Need Help!- Precision boring

[tim kelley]

Need suggestions on how you might approach this.

we have a gearbox housing that after alot of machining and other time consuming processes is assembled with a carrier and then 4 bores are machined to a finished size. The bores range in size from 1.57" dia to 2.44" dia. They are flat bottom, 2.5" deep and the bottom having a perpendicular tolerance of .0005" to the bore. The bores have a tolerance of ±.00025" and a perpindicular back to datum A. The material being machined is Rc 28-32 and a surface finish of 63 is required.

Thanks for the input.

Tim

[Boots]

There are lots of ways to do this but what I would do is rough the bores to with in .030 with a hog mill staying up off the bottom also. Then simi finish the bore to with in .005 and finish the bottom of the bore. Then send in a bore bar and only go as deep as needed to get a bore guage in to check size. Make adjustment to bore bar then send it through to the bottom. Use the boring G-Code that has spindle orientation, move off and retract so the tool won't drag coming out. If you need to be exact on position of the bore then do not make a rapid move to the bores' center. Use a feed move to get you on location for a more precise position if your machine is older. Hold part so as not to create vibration and harmonics.

Practice on similar material to get your speed and feed on the bore bar so you can get your finish.

[URguys]

If you have to you could use a G12/G13. Hog out the middle. Leave some room to play on the bottom and diameter. Then get the biggest high helix endmill you can in there and run a G13 with I,J,Q.
You might have to play around a little bit to make it work like you want it to.
Just remember that the deeper the pocket to harder to make the walls perpedicular... and 2.5" would be pushing it.