Bazmak - gearcutting

[bazmak]

Having spent all my working life in engineering I have never cut spur gears
I don't want to spend I long time learning all the technicalities but would like
to cut some spur gears.Just for the learning not for a any specific purpose
at this stage.I would like to cut some gears the same as the Sieg lathe change gears,which I think are Mod 1. A full set of involute cutters would be too costly
but I assume I can use a single hob??.Seen one on ebay from china for $40
Am I wasting my time.Cant make one economical as silver steel is too expensive here in Oz. General question. From my threads you can see I am in the process of making a dividing head.Is it feasible for me to buy a mod1 hob
and successfully make gears.Lots of comments would be appreciated

 

[moerman]

Silversteel might be too expensive but how about old files? Or other hardened tools. Can't help you with advice about gear cutting. You're way ahead of me.

 

[chucketn]

now that you have a rotary table and a dividing head, check out this link for all the info you need to make gears.

http://www.helicron.net/workshop/gearcutting/involute-gears/

Shows how to make the cutter and how to use it.

Chuck​

 

[Blogwitch]

Baz,

Cutting gears with a commercial hob requires the piece part to rotate in sync with the cutter.
The main advantage of a hob over involute cutters is that one hob will cut any number of teeth on a gear as long as the diameter for that gear is correct.

I have a full set of mod and DP hobs, plus I also have all the castings to make a gear hobber.

The one shown next to the gear is a 1.25 MOD hob, the correct one for my change gears.

http://www.collegeengineering.co.uk/?product_cat=gear-hobbing-machine

These were a left over project when my shop was producing commercial items, which mine and my wife's failing health forced me to close.

One of the first jobs I will be doing when I get up and running again is a spring winder, which I will use on a freewheeling spindle similar to your latest indexer. Once that is out of the way, the freewheeling spindle will be used to hob gears, after gashing the blank to correct number of teeth. If you don't gash, and just wack the hob into the periphery of the blank, you usually end up with a couple less teeth than required.

John

 

[chucketn]

The link I posted shows a method to cut gears where the cutting tool does not rotate the gear blank. I made a cutter and produced a set of change gears for an atlas lathe on aluminum blanks. I used my Vertex 4" Rotary Table controlled by an Arduino and stepper to step the blanks between cuts.
I won't call it hobbing gears because I got into a wizzing contest over the definition of hobbing. The resulting gears mated well with an original Atlas gear. I gave them to a former friend who never told me if they worked.

Chuck

 

[bazmak]

This is where I am confused.When I said Hob I meant a multiple tooth cutter
where the gear does not revolve but work is turned for each cut and the trailing teeth
approximate the involute section.I now know the hob has a pitch and the job needs to revolve.I made a worm wheel for the Shaper using an M20 tap
and the workpiece revolved.Rough and ready but it did work.I also made a 3 tooth fly cutter from small dia silver steel with 3 teeth to cut 2 small gears
for the model V8.It did work but rough and ready.I would like to go one step further using my dividing head
ANYONE IN OZ know of a source for silver steel.I don't mind buying some and making a cutter.A very late in life learning curve for me

 

[bazmak]

Thanks for comments everyone.Never thought of using my nearly finished indexer to freewheel for hobbing.One avenue to look at.When gashing,i assume the gashes have to be at the right pitch.(maybe by packing the
head to get the angle ?)

 

[Herbiev]

Pretty sure Hales at Kurralta park sell silver steel

 

[gbritnell]

Hi Bazmak
I have made my own gear cutters for years using, single point from lathe tool bits (hardest to make) involute style cutters with forming buttons (pain in the butt for all that's required) and multiple toothed hob type (key word type) which I find the easiest to make and use. The only time there is an issue with this type of cutter is when you have to cut low tooth count gears.
The following pictures are of the cutters I made when I made my T-5 transmission. They were made from drill rod, (silver steel) hardened and not annealed because I didn't feel like there was a thin enough area that might snap off from being overly hard. I had to make 3 different pitches and to have made involute style cutters would have been time consuming and laborious. The final gears pairs fit together very nicely, thank you.
gbritnell

 

[michael-au]

With the hob are the teeth of the gear cut to full depth in one pass?

Michael

 

[Blogwitch]

Thanks for comments everyone.Never thought of using my nearly finished indexer to freewheel for hobbing.One avenue to look at.When gashing,i assume the gashes have to be at the right pitch.(maybe by packing the
head to get the angle ?)

Baz,

You gash the blank on the level then adjust either the hob or the freewheeling blank to the degree setting shown on the commercial hob.

