Difference Between Straight Cut And Hellical

[jiffo]

It isn't that straight cut (haha get it ?) you can't really say they are ~30% stronger, there are upsides to helical gearsets other than reduced noise. for example a helical gearface actually has a greater meshing contact area to distribute forces more evenly (we are speaking relatively about the gear sizes themselves obviously) helical gearsets are also more robust when you're considering axial loading.

Yes indeed, so much re-hashed misinformation in this thread.

You're not comparing apples to apples, no mention of material strength, face width and so on.

But IF you were comparing equal materials, face width etc, the helical eats a spur gear.

But don't take my word for it, do some research.

Look at the gearing on draglines, sugar mills, ship reduction gearboxes in fact anything with upwards of 1,000,000 ft lbs torque.

It's always helical or chevron (double helical)

You'll only see spur gearing on stuff like rotary kilns and the like where the gears daily eat rocks, have no lubrication and must be CHEAP to replace.

Spur gears are simpler to cut so tooling costs are down.

Thus the manufacturer can offer large choices of ratios.

[R31Nismoid]

So even tho straight cut is stronger, A helical OS Giken would be the choice. That equals WOW.... They must be really bad in that case as a straight cut is roughly 35% stronger then a helical. So if an Os GIKEN helical is stronger then a Straight cut PAR, then basically a helical PAR would be around 70% weaker then a Helical OS Giken. LOL

Your maths is as terrible as your logic.

You've been told what it means...

But lets try an even simpler version given you've missed the point twice already:

For a car thats driven on the street - the helical is the better choice because of the way you need to DRIVE the car/box with a DOG engagement in it.

And if you don't understand the difference, then a dog box is not the choice for you, simple as that.

[The Dan]

What I meant was the choice was easy considering the bad media around the PAR brand.

If you are going to make MORE THAN 1000hp then I can understand why you would want to be this particular about what is what and which set EXACTLY to go for but like I said....THE CHOICE IS SIMPLE!!

There is a question over the quality of the PAR gearset so you pretty much don't want to pick that one. You have literally like 2 others to choose from - PPG or OS Giken. Pick one......drive the car......have fun and forget about it.

Helical gears are quieter operation and I don't think anyone makes a helical gearset that is dog engagement, they will all be synchro

Straight cut gears are whiney and you can get either synchro or dog engagement. Choose synchro if you aren't sure. It won't make a difference unless you are building a dedicated (read DEDICATED) track car.

[Nizzzm0]

Is the PAR Straight cut gears a little larger than the OS giken Close gear Helical?

[HR32GTS 4DOOR]

Yes indeed, so much re-hashed misinformation in this thread.

You're not comparing apples to apples, no mention of material strength, face width and so on.

But IF you were comparing equal materials, face width etc, the helical eats a spur gear.

But don't take my word for it, do some research.

Look at the gearing on draglines, sugar mills, ship reduction gearboxes in fact anything with upwards of 1,000,000 ft lbs torque.

It's always helical or chevron (double helical)

You'll only see spur gearing on stuff like rotary kilns and the like where the gears daily eat rocks, have no lubrication and must be CHEAP to replace.

Spur gears are simpler to cut so tooling costs are down.

Thus the manufacturer can offer large choices of ratios.

This is exactly correct! A helical gear does have its advantages over a straight cut gear. Mostly being the contact face of the gear is wider. it is not just the width of the gear itself but the length of the actual tooth. The downside to this is that the gear will have a axial or sideways loading on it, which usually is the cause to the gear failure. The way to overcome this is with a double helical cut gear, but I do not know of any manufacturer who uses these in an automotive application.

Double helical cut gear (best example I could find)

I believe the main reason people think helical cut gears are weaker is because they are used in stock gearboxes so they think "Its from factory, so it must not be as good" where as the actual manufacturing process of the gear and type of steel used is the main factor in determining gearbox strength. ie how the gear set is heat treated/ precipitation/age hardened etc.

[Nizzzm0]

Is the PAR Straight cut gears a little larger than the OS giken Close gear Helical? I am talking the actual gears themselves, would anyone know details such as this?

[warps]

Yes indeed, so much re-hashed misinformation in this thread.

You're not comparing apples to apples, no mention of material strength, face width and so on.

But IF you were comparing equal materials, face width etc, the helical eats a spur gear.

But don't take my word for it, do some research.

Look at the gearing on draglines, sugar mills, ship reduction gearboxes in fact anything with upwards of 1,000,000 ft lbs torque.

