Progress bar in tkinter not working

I compacted the loading bar I got working in an older project of mine. The only way I had figured it out was to call the progress bar handling calls in a new thread and call the work-intensive functions from this thread into another new thread.

It is bad practice to have a separate threads handling UI elements other than the UI thread, including starting and stopping a progress bar; however it does work and I've been using this project to do pretty heavy processing with zero issues for months now.

Here the progress bar is working in a small script, using Python 3.5.2 on W10 64-Bit

from tkinter import *import tkinter.ttk as ttkimport threadingimport timeclass Main_Frame(object):    def __init__(self, top=None):        # save root reference        self.top = top        # set title bar        self.top.title("Loading bar example")        # start button calls the "initialization" function bar_init, you can pass a variable in here if desired        self.start_button = ttk.Button(top, text='Start bar', command=lambda: self.bar_init(2500))        self.start_button.pack()        # the progress bar will be referenced in the "bar handling" and "work" threads        self.load_bar = ttk.Progressbar(top)        self.load_bar.pack()        # run mainloop        self.top.mainloop()    def bar_init(self, var):        # first layer of isolation, note var being passed along to the self.start_bar function        # target is the function being started on a new thread, so the "bar handler" thread        self.start_bar_thread = threading.Thread(target=self.start_bar, args=(var,))        # start the bar handling thread        self.start_bar_thread.start()    def start_bar(self, var):        # the load_bar needs to be configured for indeterminate amount of bouncing        self.load_bar.config(mode='indeterminate', maximum=100, value=0)        # 8 here is for speed of bounce        self.load_bar.start(8)        # start the work-intensive thread, again a var can be passed in here too if desired        self.work_thread = threading.Thread(target=self.work_task, args=(var,))        self.work_thread.start()        # close the work thread        self.work_thread.join()        # stop the indeterminate bouncing        self.load_bar.stop()        # reconfigure the bar so it appears reset        self.load_bar.config(value=0, maximum=0)    def work_task(self, wait_time):        for x in range(wait_time):           time.sleep(0.001)if __name__ == '__main__':    # create root window    root = Tk()    # call Main_Frame class with reference to root as top    Main_Frame(top=root)