How does this design work? (drawing provided, simple gear & shaft) 1

[Vah1D]

Hey everyone, if you look at the image, you'll see two similar designs, the main idea behind these two was how the shaft in the right hand design is cheaper to make since compared to the gear shaft in the left picture a large shoulder was eliminated and replaced by just a washer/spacer which serves the same purpose (acting as a base for the gear, and axially fixing it), which is pretty straightforward.

My question however is how these two designs actually work? The gear obviously supposed to rotate relative to shaft (shaft acting as an axle), now it seems there's a bushing on the ID of the gear which acts as a bearing, but what about the fact that it's sitting tight against the shoulder (or washer in the right hand picture)…wouldn't that create lots of friction and prevent the gear to rotate properly? What am I missing, any ideas?

If the gear thickness is slightly smaller than "shaft head" then after you mount it on to the shaft, there will be some axial play, which means gear is not clamped tight against the shoulder (or washer), so that might allow the gear to rotate easier, but still there will be a lot of contact.

This is not a school problem, just a picture I found in an old design handbook!

https://imgur.com/a/dM1GUrT

Thanks~~

 

[drawoh]

Vah1D,

I would have to see more drawings to be certain of what that is.

The section to the left on both views looks to me like a fixed, permanent structure. Whatever that is rotates inside the hole, hopefully, slowly. The section on the right appears to be a gear. The small section on the extreme left is either a nut or a small gear or sprocket. My interpretation is that everything rotates rigidly together inside the fixed structure, increasing the probability that the little piece on the left is a gear or sprocket.

Consider the possibility that someone invented this mechanism merely to illustrate a principle of DFMA.

--
JHG

 

[LittleInch]

I agree with drawoh.

It's not clear at all that the item on the right rotates around the shaft.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[handleman]

It's obvious that the thing on the right is a gear that rotates about the shaft. It is drawn as a gear, with those centerlines showing the pitch circle diameter. The shaft is clamped tightly to the housing on the left by a locking nut. On the right, there is certainly a bushing for rotation. Probably slow rotation as mentioned. A very small clearance (maybe 0.1 to 0.2mm, depending on scale) is guaranteed by the manufacturing tolerance of the shaft and gear. The clearance is, of course, too small to show in the figure, but would be apparent if the dimensions of the components were shown.

 

[Scuka]

The thing on the left is most likely a retaining nut which holds the shaft fixed against the structure.
Left side of the shaft has a gear that's mounted on a bushing. Shoulder and bushing length can be a tiny bit longer than the gear so bushing can be clamped by the rightmost bolt and washer without clamping the gear. Sure, it introduces a fraction of a millimeter of axial play, but that doesn't have to be an issue.

 

[Jboggs]

I think the item on the left is a bearing locknut (ala Whittet-Higgins style), to lock the shaft in place. The "washers" on either side of the gear could be bronze bearings, thus capturing the gear with lubricated surfaces.

 

[LittleInch]

OK, looking a little closer it seems that the LHS is anchoring the shaft to the mysterious frame which is shown only in part.

The top hat shaped element on the RHS around which the gear moves? on the second drawing provides the resistance to the nut on the LHS against the frame.

The disadvantage seems to be that if you remove the gear then the shaft falls out as there is no reaction force like there is on the first example.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[drawoh]

It's obvious that the thing on the right is a gear that rotates about the shaft.

The gear will not rotate about the shaft if the screw on the right is tightened down hard. It is not a good design unless there is a shaft key not being shown. This is one of the reasons I suspect this thing is not a real design.

--
JHG

 

[Vah1D]

Thank you all, seems like everyone is agreeing that the shaft is locked and is not rotating relative to housing. I think it threw me off because usually it's the shaft that's rotating and supported by a bearing (and rotates together with the gear, keyed), whereas here the gear is mounted directly on a bushing.

Drawoh,
Unfortunaly that was the only picture.

LittleInch,
I think the shaft won't fall out in either of the designs.

For those who are interested, this was from the book: "Fundamentals of Machine Design" by P. Orlov. It was published in 5 volumes, but for some reason Vol. 4 and 5 are nowhere to be found in English translation.

First three volume though can be found with pretty decent quality on archive.org, impressive series (at least for me, lots of great material)! (downloadable directly from archive.org)

https://archive.org/search.php?query=creator:"P.+Orlov"

Picture was taken from this specific page:

https://archive.org/details/FUNDAMENTALSOFMACHINEDESIGNORLOVVOL2/page/n193/mode/2up

If somebody has or know where to find Vol. 4 and 5 please share with us as well!

Vah1D

 

[rb1957]

this looks to be a fairly typically airplane joint (like between the pieces of a "torque scissor".

Although the outer details seems to show a toothed gear (on the RH side of the joint) ... so maybe attaching a gear to a structure ?

The only difference I can see is (a) has a narrower hub (which they seem to call "shoulder height" ... odd that)
and I'm not sure why the washer changes ??

another day in paradise, or is paradise one day closer ?

 

[Vah1D]

rb1957,

I also found the term "shoulder height" weird. Since this is a translation from Russian, I thought the author probably meant "Reduction of High Shoulder", but perhaps the translator made an error and translated it as "Reduction of Shoulder Height"? just a guess.

As far as why change to the washer, this was a DFM example, basically getting rid of the large OD shoulder and replacing it with the washer, then manufacturing of the shaft will be more cost-effective without affecting the function.

Vah1D

 

[SnTMan]

Well, I'm spitballing here, but suppose:

In Figure (a) what appears to be the shaft has an extended shoulder tagged as "m". In Figure (b) this shoulder is replaced by a washer(?) tagged as "n", thus yielding a "Reduction of shoulder height".

That's about all I can make of it.

Regards,

Mike

The problem with sloppy work is that the supply FAR EXCEEDS the demand

 

[rb1957]

what is it you're trying to get from this ? Designing a gear attachment is well understood, no?

another day in paradise, or is paradise one day closer ?

 

[cowski]

The only difference I can see is (a) has a narrower hub (which they seem to call "shoulder height" ... odd that)
and I'm not sure why the washer changes ??

In version "A", the feature "m" is milled into the shaft, creating a shoulder between the gear and whatever is on the left. In version "B", the shaft is slightly larger OD for the gear (smaller on the left), creating a small shoulder for the new washer (item "n") to fit next to. The version "B" shaft can be made from smaller OD stock. There is still a shoulder in the shaft, but much smaller than version "A"; I think "reduction of shoulder height" is accurate.

 

[rb1957]

good catch, good explanation.

another day in paradise, or is paradise one day closer ?