Rick, sounds good - funny how creating something as mundane as a dubbing brush can be addictive. What kind of wire are you using?
Goflies, hard to say what you're doing to get clumps other than the material being spread unevenly, which is a real challenge for me. However, as you pointed out, you do spread the fibers evenly, so I'm not sure.
Now, I have noticed that when these things twist, the end nearest the twister twists tighter sooner than the rest of the length of the brush. If you go preening out the wrapped fibers before they are bound tight enough by the wires, then they will pull out, leaving gaps. Even though the wire extending out past the material is twisted tight on each end, the wire holding the materials in the middle, especially if they are thick, may not be wound tight enough to hold.
I generally get the brush wound tight enough to hold the materials which twists them around the wire pretty densely, then I use my dog brush to fluff everything out. Then I'll hit the twister some more to tighten things up more, then fluff with the brush - I'll repeat that three to five times.
Also, as with tying, sparse is the way to go. The thicker the materials, the harder it is for the wire to twist around them and the more that will pull free when fluffing up. I'm using about half as much as I did when I first started and am getting a lot less waste. Although the "waste" I had when I overloaded the wire was put in to a bag and used to make another brush.
Have you tried searching Youtube for some dubbing brush making videos? There may be a clue or two there.
I tried making a brush with all silicone legs and it was a mess, the wire would not bind tight enough to hold them in. I think I may have to try again with some sparse hair and a fewer number of leg material; maybe the hair will help bind the legs in.
Thad, not a problem; I'm just a follower of this old method myself but glad to help. Good luck and let me know how you make out.