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Large diameter ball end mill on a standard Bridgeport mill

dwebster

Aluminum
Joined
May 15, 2019
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.
 
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.
 
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.
 
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.
 
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.
 
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.

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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.

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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.
 
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?

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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.
 
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:

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