Gear Hobbing - Hob Shifting on Pfauter 1501

Anyone with experience running these machines is welcome to chime in.

The gear I was hobbing was helical. After my first pass, I realized my hob was positioned incorrectly when I noticed the hob was cutting with partial teeth. Time to shift the hob. In shifting the hob, I noticed that the part was rotating - I don't remember that happening with this or any machine. Of course, the part rotates while rapid feeding vertically. The machine uses change gears and is not CNC.

In the case of cutting helical gears, I'm assuming that the hob and the part remain aligned while side shifting. I know the hob doesn't remain aligned when side shifting the hob cutting a spur gear.

My question is: is the table supposed to rotate while hob shifting and the machine is at a stand-still? I couldn't find anything in the Operator's Manual.

Thanks

^ You gotta be kidding me. You've got just about everything that can be got, got wrong.

Go find someone who knows how to run a hobber to show you how it works.

If you plan to shift the hob after you have taken a cut, you have two choices: 1) realign the hob teeth to the tooth spaces manually by disengaging the index gears and rotating the blank accordingly. 2) shift the hob a complete circular pitch. If you shift the hob less than an amount equeal to the circular pitch of the hob, the machine has no way to automatically compensate for the shift amount. The reason the work rotates when you traverse the hob slide is the machine uses the differential to create and maintain the hob/work relationship and also create the lead of your helical gear. The differential has nothing to do with maintaining the hob/ work relationship when transverse shifting the hob. The only exception to this is if your machine has a tangential hob slide, but even then the differential is only used to maintain the hob/work relationship when the taqentially feeding a worm gear hob or a single tooth fly cutter, and in that case, the hob is constantly shifting.

As EG suggested above, you really need to understand how your machine operates and what the varous functions are capable of. Good luck.

Side shifting with the machine at a stand-still does cause the part to rotate, but not always. Sometimes the part stays still but the hob rotates. Either way, the relation between the hob and the part is lost when side-shifting. Time to break out the layout dye.

What I find least intuitive is determining where the hob will be cutting (ie the roughing and finishing zones) so that it will generate the profile properly, especially on helical gears. I've used the method where, with the hob at the whole depth, you bring the hob down until it is close to nicking the part. Whichever tooth on the hob is going to touch first when in the cut should be a full tooth. But I still don't know of a way to determine where along the length of the hob it is cutting until I take a look at it after the rough cut and check the wear.

Next thing I need to figure out is diagonal hobbing.