Gearotic Query

[Steamer1915Participant @steamer1915]

I have just had a play with Gearotic and was looking at an example of a Herringbone gear. I understand that for the gears to be in line with each other (as opposed to being at ninety degrees) there will be need to be one right-hand and one-left hand gear.

The query I have is that it would appear that there is no rounding of the apex of the tooth to correspond with the radius left by the cutter at the "internal angle" for want of a better description.

The simulation doesn't appear to show any rounding of the tooth apex. Is this something that is taken care of when processing the G code?

Best regards,

Steve.

[Steamer1915Participant @steamer1915]

Herringbone teeth clearance.

[Anonymous]

I've never managed to get Gearotic to run properly, so I can't answer the question about the G-code. However, I can pontificate about herringbone gears.

Herringbone gears only run with parallel shafts.. Of course to get the characteristic shape you need a left hand and right hand segment. If the internal corner at the apex is not sharp, then the gear is not a true herringbone gear. There are ways to avoid the need to machine a sharp internal corner, such as bolting together two helical gears of opposite hand, or leaving a small gap at the apex. Herringbone gears came into prominence as reduction gears for steam turbines, ie, high speed and high power. So accurate meshing of the gears, and hence the precise tooth shape, is critical. Normal gear hobbing cannot be used to make herringbone gears. Instead shaping is needed. One way was developed by Sykes, using two reciprocating, and rotating, hobs allowing a sharp internal corner to be formed at the apex:

**LINK**

An alternative planing method, using rack form cutters, was developed by Sunderland. There must be some advantage in the true herringbone form in terms of performance, or expensive, and relatively slow, machines would not have been developed to plane them from the solid. Of course the process has now been converted to CNC:

**LINK**

Andrew

[Steamer1915Participant @steamer1915]

Thanks for that Andrew,

I had a senior moment when I said about the Herringbone gears running with the shaft running at 90 degrees. I was of course thinking about helical gears.

My question relates to Gearotic.

Anybody?

Steve.

[simondavies3Participant @simondavies3]

Posted by Andrew Johnston on 09/02/2017 11:47:20:

I've never managed to get Gearotic to run properly, so I can't answer the question about the G-code.

Andrew

+1, I always assumed it was just me!

[John Stevenson 1Participant @johnstevenson1]

OK,

I was involved from the get go on the development team with Art Fenerty of Mach 3 fame and Bob Landry.

Like a lot of software it grew in demand for added features and Gearotic 1 slowly out grew the ability of it's core program to build on.

This then changed to V2 and now to V3. Unfortunately feature creep has crept in and Art's goal now isn't so much gears an kinematic mechanisms. I slowly dropped out some where about late V2 but all isn't lost.

The early version, now known as Gearotic1 is still available from the downloads page although when you run it I think it says V4.xx or something.

I also think you need to have the latest version installed whether you use it or not to get certain dll files.

However once it's all installed you can then run the earlier version which works and is very simple. One drawback is it was never developed as far as the later versions so some things are missing line herringbone.

Now on to herringbone. These were developed by Citroen hence their chevron trademark.

Main use as mentioned was in very large reduction drives like turbines. The reason for the shape is that helical gears are quieter than spur as you have a gradual change over from tooth to tooth because of the angle. One problem with helical gears though is depending on the head they have a thrust value what is opposite and increases with the helix angle.

The Herringbone gear was developed to neutralise this as one side cancels the other. On a large reduction drive purely on helical gears, the thrust of the small pinion is enormous.

Now to the original question. The graphics draw the gear OK and code it OK but they can't take into account the cutter radius so yes you do get a small radius in the corner of the internal teeth. What really should have been done is to round the external corner to match. Art realised this but didn't do anything other than in usual Art "Lets go off and see just what we can do " mode he developed the knuckle gear. There is one in the top left corner of the web page with two helicals which are all gears I cut whilst checking code etc.

This is the picture.

But to get back to herringbone, yes they can be made on specialised equipment without the radius as Andrew says but it actually pays to put a central groove in to stop the extreme hydaulic forces when the lubricating oil gets forced into a sharp corner.

So anyone having problems with Gearotic and only wanting to do simple gears like spur, helical etc please have a go with the original program

[simondavies3Participant @simondavies3]

Thanks John, I will try again when I have a mo.

[Steamer1915Participant @steamer1915]

Thank you John,

An interesting point about relieving the centre of the gear for the hydraulic forces. Just make it wide enough to clear the cutter radius and the problem is solved. Never crossed my mind.

Steve.

[John Stevenson 1Participant @johnstevenson1]

I once saw a large set, probably in a museum or such where although they had been cut correctly they had been drilled from the front at an angle so the hole came out at the root of the internal tooth so someone else had also recognised a problem.

 

Going back thru some old photos and this one is dated end of May 2009 I did actually cut a herringbone with a centre rib but I'm now puzzled how I did it as the later Gearotic wasn't out then.

 

 

Not the clearest picture but the machine would have been one of the early X3's that Ketan at ARC used to sell a kit for. No idea what happened to the gear unless it's on the CNC display board down at ARC ?

Edited By John Stevenson on 09/02/2017 19:03:21

[Steamer1915Participant @steamer1915]

John,

Could you have cut that as two separate helicals?

Steve.

[John Stevenson 1Participant @johnstevenson1]

Wouldn't have thought so be hard to stitch two programs together as this goes from one side right through.

On seconds thoughts I might have cheated and used a form cutter in D bit form and hand coded the gear.

Not as bad as it sounds, send the cutter across at say 45 degrees to the centre point, then back, then index one tooth and rinse and repeat. Not the answer you were looking for but it's probably the correct one give the time period.

[MichaelRParticipant @michaelr]

 

Now I know what the Citroen car logo represents.

Mike . Sorry should be in the Citroen Gear Thread.

 

 

Edited By MichaelR on 02/06/2017 08:28:05

[Howard LewisParticipant @howardlewis46836]

It is not just Herringbone gears that can produce unwanted hydraulic pressures.

Gear type lubricating oil pumps can do this; and the greater the precision, the greater the problem!

Once, I was involved in solving the problem of ERW steel oil pipes splitting. As the engine was running, they "rang". When instrumented, the Bourdon tube pressure gauge was showing 60 psi, but the pressure transducer was showing spikes of 600! The solution was to increase the tooth tip clearance, to allow leakage so preventing the oil from being trapped in the root of the tooth.

Howard

[Author]

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