I apologize if my post sounded like a tirade. It is just frustrating to see people working against the materials they have.
As for the instructions telling him to use a force fit, I guess I did not read that. Well, upon rereading the thread, it is just not there so I could not read it. Nowhere does the OP say that the instructions say to press it in. Apparently they do say to drill a 1" hole. But that part is a casting and I can see an irregular surface. It is not a precision fit and without a trip to a metal lathe, it will not be. That probably means that they are going to vary from batch to batch and even from individual casting to the next individual casting.
If the instructions say to force it into a 1" hole, then they are not good instructions. Frankly, this is a poor, poor design. That is demonstrated by his two blocks of split maple. I wonder what wood the instructions specify. Or do they bother to specify any particular kind?
I will say it again, that kind of part is OBVIOUSLY not intended for a precision fit. It is not intended for a force fit. PERIOD. If you insist on doing it that way, then break out the digital calipers and take a number of measurements of the OD. Take them at different places along the cylindrical part and at different angles. You will find that it is tapered and it is NOT round to any great degree. You are trying to force a non round, tapered part into a 1" cylindrical hole. Is it any wonder that the wood is splitting?
If you are going to insist on a force fit, I would suggest switching to a softer wood, like pine and soak it in water for 24 to 48 hours before trying to drive it in. But it will probably just split again when the pine dries out.
The guy (or gal) who designed the pattern for the casting apparently knew how the part should have been used. It should be inserted into a larger hole with clearance all around and held in place with some wood screws. That's why there are two tabs with slots for those screws. And, as I said, add epoxy if you want to. I probably would.
The person who wrote the instructions had his mind on "Miller Time", not on a quality product.
I hope this does not qualify as another tirade.
You know, that tirade would make sense if the instructions included didn't say to drill an undersized hole and press the nut in, as the OP mentioned they did. Being that the company that wrote the instructions also made the kit, I'd suspect they know what they're talking about.
To the topic at hand, space, I'd suggest finding a way to press the buy into the recommended sized hole, rather than hammering it. A clamp, vise or what have you should force the nut I to the hole without imparting any lateral force that would cause the wood to split. If you have a slightly softer wood, ash say, I'd try that as well, as it would deform and accept the nut a little easier