How do they do it?

[alexccmeister]

Hi All,

I was looking at this video of a cnc lathe cutting some piece. Here is the video.



Looking at the first part of the video, I am not sure but I think they are cutting a bolt head with the lathe. Can someone confirm this. Hence my question.

How do they do this. I understand this technique is called broaching. But I still can't understand how the machine can cut straight surface with a lathe. Thanks.

[alexccmeister]

K, So looking at the whole video, I see that the cutting head is also turning. So that explains how they can cut straight surface on a lathe. I think.

Is this do-able in a home shop lathe or outside of hobby cnc? Does mach3 has such a control on this type of cutting? Thanks.

[ImanCarrot]

That's weird! I can't get my head round how the faces aren't convex or concave *scratches head*

[cdlenterprises]

It's called polygon turning. Basically a flycutter is spun in a live tooling station and the RPM is synchronized with the spindle RPM so that the flycutter strikes the round part at calculated intervals (i.e. every 45deg, every 60, etc...) As Imancarrot stated, it does not yield a perfectly flat surface. There is a certain degree of curvature in each facet so it does not yield a "true" polygon but it is close enough for many applications.

[ImanCarrot]

Aha! I get it now! the syncronisation between part rotating up and tool cutting down must be awesome. Also, I'd immagine the tool tip position of the flat cutting tool would be critical?

I am constantly amazed by people who think these things up and actualy make them work. You know like, when you think up a hairbrained idea, and everyone says "no- way that'll work" and you go and do it anyway and peeps are like "wow! how the hell...?"

I love engineering

[alexccmeister]

Hi Iman,

I am sure you know about this broaching technique. Here is a video of some amazing work using this technique. I still don't know how they actually cut complex shape inside a circular hole. I have to see it for myself.

http://www.slatertools.com/video.htm

[ImanCarrot]

Oh! I've never seen that before in my life! I do Diamond Machining- just recently got into conventional turning and milling.

Incredible video! I must find out how they do it, specialy the internal serations

The more I learn the more I realise the less I know lol

[alexccmeister]

I think the broaching technique is do-able with a lathe. You just need to get the broaching tool. I don't see much application in what I do, but making bolts that can be turned with my hands would be something useful. i.e. ridged surface.

I wonder if the polygon turning technique can be done on a hobby lathe.

[ctate2000]

Rotary broaching is old technology. Screw machine shops have been using rotary broahes since the Mayflower came over. Somma Tool also sells rotary broaches. Be careful it takes a lot of power to broach the splines you saw. The use of these tools can cause serious issues on CNC machines. If you are running an old square head Warner and Swasey you should not have trouble.

If you like that try Leistriz Whirling machines.

[Geof]

.... Screw machine shops have been using rotary broahes since the Mayflower came over.......

Now that is an exaggeration.

But it easy to figure out how they work; just imagine that you are riding on the tool.