round nose lathe bits?

joel · 2007-01-28T06:52:13+00:00

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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Robin S. 19 years ago

I sell tools on a part time basis and I'm frequently amazed that people actually ask for pre-ground form tools for these types of applications.

You should buy a set of radius gauges and a couple of HSS blanks. By grinding your own tools, you'll be much further ahead because of the experience you've gained, and you can just plunge the toolbit right into the material in one shot, instead of filing to finish your rads. Of course, the filing method will work, but the rads are so small that a form tool is nice. (You'll need the rad gauges one way or the other).

Additionally, once you have those toolbits ground, you can now use them other times when you need to put a rad on a turned part (frequently to get rid of sharp corners which are stress-risers). Also, your rollers are mild steel so you may need to replace them in time.

At the beginning, form tools are not trivial to grind. Like all skills in this trade, as you practice you'll get better and the work will be done faster.

As others have said, watch for chatter. If you get chatter (and you

*will*) _increase feed and reduce speed (rpm)_. That's all you need to know. I'd start at a low RPM like 100 for the larger wheels, and feed hard *with* coolant. Make sure the chips do not turn colour (straw, purple, blue, black, etc) and reduce your rpm if they do. Make sure your chuck has a good grip on the parts. You will very possibly push the workpiece right out of the chuck if the part's not clamped sufficiently (and you may jam/break your cutter at the same time).

Let us know how it goes.

Regards,

Robin

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joel 19 years ago

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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F. George McDuffee 19 years ago

============== For one offs this will be expensive.

Taking [or attempting to take] that wide a cut is almost sure to produce chatter.

Another approach is to use Lautard's approach with a narrow plunge tool like a cut off tool to rough the cut and then carefully file to exact size. See his bed side reader #1 or his new book of this topic.

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Karl Townsend 19 years ago

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F. George McDuffee 19 years ago

=============== One of the reasons for many projects is to have an excuse to make more tools. I don't know if your pipe bender falls in this category, but have you considered making a "ball turning" tool. Many of these will cut a concave as well as a convex curve.

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Jim Sehr 19 years ago

Doesn't anyone hand grind tools anymore? If you can not find these tools send me a couple of HSS tool bits and I will hand grind the 4 radii for a case of beer. Or you can find a cutter grinder shop in the yellow pages. Jim snipped-for-privacy@hotmail.com

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Wild Bill 19 years ago

I saw a webpage that illustrated a method like the one you describe, where the cutting tool is mounted in a low position relative to the workpiece, and the lathe spindle is run in reverse.

I can't seem to find a link to that technique now.

WB metalwork>

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Dave Lyon 19 years ago

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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clutch 19 years ago

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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Jon Elson 19 years ago

Well, he didn't tell us what class of lathe he has. I used to have a

10", then a 12" Atlas. This would have been so far above the capabilities of that light a lathe, I wouldn't even THINK of trying it, except in foam.

Now I have a 15" Sheldon, and have done the equivalent cut, and there was no HINT of chatter whatsoever. It was a quarter-round tool made from a 1/2" blank, for cutting a 1" diameter ball socket. After drilling part-way in with a 7/8" drill, I just aligned the tool to the center and plunged it in. The only sound was the crinkling of the infolding chips!

But, I realize not many home shops have a 3500 Lb. lathe!

Jon

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Boris Beizer 19 years ago

This is difficult..if... you attempt to use a production approach for a one-off job. Don't try to cut the groove in one go. A bit of planning and measurements makes this an easy job, even on a small lathe.

Use a parting tool to cut in to a few-hundredths of an inch shy of the final diameter. This is just to get you started.
Make a series of cuts along side of that groove with any handy bit ...side cutting. Just go in to get an approximate groove. You could even use the parting tool for that job. What you aim for is to get an approximation to the final groove. My choice for this application would be a side cutting tool ground to 45 degrees on both sides, so it can cut both on the left and right. The grooves you're making aren't all that deep, so you can probably do it faster by hand without using the crossfeed.

3a. Now use a radius tool just for finishing off. 3b. Now for the lazy man's approach. The dimensions aren't all that critical for this application. Forget the radius tool and just finish the groove off with a round, rat-tailed file and use a proper radius gauge to check your progress. After you've done 1 &2 above, the extra time required to finish the grooves off with a file are more than made up by not having to cut those round-nose lathe bits.

Boris

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daniel peterman 19 years ago

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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Nick Mueller 19 years ago

Of course, it can be done in all directions and positions. Vertical with the lathe in reverse or not. Behind the work's CL or not. It was easier to describe it that way. I have no links to offer (they missed that in the book from 1906).

Nick

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