ball nose reamers

It's probably not necessary for me to tell you that machine reamers are not intended to cut to the center. In order to grind one that does, you'll have to eliminate all the flutes in the radius area except for two or three, to create the needed clearance. Staggering them by grinding three instead of two could help prevent chatter if it's a problem.

If you have a cutter grinder available, you should be able to make the cutter, but it could be a tough job, though certainly possible, freehand. I think you can see what you must do to the reamer by studying a ball end mill. In principle, they would cut the same way. You'd be leaps ahead if you don't need it to cut to the center, though.

Good luck~

Harold

Thanks Harold,

I am quite intimidated by this project, but since I will be drilling a pilot hole of .125 which will leave basically no material in the center to cut with the reamer... then reaming to .160 (for example) the reamer will only have to cut a bit on the nose, and not on the very tip, just on the corner radius of the nose. Did that make sense?

Ryan

Unless you have a grinding machine or jig specifically for this type of toolmaking, you will be hard pressed to do this with any degree of precision. You will have to grind a perfect radius on the end of the reamer and then custom grind two or three flutes from the periphery to the center. On a large reamer, that would be quite a challenge without the specialized equipment. On the small reamers you need for your application, I think it will be outside the realm of practicality.

I would suggest either buying the specialized reamers you need, or contacting a shop that has the equipment to custom grind these for you. But before doing that, have you considered lapping the holes? You could ream the holes with a standard reamer to just above where the end radius starts. Then use a piece of correctly-sized rod--with a hemispherical profile turned on the end--and some lapping compound to finish your holes to size.

I'd be drilling a larger hole than what you are. Reamers can be done with a taper on the nose area if so desired and the reamer goes all the way through the material however, such shouldn't be done for that much material as a reamer is intended for doing a final trim of the hole size rather than doing massive cutting of the work. You're trying to take .035" of material which is pretty thick for a reamer on one shot.

-- Bob May Losing weight is easy! If you ever want to lose weight, eat and drink less. Works evevery time it is tried!

Yep, it did. You might be able to simply enlarge the chamfer on the reamer a little, changing it from the 45° angle it should be, to the radius you desire, without going to the center. If you choose that direction, keep in mind chip clearance. As you get closer and closer to the center of the reamer, you'll lose any room for chips, which is one of the reasons for altering the number of flutes. As you remove a few of them it will provide the necessary space for chips. Keep the clearance angle in mind as you do, too. Be very careful to not round off the cutting edge. That is a sure recipe for a cutter that doesn't cut size. It's also important that each of the flutes cut equally, otherwise the reamer will tend to wing on one tooth and cut an oversized hole. .

I think you can make this work, but you may spend a little time working it out. Well spent if you have enough holes, that's for sure.

One other thing to consider, you may desire to ream a lot less material, which will help. Reaming much more than about .008" per side can present some serious problems, and also increases your chance of an oversized or poorly finished hole, mostly due to chip loading. If you can drill closer, perhaps only ten thou under, try that to see how it goes. Drill such that the point of your drill stops shallow enough that the drill point leaves material for the reamer to cut the desired radius.

Good luck~

Harold

Find a *good* tool & cutter sharpening shop and have them done. Perhaps try a couple or three and have each do a sample to find the best at the job.

Do you really need a reamed hole? You can have special ball ends done which will not have the clearence problems of a reamer. Ream to just shy of the bottom profile and follow with a ball mill with relived flutes above the end and you won't get side cutting chatter if it's a finish you want.

michael