Shopsmith Forums

Does anyone know the max rpm for the idler bearing on a Mark V SN: 205447? Is it possible to replace this bearing alone or is it necessary to buy the bearing / shaft assembled? If I could find a bearing part # I could find it's speed rating. Thanks in advance!

The Idler spins approximately 1.6X faster than the main spindles, which nominally go up to 5200 RPM. But in another thread it's been shown that machines typically exceed the maximum speed listed and the amount they exceed it by seems to vary widely. Personally, I'd say 10K RPM would be a reasonable high RPM expectation for the Idler on a conventional headstock, 16K RPM for a PowerPro.

The "water pump" style idler bearing on "early" Mark 5/V is not separately replaceable, they are integrated with the shaft. The button bearing on the other end can re replaced. Shopsmith only sells the "new style" Idler Shaft, those bearings might be replaceable. I'm biased in favor of the water pump style and would choose used over the new style. I'm sure others disagree.

The terms "early" and "new style" are used loosely here. I'd guess the new style entered production somewhere around 2010.(?) There are also two major styles of eccentric bushing.

IIRC Bill Mayo did some evaluation of the old and new style bearings and asserted that the old style were superior even with the higher speeds of the PowerPro.

- David

Perhaps we should start referring to "earlier style " and "later style" ;-)

Thanks for the info you guys!

mharmon,

Welcome to the Shopsmith Forum.

The serial number 205447 should have a prefix of SS and this Mark V was then made in May of 1985.

To replace the bearing only you would first have to find the correct bearing, press the old one off the shaft and press the new one on. The Idler Shaft with the bearing(s) installed has always been listed/sold as an assembly by the makers of the Shopsmith Mark 5/V and the different models. As for the RPM rating, I don't know it but the Conventional Headstock Idler Shafts spin at well over 8000 RPM's (mathematically at 8320) at top speed.

The Idler Shaft Assembly in a Power Pro Headstock is different than the one in the Conventional Headstock.

chapmanruss wrote: Mon May 20, 2024 2:36 pm To replace the bearing only you would first have to find the correct bearing, press the old one off the shaft and press the new one on. The Idler Shaft with the bearing(s) installed has always been listed/sold as an assembly...

I've never seen a bad idler bearing of the 'early style' so have never attempted disassembly. But edma194 posed a link to a similar assembly without the Shopsmith machining. If you look at the 2D cutaway drawing in the picture it shows that the inner grooves that would typically be part of the inner race are actually machined into the shaft itself. There is no inner race. The bearing isn't separate from the shaft in the typical sense and isn't pressed on. My guess is that the Shopsmith 'water pump style' Idlers are like this.


- David

DLB wrote: Mon May 20, 2024 4:29 pm I've never seen a bad idler bearing of the 'early style' so have never attempted disassembly. But edma194 posed a link to a similar assembly without the Shopsmith machining. If you look at the 2D cutaway drawing in the picture it shows that the inner grooves that would typically be part of the inner race are actually machined into the shaft itself. There is no inner race. The bearing isn't separate from the shaft in the typical sense and isn't pressed on. My guess is that the Shopsmith 'water pump style' Idlers are like this.


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- David

Yes. They are integral units. The shaft is the inner race in this style of bearing. It's a great choice for this purpose, used in the band saw and strip sander also. The shaft length varies for a particular diameter, but other than cutting to length and pressing on a button bearing I don't think Shopsmith does anything else to them. Some are made with two or three rows of balls, some have one row of balls and one row of rollers. They are called waterpump bearings because of their use in automobile water pumps. Other than being sealed bearings I don't know what advantage they offer in water pumps but they are a great way to reduce parts count and simplify assembly.

David and Ed,

Thanks for adding that clarification. Out of the 7 Mark 5/V tools I have owned I have not had a problem with any of the Idler Shaft bearings. These range from 1957 Greenies to 2006. Because of that I have not had to look into replacing the bearing.

I am still learning new things about the Shopsmith tools.

If purchasing a new Idler Shaft with bearings from Shopsmith other parts may need to be changed with it for older Mark 5/V's. I have seen a non-OEM replacement Idler Shaft with a water pump type bearing for sale in the past on ebay but don't see it currently.

I believe the "new" two bearing idler shaft assembly is directly interchangeable with the "old' water pump bearing. Second retaining screw needs to be added to eccentric.

BTW the 'button' bearing is part of the control sheave.