It's always helical or chevron (double helical)

You'll only see spur gearing on stuff like rotary kilns and the like where the gears daily eat rocks, have no lubrication and must be CHEAP to replace.

Spur gears are simpler to cut so tooling costs are down.

Thus the manufacturer can offer large choices of ratios.

Finally someone with a clue!!

Straight cut have lower transmission losses, and can be used without sunchros (eg gear engagement as opposed to dogs / clutches). There endeth the advantages.

Oh, the most highly loaded gears in a dragline (propel) are spur gears. The helical gears (usually double helical) are used mainly in internal gears (hoist, drag, swing). Thes propel gears are responsible for skull dragging a 7,000 tonne machine through the dirt.

[jiffo]

Yep Warps, perhaps my dragline choice was not the best.

Last company I worked for made shafts/gearing as replacements for draglines, chiefly Bucyrus Erie.

Lots of double helical stuff but grossly under designed. Replacing some gearing monthly due to the duty cycle we push machinery in Aus.

Tiny gearing that looked so out of place in a massive machine.

The sugar milling stuff was the real deal, especially gearing sent overseas where local managers work their mills much harder than they were ever designed for.

They'd push the cane through though until eventually a massive choke up, all the roller's stalled.

So they go and open up ALL the valves on the turbine, back up the rollers and then gun it ahead and watch those rollers chew there way through until she clears, you have to trust your gearing.

Unfortunately the O/S managers don't turn those extra valves back off on the turbine so next time they get a choke it's a dig out job.

Only small double helical stuff I've come across is bull gear reduction in truck diffs. Pretty horrible, never heard double helical run nicely unless the pinion is allowed to float on its shaft.

Again the tooling costs outweigh any advantages.

[Nee-san]

I designed a mining conveyor for use in arctic climates, used chevron gears.

Worked in theory

[GTSBoy]

A mate of mine designed a bridge that was built in Fiji. Said he would never drive over it.

[Nee-san]

A mate of mine designed a bridge that was built in Fiji. Said he would never drive over it.

Civil Engineers, haha.

[warps]

Naah I'm sure the design was good - just poorly implemented

So who did you work for then, Jiffo? I run shutdowns on draglines, and we buy gears from Bucyrus (made locally under licence), as well as all the pirate companies in Oz and O/S.

Monthly changes? Man, what were they doing? I've found that when properly set up, the normal lifespan of the internal gears is anywhere between 30,000 hours and 150,000 hours, depending on application. We saw one of the Marions with incorrectly aligned bores in the hoist gear case was spitting out input pinions every 2-6 weeks until we rebored the case. This is going back a few years though.

[GTRAAH]

I found this comment on another forum interesting >>>>>>>

Yup, There may be more "teeth" in contact on Helical. But there is Less Contact Area on those teeth on contact. With helical, its contact in the center of the tooth, or on the ends. But never the whole tooth and the added up contact area does not equal the contact area of a straight cut gear. Take some gears, and put marking compound on them, then mesh them You will see how little contact there is at any one time. Ya contact might be on 2 teeth, but its 2 little sections of those teeth, at the ends, or one section,in the middle. And that middle contact section works out to roughly 2/3 of a straight cut gear. Depending on diameter of gears

Real life has proven it over and over. Like Luvmyhelis, I too have performance cars with a lot of HP. Helical gears do not last in my trannys either. Swap to straight cut, and they hold up just fine. Noiser tho. Same gears, same thickness metal etc.

Heck, look at the transmission gears in real heli's. I bet there straight cut too

Straight cut is stronger, Helical is Smoother.

Incorrect on the teeth contact area, actually there are MORE area in contact, the reason that high HP racing cars go for straight cut gears is improved efficiency and no thrust loads. The reason that car gearboxes fail with high HP setup is that the box with helical gears was never designed to accomodate the higher thrust loads, so fitting straight cut gears eliminate the thrustloads and the stock box can handle the increased HP.

Rule of thumb is,

HELICAL GEARS = quiter, higher torque loads, decreased efficiency

STRAIGHT CUT = higher noise, increased efficiency and elimanates thrust loads.

[jiffo]

I'm happy you're convinced yourself, but ........

I've no idea what your prussian blue man was trying to prove, surely he didn't think a helical gear has full face contact across 3+ teeth simultaneously. I mean really?

Helical gear contact is a moving point load across multiple teeth at varying positions on each tooth as the gear rotates. Thus you have the load spread over a larger periphery of each gear than a spur gear which is fully loaded in one small section.

Factors such as helix angle, module and PCD's will be altered by the designer to achieve the most economical outcome.

