Large diameter ball end mill on a standard Bridgeport mill
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    Default Large diameter ball end mill on a standard Bridgeport mill

    I have to make a .625 radius groove in a block of 6061, about 14 inches long. Having never done this, I was wondering how to approach it. I know that typically you don't run large diameter end mills due to the stress on the machine and the run out and possible chatter you get from a tool holder vs collet. So my question would be, is there a form cutter I could use that I have not been able to find online, that would work and not tear up my mill? I found a Ball end mill in 1-1/4" but was pretty sure that's a bit large for my mill to handle.

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    If you can get one with a 3/4 shank and don't try to cut the radius all at one time (rough it out with a square end mill and take light finish cuts with the ball end mill) , you will be fine in aluminum.

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    I was thinking I might be able to get away with doing it that way, but finding a reduced shank ball end mill in 1.25" diameter has been no joy so far.

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    Is it a full radius grove or just partial from the side? If its a partial you could get a smaller bull nose with the correct corner radius and with a little math take it is several cuts. Even if it is full radius you could still finish the bottom with a small ball endmill and small stepovers to minimize cusp height.

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    If you can access the feature from the edge, you might be able to find a radius-cutter. Using either, most of the material could be removed with regular end mill(s), and then finished with the ballend/radius cutter. It would be best to use a 3/4 collet to keep the tool length reasonable. With aluminum, you could cut it with a shaper/router core/box bit (I'd definitely mill out the waste with endmills in that case).

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    Yes, full radius. I suppose I could go with a 3/4" and sneak up on it. I was hoping to avoid having to do that and cut down on the final finish work.

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    I seem to remember there's a way to use a boring head and tilt the machine head to cut odd radii. I read about it in a thread here.

    Sent from my SM-G973U using Tapatalk

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    Quote Originally Posted by Cole2534 View Post
    I seem to remember there's a way to use a boring head and tilt the machine head to cut odd radii. I read about it in a thread here.

    Sent from my SM-G973U using Tapatalk
    You can use a square end endmill and tilt the head to cut it, but that produces an elliptical feature. Maybe close enough for his/her application.

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    Quote Originally Posted by Kyle Smith View Post
    You can use a square end endmill and tilt the head to cut it, but that produces an elliptical feature. Maybe close enough for your application.
    Maybe that was it, that you could create an ellipse that approximated a circle close enough to meet tolerance?

    Sent from my SM-G973U using Tapatalk

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    Here is the "stepping" method but in the lathe
    Attached Thumbnails Attached Thumbnails dcp_1386.jpg  

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    Do you only need to do this once? You could use a 1-1/4" core box wood router bit w/ 1'2" shank to take a finishing cut if you rough away most of the material. I doubt they are as precisely ground as an endmill, but probably better than the fudges above.

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    Is this cheating?

    I didn't have a big ball end mill, so I cranked up the speed and used a 1-1/2" diameter wood router core box bit:


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    I have done this using a 3/4" ball mill and take several passes so all I had left were very small scallops, just got to do the math. A 1-1/4" ball mill is pretty big for a Bridgeport so retract the quill all the way and lock it well, also a good idea to retract the ram as much as you can to improve the stiffness. These were for follow blocks to bend 1-1/4" aluminum tube so pretty much what your doing but in steel. The 3/4" ball mill will work fine if you make enough passes and for a one-off it would be my pick if I was doing the job, way cheaper, easier to get, and more uses.

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    Quote Originally Posted by dwebster View Post
    but finding a reduced shank ball end mill in 1.25" diameter has been no joy so far.
    Get a HSS end mill and grind down the shank if you have access to an OD grinder or even a surface grinder and a spindex.
    You could even do it in an engine lathe,albeit much slower going though.

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    Did it for years before CNCs and CAM software in the 70's and 80's. You can use any size ball end mill. Just need to due some math. The more steps the finer the finish. I had a programmable calculator that gave me the step overs and depths back then. Today someone with a CAM program can easily generate the steps and print them out for you. PM me if you need some help.

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    Quote Originally Posted by dwebster View Post
    I was thinking I might be able to get away with doing it that way, but finding a reduced shank ball end mill in 1.25" diameter has been no joy so far.
    Shouldn't be hard to find a 3/4" shank ball mill.

    McMaster lists them.

    McMaster-Carr

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    Quote Originally Posted by Frank Ford View Post
    Is this cheating?

    I didn't have a big ball end mill, so I cranked up the speed and used a 1-1/2" diameter wood router core box bit:
    Frank, did you rough it out first with smaller square or balls or just inch your way down.
    I great idea, do these come in 1-1/4?
    Bob

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    You know, I must have skipped right over that one. They are usually the first place I look. Thanks

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    Quote Originally Posted by CarbideBob View Post
    great idea, do these come in 1-1/4?
    Strangely enough, I just ordered one last night for a woodworking project. Amana 45928, about $63 from carbide.com, more like $110 list price. 1/2" shank.

    [Added in edit] Today I discovered that carbideprocessors.com carries 1-1/4" diameter core box router bits from Southeast Tools and Whiteside for about $47 and $50. Again, 1/2" shank as woodworking router bits.

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    If you can't find a reduced shank end mill you can always use an R8 tool holder with a 1 1/4" bore. Several companies sell them including:


    MSC
    https://www.mscdirect.com/product/details/01333723

    Shars
    9400108205496032081585

    McMaster
    McMaster-Carr

    Victor Machinery Exchange
    1-1/4" R8 End Mill Adapter

    I'm sure there are many more.


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