patton fan works great on high speed but on medium speed it is noisy and on low speed it slows to a stop. its a powerful floor fan to circulate and cool the shop. would the model number help to get an answer?
Model number always helps, even though Patton (or their owner Jarden Consumer Solutions) are extremely lax at providing any info about their products.
What you describe sounds like a failure of the motor bearings. Perhaps it's not too late to look at the fan blades and see if there's any dirt/hair/fibers/etc stuck to them that throw the fan rotor off balance - that's what's killing the bearings. The noise if very often the result of the blades' unbalance and the continuous vibration wears off the bearings.
In addition to the vibration it may be possible that some long fibers or hair wound themselves around the rotor and are blocking the rotation, so the motor has to work hard and on slow setting the power is not enough.
So, I would take it apart, make sure it's clean and oil the bearings (everywhere around the shaft on both ends of the motor). If that does not fix the problem, you'll need to replace the motor. See if you can write down the motor's nameplate while you have the fan open and if you like, post it here, I'll try to find a suitable replacement part for you.