It would be a lot of trouble if you were just cutting one gear, but if you wanted to cut a lot of different sized gears or a lot of the same gear with the same DP or mod, then it would be worthwhile as it would be much faster than cutting individual teeth with an involute cutter. You could gang up the blanks on a mandrel and cut many of the same gears at the same time.

Basically, you cut all your blanks to the correct diameter for the number of teeth required first ( I use a little desktop program that does all the calcs for you in seconds, blank size, depth of cut etc.) and then using your indexer, dividing head or RT with plates you gash the blanks straight across so that the hob has something to bite into as it starts to cut and keeps the blank in sync with the cutter, so no lost or gained teeth.

Once that is done, set either your mill spindle to the shown angle on the hob or your freewheeling unit to the same angle. this ensures that when the hob is cutting, it is in fact cutting straight across the blank face.

I have used involute cutters many many times, but have never tried the freewheeling hob method, but there is no reason for it not to work if things are set up correctly.
In my case, time will tell if I am correct or not.
If the freewheeling method doesn't work out as expected, then I can make the little hobbing machine instead.


John

 

[bazmak]

Learning all the time,can the hobbing machine be made without castings
Do you have plans ? Could it be my next project ?

 

[Cogsy]

With the hob are the teeth of the gear cut to full depth in one pass?

Michael

Sort of - at least with the ones I've made and used. The very first tooth is full depth but the surrounding teeth are 'started' with the first pass and get deeper as you index the blank and make successive passes. For the 5 'tooth' hobs you need to index the blank the number of teeth you need + 3 to completely cut all the teeth.

I second Chuck's link, it has all the info you need to make a hob quickly and easily.

I've bought lengths of drill rod (silver steel) off the shelf at Blackwoods, and from Bohler as well. Never found it to be overly expensive. I've also make a hob from mystery metal laying in my stockpile and successfully cut brass and aluminium gears with it.

 

[Blogwitch]

Baz,

Of course the hobbing machine can be made without castings, as can most things, and not only that, it can be modified to cut all sorts of gears, not just spur.

I have nearly a full set of Myford change gears, which this little machine uses, but if you could borrow a set, then you can make all the gears you need for yourself, they could be made out of ali or nylon.

The plans and build instructions were shown in Model Engineers Workshop, plus a later modification series followed.

If you need further info then send me either a PM or email as I have everything needed to show how to build one.

John

 

[bazmak]

On a previous thread I made a 3t cutter from a small piece of silver steel
Now in possession of Ivan Laws book on gear cutting and a little more
knowledge I will make a 5t cutter.Again I had to make up from 3 pieces
of silver steel

 

[bazmak]

Next job was the above for when I start cutting gears
On a previous thread I described machining some pieces of rebar
I started by cutting 3 pieces and it machines really well

 

[goldstar31]

Thanks Barry! He has solved my problem which laughingly has nothing to do with cutting gears- and if it was, they would be fibre ones!

I have a broken - rather cheap and nasty( badly designed?) set of tumbler gears bracket on my rather cheap, cheep little Myford lathe.

It isn't a Myford part, it's an addition which eventually will allow me to operate a dog clutch- which has nothing to do with dogs.

I await the next stage with baited/bated breath. I've also got a set of damaged twin gears which are designed to be reversed from gear cutting speeds to fine feeds and 'Vicky verky'

Whatever it was, it wasn't me that filled the gear box with mahogany dust. Yuck!

Norman

 

[John S]

There is currently a series on making a gear cutting machine running in MEW.
I think this months edition is episode 3 but not certain.

 

[Hopper]

If you are going to do a lot of Module 1 gearcutting it might be worth buying something like this set of gearcutters for $80 delivered off eBay. Or $12 per individual cutter for specific sizes:
http://www.ebay.com.au/itm/Diameter...hash=item51d8649007:m:mEi1UTWuVuKm1Q0pnIGqrIw


Cheaper than you can buy the silver steel for in Oz to make your own. CTC tools also has reasonable priced cutters.

Yes, I know the dangers of buying cheap Fleabay tooling but I have been buying endmills and slot drills off these guys in HK and China and so far have not had a bad one. I'm thinking that with all the manufacturing going on over there they must use good quality cutters in their own factories to get the productivity levels required. Just avoid the stuff specifically built down to a price for the model engineer and home hobby market and buy their run of the mill stuff.


If you have Ivan Law's book you are off to a good start. There is a bit more good info on making button-style cutter tools at http://mikesworkshop.weebly.com/designing-gear-cutters.html

 

[bazmak]

Thanks Hopper,i have ordered cutters 4,5,6 and 7 for $48
covers nom 20T t0 135T. As you say cheaper than silver steel
Nothing specific in mind just want to cut a few gears and mod 1
to fit the sieg lathe seems logical.Dont think I need under 20t or over 135t
many thanks you made my decision for me