I give up

[cessna]

After several failed attempts at making a 32dp gear hob, I finally came up with one that looked great, rows of sharp teeth, I used my oxyacet torch with a small rosebud to heat to a bright red and quenched in oil, reheated in an oven to 300deg. and left for cooling down. What I got was a hob with dull blobs for teeth. I guess the answer is get out the plastic and purchase one.
Terry

 

[Maryak]

Terry,

Sorry to read about your troubles, reads like you got the torch too close to the tooth tips. OA can be a real pain in local overheating.

I reckon it's worth another shot.

Hope this helps.

Best Regards
Bob

 

[doc1955]

You could grind up a tool bit and make a single point cutter.
I've done many gears in this fashion and have always had good luck.
Here is a link to the latest gear I cut in this way and it has worked out just fine.
http://www.homemodelenginemachinist.com/index.php?topic=6363.msg67867#msg67867

I say never surrender. :big:

 

[black85vette]

What material are you using for the hob? I have made a couple without any major problems. One trick that is worth using is a magnet. Heat up until the magnet is no longer attracted to the metal. Keeps you from going too hot.

The biggest hurdle for me to get over was making a 40 degree cutting tool that cut well in drill rod.

I made 3 or 4 hobs out of aluminum just to get the hang of it and verify all my measurements. After they were looking about right I made a trial one out of drill rod and then finally made a good one that produces some reasonable looking gears.

 

[lee9966]

For the one and only hob I have made I only heated it until the teeth were orange, I didn't try to heat the entire thing. It worked for me, not sure if it is the "right" way to do it.

Lee

 

[cessna]

Thanks for all your replies, no doubt I got it too hot, after I think about it for a while, I will probably give it another try. I am using 1/2 drill steel, and I do have trouble with cutter grabbing with hss bit I ground. Do you guys use a slitting saw to cut the lengthwise grooves after cutting the rings? I have trouble with the saw dulling quickly, I run at slow speed with coolant, they do not get hot but do not last.
The last saws I bought from Busy Bee.
Terry

 

[black85vette]

I am using 1/2 drill steel, and I do have trouble with cutter grabbing with hss bit I ground.

Do you guys use a slitting saw to cut the lengthwise grooves after cutting the rings? I have trouble with the saw dulling quickly,

I use a cobalt bit for cutting and a friend ground a carbide 40 degree tool for me to use. I run at a very low speed with my back gear engaged and feeding really slow with plenty of lube to keep it from grabbing.

To make the cuts into the rings I use a carbide 3/8" end mill and orient it so that the end of the mill cuts the face of the hob teeth. Seems to make a cleaner cut than the side of the end mill.

You have to be careful with drill rod that you do not let it work harden which it will do and dull your tools quickly. You can ask me how I know about this.

 

[cessna]

So if I understand your reply, you do not put saw cuts horizontally through the rings, you just cut the rings and then use your end mill to form the teeth?
Terry

 

[lee9966]

That's what I have done, just use the mill to make the teeth

 

[black85vette]

So if I understand your reply, you do not put saw cuts horizontally through the rings, you just cut the rings and then use your end mill to form the teeth?
Terry

Correct. I do not use saws. I think that would take too long and be tough on the blades. A good carbide end mill makes short work of it. Look on this web site and you will see how he does it. I do it a little different. As I said before I like to use the end of the mill bit to cut the face of the hob teeth rather than the side of the end mill. So I set up my mill to make the cut on the side of the hob rather than the top.

http://www.metallmodellbau.de/GEAR-CUTTING.php

You might want to read this other thread on this board. There was a lot of good info shared and plenty of links to other resources.

http://www.homemodelenginemachinist.com/index.php?topic=7674.0

 

[Artie]

long winded series of videos but does a good job of explaining how to make and use a hob.

[ame]http://www.youtube.com/watch?v=ykSOOXww0U0[/ame]

Im also very interested but feel that a single point cutter might just be a little more user friendly if your application is suitable. Good luck, Rob

 

[cessna]

Thanks Rob and black vette, I have watched all the videos that this guy made Rob, good info. The German site from black vette, altho I dont speak German the pictures are great with a lot of info just viewing them. I am going to give it another try, I am presently working on the Hoglet engine, but will find time in between to try another hob. Thanks again for all the help.
Terry

 

[black85vette]

altho I dont speak German the pictures are great with a lot of info just viewing them.

You can take the url from the German site and then go over to Google. At the top pull down under "more" select translate. Tell it German to English and plug in the url. It will translate for you. Pretty much magic stuff if you ask me. The translation is not perfect but you get a good idea of what is going on.

 

[putputman]

B85V, thanks for the lead on the translation. :bow:
All this time I have been passing over these sites with other languages.