If there is a formula or suggested ratio I am unfamiliar with it. All I can say on the matter from my own experience is that once I started borrowing money for new equipment, I started making more money. If you have the revenue and cashflow to make the payments, and reason to believe that a new piece of equipment will make your life easier, more efficient, and or more profitable then in my mind it is a sensible move. I have definitely gotten a better return for the amount paid out to employees with newer equipment. Less down time, more productivity...
I'm on the high side of whatever that ratio is as I started financing the merlo this December.... on top of my 18xp and DW1050. Between the three I'm about 8,000 (6000 for the merlo...) per month. I ran the numbers and have very modest expectations for my 2022. I have a number I can bear, a number I'm happy with, and a number I'm shooting for. In my case, I was willing to take the risk as I had spent so much time speculating on it... Won't know until I've tried. So far we only use the Merlo about 30% percent of the time. It's a bit hard to justify the amount of money I am spending on it if I am being completely honest. I've got good equity in it, though. It definitely shines when we do use it. Seems to be working out, but time will tell. I'm not married to it, but I plan to keep it at least a few years just to see how it plays out.
The new chipper and DW are very easy to justify the loan for IMO. I use them both pretty much 5 days a week. Only about 2000 per month for both in my particular case. Very easy to make the payments and huge productivity/efficiency boosters.
A wise man once gave me some simple advice that I have mostly obeyed. "If you don't use it more than 50% percent of the time - rent it".
Southsound it sound like you have a very good friend/neighbor in the log loader owner who owes favors. Very good friend to have!