Atlas 618 Change Gears- Part 1 Shop Made Gearcutting Hob

[@rodneykiemele4721]

This is going to be very interesting little series

[@arnljotseem8794]

Enjoyed this. Great description of making a hob. One thing though. I noticed that you quenched the hob after heating to tempering temperature. I see many people on youtube that do this. I believe that the steel should be allowed to cool slowly in air to allow the crystal structure to "reform". I could be wrong, but this is the way I do it.

[@TheBuildist]

My understanding is that the quench isn't chemically significant, it's merely an easy way to arrest the rise of temperature the instant the part has reached the desired temp. I too used to always do the air-cooling, but having seen so many using the quicker quenching method, and presuming it must be about as effective, I decided to start using it. I can't tell any difference in the parts I've made. But if you can point me to an official verdict on which way is better, I'd love to know it. Thanks!

[@noneofabove5586]

Very nice. I have tried this and it works well.

[@paulweiner9179]

Excellent video. Well prepared. I also have a Southbend 10 and a 618, but my 618 is a Sears vintage 1938 (model 101.07300) without a back gear and with the smaller spindle diameter. Because of these shortcomings it was only offered for one year. It has a few change gears but not a full set. Perhaps it didn't because of no back gear. It also lacks the thread cutting chart and there's no indication there ever was one. I'd like to duplicate what you have done, but I would need the full chart and a list of all change gears. Can you help me? Thanks.

[@JourneymanRandy]

Excellent just what I need to do the same. Thanks

[@johngturner]

Man, this was really well done.

[@noneofabove5586]

Waiting for part 2

[@craigtate5930]

Excellent explanation thanks!

[@isobar5857]

But how does a straight sided angled 'hob' generate the 'involute' profile of the gear tooth ? Just subscribed.

[@TheBuildist]

It's true that each of the hob teeth is cutting a straight-sided profile in the gear blank when it makes contact. But remember the hob has multiple teeth, each of which are touching the gear at a different radial point. So as the gear blank rotates through 360°, and all of the various hobb teeth are cutting their straight profiles, all of the potential gear tooth "conflict" points are cut away leaving only the appropriate gear profile behind. The resulting gear tooth involute shapes are actually stepped rather than a perfect curve, but because they are cut in dozens if not hundreds of slices, they very closely approximate a perfect curve.

[@isobar5857]

@@TheBuildist . That's a great explanation and much appreciated. Never thought of it that way. So in essence you are 'generating the involute form, not forming it. Always confused me, this process of hobbing, as you always seem to see the hob and the work piece revolving in conjunction with each other. Many thanks.

[@raminlah8661]

Hi dear What material did you use to make gear cutter?

[@TheBuildist]

wh-1 water hardening steel.

[@mrtomsr]

Excellent indeed

[@nevetslleksah]

If I may ask, where did you get the information and formulas for cutting the gear hob? Great video and I have subscribed.

[@TheBuildist]

I got the basic concept from the website that I referred to. But his hobs are metric/module and 20 degree pressure angle, so his formulas don't work for what I need. So I drew out a 24 diametral pitch 14.5 PA gear rack in CAD. From there I worked out the trigonometry and reverse engineered a working formula.

[@leviadams1793]

@@TheBuildist Did you draw a print on the hob? If so would you share it?

[@TheBuildist]

@@leviadams1793 I did make one. I've posted it to www.homemadetools.net/forum/home-made-change-gears-6-inch-lathe-73312#post135080 (scroll down, there are three pictures.)

[@leviadams1793]

@@TheBuildist Thanks!! That's an interesting looking site. I'll have to check it out.