Ball end mills

[Mr Ron]

Good morning and merry Christmas. I just got a bunch of ball end carbide end mills brand new for free plus a bunch of other end mills including an index-able end mill. I have never used ball end end mills before. Obviously they can cut a cove with a radius the same as the bit, but other than that, what else can a ball end end mill be used for?

[pete]

With cnc you can do multiple axis blending by taking incremental cuts. A guy by the name of G. Britnell on the hobbyist engine building forums has done a whole lot of extremely complex manual machining using them and the more normal end mills to build working scale model V8 engine blocks and heads from bar stock to duplicate what the factory did with castings. Just be aware that at the tip of the ball radius your tool rpm drops off to zero. For the larger ball mills that probably doesn't matter, for the tiny ones it can contribute to tool breakage. One trick around that issue is tilting the milling head. Like anything else it depends on what your normally doing for how useful they are.

[Mr Ron]

I suspect a ball end mill could be used to make a first cut to be finished by a square end mill in a slotting operation.

[pete]

Yes but given the much higher cost for those ball mills if you were buying them it's a more expensive material removal method. In a home shop that may not be all that important, but it's still something to be aware of. As another use, Rich Carlstedt mentioned to me that they found using a ball mill to spot holes before drilling in the commercial die shops he's worked at gave the most accurate location out of any other method. And carbide ball mills because of there much higher rigidity would give the best results. The mills overall accuracy that your using, dro or not having one, part requirement for it's accuracy plus what your holding those ball mills and drills with would have a direct effect on how worthwhile that method would be in a home shop.

[Harold_V]

Ball end mills have one negative, that being that the center, for all practical purposes, has 0 surface speed, yet it is very much a part of the cut. That's not to say that they don't perform as intended, but they do best when operated at elevated spindle speeds. For that reason, you are far better served to use the desired size end mill, but leave stock in the corners where the needed radii would be generated. I would avoid using a ball end mill for roughing for that reason, to say nothing of dulling more expensive cutters unnecessarily (ball end mills).

H

[Mr Ron]

I am able to get ball end mills for free because they are considered expendable. When they get dull, they get tossed, even the $300 index-able 3 flute carbide. I tried the 3 flute index-able and it cut like butter. Now I need a Bridgeport to replace my puny 6x26 knee mill.

[Harold_V]

Now I need a Bridgeport to replace my puny 6x26 knee mill.

Set your sights a little higher than a Bridgeport. They hardly deserve their cult-like following if machine rigidity is a concern. A Gorton I-22 puts them to shame, although the Gorton is not available with a nodding head.

H (who owns a Bridgeport)

[RSG]

Just be aware that at the tip of the ball radius your tool rpm drops off to zero.

I use them often when shaping fishing reels. They can be a wonderful addition to the manual mill however as Pete and Harold mentions the cutter has zero RPM at the center. This may not sound like a big deal but to illustrate the importance of this I can say from experience that should you be machining aluminum and want to have the part anodized, the center point of the surface where the flutes meet can pose a real problem due to work hardening, and if you machine a blind pocket with a ball nose you will for sure be in for disappointment.

[pete]

Afaik ball mills are generally considered as mostly a finishing tool and not what you'd use for hogging material RSG so your points make a lot of sense.

I own a Taiwanese clone of a step pulley BP and the design and layout is ok. I bought the model I did because of the built in power spindle feeds. I'd also agree with Harold about there rigidity. At best a real BP is still only considered as a light duty tool room mill. Yeah there well proven and I think over 1/2 a million have been produced by now. But on the new or used market there's definitely cheaper, heavier built and better machines according to a lot of pros. The Bridgeport series II are supposed to be a lot bigger and heavier built than the series I, but I've never had one in front of me yet. If I had the room and a concrete shop floor? Something like the big Cincinnati the last mine I worked at had would be high on my list. 50 taper on both the horizontal and vertical spindles, about a 100" x 14" universal table, built in power feeds and rapids on all axes. Probably 8k-10k in weight I'd guess. Yeah big, heavy, and a bit hard to move, especially so for a home shop unless you know how. But I'd want one for the built in rigidity all that mass gives you.

K & T were another heavy duty mill as well as those Gortons Harold mentioned.Or I'd certainly look at the rigid and much more versatile Swiss and German Euro mills like the Deckels or Acerias, but there's quite a few others. Compared to those or the heavy and big U.S. made verticals a BP is a wet noodle for rigidity. I will admit that if there was ever any specialized heads or accessories made they were also available to fit a Bridgeport or any of the clones with an R8 taper and the 3 3/8ths spindle diameter. And R8 tooling is dirt cheap compared to 40,50 taper or the Deckel collets.

[Mr Ron]

I couldn't afford a Gorton or K&T much less a Bridgeport. Since my hobby is building model trains, my 6x26 mill is all I need for the present. If I were in the market for a new mill, I would be looking at something along the lines of Jet, Bridgeport, Kondia or anything with R8 tooling as I realize how expensive the CAT tooling can be, but I can dream.

[Harold_V]

There's a distinction between the mills at one's disposal. It's simple. Heavy duty vertical mills don't have the drop spindle design that has made the BP type machines so desirable. Said another way, drilling holes with the other type of vertical isn't convenient, although it certainly can be done.
For heavy milling, it's hard to beat a K&T. B&S and Cincinnati had both built equivalent mills, and all have served well. But they don't have the drop spindle, although the Cincinnati Toolmaster does have. It's far more rigid than a BP, but still lacks in rigidity if compared to the heavy duty vertical machines, all of which lack the drop spindle.

BP achieved success because of low cost, and machine flexibility (I don't mean lack of rigidity). There was a time when a new BP was available for under $1,000.

H

[RSG]

There was a time when a new BP was available for under $1,000.

H

Ya, a guy named Fred Flintstone would have owned one at that time? LOL