We want to first start out by thanking and crediting Walter W., who was the very first user to submit a coupling question on our Have A Coupling Question? Fire Away! form.
Walter's specific application and coupling requirements: Walter was looking "to motorize a sausage stuffer with a VFD controlled 3-phase AC motor" and need "a coupling to connect a gearbox with 7/8" hollow / 3/16" key to a (approx., can provide exact) 11/16" square shaft. 1/3 HP motor is driving the gearbox." "The 11/16" square is where the hand-crank handle connects. Max 825 in-lbs. torque at 25 rpm. Service factor of 1. It will probably see less than 2000 revolutions in a given session, only a couple of times a year."
On Square Bores & Hollow Shafts: Before getting to our formal response to Walter, we wanted to specifically call out square bores and hollow shafts. Square bores (while a bit unusual) are certainly not a problem for us and generally do not change the torque rating of a coupling. On hollow shafts, as long as the shaft is robust enough to take the load (not deform, deflect, or introduce vibrations), the coupling is not really going to care all that much.
Our Response to Walter: Given a 1/3 HP motor (VFD), gearbox with 7/8" hollow / 3/16" Keyway, 11/16" square shaft, and max 825 in-lbs. torque at 25 rpm... the L150 Jaw coupling will be able to accommodate both the 7/8” shaft and a 11/16” Square shaft, while providing a torque rating of 1,240 in-lbs. with a standard rubber insert.
However, if Walter is anything more than a hobbyist making sausage for himself, he will want to ensure his system is FDA compliant... which sintered iron and rubber generally are not. The L-Line coupling is available in a dimensionally interchangeable stainless steel (a material much preferred by the FDA), and the coupling spiders are also available in Urethane (another material more preferred by the FDA). Urethane spiders have a higher torque carrying capability relative to SOX (NBR) Rubber (at the expense of dampening capacity), so the same size coupling hubs (SS150) could still be used.
Note: Even using stainless steel & urethane, couplings are generally reserved for use beneath the food preparatory table, so Walter will need to thoroughly review his application against all relevant local, state, and federal food safety guidelines. (A list of solutions targeted at the food and beverage industry can be found here.)
Now It's Your Turn to Do a Good Deed...and Ask A Question! If you have a coupling question (be it a basic question or highly focused), please do not hesitate to share it with us. If the question is in your head, other folks will likely soon be looking for the same type of information. After you ask it, we will review it and do our best to incorporate the answer into an upcoming post... making the world just ever so slightly a better more collaborative place to live!