cutting spur gears on a mill

[JasonBModerator @jasonb]

It's only the corners that were chewed up on a few teeth, OK along the face once the tap had something to mesh with. Starting with a slightly overwidth gear and then skimming each face would possibly cure it though that was the edge I started on in the video and soon found it better to come in half way along.

[brian jones 11Participant @brianjones11]

JB you were on track and then spotted this was not the proper way, dont attack from the side as the tap doesnt have space to mesh properly at first with the blank. You quickly retrenched and attacked from the middle inwards (as they do with making a worm). It righted itself and you proceed full sail to finish. The damaged teeth were a periferal result left over from your first attempt – trivially observed by the old SOD not paying attention from his armchair.

Now your first result you reckoned you made a nice knurl but you were only using 1/4 BSF 26tpi

Now I am using 1/2" UNC 13tpi so my pitch is ca 2mm and produces a more credible size gear

BUT spiral flute taps are rare on EB and larger ones get very expensive, so not a practical direction I admit

I had a cunning plan and Ive had more results from Doreen see below

[John HaineParticipant @johnhaine32865]

Who or what is Doreen?

[John HaineParticipant @johnhaine32865]

Who or what is Doreen?

[speelwerkParticipant @speelwerk]

Posted by John Haine on 14/09/2021 18:14:20:

Who or what is Doreen?

Reading previous posts by Brian, Doreen seems to be a much loved and well used Myford lathe.

[JasonBModerator @jasonb]

Someone else not paying attention, as I previously said I used 1/4" BSP which is 19tpi and 0.518" OD. That's why there is a 19G thread gauge in one of the photos.

Doreen Is his Dore Westbury mill.

Edited By JasonB on 14/09/2021 18:34:35

[speelwerkParticipant @speelwerk]

Posted by JasonB on 14/09/2021 18:34:04:

Someone else not paying attention, as I previously said I used 1/4" BSP which is 19tpi and 0.518" OD. That's why there is a 19G thread gauge in one of the photos.

Doreen Is his Dore Westbury mill.

Edited By JasonB on 14/09/2021 18:34:35

Very sorry for the mistaken gender of Doreen. Niko.

[brian jones 11Participant @brianjones11]

When I woke up from my pantograph AO drawing board this am, I was seized with a new direction . Why not try

straight slits down a bolt thread. My angle grinder disc is 1mm thick, so I made 5 axial slits coinciding with the hex head – in a heartbeat. If the gear blank is say minimum 3mm – mine was 6mm, then the cutter shouldnt come un meshed.

So this is the result

This is during the rolling and polishing process

This was just a quick try with my grinder, slitting along 6 edges to match the Hex head, done by hand so a bit naff, could do better

Not a chip in sight all round and SHOCK 74 teeth (not 73 predicted) -well it wouldnt suit a clock maker

Im not skilled in taking close ups. the gear is mucky from the brasso fluid which I applied to polish it up to please the Grommets

As you seen its a presentable form, even with rounded tips and roots?

I polished it up by using a plain bolt without cutting edges and some Brasso. I think the applied rolling pressure helped (after all they make quality precision threads by rolling process)

So even if it fails on soft metal, it can produce respectable plastic gears quickly and cheaply without complicated attachments, universal dividing head and loads of patience etc

I have some AL and brass blanks on order

Maybe look up some larger thread – 2" bsw 4.5 tpi that should knock the stuffing out of sofa dwellers

[brian jones 11Participant @brianjones11]

Who or what is Doreen?

A Dore Westbury vertical mill, as classic as the Myford (Maureen) is to a turner

they are both temperamental wimin who dont like being neglected

Edited By brian jones 11 on 14/09/2021 19:00:48

http://www.lathes.co.uk/dore-westbury/

Edited By brian jones 11 on 14/09/2021 19:21:48

[brian jones 11Participant @brianjones11]

As I am sure you are all on the edge of your seats (not possible for sunken armchairs) here's my first attempt at a brass gear

I keep forgetting to landscape my phone, notice a cheapo brass blank – 17p whats not to like

before you all leap from your electrically assisted orthopaedic memory padded comfort

YES its not perfect, there are flaws but I put that down to the rough way I chivved up my spirally sliced bolt on my vice with an angle grinder, lots wrong with that method

I have a cunning plan to make better cutting tools from bolts the proper way

More work needed

[brian jones 11Participant @brianjones11]

And for the record

this is what real hobbers use, who has those attachments?

And Im not the only one with a perverted interest in rough gears

A senior luminary on this VERY board was caught doing this a few years ago

[Michael GilliganParticipant @michaelgilligan61133]

Posted by brian jones 11 on 15/09/2021 20:09:52:

.

A senior luminary on this VERY board was caught doing this a few years ago

.

But that’s a worm-wheel is it not ?

MichaelG.

