Gears...

No.

Well, maybe... A worm gear is a type of helical gear, shown here with a pinion gear.

Found this on Wikipedia.

Did you really need someone else's help?

You could have done this search yourself.

It is doubtful that the pictured gears are capable of transmitting much of a load. Most pinion gears of a worm have a concave surface to mate with the worm gear for more uniform tooth loading. Those two gears appear to be unrelated or for a lightly loaded application like a clock drive. Many heavy duty worm drives will also have angular contact in order to have more uniform tooth loading and smoother meshing like synchronized gears have.

Dear Mr. Spinco,

The picture as it appears to me - is not HELICAL. It is WORM and Pinion.

DHAYANANDHAN.S

Same to me. Never said it was Helical SET of gears, just said it was either a lightly loaded worm and pinion set such as for a clock or the pinion wasn't the proper mating part since the teeth on the pinion were a straight helicalcut and not the concave angular cut you would generally find on a heavier duty worm and pinion set as shown below;

If the axes are parallel, definitely no. However, there might be a possibility if the axes are skew.

A spur gear has straight teeth.

A helical gear has curved teeth.

The answer is still no.

A spur gear can mesh (imperfectly) with a worm gear if the shafts are perpendicular nearly perpendicular.

This photo from Wikipedia shows such an arrangement.

Note that these are Meccano gears. (These came -- or still do?? -- in sets that could be considered toys or prototyping sets, depending upon your perspective.)

In this video you can see several sets of Meccano worm gears driving ordinary spur gears.

The mesh is improved somewhat if the shafts are out-of-perpendicularity by an amount equal to the helix angle of the worm. In practice, this is rarely done because non-perpendicular shafts cause related design difficulties. So the common alternative is to angle the spur teeth -- making the spur no longer a spur -- there is a slight helix angle.

However, sometimes for indicating purposes (such as driving a speedometer from a transmission output shaft) or other uses where the load is very low, a straight cut spur meshes with a worm (even outside the world of Meccano and Lego, where such things happen commonly).

When you look at how the mesh might be improved (so the contact is not on a single point at any instant, for example) you can make little improvements. For example you can "wrap" the spur around the worm and vice versa, creating "double-enveloping" gears. For a long time, Cone Drive held patents on such gearsets. As you can imagine, these are not simple to machine.

My lathe has a threading index indicator driven by the lead screw. The gear on the indicator shaft looks like a spur gear but is really a helical gear, with the teeth angled to match the lead screw angle. So far, this would be one step better than the Meccano arrangement -- despite the fact that there is essentially no load at all on the indicator gearing. But in addition, the indicator gear also envelopes the lead screw somewhat: a pretty fancy little gear.

A straight cut (especially nylon) and relatively narrow spur gear would serve the purpose. All the "load" would be on one corner of each spur gear tooth, and over the years, the teeth would start to look helical. But a nylon spur gear would be $.06, and a brass enveloping helical gear would be $.50... maybe even more. All around the world, there are MBAs voting for going with the nylon gear in applications like this.

This reminds me of double axle trailers, which can theoretically only go straight. But in practice they manage to skid their way around turns all day every day. Sometimes good enough is good enough. (Appliance manufacturers take this thinking much too far, in my view.)

OK,

Yes, it can be done.

But not necessarily should be done!!

In the worm gear pair, worm screw is helical and worm wheel (gear) is also helical. Of course, the worm wheel is helical with long pitch. An application may get away with a straight spur gear, if it is a toy set or non-loaded (well, much) requirement. But if used for load bearing purpose, even a spur gear is used for mating with a worm, eventually a helix would be generated by burning in.

Helical is also SPUR gear

Meshing Decoratively--YES

Power Transfer in Mesh -- NO-NO!

Crazy Proposition --YES

Neither a worm nor a spur gear is the same as a helical gear. Various persons are confusing the terminology.

NO.

You have asked two separate questions, as a pinion is not necessarily a spur gear.

A spur gear by definition has straight cut teeth. A spur gear will not properly mesh with a helical gear due to the angular force imposed by the helical design. The spur gear would continually try to slide sideways out of the mesh.

In contrast, a pinion is simply the smallest gear in a mesh. In a helical gear set where two gears are not the same size, the smaller gear would be appropriately called a pinion.

Seems to me that there is an underlying question here, for example, "if I have a certain gear configuration, can I drive the same gear in two different ways - linear and rotational?" or "how can I best vary the rotational velocity of a gear over a single cycle?", or some other similar question. Is there an underlying question that you are wondering about?

If you are just looking to "trip out" try:

http://www.core77.com/blog/object_culture/wrap_your_head_around_these_gears_21784.asp

Had a comment but nevermind!