Making small helical gear(s)

[Dave Smith the 16thParticipant @davesmiththe16th]

I have a lathe already and should be picking up ths SX2 mill on Tuesday.

I dont have the full dimensions yet, but i may need to make a few helical gears in aluminium or brass. If they were straight then no issue, just cut a length and chop out the required number, but what can be done with a slight helix on the gear?

Limited skills and tools as usual

Any simple methods to creating more than 1 gear easily? Or should i just get comfy and make them one at a time?

Thanks again. (i have so many questions)

[Dave Smith the 16thParticipant @davesmiththe16th]

[John ReeseParticipant @johnreese12848]

Traditionally they would have been done on a Universal milling machine. That is a horizontal mill on which the table could swivel to the helix angle. The work would be held on an arbor on a universal dividing head. The shaft of the dividing head would driven through a gear train from the X axis lead screw. A standard involute milling cutter would be used.

Most of the early 20th century machining texts show the setup.

It is not something a hobby machinist is equipped for. Other than shops specializing in gears I do not know of a machine shop within 100 miles that would have the equipment or know how to use it.

Most helical gears are cut on hobbing machines.

Try to find a source of stock gears.

If you are willing to build a machine to make your gears there are kits and drawings available to build a small hobber. I think Hemmingway sells such a kit. I am not sure if the kit will handle the lead angle you want. I believe the hobber is shown in illustrations in Ivan Law's book on gears and gear cutting.

[JasonBModerator @jasonb]

If you wait for ME 4536 there will be an article by Rod Jenkins on making small helical gears in the home workshop which should answer your questions.

J

Edited By JasonB on 22/05/2016 07:24:11

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

It is not difficult to make helical gear as i did in this method. See the movie..

[Nigel McBurney 1Participant @nigelmcburney1]

A universal mill is not essential for cutting spiral gears, providing a universal dividing head with a full set of gears is available spiral gears ,worms,and short threads can be cut on a turret hill ,or a plain horizontal mill with a bolt on vertical head, which can swivel to 90 degrees either way,The universal mill with swivelling table has a couple of advantages, the horizontal arbour is more rigid than a vertical head (stub arbour)and additional arbour supports can be used in some circumstances, so production cutting with lower number DP cutters is easier and quicker,plus it is easier to centre the gear ,over the gear blank then swing the table to the correct angle,the snag with the swinging table is it usually swings to 45 or 50 degrees so cannot deal with short lead spirals say for 2 to 1 side shaft gears on horizontal i/c engines.in that case the table is set a zero and the vertical head swivelled to the required angle or the vertical head is swivelled to 90 degrees i.e. spindle parallel to table,and the table swung to around 25/30 degrees .For thread milling over a reasonable length a universal head was made for for horizontal mills which had a double swivel and smaller spindle to reduce the bulk of the head to give sufficient space for the head to clear the work. I have both a universal mill and a turret mill and have cut lots of spiral gears for stationary engines,and large worm for a full size Burrell . With a lot fiddling the spiralling tooling can machine good spirals in plain bearings.If any one is buying a mill with possibly the idea of machining spirals in the future make sure the the head on the turret mill will swing a full 90 degrees a lot of imports only swing to 45 degrees,this also applies to vertical attachments for horizontal mills.

[Michael GilliganParticipant @michaelgilligan61133]

Very informative videos, Jens

Thank you.

MichaelG.

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

You can not use same gear cutter to cut helical gear such as gear cutter for 12-13 teeth in helical gear who need 12 teeth. The gear cutter is choosed depending on angle of helical gear and counts of teeth. Read through from page 14-13 to 14-14 about how to manufacturing a helical gear.

To choose the gear cutter to mill helical gear choosed by angle and counts of teeth, read though from 14-9 to 14-11 how to choose the right gear cutter in this link –>

**LINK**

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

Posted by Michael Gilligan on 22/05/2016 09:54:59:

Very informative videos, Jens

Thank you.

MichaelG.

Thanks

[Dave Smith the 16thParticipant @davesmiththe16th]

A little bit of whoosh, something flew over my head there I can see if rotates but how? and i think its a bit too much for me as yet. (small angle required)

The angle is very small, virtually a spur gear, which im hoping will work but i am guessing that it will need that small angle cut into it.

The size/shape is unlikely to be an off the shelf item.

Just seen the price of gear pitch gauges, a big ouch. Is there an online reference to compare gears?

Hoping to just mount it on a shaft and offset by x degree and then take a cut, i was just curious as to whether i could make more than one gear at a time?

Thanks.

[Dave Smith the 16thParticipant @davesmiththe16th]

Can anyone help with the gear size?

20 tooth and 29mm diameter, the lowest part of the tooth does not extend to the highest part of the next tooth, thats how little a helix it is.

Thanks.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Dave Smith the 16th on 22/05/2016 15:45:39:

Can anyone help with the gear size?

20 tooth and 29mm diameter

.

I make that a little over Mod 1.3 … Which is possible, but unlikely

… Could you please double-check that diameter ?

MichaelG.

.

P.S. … It's a simple calculation, but I've just found this very handy page.

Edited By Michael Gilligan on 22/05/2016 16:23:22

[JasonBModerator @jasonb]

Try 20 DP, only 0.001 over 29mm looking at HPC's helical gears. I think its a different calculation for helicals so spur gear calculations won't work, also varies for parallel or crossed.

 

Edited By JasonB on 22/05/2016 16:48:07

[Michael GilliganParticipant @michaelgilligan61133]

That's better, Jason

Although I make that 29.21mm O.D.

… I couldn't find an 18 DP listed anyway

MichaelG.

Edited By Michael Gilligan on 22/05/2016 16:49:38

[John ReeseParticipant @johnreese12848]

My thanks to all of you who have added to my education. Model Engineers seem to have a particular talent for figuring out how to get the job done without the "right" tools.

