long through hole

I like the idea about not drilling the small hole all the way through, and using each drill as a center for the next size. I will give these a try. Thanks
 
Ok, I can tell you the secret to success. It may seem simple, but the key is to never "crowd" the drill. And by this I mean clear the chips more often than you think you need to. After center drilling, Use the best (maybe brand new) drill you have which is the size you want to end up with. Go as deep as you can with it. Then switch to the longer drill. Of course it's nice if its been properly sharpened, but by this time it will want to follow the hole that you've already started. What will make the drill "walk" off center is applying too much pressure, and not clearing the chips often enough. To guarantee success you need to clear the chips every 1/8 of an inch you drill, I know it seems tedious, but it will work. The only reason I would turn the work around is if I didn't have a long enough drill.
I've successfully drilled 1/4 inch holes through solid steel a distance of 24" using this method. I've also seen the same job screwed up by someone who didn't have the patience to back off a little.
Levi
 
Walt said:
I confess to having no relevant experience, but what about a gun drill? Not sure how the coolant hookup is done.

http://en.wikipedia.org/wiki/Gun_drill

Walt
Click to expand...

The fluid flows through from the center of the shank.. The coolant/fluid along is along the lines of differential oil or gearbox oil. It was kind of thick and under quite a bit of pressure.. There is is an o-ringed cup that you put on the back of the hole, where the drilled hole would punch through while drilling, the o-ringed cup is vented with a tube and catches the pressurized cutting fluid, keeping it from blowing all over the shop..

A gundrill is pretty fun to watch, not to fun to run.. Well its ok if its running good, you would be surprised how fast you can drill a hole over 36" through an h-13 block of steel..

The drills it uses is interesting..
 
It can be done, but you have to use the right kind of drills. If you try to do it with just an aircraft extention drill, it probably won't work.

How many pieces are you going to do? You might get away with it if you're doing one piece, but if you're doing several then gun drilling will probably be the way to go.

I do some deep hole drilling on some parts I make for model boats. I make one part that requires a 1/8 inch diameter hole to be drilled 4 1/2 inches deep in a piece of aluminum that is only 3/16 thick. I have spent the time and money to learn how to do it and now I can drill 200 pieces and not have any break out the side if the part. It's all in the set up, and the brand and style of drills used. I don't use anything but Guhring drills for that application. Guhring drills are expensive, but I have seen other companies try to drill the same parts I do, and they will lose one part out of every 6 because the drill will break out the side of the part.
 
first thing you need to do is practice on some scrap 416 material.... 416 stainless will be your biggest problem, not the hole..


Use a good quality cobalt drill and nothing else, you also dont want the drill bits cutting edge extremely sharp... I wouldnt use highspeed, and not an import drill, if you do you will probably be stuck with a chunk of 416 with a drill bit stuck in it..

definitely research your drill point angle. I like a flatter angle on my drill points when working with stainless, I will also take a stone and break the real sharp edge off a freshly sharpened cutting edge.. Stainless is bad about grabbing and breaking drill flutes.

stainless is also notorious for closing back up onto a drill as you progress through the hole..
 
I would definitely do it in your 4 jaw chuck. That way you can indicate it perfectly on center and straight. I would also drill from both ends and ream from one end. Your reamer will follow the drilled hole and if you ream from both ends and the 2 holes don't line up, your reamed hole won't line up either.
 
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