, do I do it in one pass or multiple passes? I have never used a ball end mill before. It is a carbide mill. The grove will be used for indexing on the shaft. A spring loaded ball thingy will be mounted in a block of steel. The ultimate use will be for a table on a belt grinder. Do I use the same speeds and feeds as a normal carbide endmill?

[dian]

you might want to tilt the endmill, so you get around the zero cutting speed in the center. otherwise as fast as possible. one pass imo.

[Alan Smith]

Yes, agree with Dian. Tilt the mill head.

[GadgetBuilder]

What size ball will you use? If the ball is 6mm then it may be difficult to rotate the shaft, if this is what you intend.
A "V" groove with perhaps 2mm width would provide indexing but would need a locking mechanism on the shaft.
Or perhaps I don't understand what you have in mind....

[BCRider]

I've used ball end mills a half dozen times now for making finger grooves in items where the center speed issue was present. The others are right about the center and while it did cut it leaves a gnarly looking center line. It took a fair bit of emery work on a round form to clean the groove up. So I'd either tilt the head as suggested or if you'd rather spend your time sanding instead of tramming then leave it and clean up the center after.

To be honest I didn't think about tilting the head even just a few degrees and trail the cutter. Have to keep that in mind for next time. It would certainly be easier than emery sanding on a blind ended finger groove or in your case where it'll be quite narrow. And of course this assumes you care about the grooves appearance in addition to the size.

Mind you my finger grooves had me using bigger size ball end mills and only cutting a portion of the radius. That being said the gnarly line down the middle is related to overall diameter too. On your 6mm groove and being that deep you likely won't be able to see the line enough to matter. Or if only size is important and appearance is a non issue then I'd just do it in two passes related more to a true to size width of the final slot with clean edges.

[strokersix]

While either will work, I think a vee slot would probably work better than a round slot if you intend to engage it will a ball.

Could get into a discussion about cam shapes, motion, forces but I'll try to boil it down with example:

If the round shape slot is a little bigger than the ball it won't have any centering force when in position. If the round slot is a little smaller than the ball it will just touch the edges and then the slot shape becomes irrelevant. A vee slot will hold centering force right on position as the ball is touching both sloped walls.

[DR]

If the job justifies the cost, you're much better off using a cutter like a key seat cutter with a radius ground on the cutting tips. Then you approach the work from the side. No dead zone of the cutter as with the tip of a ball end mill.

In a pinch I've been known to even hand grind a radius on a single tip cutter to accomplish the round shape slot.

[Black Forest]

The V grove does sound like a better solution. I need to measure the only V grove end mill I have. I think it is too big and I just bought 3 solid carbide round end mills!

[Fasturn]

Ball mills are like threading tools. First or 2 pass can be pretty deep, but the finish cut is light or just a spring pass. Also depends on how ridged your machine is ? Turning the head is a interesting idea, but then you have to tram it back in. I am too lazy to do all that.

[old mart]

Try one pass if you have more than one cutter, I would tend to chicken out and go for three passes, 5/8, 7/8 and finish. Or rough out with a more conventional shape.

[tom_d]

If the job justifies the cost, you're much better off using a cutter like a key seat cutter with a radius ground on the cutting tips. Then you approach the work from the side. No dead zone of the cutter as with the tip of a ball end mill.

In a pinch I've been known to even hand grind a radius on a single tip cutter to accomplish the round shape slot.

This. If the setup allows. A piece of HSS mounted in a fly cutter and away you go. Otherwise, ball end mill tilted if the setup allows. If the spindle must remain perpindicular to the work, then run the spindle at max rpm, around 5000 if possible. I would do it in two or three passes.

[Rich Carlstedt]

I need to make half round groves in steel with a 6mm round end mill. So the final depth will be 3mm I suppose. The grove will be in a 30mm round shaft. My question is, do I do it in one pass or multiple passes? I have never used a ball end mill before. It is a carbide mill. The grove will be used for indexing on the shaft. A spring loaded ball thingy will be mounted in a block of steel. The ultimate use will be for a table on a belt grinder. Do I use the same speeds and feeds as a normal carbide endmill?

We did most of our mill work in the die shop with Ball Endmills.
You should have no problem doing your task with one pass. If it is a 4 flute, then I suggest air or coolant to clear chips. A 2 flute works pretty good
Your 3 mm depth means the cutter will not be at full depth as you are only 10% of shaft Diameter and the shafts radius will not have a 6mm groove width .
You shouldn't have a issue with the center mark from the ball mill, but if it is obnoxious, use a 6mm cartridge roll for polishing
Suggest a OSG ballmill if you want quality
Rich

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[GadgetBuilder]

The V grove does sound like a better solution. I need to measure the only V grove end mill I have. I think it is too big and I just bought 3 solid carbide round end mills!

Could you use a common end mill and offset from the center of the shaft so you contact near the 45 degree point?
A little trig (or CAD) should allow you to find the offset you need to get the desired width of "V".

Another option would be to scribe a line centered where the ball will contact the shaft. Then use a spotting drill to make divots on this line at the desired angular positions; the ball will index at these positions. Again, you may need a shaft lock if there is any appreciable torque on the shaft.

[Illinoyance]

If you want to be able to rotate the shaft past the detent position the groove is too deep. If the shaft will be permanently held by the detent your 3mm depth is fine.

[john b]

Jeez, it's an endmill that was designed to do what you want it to do. Cut your groove.