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General Mach Discussion / Re: Lathe feed errors due to timing pulley runout
« on: March 01, 2012, 05:26:48 PM »
I have redrilled and reamed a lot of timing pulleys and never had the problem you are describing. The cast ones from Browning are quite good, by that i mean, if you have an accurate three jaw chuck it will center them accurately. If the casting is bad one can always use a mandrel to true up the hub of them before placement in to the chuck. As you said repeatable inaccuracy per revolution can appear. Timing belts to my surprise are really quite accurate but you can loose a few steps per rev depending on the tension used but that is repeatable.
I would think that it's more a problem of the lead screw and backlash / non use of a good ball screw . A small backlash can come from the thrust bearings if not adjusted just so and can
make a big difference. Another item to look at is the coupling ( if say a bellows type ) since they can give some and cause inaccuracy and you may not notice it.
The smaller the error you try to get to the more anal one must get and comes at a price also. Just a fact of CNC.
BTW, 0.02 mm =.0008" on a diameter.... you must have some backlash ( zero is imposssible else the axis wouldn't move). Only you can define how much time, effort and money
you want to put out to get 1/2 the current value?
RICH
I would think that it's more a problem of the lead screw and backlash / non use of a good ball screw . A small backlash can come from the thrust bearings if not adjusted just so and can
make a big difference. Another item to look at is the coupling ( if say a bellows type ) since they can give some and cause inaccuracy and you may not notice it.
The smaller the error you try to get to the more anal one must get and comes at a price also. Just a fact of CNC.
BTW, 0.02 mm =.0008" on a diameter.... you must have some backlash ( zero is imposssible else the axis wouldn't move). Only you can define how much time, effort and money
you want to put out to get 1/2 the current value?
RICH