round nose lathe bits?

Finding pre-ground lathe bits may be a problem, but ball-nose end mills are readily available. You may think of several ways to use these on either the lathe or the mill to make your parts. If used on the lathe there would need to be means on the crossslide to spin them as the work turns so they are milling as they were designed to do.

If you would really prefer a form tool in the lathe, you could always grind one appropriately. It ain't how I'd do it, YMMV.

I have made form tools by silverbrazing sliced ball bearings onto a bit. They worked, but a diegrinder on the crossslide with a ball end mill worked a whole lot better for me.

Joel, I'm surprised that you can't find round carbide inserts of the diameters you want. Round inserts of 1/2" and 3/8" are very common with positive and negative rake, with and without center hole for mounting on a tool holder.

Smaller ones are a little bit trickier to find, but available. The current (2007-2008) KBC Tools catalog

There are "dog-bone" inserts with tips of various radii. I don't have a catalog showing them. Go the the on-line catalogs of the various carbide insert manufacturers like Valenite, Carboloy (now Seco), . Google "carbide insert."

The problem is, of course, that you must buy a tool holder to match each size insert, and that can get pretty expensive. Alternatively you can braze the inserts to a steel shank that has been relieved to support the insert at the proper rake.

The other problem using these round inserts as form tools is that, unless you have a very rigid lathe, they will chatter very badly due to the large area in contact with the work, possibly fracturing the insert.

Another possibility is to purchase carbide rods of the various diameters you want and make tool holders to hold them vertically (almost) as form cutters. As they dull or fracture you can have them ground flat on the tip to form a new cutting edge or grond them yourself with diamond wheels.

awright

Joel, Grinding tools with those radiuses are simple and effective, but you said to a depth of the full diameter. I believe you meant radius as the diameter must be shared equally by the wheel and the former to function. As a tip, in order to relieve the stress on the machine, hogging the rough shape with a parting tool and final forming only with the radius tool works well, when only a limited number of wheels are required. Please also note that with the quality benders the former is a milled bar, not a wheel. This design is desirable when bending heavy wall, stainless, hydraulic tubing. The design includes a geared wheel, typically 16:1. Steve

Normally you cut from side of part. If you take a piece of drill rod and mount to tool holder, you could just use the rod to cut the radius. You would have to contact the part at top or bottom for the geometry to work out. I hope I am clear enough.

Wes S

I hope you are going to turn these with a lathe that has at least 5hp and is solid and rigid. Going full depth with a cutter that bit is gonna be chatter city

Gunner

"Deep in her heart, every moslem woman yearns to show us her t*ts" John Griffin

Ayup. Put em on a dividing head and crank it against a ball nosed end mill

Personally..Id have it down on a CNC.

Gunner

"Deep in her heart, every moslem woman yearns to show us her t*ts" John Griffin

I made a large number of these for our bender, Ruff the cavity out with a cut off tool. For the small sizes, a hand ground form tool out of HSS will work fine to finish the cut. Remember bent pipe is about 10% bigger than nominal diameter, the cut out is actually an oval.

For the larger diameters of pipe, I manually CNCed the cut. Make an Excel spreadsheet of how deep the cut off tool should go every 0.050". Move to first Z point; go in, then retract tool. Move over 50 and repeat. Doesn't take very long. File smooth with a rat tail file.

Karl

Adding to the other answers about CNC'ing or regarding chatter (you will have, the length of cut is very long), there is a trick for formtools that reduces the length of cut.

That trick has been used in the pre-CNC-times for mass-production, but you can adopt it for one-offs:

Get a round HSS bit in the desired diameter. Clamp it such, that it is laying horizontal and pointing along the axis of the cross-feed. Adjust height so that you get the right diameter of the groove. Now if you feed it with the cross-slide, it will cut the groove (but you still get the chatter). And now for the trick. If you look from above onto your bit, just cut a bevel. With that bevel, only a small part will be cutting at a time. While feeding inwards, the cutting part will move along the tool. In this case from left to right (looking at the picture).

A picture:

|\ | \ | \ | \ | | | | | |

The center line is along the cross slide axis, the tool passes *over* the work's CL. Diameter of the groove is adjusted by adjusting the height of the tool. Low RPM and lots a oil!

I have that trick out of a book by Joseph V. Woodworth from around 1907. Unfortunately the translation I have doesn't mention the originals title. It should be something like "Making tools for mass-production". That book is **full** of *damned* *clever* tricks. Get it if you can!

Nick

joel wrote in news:joelrf600r- snipped-for-privacy@comcast.dca.giganews.com:

You will find these in insert tool holders by most manufacturers. (Kennametal, Iscar, Sandvik, etc). The problem is that each diameter insert is going to require a different holder. You are looking at 4 different inserts/holders.

I made a 4" ball bearing a few years ago, Easily found 1/8" half-round

As several other responses show, the approach that many home shop metalworkers use is to rough-cut an approximate shape with a cut-off/parting tool, then carefully smooth the radius with finish cuts. Large industrial lathes are capable of plunging into a workpiece to cut those profiles, but not the machines I'm using.

The last radiused roller I made was for 1/2" OD copper tubing. I had a flea market die (maybe 4" diameter), but my attempts to make a radiused straight shoe/former were unsuccessful (delrin between two steel plates). I made the steel roller with a round (not oval) radius, and it formed the tubing nearly perfectly as it passed under the roller (around the die).

The roller was turned on a lathe and finished with a round file, making final size adjustments until the tubing just fit in the combined opening of the die and roller.

The deformation of the tubing was very slight, and the tubing bends were very close to the radius of the die. The roller worked so well that I was able to rebend some bends in the opposite direction, on some practice/scrap tubing.

For searches, you might have more luck searching for form cutting or forming cutting tools.

WB metalworking projects

Button inserts are easily silver soldered to a chunk of flat stock.

Gunner

"Deep in her heart, every moslem woman yearns to show us her t*ts" John Griffin

You may not need wheels of all those diameters (3/4 to 3 1/2). Depends on the accuracy of each bend---- you could make one die with the 3/4" diameter and then use the "follow-along" method to bend. That is: feed in a little bit of stock, bend a little (to a stop) feed more stock, bend a little, (to the same stop), etc. I use this method often with my Hossfeld. You didn't say what materials you are going to bend. Maybe you should take a trip to the auto parts store and see what they have for bending gas lines and brake line tubing.

Pete Stanaitis

joel wrote:

I might too, if I had one or had access to one. I've managed to bravely perservere in my miserable CNC-impoverished existance thus far.

A dozen donuts and a case of Pepsi goes a very long way in some shops towards "brother-in-law" jobs. Just find a small shop.

Gunner

"Deep in her heart, every moslem woman yearns to show us her t*ts" John Griffin

He doesn't have to go to that much trouble. There's an apple farmer that owe's him tons of favors.

Karl