Creating radius with ball end mill

[seal killer]

All--

From 3/8" x 3/4" x 1 1/2" bronze stock, I need to create a 5/16" diameter piece about a half inch long with a shoulder on one end. Below the shoulder the piece is rectangular. (The remainder of the 1 1/2" length is for work holding.) Between the diameter and the rectangular part I want a radius. My idea is to mount the workpiece (vertically, so it is 1 1/2" tall) on one of my little rotary tables on the mill and use a 1/8" ball end mill to create the radius. But, I do not know the procedure to rough it down from that 3/4" dimension to something close to the 5/16" diameter.

I have only used a ball end mill once, so I have no real experience with them.

(As I type, I wonder if I am answering my own question.)

Should I rough it down to around 3/8" square with a larger end mill and then finish it with the 1/8" ball end mill, which would result in creating both the diameter (as I rotate the table) and the radius?

Alternatively, I could mount it in the four-jaw and turn it with a bit with the appropriate radius, but using such a bit puts me on even less familiar ground.

--Bill
ps I plan to clamp the workpiece in a little precision tool maker's vise which is aligned with the rotary table which is aligned with the mill's spindle. I have quite a bit of experience using a rotary table in such fashion.

[Mr Ron]

I would turn it on the lathe holding the piece in a 4-jaw. The tool bit would be a round nose with a 1/16" radius. Feed from right to left; then back out to face the square portion.

[GlennW]

I grind the end of the tool to about 85° and then grind the radius using a radius gauge. You'll need relief ground on the end, around the radius, and a little ways back on the leading edge depending on the depth you need to cut.

I skew the tool a couple of degrees in the holder (my tool post always remain square to the spindle) so there is a couple of degrees of clearance on either side of the radius so when you cut toward the chuck the flat on the end of the tool will not drag and only the radius will cut. It will be the same for facing.

This is just a quick, basic, nothing fancy, tool just to do a similar job to yours.

[seal killer]

Mr. Ron and Glenn--

Mr. Ron and Glenn, thank you for the recommendations. Glenn, thanks a LOT for the picture . . . I can do that.

I will make the rectangular (3/4" x 3/8") workpiece 3/8" square on the mill and then turn it down to the proper diameter on the lathe with the four jaw using a tool like the one Glenn shows.

--Bill

[seal killer]

Glenn and Ron--

I did it like you said and it worked fine. I did the whole thing in the lathe. I roughed it with a HHS insert tool and then ground a bit like you described, Glenn. (I used a 1/4" x 1/4" piece of Vasco Supreme.) But, I did not angle it in my tool holder. I angled the tool holder a few degrees. What is the advantage of your method?

Here is a quick iPhone picture of the results . . .

--Bill

[Harold_V]

What is the advantage of your method?

I can't speak for Glenn, but I sure can for myself.
The last job I held, I met the finest lathe man I ever knew, and he insisted on two thing with which I do not agree. One of them was that he kept his compound rest set exactly at 30°, and the other was that he kept his tool post (KDK) set square with the spindle. I learned that when I changed both, and was well dressed down for "altering" his machine, which I ran one night (opposite shift).

His theory was that he could place his tools in the holders without concern for orientation, as he relied on the holder to orient his tools. That's not a bad idea, but now you have to ensure that all of your tools are ground accordingly, otherwise the purpose is defeated. That overly complicates the grinding of tools, especially when they are ground freehand, as they are expected to be.

I strongly object to setting a compound @ 30°, as there is nothing to guarantee that the markings are exact. That leads to the possibility of creating a stepped trailing flank on 60° threads. In fact, because I prefer to never have that experience, which is quite likely on low quality machines, I set my compound @ 29°. It makes no difference in how a threading operation performs, and ensures that the trailing flank has no steps.

Harold

[GlennW]

But, I did not angle it in my tool holder. I angled the tool holder a few degrees. What is the advantage of your method?

Not having to reset the tool post for the next operation, such as parting off what you just made. I prefer to leave the tool post square to the spindle axis and let the tooling do the work. It's much quicker that way.

Mine has been square for about seven years now without any issues.

I view rotating the tool post about like I do tilting the head on a mill. If you really don't have to, why do it?

[warmstrong1955]

Mmmm....I'm not the expert like Glenn & Harold....but I do, I think I do, as both of 'em say....

As far as compound angle....I don't much care, unless I'm making a taper or lead in where I need a particular angle. I care about the tool angle to the work. Most cases, the tool holder is square to the work, and I adjust the tool(s) accordingly. Easier that way, especially with multiple op's.
For machining a 'step', like the attached pics, I like a degree or two of angle like Glenn said, so the edge of the tool isn't dragging on the face as you advance. I found things can come out 'warped' doing that....

About all my rad cutters, are HSS & hand ground. The pics are of some prism mounting shafts I made (surveying equipment)
Test run was just that...notso pretty....but to make sure I had the dims right, and to check the fit with the mating mount assy. Leftover piece of hot roll...or cold roll....or who knows......
The real ones are 1045, shown before a bit of polishing. I also made some with 304L.

The rad cutters I use for hydraulic cylinder rods and other goodies, are about the same, and I mount them in the tool holder at a touch of an angle, and make my finish cuts with 'em.

I scrounged around lookin' for pics of some cylinder rods I have done....but came up empty. Hope the attached pics give you an idea how I do things.....right or maybe wrong. I'm sure if I'f missing something, Glenn or Harold will let me know!

Bill

[GlennW]

Well, first, I neglected to mention that the part and the tool look great, Bill. (Real Bill)

Second, I do rotate the tool post for one recurring job, which is parting off conical washers using the compound for infeed. In that case, the tool post is set square to the compound travel and the compound rotated to the required angle. Requires a funky lookin' parting tool to get the required relief to make it work.

Good lookin' stuff there as well, Bill. (Other Bill)

[seal killer]

Harold and Glenn and Bill--

I understand. I am not "there" yet with my hand ground tools. They all work well, but the next one I grind may not look exactly like the last one. I will experiment with leaving the compound at 0* when using my HSS insert tools.

Bill, thanks for the pictures. I am always impressed by your great work.

--Bill

[Harold_V]

Bill,
The issue with the compound isn't related to the alignment of the tool post. I threw it in just for conversation's sake. It plays no role in how you mount your tools, only how you feed a threading tool. That was my point. Hope I didn't lend confusion to your world.

Most folks keep the compound set @ 5:00 (for me, 61°, which is really 29° off the cross slide), so it's out of the way, yet ready if threading is called upon. The only thing I do beyond that is keep it locked (by tightening the gib). I want my compound to stay exactly where it is, so my dial readings on the cross slide and carriage are reliable. I back off the gib only when I use the compound. The added benefit is a more rigid (carriage) assembly.

Glenn's comment about keeping the post square with the spindle is quite valid. If I used that type of tool holder, it would be my choice as well, as parting is generally one of the operations in a setup, and with rare exception (he described one), the post should be square, so the tool is at the proper attitude. That wasn't an issue for me, as I used a totally different approach to my lathe setups. For one, I hand ground all of my parting tools, so I was not at the mercy of having to have the tool block (which I use, not a quick change) set at a specific attitude. I do final alignment by how the tool is held in the block. I do not rely on features of the block to orient my tools.

Harold

[seal killer]

Harold--

I was confused. Thank you for seeing that and for the clarification.

--Bill