I thought I would post this in the open forum and solicit some feedback. I have been looking for sources for gear manufacturers and if they are out there thy advertise very little and generally seem to trey to tell you as little about the manufacturing, heat treatment, grinding / shaving as humanly possible. I found a supplier in Japan, who I have not yet given anything to quote, but who do have an excellent English language educational material on all variety of gears and they even have gear calculation software which requires registering with their server and the calculators are very detailed as they work through the gear design process.
Below the english website with their stock gears. https://khkgears.net/new/
View attachment 165190
The educational part of the site, many pages of detailed info. https://khkgears.net/new/gear_knowledge/
View attachment 165191
Here is the signup page for their gear calculator
https://khkgears.net/new/gear_calculator.html
Here is the gear calculator page for spur gears
View attachment 165192
You can see it is arranged like a spreadsheet with different tabs, with the first tab being "Size calculator", followed by "Strength Calculation" and so on. Obviously the Japs use SI units. Comfortable for me.
The second tab is where it gets interesting, because for the strength calculation all of the sizing factors come into play (geometry) as well as the choice of accuracy class, material selection, heat treatment (quite detailed). These details determine the maximum allowable stress on the gear tooth and thereby the torque capacity of the smallest gear, the pinion. Until you can achieve the needed torque capacity with appropriate factor of safety and load factor (based on number of cylinders and shock loads) you have nothing.
Looking at the "Strength calculation" page, there are many variables.
View attachment 165193
Now there is a lot going on on this page. In the previous page we set the module to 2.5 with a 20 degree pressure angle. # of teeth on the pinion set to 30 and idler set to 65. This gets us away from the critical range on the pinion of 15-20 teeth where undercut can be a problem. Im also trying to make a large offset gearbox (350mm+) so I dont feel constrained to have a small diameter pinion.
Now on the second page we define the gear width (20mm), the accuracy class (JIS1 is the highest offered). Then we are picking a carburised heat treatment. one of their recommended alloys SCM420. From Matweb, Im posting a snapshot of SCM420, it is a bearing grade steel made for carburizing. It has Cr, Mn and Mo as main alloying elements and a base carbon content of 0.2%. This carbon content will be raised to higher levels near the surface of the gear by carburizing it for higher surface hardness.
View attachment 165194
The tool allows you to select a core hardness value and separately a surface hardness value, based on the alloy you chose.
Number of load repetitions >10 million - default
Now this next parameter "Direction of load" is something Im not totally clear on. My application involves a 3 cylinder engine, thus I expect a significant load reversal 1.5x per revolution. Not a fully symetrical load reversal but perhaps a +3 to -2 level. So I have kept this box checked (the default) for my application. It does significantly reduce the torque capacity of the pinion. To remind everyone I am trying to do a 120hp (90kW) engine at 6000rpm which calculated out to a torque of 148Nm and a torque peak at 4000rpm of about 163Nm.
Finally, I have used a factor of safety of 1.5x on the left and a service factor of 1.5x on the right.
Running the report on this configuration yields the following: Dont worry about the reported power, its a function of their arbitrary RPM input which I cannot change. The torque number is what matters and its within 1Nm of my target value.
View attachment 165195
Feedback ? Have you seen a supplier offer a tool like this for free before ? Any comments on the load direction parameter ?
Below the english website with their stock gears. https://khkgears.net/new/
View attachment 165190
The educational part of the site, many pages of detailed info. https://khkgears.net/new/gear_knowledge/
View attachment 165191
Here is the signup page for their gear calculator
https://khkgears.net/new/gear_calculator.html
Here is the gear calculator page for spur gears
View attachment 165192
You can see it is arranged like a spreadsheet with different tabs, with the first tab being "Size calculator", followed by "Strength Calculation" and so on. Obviously the Japs use SI units. Comfortable for me.
The second tab is where it gets interesting, because for the strength calculation all of the sizing factors come into play (geometry) as well as the choice of accuracy class, material selection, heat treatment (quite detailed). These details determine the maximum allowable stress on the gear tooth and thereby the torque capacity of the smallest gear, the pinion. Until you can achieve the needed torque capacity with appropriate factor of safety and load factor (based on number of cylinders and shock loads) you have nothing.
Looking at the "Strength calculation" page, there are many variables.
View attachment 165193
Now there is a lot going on on this page. In the previous page we set the module to 2.5 with a 20 degree pressure angle. # of teeth on the pinion set to 30 and idler set to 65. This gets us away from the critical range on the pinion of 15-20 teeth where undercut can be a problem. Im also trying to make a large offset gearbox (350mm+) so I dont feel constrained to have a small diameter pinion.
Now on the second page we define the gear width (20mm), the accuracy class (JIS1 is the highest offered). Then we are picking a carburised heat treatment. one of their recommended alloys SCM420. From Matweb, Im posting a snapshot of SCM420, it is a bearing grade steel made for carburizing. It has Cr, Mn and Mo as main alloying elements and a base carbon content of 0.2%. This carbon content will be raised to higher levels near the surface of the gear by carburizing it for higher surface hardness.
View attachment 165194
The tool allows you to select a core hardness value and separately a surface hardness value, based on the alloy you chose.
Number of load repetitions >10 million - default
Now this next parameter "Direction of load" is something Im not totally clear on. My application involves a 3 cylinder engine, thus I expect a significant load reversal 1.5x per revolution. Not a fully symetrical load reversal but perhaps a +3 to -2 level. So I have kept this box checked (the default) for my application. It does significantly reduce the torque capacity of the pinion. To remind everyone I am trying to do a 120hp (90kW) engine at 6000rpm which calculated out to a torque of 148Nm and a torque peak at 4000rpm of about 163Nm.
Finally, I have used a factor of safety of 1.5x on the left and a service factor of 1.5x on the right.
Running the report on this configuration yields the following: Dont worry about the reported power, its a function of their arbitrary RPM input which I cannot change. The torque number is what matters and its within 1Nm of my target value.
View attachment 165195
Feedback ? Have you seen a supplier offer a tool like this for free before ? Any comments on the load direction parameter ?
