I used to help Randy out from time to time when I came to the yard. The key items to insure that the mill tracks true are as follows:
1. The frame MUST be square, he used a table jig
2. I think he used 1.5” tubing. If you are going to use aluminum I would step up to 2” due to the weight not the tensile strength of the metal
3. The slats and the belt are very often over looked. I think he was using 2.25 and I don’t remember what they were in thickness. What I can assure you is that if the slat are too small or to large you will get slat rock.
4. The belt I honestly don’t remember anything other than he used the clipper laces and had them shipped to him.
5. The roller bed should be attached to the frame in a manner that minimizes the transfer of vibration to the vertical support members of the frame. Randy used 4 stud point with rubber washers located on the horizontal supports of the frame.
6. The main wheels are adjusted just like a motorcycle rear wheel he used split hub 6” wheels
7. Roller bed wheels and all bearings are about how much you want to spend. Not that the distance between wheels can not be greater peak to peak than the slat. So if you are using wheels that are roughly 2” this works well with a 2.25” slat.

All in all it is not hard to do at all, but you are looking at $500-$600 or close in parts for a budget build, minus tools and your time. Is it worth it, depends on how much time and or money you have. Randy built his first mill because he needed it to work Ranger, not because he felt like making mills. It honestly was something that Tom kinda pointed for him to be able to make a few bucks ontop of the dogs.

Anyway, I can provide a few sketches of any areas where you have issues, I don’t have the time to make CADD drawings right now. If people are really looking for more details PM me and I’ll honestly give some thought to pulling together a set of DIY plans and parts. I hope this helps!

YIS