Free hobbing - a rogue method?

[lbender]

FWIW, 6TPI Acme screws mesh beautifully with 18 DP, 14.5 PA gears, and should do a nice job of hobbing the same.

6 TPI hobs 18.85 DP.
18 DP would require 5.73 TPI hob.
So if you cut a 5.75 thread like your SouthBend can, you can make a hob that makes 18.000 DP gears.

[nickel-city-fab]

6 TPI hobs 18.85 DP.
18 DP would require 5.73 TPI hob.
So if you cut a 5.75 thread like your SouthBend can, you can make a hob that makes 18.000 DP gears.

Thanks for the correction, I was a bit suspicious of my numbers. It had been some time since I checked it.

[nickel-city-fab]

Huh, that's pitiful regarding the fractions. We were required to have that all down by the time we were ~10 yrs old. Calculators didn't exist yet. I use fractions as well as decimal Imperial units daily on the job, doing the math in my head as required.

But as far as the DP and AGMA, try that one over at Practical Machinist. Some of the posters both there and here, happen to actually own gear manufacturing companies. And hence are well-qualified to speak.

[Robint]

OP has deleted this post

[The Artful Bodger]

FWIW this much derided thread has had 1700 views in 4 days

But no likes?

[nickel-city-fab]

NCF

BTW thanx for the tip about going to practical machinist - you are right they do have some really knowledgeable people there - I should get on well as I will be in good company

Beware of Practical Machinist, they do not tolerate as much as we do here -- that's why I hang out here, the company is much more polite and easy going. At PM they have no problem with making mincemeat out of you before 8 AM in a very public and embarrassing way if they feel like it -- they are very serious folks over there, working pros. Speaking from experience.

[davidwdyer]

I just went into the archive and pulled that issue. I won't copy it, its under copyright, and we're here on this site by the good graces of a magazine publisher. Model Engineer and other mags are a wealth of info but they are often hard to give away....so if someone wants a copy they are out there to buy. The second part, in the April 4th issue, is the issue Eric Whittle began his great series on the Aero V8 - great stuff! On the gears, I'll describe the basics below and anyone can fill in the details, i.e. common knowledge available through searching

Its a good article and gives lots of info on making hobs. The hob is held in the lathe and the work mounted on an axle which is bolted to the vertical slide. In his set up, the axis of work end ups parallel to the X axis (cross slide) and is positioned under the hob (on the Z axis). The cross slide is the feed, and the vertical slide the depth. As anyone with any gear knowledge has said repetitively in these threads, the verticle slide assembly (on the cross slide) is rotated (around the Y axis) to match the hob's helix angle (to a good tooth form) and the work is rough gashed in advanced. That's the short synopsis of the article. He gives a detailed description of making a gear and also goes onto helical gears.

This should create a reasonably good result suitable for lots of purposes, however when making ones own hobs the challenge becomes getting the hobs pitch to that of a standard diametrical pitch or module gear. IT can be done with change gears (or a DSG does it)....or if its a closed system, gears only used with themselves, it won't matter. Of course if you are buying a hob, its moot.

I would love to have a copy of that article. Where can I buy it? That sounds like a wealth of information!

[sid pileski]

"BTW thanx for the tip about going to practical machinist - you are right they do have some really knowledgeable people there - I should get on well as I will be in good company"

You really are full of yourself!

Why would you even bother trying to educate us dumb asses?

Don't let the door hit you....

[Jim Stewart]

Sure, head on over to PM. They'll welcome your wisdom gratefully. Really. I guarantee it.

-js

[The Artful Bodger]

I am heading over now to see if I can get a front row seat!!!

[nickel-city-fab]

I am heading over now to see if I can get a front row seat!!!

I was just over there, no sign yet. Will continue looking.

[Jim Stewart]

Don't forget to grab a bowl of popcorn...

[The Artful Bodger]

I must say that I have had very informative and friendly conversations over there.

[The Artful Bodger]

There is nothing new under the sun, not even on PM!!

https://www.practicalmachinist.com/vb/antique-machinery-and-history/gear-hobbing-universal-mill-without-index-head-373736/

[Robint]

I shall miss the hostility from bigoted armchairs and thanx to all the 2000 viewers who dropped by over the last 5 days


Robin has left the Building