How to bore aligned holes?

[flathead]

Can anyone tell me how the manufacturer of this fuel injector would have machined the bore holes for the throttle shafts? Are they gun drilled? Or are cores placed in the castings and then the holes reamed to size, maybe?

The castings are about 20" long. The throttle shafts themselves are 5/16" diameter. The holes have to be perfectly aligned to prevent binding of the throttle plates as they rotate.

I'm working on something very similar to this and I would like to get a good idea on how this should be done.

thanks

[Joe Engel]

I would venture to say some special tooling was used. I've done similar holes. Stepping to a different level and drilling through again. It all starts with the first hole. C'drill and drill it under size. True the location and size it by boring it or using an endmill. You can now use that hole to guide the next section with a bushing made to suit. The tooling could be reduced shanked and the bushing could slide on from the shank end before inserting it into the tool holder. Depending on the distance between each hole, the process may vary. But using a tool that will cut a true location each time will ensure accurate alignment. The bushing will prevent chattering and help with alignment also. There's a lot of time with special tooling involved. But, this is a special hole...

Another way is to fixture it. You could make a fixture with drill bushings and slide the piece over the fixture, secure, and then drill away. Imagine pieces that slide into the large cavities with the bushings at 90°. The pieces would be precision machined and attached to a fixture plate with dowel pins. The first one would be outside of the casting for starting the first hole. I've attached a crude drawing of a fixture.

Again alot of work. Hope this gives yo some ideas...

-Joe

[John Welden]

Originally Posted by Joe Engel Another way is to fixture it. You could make a fixture with drill bushings and slide the piece over the fixture, secure, and then drill away. Imagine pieces that slide into the large cavities with the bushings at 90°. The pieces would be precision machined and attached to a fixture plate with dowel pins. The first one would be outside of the casting for starting the first hole. I've attached a crude drawing of a fixture. -Joe

Something like that sounds like a good idea to me. If you did a nice job on the fixture it would surely work well.

[flathead]

Joe,

The fixture idea sounds great! I hadn't thought of that. It wouldn't be too hard to build either.

thanks

[DareBee]

It could be done in a CNC with right angle head. Go in each large hole and mill the shaft hole.
Not how it would be done in production, but is feasible for a 1-off.