Hit me - Miss me?

[mklotz]

It's called the "Curie temperature" if you want to research it further.

 

[Jack B]

Bob I see things are progressing nicely on this site.
Jack B

 

[Maryak]

Marv,

Thanks for the nomenclature - Curie Temperature. :bow:

Jack B,

Thanks for your support. :bow:

Well, I actually finished the pinion and made a start on the gear. I am pretty pleased with the hob and the pinion looks right, so hopefully it will be right. :

The hobbing of the pinion is complete.

Drilling for the locking screw.

The completed pinion after dressing and parting off.

Roughing out the gear blank.

And on that happy note another week has passed by.

Best Regards
Bob

 

[Deanofid]

That pinion looks like it came out well, Bob. Same amount of teeth and spaces. Always a good sign, eh?

Dean

 

[Maryak]

That pinion looks like it came out well, Bob. Same amount of teeth and spaces. Always a good sign, eh?

Dean

Thanks Dean, :bow:

It is a good sign

Now for the gear. ;D

Best Regards
Bob

 

[steamer]

Lots good Bob! That'll do!

Dave

 

[arnoldb]

Very well done Bob :bow:

Kind regards, Arnold

 

[Maryak]

Dav and Arnold,

Thanks for the kind words and support. :bow: :bow:

Best Regards
Bob

 

[RichD]

Bob,
Lots of calcs in making gears. I've saved your PDF file for future reference. Good hard to find info.
Looks like your hob worked out great. Congratulations, and thanks for the great writeup and pics. Did you end up with any nicks or undercutting? Also how did you align the tool to the work? By tooth on center...or gap on center?
Rich

 

[Maryak]

Bob,
Lots of calcs in making gears. I've saved your PDF file for future reference. Good hard to find info.
Looks like your hob worked out great. Congratulations, and thanks for the great writeup and pics.
Rich

Rich, thanks for your kind words and support. :bow: :bow:

To try and answer your questions.

Did you end up with any nicks or undercutting?

Fortunately there were no nicks. Undercutting was avoided by using the older pressure angle of 14.5 deg rather than the more modern convention of 20 deg, (much more important for the pinion than the gear because of the smaller number of teeth).

Also how did you align the tool to the work? By tooth on center...or gap on center?

I aligned by the hob tooth on centre. I brought the bottom of the tooth to centre using a surface gauge then lowered the hob by half the tooth width using the fine quill feed. I pondered which would be better (tooth or gap) and settled for tooth as I figured that when the upper and lower hob teeth started to cut I could see any misalignment and correct up or down to ensure true centre without any permanent tooth damage also I was sure using the tooth that my whole depth would be as correct as I could make it.

I hope that explains things.

Best Regards
Bob

 

[Philjoe5]

Thanks Bob for posting this interesting procedure. I had heard of it but never saw it carried out in steps. I'm enlightened ;D

Cheers,
Phil

 

[RichD]

Bob,
Thanks for the info.

I was reading up on undercutting in my copy of Machinery's Handbook 12th edition.
According to them:
"Slight undercut begins when a pinon of 31 teeth is generated by a straight-sided unmodified rack or hob type of cutter, and this undercut may be excessive when number of teeth is less than 22."

To find the minimum No. of teeth for a given pressure angle use this formula...
Min. No. of teeth=(tan2pressure angle+1/tan2pressure angle) x 2

(tan 14.5°=0.25862)
(0.258622+1/0.258622) x 2 = 32

(tan 20°=0.36397)
(0.363972+1/0.363972) x 2 = 17.1 or 18 teeth

And stub teeth use .8 instead of 1 in the same formula yielding 14 teeth

Seems the shorter broader teeth work best for a small number of teeth.

Rich

 

[Maryak]

Rich,

Thanks for your information. :bow: I obviously got my 20 deg and 14.5 deg pressure angles base over apex.

Still I am not quite sure what it all means.

As far as I can tell reading my MHB 16th Edition the 32 teeth minimum is for a 1 DP gear. The formula in my edition is:

n = 2 x addendum x cosec2 PA

for a 16 DP Pinion with 14.5 deg pressure angle.

n = 2 x 0.0625 x cosec2 14.5 deg

n = 0.125 x (1/sine 14.5)2

n = 0.125 x (1/0.2504)2

n = 0.125 x 15.9514

n = 1.9939

for a 16 DP Pinion with 20 deg pressure angle.

n = 2 x 0.0625 x cosec2 20 deg

n = 0.125 x (1/sine 20)2

n = 0.125 x (1/0.3420)2

n = 0.125 x 8.5496

n = 1.0687

Oh, I wish I hadn't done that, :wall: now I'm baffled by science or is it th_bs

Best Regards
Bob

 

[RichD]

ok,Now I'm baffled...but that's my normal mode according to my wife. ;D

 

[Maryak]

Hi Guys,

Cut the gear today and here are the results.

Proving nick.

The hobbing is complete.

The almost finished gears - Now they need a jig and bedding in.

What did I learn from this ???

1. Gear Hobbing is a viable and satisfactory way to make gears in the home workshop.

2. The next hob I make will have a heavier shank (3/8" min) and will have a larger OD (from 5/8" - 3/4").

3. The tooth land will be reduced from 1/32" to 1/64" or smaller.

4. Whilst I have not tried a cast iron or steel gear with a drill rod hob. The cutting speed needs to be max half the HSS speed.

5. A six tooth hob may be smoother cutting than a 4 tooth hob.

Best Regards
Bob

 

[arnoldb]

Nice gears Bob Thm:

And I must say I agree with the points you made ;D

Kind regards, Arnold

Я не думаю, любой из моих тетушек есть яички ;D

 

[Maryak]

Я не думаю, любой из моих тетушек есть яички ;D

My dad's sister came close. She qualified as a genuine English witch, they were probably pretty small from riding her broom. :

Best Regards
Bob

 

[Cedge]

Bob...
Gorgeous work!! After the single tooth experience, I'm really wanting to try the hobbing technique. In one of the Youtube demos I've watched the guy made his hob with 10 teeth.

Steve

 

[kustomkb]

Good job on your hob Bob! :bow:

They look great, thanks for the info.

 

[Deanofid]

Nice work, Bob. I really like that you can use the same hob for both sizes.

Dean