I have built a little machine out of a few pieces of wood that trains your thumbs like no other. I really cannot describe it well, but I will try to get a picture of it and will post it here. It is very easy to make and trains your thumbs very well!
I have actually made a thumb machine myself. You wouldn't have read the John Brookfield book by any chance? We will be adding an article to our website about this thumb machine, which is fairly simple to construct and provides great thumb training that is similar in nature to the training that Heavy Grips hand grippers provide for your other four fingers. When the article is done, I will post its link here. In the mean time, if you get a chance to post a picture of your device, I would be interested in seeing it!
This is the thumb machine that I referred to earlier. I will be posting an article on www.eiyc.com this weekend to explain how to use it and how you can make your own. It really is a great way to build up your thumbs.
Hope this helps!
There are a few ways to strengthen your thumbs which are very effective and very cheap. One way is to buy a Pony clamp and do inverted closes with it. It mimics the type of exercise dipicted in the picture above this post.Also using block weights is another great way to develop a good thumb strength base. Also do thick bar holds with dumbells with enough weight you can hold for a maximum of 5-10 seconds at a time. Make sure the Handle is very thick over 2" 2.5" would be ideal maybe even 3" As mentioned before plate pinch holds are good as well. And last but not least pinch block holds using a 4x4 piece of wood. Good luck.