Radius Cutter

[wareagle]

Well, this project has been one of those on again off again deals that gets picked up when I have time. It has been on going for about eight months. I had some time today and went out and got a few things done on it today.

I should be able to cut convex and concave radii from tiny to about 4 inches. I have a few more things to make for it, but it is coming along nicely. It isn't pretty, but I am not really going for pretty, either. Rigid is what the desired result is with this one.

The turret is some sort of unknown steel that really is not very fun to machine. I call it scrapatanium. It seems to have a tendency to work harden if the feeds aren't aggressive (it's certainly not stainless), and the surface looks as if the metal is being pulled off rather than cut. Rake angle changes didn't seem to help any.

There are also some spots that are soft compared to other areas, and that makes for some interesting effects on the surface as well. I have used carbide tooling to machine it because high speed steel didn't seem to be up to the task and wouldn't hold an edge.

Threading it is an exercise in patience with this mystery metal. I haven't broke a tap in it yet, and hope to not start that now! The taps will cut certain areas easilly, and other areas it is like tapping a file. Oh well, what does one expect for free!!

 

[Cedge]

You'll be surprised at how much fun the radius cutter will be and just how often you'll find a use for it. Once you own one, it's amazing just how many things really need balls and curves on them... LOL. Nice work... wish I'd gone the dovetail route here too.

Steve

 

[Lew Hartswick]

Intresting. What is the tool hiolder going to look like? How will the height
adjustment be made? etc.
I have been doing some ball turning with a Holdridge and several home
made bit holders to get nearly complete balls on the work. ( the Holdridge
will only go a little over a hemisphere)
...lew...

 

[Cedge]

Lew
With this style of Radius Cutter, the height adjustment is typically done by re-positioning the cutter manually in the cutter section of the tool and clamping it in place. The only draw back to this style is that working close to the lathe chuck can be tricky. It does quite a nice job on contour cuts, but the cutting head has to be watched closely on the back half of the cut so that it doesn't encounter the spinning chuck... (don't ask....LOL).

I've come to like the"boring head" design for full spheres, covex ends and in tight spaces, but it's hard to beat the style that Wareagle is building, for nice clean contour curves or concaved end cuts, where work space is not a problem.

Steve

 

[wareagle]

For this tool, I am going to incorporate some safety stops to keep the tool out of the chuck. In just a few more years, I figure my son will be out there making chips with me, so I am looking ahead and trying to incorporate as much safety into the designs of the shop made tooling as I can where appropriate. The trade off is that the tooling may not be as flexible for a range of tasks, but then if the machinery has been crashed, it is a moot point anyway.

For mounting the cutter, I actually haven't quite got that figured out just yet. The design will be modular in that there will actually be two cutting heads that can be changed out depending on the task, one for inserts and the other for tool bits. The head for the inserts is pretty straight forward, but for the tool bits, I am brainstorming at this point. I haven't quite decided the way I am going to approach the mount for the tool bits. :?

 

[Graybeard]

Where can I get a set of plans for a radius cutter. I like what you've done here.

Cliff.

 

[DICKEYBIRD]

Here's a link to Steve Bedair's version:

http://bedair.org/Ball/ball22.html

 

[Graybeard]

Thanks, DB. That'll do it just right. I had found another one, but it was so complicated and required a right-angled motor gear mechanism - not in my game plan...

Cliff.

 

[skoot]

thanks for the plans that looks great

 

[Lew Hartswick]

Can either of the "radius turners" which have been involved here do a ball like this?

The "Holdridge" one at school won't do but a little over 180 deg. I am thinking that
maybe the "boring bar " (as used in a vertical mill) may but can't quite picture the
shape the cutter would have to be. I had to come up with a (way too complex)
atachment to do these. Am trying to find a simpler way to make these in several
sizes.
Thanks for any ideas.
...lew...

 

[Bogstandard]

Hi Lew,
As you know, the boring head method goes over the top rather than side to side, but the same cutter profile that you have should work with that as well, it is just that their operation is the same but in a plane 90deg apart so there is really no advantage by going to that method. I have included a sketch showing required profiles for the ball turning tool - number 1, which is almost exactly the same as yours.