[JasonBModerator @jasonb]

And the other a helical gear if I remember rightly

[brian jones 11Participant @brianjones11]

Well MG – think out of the box

if that cog was 10x dia then its a spur gear, just shunt the tap across the z axis, not so easy on a lathe without a vertical slide – but doable

innit?

 

obtw you would have to tilt the axis to match the helix angle to get orthogonal teeth as JB has pointed out before

Edited By brian jones 11 on 15/09/2021 21:02:56

[Michael GilliganParticipant @michaelgilligan61133]

Posted by brian jones 11 on 15/09/2021 20:54:05:

Well MG – think out of the box

.

.

I’m leaving that to you, Brian

I’m happy just observing … and chipping-in with the occasional fact-check

MichaelG.

[Pete RimmerParticipant @peterimmer30576]

Posted by brian jones 11 on 15/09/2021 20:09:52:

And for the record

this is what real hobbers use, who has those attachments?

That ain't hobbing. Not sure what it is from this angle some kind of spiral gear setup but it's using a form cutter to cut the tooth directly not a hob to generate the involute.

[brian jones 11Participant @brianjones11]

Well PR post a pic of a hobbing attachment – not a specialised hobbing machine – that doesnt count, its not for the hobby machinist.

My point here as I expect you noticed is that we all take for granted that a lathe is generally designed to be able to make screw threads. Its no big deal

But a mill isnt set up to make gears in a similar way (nor a lathe for that matter)

In both cases you can go for a dividing head and laboriously rake out each tooth

I dont know of a simple system that allows you to cut gears with ease and speed (I am discounting the modern use of stepper motors for the job for the purposes of this discussion. No electronics allowable

You need to lock the spindle rotation with the gear blank rotation by suitable gear chain and the whole should run and chew out a gear – you may need some movement of the cross slide if its a thick blank of course

Thats hobbing on gas

So is there a ready made attachment for mill hobbing?

Hence my pursuit of a cheap charlie way of knock up spur gears – we already know the worm gear method

and this is an expansion of this method

[John HaineParticipant @johnhaine32865]

Indeed, looks like cutting a helical form, the rotary axis is driven from the table X feed not the cutting spindle.

[JasonBModerator @jasonb]

Brian, you have not said how long those gears took, could you enlighten us as to how long each took and did you take any photos during the machining?

Interesting that you seem to have about 47 teeth from a quick count up, with a 13tpi cutter and a 27.3mm dia blank I would have thought 42 teeth, so the method is very unreliable.

From the one I cut I would not say it's super fast as I found the feed along the work needed to be increadably slow to get an even finish rather than a "shallow worm wheel" effect in a helical form along the face related to my feed rate.

The milling setup with the driven dividing head is one of Andrew's photos for one of his hobby projects, not sure he has an arm chair either as his front room has too much engineering tools in it to find space for one.

 

Edited By JasonB on 16/09/2021 07:12:54

[Howard LewisParticipant @howardlewis46836]

As a spectator, a long and interesting debate, from which i have learned a few things.

1 IF this method is to be used, a spiral tap is probably the better way to go.

2 There are some quite short fuses about.

3 To maintain an accurate NUMBER of teeth (Not necessarily Form ) pre gashing is required.

Since this is required, will this be a lot quicker than using a gear cutter, considering the need then to reset from some means of Dividing to allowing the blank to rotate?

This ignores the fact that most of us will have a slitting saw, and the likely absence of the required gear cutter, and the cost of buying one.

A while ago, I did consider using a tap for gear cutting, but since a definite ratio, and an accurate gear was required, I took the coward's way out and bout a spur gear and a worm of the same Module..

Horror since the two will not be an exact match. But for unloaded very low speed operation, this is considered to be a small problem.

For other spur gears, I shall continue to use gear cutters. So far, cutting a gear has never taken as long as reading this thread. .

Howard

[John PParticipant @johnp77052]

Posted by brian jones 11 15/09/2021 22:27:24

Well PR post a pic of a hobbing attachment – not a specialised hobbing
machine – that doesnt count, its not for the hobby machinist.
My point here as I expect you noticed is that we all take for
granted that a lathe is generally designed to be able to make screw
threads. Its no big deal
But a mill isnt set up to make gears in a similar way
(nor a lathe for that matter)
In both cases you can go for a dividing head and laboriously
rake out each tooth
I dont know of a simple system that allows you to cut gears
with ease and speed (I am discounting the modern use
of stepper motors for the job for the purposes of this
discussion. No electronics allowable
You need to lock the spindle rotation with the gear
blank rotation by suitable gear chain and the whole should
run and chew out a gear – you may need some movement
of the cross slide if its a thick blank of course
Thats hobbing on gas
So is there a ready made attachment for mill hobbing?
Hence my pursuit of a cheap charlie way of knock
up spur gears – we already know the worm gear method
and this is an expansion of this method.

