Originally Posted by
NIC 77
What, that big hold in the middle?
Apologies, I thought you were talking about about the surfacing attempt in your photo that looks to be about an inch wide and looks like it was cut by a drunk sailor wielding an oxygen torch.
Oh, crud. Ha ha. Your picture looks like two different things depending oh how you look at it. Of course you wouldn't notice this because you already know what the shape is.
Were you climb cutting or the other one? Clockwise or counterclockwise? Try going the other way. That's a long bit then. Try a half inch bit.
The overall difference in hole diameter between top and bottom, that's because of runout. I hope you don't need a tight tolerance for that hole size.
The poor finish quality, I think that's mostly because of your machine's lack of stiffness, and the fact that this is die cast aluminum. You may be able to get better results by trying different feeds, definitely use a stouter, larger diameter bit, and seeing what the difference is between clockwise and counter clockwise as to your finish. Of course, runout could be a contributing factor, but I don't see it as the overall cause. Do you have more of these to do?
At the end of the day, it doesn't matter what you do (unless you want to spend more than you paid for the machine to try and make it better), you will never get a good finish on a milling operation of this kind from this machine. You may improve upon what you have, but it will never be a "good" finish. So grab yourself a six pack of beer and a 12 pack of sandpaper and have at it.