Need help with machining

[samthedog]

You could always grind the large radius. If you find a grinding stone and dress it to have the correct profile, you could chuck it in the mill and secure your job in the rotary table. Just make sure all the ways are covered up to avoid dust. Of course make sure you remove the bulk of the material with a lathe first. This solution would work with pre-drilled or post drilled holes too.

Paul.

 

[markknx]

I would turn the taper in it first before using the ball turner. This will save time on theball turner.

 

[chips&more]

I would use your mill, rotary table and fly cutter. Centrally mount the part on your rotary table. Adjust the tool bit on your fly cutter for the 40mm radius and make your concave form. And while you’re at it, you can do the holes too, if they are not done yet...Good Luck.

 

[DMS]

I was going to suggest something very similar to chips&more, except I was going to suggest a boring head. If you already have one, they are easier to dial in that a fly cutter. If you don't have one, you can make a fly cutter in an afternoon.

 

[benmychree]

You cannot use a broad nose form tool to do that radius. it will chatter like crazy. You MIGHT get away with using one though,if you turn the lathe spindle by hand while carefully applying the form tool to the work. First,used stepped cuts to get the radius as close as possible,then use the form tool.

Of course,what you really need is a large ball turning tool. I have no idea how large your lathe is,or if you have a ball turner.

Having made those holes first will cause problems. You might have to start over and do the radius first. Then,you could even finish the concave surface by filing it in the rotating lathe if necessary.




If not for the holes,you could even rig up a tool rest and freehand the radius with wood lathe chisels. I just stick a length of square steel in a tool holder on my HLVH to use as a rest for freehand wood lathe tools. I do that often. You can get quite close to a finished radius like that,then file and sand the rest of the way. You may have to start over and do the radius without the holes,or possibly jam tight plugs in the holes and turn them flush. Turn the radius and drill the plugs out.

Do not reject broad nose tools out of hand; they can be manipulated so as to not cut on the full face; a little on this side, a little on that side, a little in the middle, and so on until the whole face can be achieved; running the lathe as slow as it can go, and possible as suggested, rotate the spindle by hand; I have used this approach many times in the past 50 years or so as a journeyman machinist.