Have a look at Jeff Thyers gear hobbing unit made
for use on Maureen seen in MODEL ENGINEERS'
WORKSHOP magazine, issues 258 & 259
and at the video here.
https://www.youtube.com/watch?v=vuXyHe3VUpY

I cut many gears on my Doreen using the
methods seen in the book Gears and
gear cutting ,the gear cutting is all based
on using this machine with a little ingenuity
and the Jeff Thyers setup you may be able
to adapt the machine to hob gears on your
Doreen.

John

[Anonymous]

If the OP is going to misappropriate my photos he might at least attempt to get the descriptions correct. The first photo is not of a gear hobber. It's a universal dividing head set up to cut a high helix angle helical gear, as shown here in more detail:

And the finished gear:

Such dividing heads are normally used on a universal mill, ie, one where the table swivels. The table on my universal mill only swivels ±45° so in order to cut a gear with a 70° helix angle it was setup on the Bridgeport with a right-angle head. This equipment would have been common in commercial workshops up until at least the 1980s when CNC started to make inroads. There are many forum members using ex-industrial equipment, so I doubt I'm the only member with this sort of capability.

In the second photo "caught" is hardly the right word, given the photo is in a public album. The idea that increasing the gear OD makes it a spur gear is nonsense. Long ago (50+ years when I was still at school) I cut a much larger gear using the same method, with a straight flute 2BA tap, just to see if it worked. As in the photo the larger gear was also a worm wheel.

It would be interesting to know how the OP would tackle this gear:

It would need one hell of a tap!

An underlying theme in posts by the OP shows an obsession with sofas and armchairs. Even if I had them nothing he's posted so far would have stirred me to get off them.

Andrew

[SillyOldDufferModerator @sillyoldduffer]

Posted by brian jones 11 on 15/09/2021 22:27:24:

…

I dont know of a simple system that allows you to cut gears with ease and speed (I am discounting the modern use of stepper motors for the job for the purposes of this discussion. No electronics allowable

…Hence my pursuit of a cheap charlie way of knock up spur gears …

But Brian, you should know of a simple system! I've mentioned it at least twice in this thread, provided a picture, and linked to Neil's Orrery Thread where he used the method to make many gears.

On the 20th August, I typed:

Using a tap to cut gears isn't new. I've experimented with it, but got much better results with a Sunderland Rack cutter and Rotary Table:

Neil Wyatt made a lot of gears this way for his Jovilabe Orrery a few years ago.

Unlike a tap, Rack Cutters get the number of teeth right and, with a little care, they cut an accurate involute. Rack cutting and Hobs do take longer!

Boils down to how much the operator needs an accurate gear as opposed a quick approximation. If gashing gears with a tap is 'good enough' for the job in hand, go for it! No-one objects.

The much despised armchair is a valuable engineering tool. They're good for research and thinking.

Is Mr Sunderland's method too complicated? It requires a:

1. Lathe and V cutter ground to turn the Sunderland Rack Cutter
2. Mill, milling cutter and horizontal rotary table (or other indexer) to relieve the Sunderland Cutter. (Could be done with a file.)
3. Mill with horizontal rotary table or other indexer, plus chuck to hold the gear blank.

The results are predictable. This home-made gear has the right number of teeth, it sits on ½" Meccano centres, and it meshes with the commercial plastic gear without shredding it:

Hobbers are preferred for mass-production because they churn out well-made standard gears quickly and efficiently. Sunderland is mostly used by industry to cut big bespoke gears, often by planing, but same principle.

Sunderland is slower, but there's no need to make a special hob, and it's possible to generate accurate involutes. The Sunderland method can be created in a small workshop without too much trouble, no pre-gashing is required, and results are reliable and predictable. I'd expect Sunderland to be faster than Brian's free method in practice because Sunderland produces fewer rejects. Sunderland wins whenever the centres, or exact number and shape of teeth matter. Sunderland versus Hob is a different debate!

Dave

[Martin ConnellyParticipant @martinconnelly55370]

Dave, I have made a single tooth, four cutting edges rack cutter (I know it doesn't make sense put like that) using a ground and polished carbide insert to turn a round piece of HSS. Coupled with a CNC mill with an A axis it is easy to cut gears, just a bit slower than a multi-tooth rack cutter, but since it is CNC you don't need to stand over it. As with a lot of this work more time is spent in the preparation and set-up, the actual machining time is not always the issue. The advantage of the single tooth is that one cutter with the correct pressure angle will do lots of different module or DP gears.

With CNC a lot of productive work is done sitting in a comfortable chair.

Martin C

[Anonymous]

If the gear profile can be drawn in CAD, then a special cutter isn't needed for CNC. Just use a standard ballnose endmill:

Andrew

[Author]

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