Pulley Wheel

[Bill Kirkley]

I want to bend a one inch solid round bar about 90 degrees. The bend needs to have a 1/2" radius. I plan on bending the other end about 45 degrees to a 3/4" radius

I plan to attempt this hot on my fly press. So I needed to make a set of bending dyes for the fly press. Thus, the one inch diameter round groove in a 2 1/2" mild steel round bar, and two wheels, one in a 1 15/16" inch round bar (its all I could find) and one with the bar turned to 1 3/4" diameter.

I got a one inch carbide insert on eBay and made a holder for it. I felt trying a plunge cut with the insert would be a disaster so I made a spread sheet with the formula for a circle to cut a series of .05" wide grooves to rough out a circle.

The grooving went well. Trying to make the final cut with the 1" diameter carbide insert was a disaster. No matter what I tried (speed variation, tool hight variation, moving the tool back and forth, lots of oil) it kept rubbing, really bad!

I finally got the job done but it isn't pretty. Fortunately, I don't think it will matter.

It is a little after the fact but can anyone tell me what I did wrong. How do you prevent the rubbing?

 

[darkzero]

Is it a positive or neutral insert? Looks like you have it held down with a screw so I'm guess it may be a positive insert?

When you say rubbing, what exactly do you mean? As in the material was rubbing on the side of the insert or do you mean chattering while cutting? Asking also cause I see chatter marks.

 

[Bill Kirkley]

Is it a positive or neutral insert? Looks like you have it held down with a screw so I'm guess it may be a positive insert?

When you say rubbing, what exactly do you mean? As in the material was rubbing on the side of the insert or do you mean chattering while cutting? Asking also cause I see chatter marks.

The insert is flat on top. It tapers to about 15/16" on the bottom. I aligned it maybe a few thousands below the center of the round bar.

I guess chattering is what I experienced. It turned the sides of the circular groove without a problem. It was when I reached the bottom of the roughed out circle that I had the problem.

 

[Bill Kirkley]

So, I guess it's a neutral insert.

 

[darkzero]

Ok sounds like a positive insert & no need to add negative rake to the insert holder/tool like if it were a neutral insert.

So chatter, that's what I assumed you meant. Round inserts are great for finishing due to the large radius compared to "pointy" inserts & they last long cause they have an "infinite" amount of cutting edges/tips rather than 2, 3, 4, etc. But the way you are using it is as a form tool. 1" is a pretty hefty form tool so it's gonna want to chatter.

Speed, keep slowing down the spindle until the chatter improves, you may get down to your slowest spindle speed & can't do anything about that. Rigidity is important, how rigid your lathe is is what you have, can't do much about that. You could make a solid plinth to take place of your compound slide but who know if that will make the difference or not.

A few little tricks you can do to make sure you're no loosing rigidity. Set your compound slide parallel to the bed ways since you are making a plunge cut. Make sure you don't have the compound slide hanging out so that the tool post is left unsupported. Position the compound slide so the tool post is closer to the pivot point of the compound slide. Lock the compound slide, lock the carriage. You can also try snugging up your cross slide gib. And remember, go slow (spindle).

If the work piece already has chatter marks & you're trying to clean it up, naturally the chatter will continue. So when you start the cut again, you have to feed very very slow to try and machine away those chatter marks before you can feed faster. Or you can try filing them away.

 

[darkzero]

So, I guess it's a neutral insert.

Sounds like you have a positive insert. If it tapers from the top & gets smaller at the bottom it a positive insert, cutting edge is only on top. Positive inserts are usually held on with a screw.

Neutral insert will be 90° from the top to sides, cutting edges on both sides of the insert, meaning it can be flipped. Neutral inserts are usually held on with a clamp and/or a cam pin/post.

 

[darkzero]

I aligned it maybe a few thousands below the center of the round bar.

Getting it right on center is ideal but if you can't, set to just slightly above. If you go too high the material will rub on the side of the insert. Slightly above is better here cause if your insert holder flexes, the insert will want to dig in & push down.

With this & trying the tips above I think you should be able to do just fine if you need to make more. The ones you made look good already & sounds like they'll work fine as is.

 

[mmcmdl]

I guess chattering is what I experienced. It turned the sides of the circular groove without a problem. It was when I reached the bottom of the roughed out circle that I had the problem.

That is a lot of surface area on the radius tool . What I would recommend is when reaching full depth , turn the spindle off and rotate the chuck by hand . You'll be able to get the chatter marks out of the pulley . They really don't look too bad though .

 

[Bill Kirkley]

Thanks for your help! Yes, based in what you said it is a positive insert.

I did have the bolder bend down and dig into the work piece. It stopped the lathe! My tool holder was made out of mild steel so it is probably not ridged enough for this job.

 

[Bill Kirkley]

That is a lot of surface area on the radius tool . What I would recommend is when reaching full depth , turn the spindle off and rotate the chuck by hand . You'll be able to get the chatter marks out of the pulley . They really don't look too bad though .

Turning the chuck by hand is a great idea! Wish I had thought if it.