round nose lathe bits?

the problem in a nutshell: I need to make several pipe bender dies/wheels with the wheels having a number of diameters ranging from 3/4" up to 3 1/2". The tubing will be
3/16", 1/4", 5/16", and 3/8", so I need to cut grooves with the appropriate round profile in the correct radius for each tubing size. The wheels will be mild steel.
the question: Who makes lathe bits already pre-ground to these sizes? Carbide or HSS shouldn't matter, but they need to be ground to allow the cut to go to full diameter depth at a minimum
apparently, my Google-fu on this sucks because i can't seem to find anything.
thanks, --Joel
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On Sat, 27 Jan 2007 22:52:13 -0800, joel

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.
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On Sun, 28 Jan 2007 01:32:18 -0600, Don Foreman

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 tits" John Griffin
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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. <G>
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On Sun, 28 Jan 2007 12:29:33 -0600, Don Foreman

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 tits" John Griffin
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He doesn't have to go to that much trouble. There's an apple farmer that owe's him tons of favors.
Karl
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Thanks for all the responses! To elaborate a bit and simplify:
1) yes, my lathe can handle it: 13" clausing with 5hp motor. I just finished re-adjusting/leveling everything since i just moved it across the garage, and everything is nice and rigid. no slop. 2) I will be using a parting tool to clear the majority of the materiel, and then use the form tool for the finish. 3) If I had the tool grinding experience (some), a reasonable quality grinder, and a set of radius gauges, I probably would be doing it myself. Unfortunately, while this is a relaxed timeframe to get these done, I'm not sure it's relaxed enough to do that *and* have me learn how to grind the tool myself on my own. 4) I really dig the idea of getting some round inserts and brazing/silversolder it onto a shank. this seems like a quick way of getting a quality form tool.
since i like #4, here's the follow on questions: braze or silversolder? can you do it to TiN coated or is it best for uncoated carbide? for the shank, just use a HSS blank or...?
thanks again, --Joel
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http://www.carbideprocessors.com/Brazing/book/index.htm
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You really should consider doing it this way. You shouldn't have any trouble holding the accuracy you need on a HSS tool blank. The clearance angles really aren't that critical if you're not using the tool for production. If you don't have a radius gauge, all you have to do is take a small piece of steel, and cut the radii you need with the side of a standard end mill.
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I've only been playing with silver soldering carbide to steel for a few days so I might not be your best response.
I took an old TiN coated insert, rubbed the side that I was going to silver solder across my diamond knife sharpening stone to remove the coating, used 56% silver content solder with black flux. It appears that I am getting adequate bonding based on a few tests to destruction. I did this with a mapp gas torch.
To get a good idea of bond, I was bonding side to side of two square carbide inserts so I could clamp one in the vise and break the other using a wrench to act as a lever.
As far as shank, there isn't much difference at all between hard steel and soft steel as far as stiffness.
HTH,
Wes S
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I've got a nice set of radius guages I would like to sell. They are in a tiny leather pouch. Old but barely used. Also have about 50 lbs of HSS and carbide form tools and blanks of various description. Most are 5/16. San Diego Came from the estate of an aerospace tool and cutter grinder
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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 (www.KBCTools.com), page 331, shows an insert type GIE-7-SC-3-R which is a 1/8" diameter half-round tip on an indexable insert.
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
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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

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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
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On Sat, 27 Jan 2007 22:52:13 -0800, joel

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 tits" John Griffin
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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
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Most of the time you do NOT want the pipe to oval out, the bend die should be cut to fit the tube/pipe snugly. Making it oval just makes it a bigger oval, does not help support the far (outside) side.
Karl Townsend wrote:

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It depends on which way it's oval, looks like you assumed its oval the way the tube would tend to flatten which is the incorrect orientation of the oval. Have a look at US patent 4765168 for some info, strangely I was looking at this yesterday.
RoyJ wrote:

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Yes, if you cut the oval so that the long axis is toward the center of the bend, you will move the neutral axis toward the center, makes the outside flatten a bit less. I'm more familiar with full tooling draw bend dies where you are attempting to maintain full cross section through the bend area. My shop guys used to do thin and thick wall bends where the center line radius was equal to the tube diameter. Wall thickness on the inside was about 30% thicker, outside 30% thinner than when you started. Takes some good dies, wiper, mandrels, and pressure die assist to do that kind of work. Not to mention an artisan for an operator.
David Billington wrote:

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joel wrote:

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
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