Where to place an idler pulley

[territorialmillworks]

Distance between 18" pulley and 3" drive pulley will be 36" - 48". Final speed will be 300+-rpm I want to use an idler pulley to act as a "clutch". Do I put the idler pulley on the driven side of the belt or on the slack side of the belt? Should the idler be in the center or near the 18" or 4" pulley. Thanks, Keith..

[Warren Nakkela]

Hello Kieth, Merry CHRISTmass, The idler should be on the slack side of the belt and if possible close to the smaller drive pulley.
Warren

[David Einhorn]

If I remember how the line shafts were set up in the Industrial Museum in Baltimore, I believe they had the idler arrangements at or near the drive wheels on the overhead shafts. That way the belts hanging down to each machine only moved when the that machine's lever was engaged. So putting the clutch wheel/mechanism near the drive wheel on a machine makes sense. Just make sure that the clutch and belt can't accidentally engage and become a hazard to life and limbs.

[HWooldridge]

My Beaudry has the belt on the driven side and is the idler is slightly closer to the large pulley on the hammer. I think the reason for this is that the idler pulls close to the large pulley and increases the amount of belt surface contact. In other words, you get more than 180 degrees of belt contact. However, I've also seen lathes set up like Warren described so I can't really say if there is a "right" way.

[devon blacksmith]

another way is with fast and loose pulleys to turn the drive on and off

[mcraigl]

Not sure if it matters or not, but seems that on most of the rigs I've seen that were designed for use with a line shaft, if the idler pulley serves as the clutch, then it is part of the machine, and so a "constant" distance from the driven wheel, but the distance to the drive wheel could be anything, depending upon how high the lineshaft was mounted. It seems that those arrangements usually have the idler on the driven side of the driven wheel?? Seems that if the idler was "just" an idler it wouldn't matter too much. Take with a big grain of salt as I don't own anything driven from a lineshaft, and haven't seen as many such machines as others around here. I did help set up one old power hammer that used an idler as the "clutch" and we set it up as I described and it works like a champ for what it's worth.

Edited January 7, 2009 by mcraigl
clarification