John

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 22/05/2016 16:27:33:

… I think its a different calculation for helicals so spur gear calculations won't work, also varies for parallel or crossed.

.

… and I hadn't realised how big that variation is

[Neil WyattModerator @neilwyatt]

Saw a great device at Harrogate that apparently was described in ME some years ago. In short its a small dividing head and tailstock on a slide. The head end has an angled template and you reset it before each tooth then it makes a part turn as you feed each tooth space past the cutter. Much easier to understand when you see it in action.

[JasonBModerator @jasonb]

Couple of photos of Mike Sayer's spiral gear cutter here which is what Neil is talking about

Edited By JasonB on 22/05/2016 19:16:34

[Anonymous]

As a first pass the number of 'teeth' used to select an involute cutter for a helical gear is the actual number of teeth divided by the cube of the cosine of the helix angle. Here's the proof:

The OD is also related to the helix angle, so not fixed for a given number of teeth.

Andrew

[Jens Eirik Skogstad 1Participant @jenseirikskogstad1]

Found the easy way to create the tool to mill helical gear in Youtobe. Really simple than my tool as i showed in early post of my movies. Function is about same as my tool. Be sure there are no play in the tool before you are creating the helical gear.  

Edited By Jens Eirik Skogstad on 22/05/2016 20:00:12

[John PParticipant @johnp77052]

Seen in album " gears " 3 photos. Helical gear 1, The pair on the left
are 1 mod hobbed gears made as a test piece. The centre pairs are hobbed
gears for a reduction gearbox to drive work on the Universal grinding machine.
Both of these were made on the hobbing unit featured in the article in MEW 193
"Gear hobbing in the mill ". This electronic Syncron system which conrols this was
designed and made by Richard Bartlett (Compucut).
The hobs were from Arc Euro I think these are now all sold out and they now
don't seem to sell them anymore which is a shame as they were a very good
cutting tool. Obviously there is quite a lot to make to be able to produce these
type of gears in this way and to some extent depends on how many
gears you need.
The gears on the right were cut on the Dore Westbury cnc mill by inclining
the head to the helix angle and using a suitable disc gear cutter ,the lead
is taken care of within the control system to syncronize the table movement
and rotation of the gear blank.Rotation of the gear blank to index to the next tooth
forms part of the cnc control file and as such once started can be left to get on
with it to completion.

The photo helical gear 2 shows a 100 tooth 1mod gear 5 deg left hand
helix .This would seem to be a similar helix angle as described by the OP
for the 20 tooth gear at 29 mm od .At 20 DP at this angle (5 deg) would work
out as 1.104 inch or 28 .03 mm ,The HPC gear angle is 17 deg 45 min
increasing the od to 29 mm .With hobbing it is possible to cheat and still
get to the 29mm od by increasing the blank size to the required size
and then cutting the required tooth number.
This is normal practice for gears with low tooth counts where the PCD
is increased to avoid undercutting at the tooth roots .

The last photo helical gear 3 is similar to the photo 2 except the hand is
opposite ,this is a replacement Align mill power feed gear of 106 teeth
but should be 107 tooth (i mis-counted the original ) .So the 106 tooth is cut
on a 107 blank ,it fits in and runs fine.

Getting back to the OP's original question ?

"Limited skills and tools as usual" . We have all been there at some time.

Any simple methods to creating more than 1 gear easily? Or should i just get comfy
and make them one at a time?

Probably not as to make anything such as this requires some commitment in time.

As answers i doubt this is of much help but is probably true.

John

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Andrew Johnston on 22/05/2016 19:40:55:

… Here's the proof:

.

Thanks, Andrew

That's my learning point for the day

MichaelG.

[Roger HeadParticipant @rogerhead16992]

Just in case anyone was wondering about the manual that Jens' 'Chapter 14' document came from, it is the USN 'Machinery Repairman', NAVEDTRA 12204-A. Widely available, one link is http://www.maritime.org/doc/pdf/machinery-repairman.pdf

Roger

[Dave Smith the 16thParticipant @davesmiththe16th]

So much to take in, the size is correct 29mm maybe a tiny fraction under but mostly its spot on 29mm for a 20 tooth gear. I used a gear creation tool on the thingiverse website and used the MOD 1.314? created with a 5 degree helix and opened in freecad. The gear measured 28.9mm so its close enough. 5% angle maybe a bit borderline though. Maybe 8 – 10%?

Does that equate to an imperial standard? I used a thread gauge and the MOD 4 seemed to fit the gear spacings. I had a quick look for gear pitch gauges and they are pricey.

The original gear is plastic (nylon)? So swapping it out to aluminium, could i use a straight tooth instead? Its a slow motor thats used infrequently in its application. (seat motor if thats of any use)?

Looking at all the methods and have lots of questions. When hobbing a gear does it space the teeth correctly when taking the initials cuts? Thinking out aloud.. The tool is approx 1mm further away from its final cutting position. Wont that try to cut an extra tooth or so?

I watched the Myfordboy video and he precut the teeth on a gear, for that reason?

Thanks.

[HopperParticipant @hopper]

It would help greatly if you could tell us some background on what you intend to use these gears for.

45-degree helical gears for transmitting power at high rpm, say driving a model car with IC engine, or for gearing down airplane prop speed is one thing. Requires full spiral milling as described above.

But a 4 degree helical gear for use on a worm and worm wheel type application, say indexing a dividing head or rotary table etc. can be bodged up by simple straight cutting with the blank held at a 4 degree angle to the cutter.

And it might even be that straight cut gears could do the job for you, if we knew what the job was.

Once cheap source of small helical gears is from RC model car suppliers. Might be worth a look.

[Author]

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