cutting spur gears on a mill

I have seen vids of using diving head for use with a milling form tool for cutting a spur gear say 3" dia, 1/4" thick with say 80 teeth

OMG what a painfully slow process as you mill each one

Yes there are powered head linked to spindle to cut these also - v expensive attachment

Now I was looking at some large bsw plugs taps i have and wondered if these might work

Then I saw a vid on making worm gears using this method, where the blank is mounted freely rotating on a mandrel. The rotating tap held in a lathe chuck and the blank is brought crossways to meet the tap. The action of the tap screws the blank around as it cuts and you end up with a worm gear which can be operated by a bolt

https://www.youtube.com/watch?v=XIzlg_uObwQ

Now I can see the FES going nuclear on this

Yet I have not found a vid on using this technique for a spur gear

Consider a 3/4" bsw x 10 tap on a 3" x 1/4" thick blank gives ca 100 teeth

So the tap is mounted in the spindle and the blank on a horizontal mandrel

First pass will get the thread depth, then the bed will be slid across on the x axis to get a flat bottom for the tooth form (I think)

Primitive but very quick and only suitable for light load low speed apps and probably noisy

put them in a gearbox with heavy oil and used nylons or sawdust

Anyone ever tried this

Seems too good to be true

Why spending time on making if you can buy them for little money, plenty of suppliers, see **LINK** Niko.

followed up on Madler website, very comprehensive, BUT I cannot see how to buy anything, no on line shopping cart or any hint of a sales facility

I am lost here pls advise

See **LINK**

Also several threads on this site about variations of the process including what you describe, also known as free hobbing.

Posted by brian jones 11 19/08/2021 12:05:43

"Seems too good to be true"

That's probably because it is ,the way forward is for you to give it a try
and let us all know how you get on.

Most good engineering requires some commitment in time and inevitably
some cost for tooling .
Here is a photo of some spur gear hobbing ,i can tell you where you can
get all of the items needed to do this , some of the links will
be taken down almost instantly by the North Koreans so if you want to
know you will have to send a PM.

John

You select Branche Offices at the top of the page, find the UK distributor and contact them. Niko.

Great Britain Huco Engineering Ltd. 5-7 Merchant Drive GB-SG13 7BL Hertford Tel.: +44 (0) 1992 50 19 00 Fax: +44 (0) 1992 50 98 90 [email protected] **LINK**

The method mentioned works fine for cutting worm wheels, although spiral flute taps are helpful:

Getting the correct number of teeth is a bit hit and miss. One can free hob a worm wheel, but it needs to be pre-gashed:

For spur gears it's a useless method. First, the work would need to be swivelled to the helix angle of the tap in order to get straight teeth on the gear. Second, the work would need to be rotated at the appropriate rate, same as when using a hob. Third, the tooth form would be non-standard, and the gear would only work with other gears made by the same tap.

It doesn't take that long to cut spur gears by conventional methods, provide one gets on with it rather than pontificating on forums, two gears at a time in this case:

If I want a quick gear, and don't have the appropriate cutter, I simply design it in 3D CAD and let the 4-axis CNC mill get on with it. As was the pinion:

For mating with this internal gear:

Andrew

For larger tooth counts the tooth form will surely be involute as the tap is in effect a rack form cutter? But indeed the pitches will not mesh with other "standard" gears. A 10 tpi tap as the OP suggested would cut teeth of ~31.15 DP which isn't any kind of standard, and pressure angle 27.5*.

I feel like giving up sometimes, why not just got to the web address for Huco that is in Speelworks posted image, then go to products and then gears which give you this. Do you need more help getting to a specific type of gear?

Personally I find the ones from Belting online very reasonable, MOD are cheaper than DP.

Well I shall try out this free hobbing method

I agree the gears will only mesh with others produced by the same tap

but it will be interesting to see how two such gears perform together and if they would suffice for light duty

dont you think

and BTW I belong to the school of thinking first and asking around before making chips, unlike the suck it and see brigade.

quote

It doesn't take that long to cut spur gears by conventional methods, provide one gets on with it rather than pontificating on forums

as per AJ with his superior minded 4 axis CNC machine

Obviously forgotten how long it does take to cut spur gear - the point of my original post = as they used to say "read the question carefully first, dont give an answer you would like to be asked."

I was just thinking out of the box

Its not helpful to throw a hissy fit, I did this already

this is the link from the pic above

http://www.maedler.co.uk/

try it yourself, for me it just leads to a dead end back to germany

being given a dead link is very frustrating and wastes a lot of time

you found your link by doing a separate search for Huco

There's a thread on here where someone free hobbed with a tap, if I remember correctly the tooth count was wrong (as in fractional teeth) till the blank was much smaller than required.

try it yourself, for me it just leads to a dead end back to germany

There is a phone number quite clearly indicated and easily called. Why not call it? Seems a simple enough way to get sorted? A lot of people seem to miss the simple options to sort out a problem.

No as I said it's in the image Speelwork posted, You have even highlighted what I said in your quote!

"why not just got to the web address for Huco that is in Speelworks posted image" NOT LINK

I've highlighted it for you, can't really make it any clearer.

Edited By JasonB on 19/08/2021 18:42:40

I ordered from Madler Germany directly or from their Dutch branche Koppe, for little money they even made it to your spefication, all very friendly and helpfull, just phone or mail them. Do not know of course about Huco but expect them to be the same. Niko.

I Recall this method of using a tap to cut a worm wheel was used in an article in MEW some time ago, The article was precise angle adjustment of the table on the Worden T&C Grinder I tried it out worked beautifully.

Edited By JasonB on 19/08/2021 20:47:10

Not really. It depends what machine you have, and what material you're using, but if you use a proper gear cutter I wouldn't say it was painfully slow, and a lot easier than trying to jury-rig something with a tap.

Home-made single tooth cutters are slow and tiresome, but work if you don't want to fork out for a proper gear cutter.

Another approach if you don't have a mill is to use a single-tooth cutter in the lathe toolpost, shaper-wise. That really would be painful, but again, you'd get there in the end (I haven't tried that one myself, but I don't see why it shouldn't work given sufficient patience).

I have made gears using a proper shaper and a home-made cutter. It works fine, but it's very easy to forget to wind the toolholder back up before indexing to the next tooth. Result - a loud bang as the shaper punches out the entire tooth* in one go, but, surprisingly no discernible difference in tooth quality, at least with benign materials like nylon or bronze. Best avoided though I think.

*Really the gap between teeth of course

Fair point. The teeth on the worm wheel I free hobbed with a tap look triangular. But the wheel is quite small (~1/2" diameter) so any involute curvature will be also be small. The tap was UNF so the pressure angle will be 30°. Since the tap form is triangular the gear teeth will tend to a triangle rather than the more familiar rack form. No doubt gears made by the same method will run together but there will be significant forces pushing them apart.

The small worm wheel shown is for a speed adjuster on a Pickering governor, so I doubt it'll ever get turned:

Andrew

Unfortunately you seem to have mislaid the first step. If the tap is skewed by the helix angle to get straight teeth on the gear how does it drive the gear blank as there will be no tangential force. The tap drives a worm wheel because it creates teeth that are not straight and hence there is a force causing the blank to rotate.

Andrew