Number 2 is a sketch of a gauge plate profile tool, that was most probably the way they did the originals. If you are only going to be working with brass then there would be no problems. Because brass requires no top rake, you can just drill or machine straight down, then file or machine up the left side of the hole to the shape you require. The plate is then hardened in the same way as drill rod, and sharpened by rubbing a fine stone over the top face. It is used by mounting horizontally into your toolpost (not overhanging at the left like a normal tool but mounted centrally in the toolholder) and plunged straight in, like using a shaped parting off tool. It has to be set on exactly centre or slightly below, never above.
It is not for the faint hearted because of the noise, and not for the likes of a small hobby lathe, they just don't have the power to support such a large cutting area in one go. Once you have one set up correctly and cutting sweet, they can be used to make hundreds, if not thousands of parts, with just a light rub over the top to keep the cutting edge keen.

I do hope that this helps.

John

 

[Powder keg]

OK Lew, I'll ask. What's it do? it looks familiar, But I can't quite place it.

Also, If you are just machining brass, you could make that form tool on a mill. Make it out of O-1 toolsteel. Using the radius of the cutter. Then tip your new cutter at the proper angles and you have your relief all ready to go. Then it's fairly easy to heat treat with a torch.

Thanks,

 

[Bogstandard]

There is no need to tip the form tool at all, as brass prefers no top rake, as described below, it is used in a totally flat position.

John

 

[DickDastardly40]

Apologies to those who have seen these pictures before but I attach them to ilustrate an alternative for forming a curve.

I stepped out the Ogive of a .50 cal bullet from a chart of diameters each .100" wide and formed the curve with a file and dressed with emery.

I'm quite pleased with the result.

 

[Bogstandard]

Hi DD,
Nice bit of profile work there.
I did do a bit of a post on profiling some time ago.
But it does show that with a bit of planning and very few tools, complex shapes can easily be turned out.
It is a bit wasted on this lot though, they can just go out and buy the real thing.

You're not showing off with that digimike are you? D-r-o-o-l
I suppose the broad arrow brigade supplied that ;D

John

 

[DickDastardly40]

You're not showing off with that digimike are you? D-r-o-o-l
I suppose the broad arrow brigade supplied that

Busted! Paid for by the Queen herself. This model is a quick mike which opens 3 x the speed of normal and has a rachet only, making it difficult to feel. I have use of it about 4 months and am still getting used to it.

I only used it for this job as my digital caliper was at home and I included it in the pictures for some ambiance.

Al

 

[DICKEYBIRD]

You're not showing off with that digimike are you? D-r-o-o-l
I suppose the broad arrow brigade supplied that ;D

John

OK, translation please. What the heck is "the broad arrow brigade." I work with a few Brits and am familiar with some of the expressions but that's a new one!

Milton

 

[Bogstandard]

Hi Milton,
It is just two brits using military language.
A quick explanation, everything supplied to the military is usually marked in some way with a broad arrow, similar to the arrows shown on old convict uniforms.

Hope you are now a bit wiser.

John

 

[DICKEYBIRD]

OK John....now I'm "happy as a sand buoy."

 

[Lew Hartswick]

OK Lew, I'll ask. What's it do? it looks familiar, But I can't quite place it.

Also, If you are just machining brass, you could make that form tool on a mill. Make it out of O-1 toolsteel. Using the radius of the cutter. Then tip your new cutter at the proper angles and you have your relief all ready to go. Then it's fairly easy to heat treat with a torch.

Thanks,

Which are you refering to? The little balls on the ends of the tube? The assy is the
bubble vial holder for a special antique transit.
Form tools with that wide a cut are just too much for any lathe I've got.
I did some in 1" aluminium for knobs on a few corner tables recently also. The
second pix above is 1" brass. Have also done a few acrylic to see how they would
look. With regard to the step cutting, I did that with all the large balls I'll post
a shot of the brass one if intrested.
...lew...