Author Topic: Chucks Helical Gear Cutting fixture  (Read 7917 times)

Offline michelko

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Re: Chucks Helical Gear Cutting fixture
« Reply #45 on: May 16, 2020, 08:21:17 PM »
Hi Stefan,
http://metallmodellbau.de/GEAR-CUTTING.php
Maybe you find this helpfull? Not sure if the hob method works for helical gears.
Michael

Offline Don1966

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Re: Chucks Helical Gear Cutting fixture
« Reply #46 on: May 17, 2020, 12:16:34 AM »
Stefan the gear sheets I sent you has the information to make your own cutters and gear hob. It has tabs to select which gear your making alone with making cutters and Hobbs. If you have never made cutters get the book “ Gears and gear cutting “ by Ivan Law. It cost no more than 8 dollars on amazon. money well spent to understanding gears and making gear cutters to cut your own gear. By the way nice looking gear.

Regards Don
« Last Edit: May 17, 2020, 12:19:54 AM by Don1966 »

Offline Craig DeShong

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Re: Chucks Helical Gear Cutting fixture
« Reply #47 on: May 17, 2020, 12:29:32 AM »
Chuck had a spring on his fixture to keep constant load against the roller bearing. I decided to try it without it and just make sure that I always has pressure against the wheel. It worked fine. The only thing you have to remember is to conventional cut otherwise the cutter will pull the blank into it.
gbritnell

Like George I omitted the spring.  Just remember to keep pressure against the wheel (as George says) and you’ll have no problems.
Craig

Offline stefan-k

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Re: Chucks Helical Gear Cutting fixture
« Reply #48 on: May 17, 2020, 07:50:52 AM »
Stefan the gear sheets I sent you has the information to make your own cutters and gear hob. It has tabs to select which gear your making alone with making cutters and Hobbs. If you have never made cutters get the book “ Gears and gear cutting “ by Ivan Law.

Regards Don

Thanks Don, i just found it and already ordered the book.

Regards Stefan

Offline stefan-k

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Re: Chucks Helical Gear Cutting fixture
« Reply #49 on: May 17, 2020, 07:54:23 AM »
Hi Stefan,
http://metallmodellbau.de/GEAR-CUTTING.php
Maybe you find this helpfull? Not sure if the hob method works for helical gears.
Michael

Hi Michael

Just took a look at the site. It´s interesting! Keeping an eye on it......
BTW: Funny! Two Germans talking english to each other........ :Lol:

Offline jadge

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Re: Chucks Helical Gear Cutting fixture
« Reply #50 on: May 17, 2020, 08:47:34 AM »
I expect the 'hob' method would work for a helical gear, but the indexing and offsetting would be interesting. Here's a link to a thread on another forum discussing the method:

https://www.model-engineer.co.uk/forums/postings.asp?th=155945

Personally I wouldn't use the hob method. I'd either make an involute cutter or just machine the gear direct on the CNC mill.

Andrew

Online Mcgyver

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Re: Chucks Helical Gear Cutting fixture
« Reply #51 on: May 17, 2020, 12:38:27 PM »
Personally I wouldn't use the hob method. I'd either make an involute cutter or just machine the gear direct on the CNC mill.


whats shown there isn't a hob as I suspect you know as you put it quotes.  I call them faceted gear cutters.  They work for undemanding applications, however with smaller teeth counts quality breaks down.  Their advantage is only one cutter is needed, they're quick cheap and home made....but you will get a better profile with a involute cutter for spur or helical...which of course is a reasonable approximation of what you'll get with a hob (generation = most accurate)

Chucks creation is really something, I admire the simplicity and how well it functions on what many/most would view as a really challenging home shop task; helical gears.  Good stuff, part of his legacy.
« Last Edit: May 17, 2020, 02:03:45 PM by Mcgyver »

Offline jadge

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Re: Chucks Helical Gear Cutting fixture
« Reply #52 on: May 18, 2020, 09:20:44 AM »

whats shown there isn't a hob as I suspect you know as you put it quotes.  I call them faceted gear cutters.

That's an elegant description. In the linked thread it was discussed that the method gets less accurate as the number of teeth decreases. Even some of the gears with large numbers of teeth looked to have a poor tooth form. Although one needs to bear in mind that the gears were physically small.

Conventional hobbing still produces a series of facets, just many more of them. For ordinary gears the hobbed finish is fine. But for precision gears the gears were often shaved and ground after hobbing. Two big advantages of hobbing are that only one cutter is needed and no time consuming and error prone indexing is needed. A disadvantage is that hobbing can create undercutting of the tooth even when it isn't needed for clearance of the mating gear.

Standard involute cutters are only correct for the lowest number of teeth they're listed to cut. However an involute cutter designed and made for a specific number of teeth may well be more accurate than a hobbed gear. Depending of course on how accurately the involute curve is formed.

From a practical viewpoint I doubt many of us would be able to measure the differences discussed above. In the commercial world there are many tweaks and twiddles applied to the tooth form to promote smooth running of high speed and highly loaded gears.

Andrew

Offline john mills

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Re: Chucks Helical Gear Cutting fixture
« Reply #53 on: May 18, 2020, 01:20:11 PM »
The advantage of Hobbing is it generates the tooth shape when you talk of under cutting when low numbers of
teeth that can be adjusted by increasing the size  the centre to centre difference can be maintained by reducing the size of the matting gear or increase the size of the matting gear and adjust the centre to centre distance to
suit  .I had to cut gears with 5 teeth there was no undercut.but the sizes did not work out with the formulas i could find un til i found old machinery hand book where it was explained and  the formulas to work  out so no undercut. which did match the drawing sizes.when you hob gears you can alter the sizes quite a lot . 
                   
              John
« Last Edit: May 18, 2020, 01:25:01 PM by john mills »