gear cutting with hob

[cessna]

Hi, I have ordered a 0.7 metric gear hob, it has a 12mm inside measurement, I would like to use it on my mill to cut the gears, can anyone tell me the method of mounting the hob so as to put it into the quill (r8) ? I have made hobs before with a stub end to mount into an R8 end mill holder.
Thanks
Terry

 

[Swifty]

I would make a simple arbor with a washer and thread on the end, use a suitable size material to fit one of your collets. If you are manually indexing the blank in a dividing head, just be aware that the hob may have a lead on it for use on hobbing machines.

Paul.

 

[cessna]

Thanks for the reply Paul, I thought I would ask as I have never used a commercial hob before.
Terry

 

[gus]

Hi Terry,

As the hob cuts in the gear blank will rotate. That is the hob will act like a worm and the gear blank a worm wheel. Be prepared to get one or two teeth less. For now make sure the gear blank is free to rotate. I did some hobbing with a 12 mm spiral tap. Was going for a 72t but ended up with 71. YouTube made it look so easy. To get 72t I was advised to make 72 gashes to aid the hob by a HMEM Forum member.
In real life the gear is driven by a gear train by the hobbing spindle to get the number of gear tooth. I did see a very simple hobbing machine with gear train working in the YouTube.

 

[cessna]

Thanks Gus, I have done worm gears using this method, I would like to use the hob on my mill so would have to adapt it to the mill spindle.
Terry

 

[gus]

Will be watching your thread on real gear hobbing. Hobbing is so much faster than the tedious tooth by tooth gear cutting.

 

[SmithDoor]

Gus it does not take long as the cuts are short
After you get start it take less min per tooth most time is setting up for next cut

Dave

Ps I have wonder about hob how they would get the right number with out gashing first Thank you for your post

Will be watching your thread on real gear hobbing. Hobbing is so much faster than the tedious tooth by tooth gear cutting.

 

[Blogwitch]

Cutting with a home made straight hob is totally different to the commercial hob you have ordered.

The commercial one is made like a screw thread, so you can't cut individual teeth with one, they are designed to cut around the circumference in one go.

You can get away with a free wheeling setup if you have gashed the blank first for the required number of teeth, but you will need to hold either the blank or the cutter at the angle marked on the hob otherwise you will not get any decent results at all, the teeth will come out angled across the width.

I have a full set of MOD and a good set of imperial DP hobs plus a full set of castings to make a gear hobber, but I was going to experiment with the free wheeling system before building the hobbing machine, but never got around to it.

There is a video and book called 'Making gears the easy way' that goes into the details of using these commercial hobs or you own home made spiral hobs, and it explains how to do it using the freewheel method.

John

 

[gus]

Gus it does not take long as the cuts are short
After you get start it take less min per tooth most time is setting up for next cut

Dave

Ps I have wonder about hob how they would get the right number with out gashing first Thank you for your post

Hi Dave,
Too many hobbies to chase and also one too many on the ''to do list''.
The next time I cut a worm wheel for an urgent job ,will gash the tooth.
I have 30 40 50 60 70 80t gears to use as direct index. For odd gears I will
have to DIY dividing plates for the DIY Rotary Table. Will be fun DIYing same plates. Too much to do and so little time with only two hands.:wall:

 

[OrangeAlpine]

I hobbed a 72 tooth gear using Gus's technique. It came out with too many teeth, so I adjusted the diameter, ending with 72 teeth. Hobbing two gears is child's play compared to making 72 gnashes, especially when I have no way to index the gear.

Bill

 

[gus]

I hobbed a 72 tooth gear using Gus's technique. It came out with too many teeth, so I adjusted the diameter, ending with 72 teeth. Hobbing two gears is child's play compared to making 72 gnashes, especially when I have no way to index the gear.

Bill

Hi Bill,

Cutting 72 gashes was really a humongous task when you could hob all teeth in less than a minute.The nearest to 72t was 71 t . Will find the time to get 72t spot on. Due to urgent requirement to get RT done to cut cams,I flew in precision worm and wheel for USA vendor. No regrets. The RT stood up well with no backlash and no chatter. The Japanese worm and wheel was not up to par.