Pro Tip: Here are seven steps to help users decide what gearbox ratio they need.
The first hollow shaft gearbox I ever saw was an Opti-Mount made by Boston, and it required brute force surgery to remove from the shaft. Luckily, most of today’s hollow shaft gearboxes are built with pre-engineered devices to aid in their removal (or tapered collars).
For some, the challenge can be determining what gearbox ratio is needed, especially if the old system was the typical chain and sprocket set up. Normally, you want to get the conveyor to run the same feet per minute (FPM) after the conversion is completed, whether at a fixed speed or even when using a variable frequency drive (VFD). In either case, I’d almost always recommend you base your desired readings at 60 hertz.
Most systems will use a VFD or inverter for fine tuning, but it’s nice to design the conveyor system to run close to the desired speed when it’s at 60 hertz. Not only does that put the motor and/or VFD in a sweet spot, but it also allows you to run the operation in the event the inverter fails and you must switch over to straight house power.
Here are seven steps for discovering what gearbox ratio you will need:
Step 1: Determine the current speed of the conveyor before removing the existing drive system using a tachometer that provides a conveyor surface reading in FPM.
Step 2: Remove the drive belt or chain from the shaft that you intend to side the hollow shaft gearbox on (post purchase of new gearbox).
Step 3: Whether you have a belted conveyor or one that has tabletop chains, simply mark the belt or tabletop chain and put a corresponding mark on the conveyor frame.
Step 4: Turn the main drive shaft of the conveyor (the one the hollow shaft gearbox will be installed on later) one full exact turn.
Step 5: Measure the distance the conveyor moved between the two lines.
Step 6: Repeat steps 3, 4 and 5 three times, and then add all three measurements together and divide by three to get an accurate value. This will give you the distance you can expect per rotation of the shaft. An important thing to note is that a typical motor in most applications is a 1,725 RPM motor, but you need to confirm what you plan to use when running at 60 hertz.
Step 7: Use this formula to determine the gearbox ratio:
For example, an 1,800 RPM motor divided by the current conveyor surface speed of 45 FPM = 40.
Now multiply the 40 by the distance the conveyor moved on one rotation of the shaft. Let us say, for example, it was 9”. 40 x 9 = 360. Next, divide 360 by 12 to convert this to the required gearbox ratio you need to order. 360 divided by 12 = 30. In this example, you would order a 30:1 ratio hollow shaft box.
Many times, the ratio will not be an even number, such as 33.666. In this case you have three choices: A) Round up to the next nearest ratio your manufacturer sells, which will slow the conveyor at 60 hertz compared to the desired speed; B) Round down to the next nearest ratio your manufacturer sells, which will increase the conveyor speed at 60 hertz compared to the desired speed; C) Choose a manufacturer that sells the exact ratio you require.
By following these steps, you can easily convert your conveyor to direct drive, therefore increasing your reliability. No gearbox means less parts to keep on hand and less maintenance.
Rowdy Brixey is founder and president of Brixey Engineering Inc.
You can connect with him on LinkedIn.