Best way to turn a 2" concave radius

[Vince]

I need to make some guide rollers that would align a carriage on 4-2" shafts. There will be 16 guide rollers
What would be the best method and/or setup to turn this radius in 3" Delrin?
Thank you for any suggestions

 

[Karl_T]

Piece of cake on my CNC lathe

On a manual lathe make yourself a radii tool holder. Many many have built this. Mine was very simple. Make a tool holder that holds a bit right at the center of the compound axis of rotation, looking staight down from above. Make a spot for a long cheater bar. Leave the compound just slightly loose, push the cheater back and forth to rotate. Adjust the compound in/out for the correct radii.

 

[Dabbler]

A quick answer is to take a HSS parting tool, preferably one of the ones that are wider on top than on the bottom. Using a radius gauge, make a 2" radius form tool with your grinder. If you have an Aloris type holder you can mount it directly. Mount it on the side parallel to the work and you can directly plunge cut with it. It will be plenty strong enough to cut Delrin.

I recently bough some 1" by 1/8" cutoff blades for about 9$. They would work well for this application.

 

[chips&more]

Hi and welcome! Sorry, I’m not getting it? Is this a 2” or a should be 1” radius? Is this a concave radius or a concave sphere? Can you provide a sketch or some kind of pic?

 

[RandyM]

Hi and welcome! Sorry, I’m not getting it? Is this a 2” or a should be 1” radius? Is this a concave radius or a concave sphere? Can you provide a sketch or some kind of pic?

He is trying to make 3 inch guide rollers with a 1 inch radius machined into the side of them to ride on 2 inch shafting. Hope this helps.

Kinda like this.



Not sure if they'd really need the radii, a V-groove may work just as well and be easier to make.

 

[chips&more]

Thanks Randy! Even for Delrin, to plunge cut that in one operation would likely be too much tool pressure and probably chatter. I would do it on the mill with a rotary head and 2” cutter (if it’s 1” radius). Once set-up, I visualize making 16 of them very fast and easy to do…Dave

 

[Jimsehr]

I made a simple tool to do just that. It is a disk that turns on a plate bolted to lathe .
I used a socket head bolt as an axis and drilled and reamed a 1/4 hole off center so that the outer edge of 1/4 hole was the radius I wanted. Then I took a 1/4 round hss ground the end and used that as cutting tool. Held tool in disk with a set screw and used a longer bolt as a handle. I was cutting steel and it worked great.

https://photos.app.goo.gl/rOj3NP2KIKOMLStA3

PS you don’t need to give the cutter clearance to cut a radius. Just get top of tool on centerline.

I used this tool on a 11 inch Logan. After making tool ( 2 hours work ) bet I could cut them less then 5 min each.

 

[Vince]

He is trying to make 3 inch guide rollers with a 1 inch radius machined into the side of them to ride on 2 inch shafting. Hope this helps.

Kinda like this.

View attachment 249189

Not sure if they'd really need the radii, a V-groove may work just as well and be easier to make.

Exactly, Can't use V groove because they will be trussing up a lot of vertical weight that has to move about 4 feet

 

[Vince]

Thanks for all the replies. I don't believe my lathe would like a form tool, it's a decent size lathe, but I think plunge cutting a 1" radius would be asking an aweful lot of it. I was thinking about taking a piece of round stock and machine it to hold a 3/8 tool bit and be able to set it on a radius then pivot it around it's C/L. At least that's all I was able to think of.

 

[JerryK]

I have set up my manual lathe like a tracer lathe.
A template and stylus, then rough bump out the radius.
After a couple finish passes with light pressure,
it’s easy get the feel of it.