Thread: Spur gear noise and D.P

I am glad you opened this thread, I just finished uploading and chasing pictures for you.

I don't find mine to be noisy, mainly the out board gears that you change.

I found the picture in my manual that give you the position of each gear, then the other chart I posted earlier gives you the teeth numbers.
I also included the charts that go with it for threading.












Dave

Selection of pitch size when designing gear trains is as much about tooth strength as anything else. For a train such as for thread cutting on a lathe it probably doesn't matter. For a car gear box it may - if you think about the cross section of the tooth, a larger DP is going to be thicker and so stronger.
Noise is an interesting thought. I have no information on that but my theory is that as the teeth engage in an imperfect train new teeth just starting to engage will hit a tooth on the opposite gear (a perfect gear train will be in perfect mesh all the time). Because of that, tooth size will have little to do with the noise generated (may influence frequency though). All of the gears I've cut are steel which rings like crazy anyway, so an impact anywhere is noisy.

Michael

Thanks Michael,
Nice point on the strength thing, but as you say, a QC gearbox isn't really a problem. My lathe currently has 14DP gears, and they are more than ok at say 500rpm, but as you approach 1000rpm they get real noisy. I know it they are not engaged properly that won't help, but just wasn't sure if more teeth engaged at the same time would mean a smoother and quieter drive. I was planing on making mostly steel gears but with brass "engaging gears", and make a few spares so the steel gears should last forever. The time it takes to cut doesn't worry me, i want to set the shaper up and i can just sit back and be mesmerized.....

Spiral cut gears are quieter because they are "continuously" engaged with the mating gear. Spur gears will always be noisier I think because of the action they have. One trick I have seen to help set engagement is to use a strip of paper between the gears, set them "hard up" against each other and then remove the paper - it gives a very small clearance. It may help but relies on the teeth being concentric with the shaft (that is, no high spots on the gear(s))
The main issue to me seems to be the ringing of the gears when they are impacted. If you are trying to get a quieter train, then perhaps gears made of an engineering plastic like Acetal, Nylon, Tufnol or others that don't ring as much may be worth thinking about. Brass would perhaps be a little quieter, but the steel gear will still ring from metal to metal impact even if the brass doesn't.
I was also thinking about a steel gear with some sort of dampening element in it that would stop it ringing, either by cushioning the tooth or some sort of damping or isolation device to stop the whole thing acting like a cymbal. (Maybe some lead plugs in it, or a sheet of softish rubber sandwiched to one face)

Michael

Originally Posted by Ueee

Hi,
Just a question about gears, we all know that spur gears are noisy, but does the D.P or module of the gear affect the noise? ie will a 20dp 32 tooth gear be as noisy as a 10dp 16 tooth?
I did some googling but couldn't find any info relating to noise, or how to choose pitch sizes when designing gear trains.

Hi Ewan
I heard somewhere that if you threw a handful of casting sand in the gearbox you can have lapped gears. That will make 'em quiet
Seriously though, lapped gears are quieter.

Phil

Originally Posted by Steamwhisperer

Hi Ewan
I heard somewhere that if you threw a handful of casting sand in the gearbox you can have lapped gears. That will make 'em quiet
Seriously though, lapped gears are quieter.

Phil

Yeah i heard that somewhere lately too?????

Once i have the shaper set to up to cut spur gears, i may try to angle the jig by 5 or 10 deg on the table and cut the "fake" spiral cut gears i posted about a few months back. I guess i could run the box in with some lapping compound in a syringe and go through them one by one.....although i would be better doing it before hand with a jig and some sacrificial bearings.
Surely if lapped gears are better, so would lapped bearings? H&F seem to think they should lap everything...

I think these lathe gearboxes are just assembled on a bench strait from the painters. I couldn't see them lapping anything, (other than the block when arriving at work to get a bike parking spot)
They did lap my mill head to fit the quill, it looks like they took to it with a rough honing stones on a hand drill to get it to fit. Very nice (nasty) finish if may say so.

Interesting discussion on the gear noise, it bothers me as well with the out board gears ringing, sometimes I go to pick up and answer them.

I wonder if the centre portion was machined out say 3mm deep and something poured in would help with dampening?

Dave

When i was an apprentice, we had a saw blade that rung like the local telephone exchange..... It had the typical expansion slots, ending with maybe 1/4" holes. We filled the holes with epoxy and the blade never rang again...that was until the epoxy came out.

I think some saw blades have a shallow "fuller" in them about 1" from the gullets, i was told this was to stop any resonance in the blade. I think drilling a couple of holes and filling them with lead might be a good solution. (for gears that is)

The noise i get though is not what i would call a ring.....its just damn noisy! I'll try to record it......

Originally Posted by Dave J

I think these lathe gearboxes are just assembled on a bench strait from the painters. I couldn't see them lapping anything, (other than the block when arriving at work to get a bike parking spot)
Dave

What, you mean they let them leave the factory at night???? but they could be working!

Is there enough clearance in the gear train.

Originally Posted by pipeclay

Is there enough clearance in the gear train.

Yes i think so.....some of the gears are not quite concentric so setting up is a bit tricky. Of course the lack of concentricity will be adding to the noise somewhat, but i don't plan to use any of the old gears at all when this all come to fruition.

Originally Posted by pipeclay

Is there enough clearance in the gear train.

Hi Peter,
Not sure if this is directed at me, but I have tried everything to quieten them down, but gave up many years ago.
It's not that bad really so I just put up with it, but if there was a simple fix it would be good as that is the nosiest part of the drive and I leave it engaged always.
I have tried the paper trick, by eye, with oil, with grease, etc, etc.
Just after buying I I made sure everything was in alignment, and found it's all is.
Like I said it's not that bad, but would be good to get rid of that noise.

Dave

One problem I had when I got my lathe was the arm that holds the change gears(quadrant?) and the bolt for locking it weren't square to each other so when you tightened the bolt it twisted the gears. Although it was awhile go I do think it made more noise. I made up spherical washers so the bolt wouldn't pull the arm when it was tightened. I dont think it was my week with the camera so I may not have any pictures, though I could get some if anyone needs them.

Stuart

How about some banana skins? Works for noisy diffs.

From what I know about gearboxes (mostly GM) the angle of the tooth relative to the gear axis has some bearing (LOL!) on noise. For instance boxes like the Saginaw were quieter than the Muncie 'Rockcrusher' which has a gear angle of only 7 degrees.

If a gear has teeth, say, of 20 degrees it would follow that for a constant diameter, number of teeth, etc that there would be more tooth surface in contact with other teeth compared with a 'straight cut' gear, and would be smoother and hence quieter.

Curved teeth would give even more surface area in contact than straight teeth because a curve is longer than the chord of a circle.

I'll shut up now. I'm starting to scare myself.