Perhaps a Skyline owner could imagine it thus:

Put a jack under your chassis rail, start jacking and its going to buckle the rail.

OR Place a piece of timber on the jack to spread the load and it won't buckle the rail so easily.

OR Place 3 or 4 jacks under your chassis rail, again the load is spread over a larger area.

Like I said previously all big gearing is helical, for a reason.

Small automotive spur gears are also made for a reason.

[Nee-san]

I'm happy you're convinced yourself, but ........

I've no idea what your prussian blue man was trying to prove, surely he didn't think a helical gear has full face contact across 3+ teeth simultaneously. I mean really?

Helical gear contact is a moving point load across multiple teeth at varying positions on each tooth as the gear rotates. Thus you have the load spread over a larger periphery of each gear than a spur gear which is fully loaded in one small section.

Factors such as helix angle, module and PCD's will be altered by the designer to achieve the most economical outcome.

Perhaps a Skyline owner could imagine it thus:

Put a jack under your chassis rail, start jacking and its going to buckle the rail.

OR Place a piece of timber on the jack to spread the load and it won't buckle the rail so easily.

OR Place 3 or 4 jacks under your chassis rail, again the load is spread over a larger area.

Like I said previously all big gearing is helical, for a reason.

Small automotive spur gears are also made for a reason.

I'm almost moved to tears.

[GTRAAH]

Convinced? Who knws you 2 can debate this if U ever find him...

But you know how you said "But IF you were comparing equal materials, face width etc, the helical eats a spur gear"

Does this mean automobile straight cut gears usually have a bigger facewidth to make them stronger? because why else would they be sold and marketed as being stronger

[The Dan]

Like I said previously all big gearing is helical, for a reason.

Small automotive spur gears are also made for a reason.

Yes, the reason big gearing is helical is because it's big. You create enough of a harmonic on a straight cut gear that's THAT large it would shake the machinery to pieces. Just because large machinery uses helical gears, doesn't make them stronger. The gear on gear strength may be stronger (if you say so) but the GEARBOX as a whole is weaker because the two gears are always trying to seperate each other. Seperate them enough and they tear themselves apart.

[The Dan]

Convinced? Who knws you 2 can debate this if U ever find him...

But you know how you said "But IF you were comparing equal materials, face width etc, the helical eats a spur gear"

Does this mean automobile straight cut gears usually have a bigger facewidth to make them stronger? because why else would they be sold and marketed as being stronger

It's a conspiracy. I will start importing second hand skyline gearboxes. All you guys just keep running them. They are stronger I tell you.

I'm going to be rich!

[warps]

Yes, the reason big gearing is helical is because it's big. You create enough of a harmonic on a straight cut gear that's THAT large it would shake the machinery to pieces. Just because large machinery uses helical gears, doesn't make them stronger. The gear on gear strength may be stronger (if you say so) but the GEARBOX as a whole is weaker because the two gears are always trying to seperate each other. Seperate them enough and they tear themselves apart.

How big is big? The gear shown below is straight cut, and no harmonics to speak of.

Also, what do you mean by the gears trying to separate each other? If you mean radial load, then that's a function of the pressure angle, not whether or not it's helical. The pressure angle is generally between 20-25 degrees (rule of thumb)

If you're talking about axial thrust, then this is one of the problems already discussed re: helical gearing. Big torque loads will cause big thrust leads, which can cause a problem

[The Dan]

How big is big? The gear shown below is straight cut, and no harmonics to speak of.

Also, what do you mean by the gears trying to separate each other? If you mean radial load, then that's a function of the pressure angle, not whether or not it's helical. The pressure angle is generally between 20-25 degrees (rule of thumb)

If you're talking about axial thrust, then this is one of the problems already discussed re: helical gearing. Big torque loads will cause big thrust leads, which can cause a problem

What I am talking about is the spiral separation of the gears trying to twist off each other. I am fairly sure that is what you are referring to as axial thrust (I don't know the technical term) but it definitely causes problems due to that thrust.

You are correct though, pressure angle is usually about that amount.

The helical gear itself is stronger but due to the thrust loads you have mentioned, these boxes suffer as a result. That's why straight cut gears are generally referred to as 'stronger'.

The reason a helical gear is stronger compared to an equivalent spur gear is because of the surface area of engagement (yes I know you know this - others may not). There is a certain amount of vibration in spur gears when used in higher RPM situations. That gear pictured....what rpm would it be spinning at?

At the end of the day it all comes down to the material used. A nissan helical gear is never going to be as strong as a billet or forged helical or spur gear in the same application so a lot of people get confused when 'helical is stronger than spur gear' is mentioned