Freehand radius ends

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usamech

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Newbie looking for some techniques and best practices to freehand a full radius on end of stock.

I got a Clausing 5917 on a dolly with casters for mobility in my small shop. I finally have it in a location where I hope to leave it alone for a while. So now I can concern myself with leveling it correctly. I got a new Starrett 98-6 and leveling it clearly makes a difference.

Adjusters made from A193 B7 all-thread, 1-1/8-8, and am now putting a radius on the bottoms which will seat on a large .230 D washer with a .700 hole. I’m pretty much done with two for now and have two to go. Will also have to chamfer or dish the washers to match. I had to just try it out myself before asking. Curious about any tribal knowledge to improve freehand cutting without the use of radius tools.

To start, I found the charted Minor Diameter to be .9695, (where I should expect an uninterrupted cut at bottom of thread). So, for an imprecise newbie, I’d round up to .970, divide in half, and get a .485 radius. From faced off end, this is also my Z-in stop where the radius begins. All done around 370 rpm, with a brazed carbide cutter. All turning from head to tail, I just took some freehand cuts to take off the corners. Then used auto-feed of .0022 head to tail and worked the crosslide as necessary. Ending with a double-cut file, single cut, and then 220 grit cloth.

End result is one with a final OD of about .900 and a Z of .485, and the other an OD of .920 and .485. Closest radius gage is a 15/32, .468R/.9375D. did say imprecise, right? Without a radius gage on it, it actually looks ok. So, what do you think?



IMG_5849.jpgIMG_5850.jpgIMG_5851.jpglathe dolly.jpgI
 
What is the object of the radius? Is it to reduce friction? I'm just wondering if you couldn't simply turn a "peg" instead that fits the hole in the washer?
 
Looks good from here! I'm a newbie also so I'm no help on getting it done.
 
Yes, reduce the friction. The washer is the base sitting on concrete floor. The all-thread Adjuster screws through a fixed nut welded to base of dolly. Adjust and secure with a jamnut.
In my opinion, in trying to "screw" a flat surface (bottom of screw) onto another flat surface or plate; there is a tendency for the heaviest edge of the screw to walk sideways because it can't' dig in. Basically, since it can't go straight down, it'll move the whole lathe/dolly sideways versus vertical. I saw this trying to level it without any radius. Kind of like turning a nitrogen or other large cylinder bottle by hand with it standing straight up. You just can't turn it in place without it moving horizontally one direction or the other.
 
Almost ready to run ? :encourage: I can't see it from my place either but it looks good from where I am tonight ! :)
 
An easier-to-make conical form would probably work as well as your hemisphere. But your rounded ends look pretty nice, and the application doesn't require a whole lot of precision anyway.
 
usamech said:
<snip So, what do you think?
Click to expand...

I think there is an easier way to do it, since you don't have a radius turner.

Buy some bearing balls to use as your spherical joint element. Use a ball end mill to machine a hemisphere in the all thread, if you must. A simple conical recess will do the job and leave a void to fill with grease.
 
I just step a squarish tool 0.025" on the X-axis and plunge into the work to the corresponding depth. It leaves a staircased result, but then a file cleans it right up.

For example:
0.000 0.000
-0.025 0.010
-0.050 0.030
-0.075 0.055
etc, etc, etc, until
-0,250 0.250

Below is an example of the finished product.

1660335465825.png
 
Last edited:
RJSakowski said:
I cut a shallow cone on the adjusting screw and a matching depression on the foot to keep the adjusting screw from walking. https://www.hobby-machinist.com/threads/on-the-level-further-adventures-with-the-g0602.72338/
Click to expand...
I like this idea. Other ideas are great too, but I've already committed to the radiused end months ago when I built this dolly, and the fact that I have already made two yesterday. Was mostly looking for good techniques on how to make the radius by hand and see if I was on the right track. I just didn't know how best to make the radius. I made the other two today and got much faster and more efficient with it.

I'll probably scrap the washer idea and try to dish or make a concave cut in .250 plates. Is yours actually conical or a concave arc? If conical, how do you cut it? Guessing it's a combined crosslide and compound slide movement? This would be a new cut for me. By the way, I don't have a mill. Thanks!
Usamech
 
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