I asked this in another post but it probably deserves a thread of its own. I would like to switch from a 4 inch aluminum pulley to a 7 inch steel for more belt reduction. The belt is 15mm wide gt2 design ,to give you an idea about how thick the pulleys are. I am trying to find out if the inertia of the steel pulley is going to be a problem?

The inertia of the pulley is going to affect your motor to load inertia ratio which in turn has an effect on the maximum acceleration rate, the up side is the inertia ratio is decreased by the square of the reduction, so there is some automatic compensation by going with the larger pulley.
Al.

Perhaps drilling/milling some lightening holes would help.

Perhaps drilling/milling some lightening holes would help.

Similarly, if it has a large boss on one side to allow for large size bores, this can often be turned down significantly for the same effect.
Al.

Thanks for all of the help

Here is a link to the pulley, I have not purchased them for my machine because I didnt know if it would be a good idea yet. Good thinking on lightening . The pulley uses a sk bushing it is the last pulley in the chart on the following link. Should I drop down to 9mm belts instead of 15mm thick? Any idea how bad this will increase the load ratio? Am i better off staying with what i have?

You might want to consider going to AT style belt teeth instead of T style - definitely the more modern version.

I have not done business yet with this company, but I have learned a great deal from reading their web site.

http://brecoflex.com/