What is the consequence of a very low number of teeth on a gear?

[Factao]

TL;DR

I've got two gear, one with 10 teeth and one with 20 gear (despite the fact that I should avoid repetitive pair of teeth contact). Is there is any issue with using gear with that little amount of teeth?

As summarized, I've got these two gear, and another stage of 15:10. I need my gear box as small as possible, and I've never work on this scale with gear (the module is 0,9mm, so this is pretty small). I know that this question is very simple, but I did not find anything relevant on the web, so don't mind sending me on another topic or whatever that is related.

 

[jrmichler]

It depends. If a gear has too few teeth, the teeth are undercut, which weakens them. Lightly loaded gears can tolerate undercut. If you are using gears from a catalog, the catalog load ratings take any undercut into account.

I once designed a gear with six teeth and no undercut by using profile offset. It worked very well.

 

[Factao]

There is no precision issue?

 

[Baluncore]

There is no precision issue?

The speed, torque and MTBF specifications will determine the precision required for the material and manufacturing technique employed. You have not yet specified those parameters.

 

[Factao]

The speed, torque and MTBF specifications will determine the precision required for the material and manufacturing technique employed. You have not yet specified those parameters.

I am 3D printing (FDM) my gears with PLA, so I am expecting a low torque, a low speed and a MTBF as considerable as the error margin. However, I could reformulate my question: If we consider the same manufacturing processus, material and similar usage condition, will a pair of undercuts gears be precise as a pair of more conventional gears?

 

[Factao]

I am 3D printing (FDM) my gears with PLA, so I am expecting a low torque, a low speed and a MTBF as considerable as the error margin. However, I could reformulate my question: If we consider the same manufacturing processus, material and similar usage condition, will a pair of undercuts gears be precise as a pair of more conventional gears?

I want to gear up the torque of a servo motor ,without reducing its precision, while saving space with smaller gear, despite the FDM precision default for small detail.

 

[Tom.G]

without reducing its precision = anti-backlash gears, precision (instrument) bearings, precision machining

while saving space with smaller gear = planetary gear train

Alternative-1: rewind the motor with larger wire to allow higher continuous current without overheating.

Drawbacks to Alternative-1:

• This works only until you reach magnetic saturation in the motor
• Must reduce motor Voltage to maintain same speed

Alternative-2: If duty cycle is low,

And needed torque increase is low,
And speed is Not critical,
Then Increase motor voltage
​

Alternative-3: Purchase a servo with the gear-train included as a pre-assembled unit.

Small, Strong, Precise, Cheap. Pick 2 (or maybe 3 if you're a magician)

 

[Factao]

Small, Strong, Precise, Cheap. Pick 2 (or maybe 3 if you're a magician)

http://emanual.robotis.com/docs/en/dxl/x/xl430-w250/#specificationsThis little beast is quite balanced for its price.

As for the gears, I understand, from your reply that undercut gear doesn't affect the precision more than normal one, unless I miss something.

 

[Tom.G]

This little beast is quite balanced for its price.

Wow, sure is. I was going to suggest you try for the next larger torque rating but I see the price goes way up.

As for the gears, I understand, from your reply that undercut gear doesn't affect the precision more than normal one, unless I miss something.

I'll defer to @jrmichler on that. He's a local expert in that part of the field and I am definitely not!

Cheers,
Tom

 

[Factao]

Well, thank you for this, I will massage him.

 

[jrmichler]

Undercut affects tooth strength. Precision affects running smoothness, noise, and fatigue life at high speeds. They are two different things. Here is an image showing an undercut gear meshing with a rack:

Undercut can be eliminated by redesigning the gear with profile offset, but that increases the sliding action when the gears mesh. Search undercut gears for more information.

3D printed plastic gears will not be precise. If your application is low load and low speed, then design for the fewest number of teeth and use profile offset to reduce/eliminate undercut. If you are designing with SolidWorks, there is a module available for designing gears that makes it easy to specify variables such as profile offset. It's Gearcalc or Geartrax or something like that. The high end gear design package is Kisssoft, but I don't know if it integrates with solid modelling packages.

Well, thank you for this, I will massage him.

Massage no, message yes.

 

[Factao]

Thank you for this.

I kind of forget how to set this tread as resolved... How do I do that?

 

[rcgldr]

One issue with a small number of teeth on a gear is the number of teeth engaged at anyone time is reduced, but this would be taken into account for the specified torque rating.