Deep hole drilling

[snowkilts]

Anyone know of some good resources for deep-hole drilling with a 3-in-1?

I'm trying to put a 7/8" hole through a 6" long piece of 1-1/2 delrin, and getting the hole off-center at the exit by .030" - .050".

Thanks,

Jon

[tarzan]

It is hard to give advice on this without knowing your current process.
I'll tell you how I would do it though.
I would use a lathe and face, center drill, and drill one end just past half way through with a drill about .03 to .06 smaller than the finish size.Then flip the part around and repeat this process.
If you are using a drill with the web equal on both sides, then your drill should drill pretty straight.If your drill is not ground even or is not sharp,It will be difficult.
Also, plastic heats up easy, so if you can use a coolant, that will help greatly.Also slow speed and a heavy feed, along with a clearing peck every couple hundred thousands, will help keep things cooler.
After you have a through hole all the way through, then run your finish drill or reamer through it.

[snowkilts]

Thanks for the response, I will try drilling half way and then flipping on my next part. I was trying to go all the way through.

I have the work in a chuck turning at the slowest speed available. I've been center drilling (but not facing -- I'll do that next time as well). I've been putting the drill in the tailstock and feeding with the quill. I pull it out every half inch or so to clear the chips. This is laborious but it's all I have. No coolant available but I put a squirt of tap magic in when I pull the drill out. Not sure if this helps.

I have tried both a spade and twist drill. I got much better results with the spade drill despite its relative lack of rigidity, and the fact that the shaft on my drill is slightly bent. Much less heat with the spade drill as well.

Cheers,

Jon

[Harold_V]

Facing is important. If the face has any deflection, it translates to the drill, shifting it slightly off center, which, in turn, steers the drills opposite the high side of the face. If you prefer to drill without facing, face the area in which the drill makes contacts so it doesn't influence the drill as it starts the hole.

Harold

[Jose Rivera]

The only way I know is as follow:

1) Drill the hole some 1/32 smaller diameter an inch or so deep. Then using a boring bar bore the hole some .001" bigger than the drill size.
Doing this you'll have a guide area that will keep the drill straight and from wondering. Some times even doing this will end up with some run-out at the other end.
This will give you a true diameter as the guide keeping wondering at a minimum.

2) If the hole does not need to be perfectly straight, as already mentioned, drill half ways and turn around to finish meeting at the center (more or less) this will split any run-out and put it at the center of the length, leaving both end with a concentric condition.