Attachment for turning a large radius convex surface

All discussion about lathes including but not limited to: South Bend, Hardinge, Logan, Monarch, Clausing and other HSM lathes, including imports

Moderators: GlennW, Harold_V

User avatar
WesHowe
Posts: 176
Joined: Sat Sep 19, 2015 9:52 am
Location: Huntsville, Texas

Re: Attachment for turning a large radius convex surface

Post by WesHowe »

I admit the pictures are not top-notch professional stuff, and they suffer even more from being reduced in size to share here. But in the pictures of the bar I have that attaches to the crossfeed frame (the upper part) there are multiple holes drilled in it (about every 3 inches). Those serve to reduce the distance from the crossfeed table to the pivot, not that it should be a problem, but the less stress the better. The fixed pivot is totally adjustable, because it clamps to the ways.

With those multiple holes, reversing the attachment from convex to concave is easy. With the fixed pivot nearer to the spindle, you get a convex path. Using the fixed pivot further from the spindle yields a concave path.

There are some practical limits to what you can do with it. For one, I would be unable to make a cut much larger than 4 inches diameter with the smaller lathe I have. Given the length of the bar itself, which consumes most of the space I have available without removing the tailstock, I can't do radii much longer than 8 or 10 inches. The longer the radius, the closer you get to a flat surface. I built this to turn some small dies, in pairs, to press small sheet metal items into a curved shape. That works.

Another application for radius cuts would be making self-aligning machine support feet. For that, a convex surface would be placed on a piece of bar stock to attach to the equipment, and a flat plate would have a concave surface of matching radius on it. With that arrangement, a slight mounting angle will not prevent a large contact surface between the two pieces. Might be handy for making leveling feet for a lathe when the concrete floor is sloped or uneven.
spro
Posts: 8016
Joined: Mon Feb 20, 2006 11:04 pm
Location: mid atlantic

Re: Attachment for turning a large radius convex surface

Post by spro »

It all works and a great topic. This also leads me to reinvestigate the Hoffstappel (forgot the spelling) ornamental lathes. They had one feed driving another to wonderous works. It's inspiring even when seeing before and forgetting, what is a true jewel, when seeing with a fertile brain.
Inspector
Posts: 721
Joined: Mon Feb 23, 2009 4:25 am
Location: Saskatoon, SK, Canada

Re: Attachment for turning a large radius convex surface

Post by Inspector »

spro the name is spelled Holtzapffel. I'm with you in believing OT turning is both fascinating and beautiful.

The attachment for turning radii is cool but my lathe doesn't have the T slots the OP has in his carriage so I'll hold off making one until I really need one.

Pete
spro
Posts: 8016
Joined: Mon Feb 20, 2006 11:04 pm
Location: mid atlantic

Re: Attachment for turning a large radius convex surface

Post by spro »

I really butchered the name, Holtzapffel . I should have it tattooed on my arm but wouldn't deserve it. Yes. T slots are great things to have in the saddle or cross slide for various reasons. It turns that our friend, Wes, has shown again, another. Or the other, again.
A link to your lathe or similar would be eye candy.
User avatar
WesHowe
Posts: 176
Joined: Sat Sep 19, 2015 9:52 am
Location: Huntsville, Texas

Re: Attachment for turning a large radius convex surface

Post by WesHowe »

Spro: The lathe is a Grizzly 9729 3-in-one. http://www.grizzly.com/products/Combo-Lathe-Mill/G9729. As things go, I am in the middle of replacing it with a G0776 (13x40) lathe. A year or more ago I bought a milling machine, so I no longer use the milling part. Overall its a useful machine, within its limits. I feel I have passed those, at least in ambition.

The slots are there because the apron also serves as the milling table. I used them as an attachment point because it was easier than drilling holes in the unit to attach something to. On a regular lathe I probably would have set it up along the back edge, the way taper attachments usually are. There is no reason that the pivots have to be in line with the spindle, just that to get a smooth curve cut across the diameter the pivots need to align along an axis parallel with the spindle when the tool tip is centered on the part. That will make the curve maximum (or minimum for concave) be on the part center. A misalignment would make a disjointed pair of curves, similar to a bullet shape.

- Wes
stephenc
Posts: 311
Joined: Sat Jul 05, 2014 6:13 pm
Location: youngstown ohio

Re: Attachment for turning a large radius convex surface

Post by stephenc »

thanks to Harold and his likening it to a crankshaft the light bulb finally went off in my head , and i think i have the concept firmly rooted in my brain .
i dont care if i have no real use for making a concave/convex surface at the moment , this is now on my projects list . i have to have one .

funny ... but i never used to be a gadget guy until i got into machining for a hobby
RSG
Posts: 1541
Joined: Fri Feb 04, 2011 9:59 am
Location: Ontario, Canada

Re: Attachment for turning a large radius convex surface

Post by RSG »

You'll have to let us know how it works on your new 13" x 40". My thought is it might not due to the amount of force required to move the carriage on it's own let alone with this apparatus which it a real shame because it is a great idea and I would have a real use for this tool in my shop.
Vision is not seeing things as they are, but as they will be.
User avatar
Grantham
Posts: 75
Joined: Thu Mar 04, 2004 9:36 am
Location: Minnesota
Contact:

Re: Attachment for turning a large radius convex surface

Post by Grantham »

It seems you folks like to over complicate things<g>. My
video showing an attachment made for crowning a pulley
for a belt sander on YouTube might be helpful for some of
you fine fellows.
https://www.youtube.com/watch?v=vXLXDj-L8aw&t=2s
Rod Grantham
Inspector
Posts: 721
Joined: Mon Feb 23, 2009 4:25 am
Location: Saskatoon, SK, Canada

Re: Attachment for turning a large radius convex surface

Post by Inspector »

Rod how would you go about using your tool to cut the end of the work as shown in the first post picture? Yours would have to have the pivot well under the chuck or in the headstock someplace if it didn't hit the chuck itself. Don't get me wrong, your tool is great for working along the axis but I don't see it cutting larger convex and concave radii across the axis.

Pete
User avatar
WesHowe
Posts: 176
Joined: Sat Sep 19, 2015 9:52 am
Location: Huntsville, Texas

Re: Attachment for turning a large radius convex surface

Post by WesHowe »

Nice video Rod. And an excellent project... I gave it a like,

We were solving different problems though. I was turning the end face of a cylinder, you were turning the sides. You can do small diameter faces well enough using a boring bar in a tool holder. But for larger pieces and radii you get too much projection on the boring bar and lose accuracy due to flexing. Additionally, since convex surfaces require the pivot to be closer to the spindle than the cutting bit, both the boring bar or even a modification of your tool will suffer from interference with the work, or the chuck. That is why mine is located outboard and behind the carriage.

- Wes
User avatar
Grantham
Posts: 75
Joined: Thu Mar 04, 2004 9:36 am
Location: Minnesota
Contact:

Re: Attachment for turning a large radius convex surface

Post by Grantham »

I stand corrected. Your kind words about my crown attachment are appreciated. Rod
User avatar
WesHowe
Posts: 176
Joined: Sat Sep 19, 2015 9:52 am
Location: Huntsville, Texas

Re: Attachment for turning a large radius convex surface

Post by WesHowe »

I have filed it away in my "I'm going to do that one day" chasm... many things go in, rarely ever to again see the light of day!

Seriously, a grinder like you built is on my list. And now I know how to produce the crowned wheel for it. The attachment I made, if turned 90 degrees, would also do that, but it would require that the crossfeed rod be removed, or at least detached, so that the table moved in and out freely. Your solution is much simpler.

- Wes
Post Reply