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Advice on drilling a 5" hole?
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Author:  EverHopeful [ Thu May 15, 2014 9:26 pm ]
Post subject:  Advice on drilling a 5" hole?
I'm slowly building myself up to making a breech. I'm planning on starting with .75" aluminium round, 5" long. The first hurdle is the initial bore down the middle which I plan to do in the lathe. I can do the first 1.5" or so with a normal 3/16 drill, and I've ordered a 6" long drill to go further.

Would it be better to try and go all the way through from one end, or to flip the work piece and start from the other end and meet in the middle? If I do it in a single pass is there a risk of the long drill wandering off centre?

Once I have the 3/16 bore all the way through I hope it will be fairly easy to open up the bolt end to 1/4 and the barrel end to 7/16, just leaving 3/16 where the loading tray will be.

Jim
Author:  GerardSamija [ Thu May 15, 2014 10:28 pm ]
Post subject:  Re: Advice on drilling a 5" hole?
You should probably centre the piece very carefully and do it half way from each end. Going very slowly with some lubricant. New drill bit. Preferably one of the self-centering stepped bits, where there's a half-size portion for the first couple of millimetres. And drill under-size, then once your holes sort of meet in the middle, almost, use a reamer to bore to final dimension and line the holes up. In that small a size using a bit on a tool post isn't an option, but for larger holes it's definitely preferable to using a twist bit. Also chuck your bit as deeply as you can to minimize flex in the bit, so in this case just leave a hair over 2.5" of drill showing.

All that said, Rick should probably come in here and correct me every which way... ;)
Author:  rrdstarr [ Thu May 15, 2014 11:40 pm ]
Post subject:  Re: Advice on drilling a 5" hole?
Tons of coolant! Take .125 or 1/8" deep and clear the chips.
1200 rpm.
Everything else Gerard said is correct.
I don't have a Carbide .250 reamer to lend you that is long enough! Might have a HSS?
Author:  EverHopeful [ Fri May 16, 2014 6:02 am ]
Post subject:  Re: Advice on drilling a 5" hole?
Thanks guys. Good thing I have plenty of stock, so if I mess up the first one I can always try again. I'll let you know how it goes once the drill arrives. I really should think about getting a couple of reamers - good tools are so darn expensive!

Jim
Author:  Jon [ Fri May 16, 2014 1:59 pm ]
Post subject:  Re: Advice on drilling a 5" hole?
Pretty much as above but do it all in situ without turning round.
If you slacken and retighten the piece it will need clocking up, same when removing or turning round.

Done a fair few years ago from 1 1/4"x1", some 6 1/4", some over 7" long. Drill through undersize and keep clearing. Bigger drill same again, then ream 12mm dia. All cock on no runout surprisingly.

I have loads of drills but rarely use, the long ones up to 5mm even 6" long will surely flex and veer off.
Far easier to make say 12mm bore or greater, bolt same size and sleeve up for pellet channel.

Been on hold 12 years :( Too busy sorting you boys out.
http://pic20.picturetrail.com/VOL15/728 ... 513282.jpg
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http://pic20.picturetrail.com/VOL15/728 ... 431797.jpg
Author:  EverHopeful [ Fri May 16, 2014 6:02 pm ]
Post subject:  Re: Advice on drilling a 5" hole?
Looks interesting Jon. I'd love to get to the stage of having everything milled out of a single block of aluminium!
Author:  rrdstarr [ Fri May 16, 2014 8:44 pm ]
Post subject:  Re: Advice on drilling a 5" hole?
I have two breeches I made from scratch and one is being given to a friend! Need to finish up the other one. Taken two years to get them done when I get the time!
Author:  green machine [ Mon May 19, 2014 6:50 am ]
Post subject:  Re: Advice on drilling a 5" hole?
Drill from one end thru. As long as you keep the chips clear, and have a sharp drill, it will follow path of least resistance. The center of the work, that is the least amount of material to remove. Start with a Centre drill, then your short drill, then go to your long drill, pulling it out of the chuck as you go. Rick's speed should work, I don't imagine your lathe will go any faster.

Edit: if you plan on reaming, make sure to chase your hole for a 1/4 inch or so. Use an undersized end mill in the chuck, or bore undersized. The reamer will follow whatever is there, so you need to make sure you start straight.
Author:  EverHopeful [ Mon May 19, 2014 4:09 pm ]
Post subject:  Re: Advice on drilling a 5" hole?
Thanks again for all the tips. I have plenty of stock, so I'll probably end up trying it both ways and see how it works out. I think I'll try going straight through first as I don't yet have a dial indicator, so my ability to re-center the work is quite limited. I don't have any reamers, but I just finished up the steady rest, so at least I should be able to support the piece properly. Need the drill to arrive now :)

Jim
Author:  EverHopeful [ Wed May 21, 2014 7:52 am ]
Post subject:  Re: Advice on drilling a 5" hole?
I decided to make a new air stripper for the 2240, and thought I'd use the initial bore as a chance to practice for the breech. I'd forgotten just how tricky it can be to drill a hole that is so much longer than the diameter. I only have about 1.75" of travel in the tail stock drill, so anything beyond that really slows down as you can't clear the chips without stopping and backing the whole tail stock out. The stripper is only 2.5" - a 5" breech is going to be a challenge!

Jim
Author:  rrdstarr [ Wed May 21, 2014 3:52 pm ]
Post subject:  Re: Advice on drilling a 5" hole?
EverHopeful wrote:
Thanks again for all the tips. I have plenty of stock, so I'll probably end up trying it both ways and see how it works out. I think I'll try going straight through first as I don't yet have a dial indicator, so my ability to re-center the work is quite limited. I don't have any reamers, but I just finished up the steady rest, so at least I should be able to support the piece properly. Need the drill to arrive now :)

Jim


I have a 6" and 12" 1/4" drill bit if you want to borrow?
Author:  EverHopeful [ Wed May 21, 2014 4:00 pm ]
Post subject:  Re: Advice on drilling a 5" hole?
Thanks for the offer Rick. I should be ok for the 1/4" section as I'll only be running that from the back of the breech to the loading port. It's the 3/16 that I need to run all the way through, and hopefully that drill will arrive in a week or so. I'm also waiting on a ball nose end mill to cut the bottom of the breech, so it's going to be a while before it all comes together :)

If the 3/16 turns out to be too difficult I can always use Jon's suggestion and run a 1/4" through and then sleeve the loading port. Be nice if I can do it without the sleeve though.

Jim
Author:  rrdstarr [ Wed May 21, 2014 4:03 pm ]
Post subject:  Re: Advice on drilling a 5" hole?
Jim let us know how it goes. My lathe at work has 4.5" of travel so deep holes aren't so awful!
the company I work for has lots of scrap material, so if you need more of something let me know.
Author:  green machine [ Thu May 22, 2014 8:48 pm ]
Post subject:  Re: Advice on drilling a 5" hole?
Set your carriage over to contact the tailstock. When the hole gets deep enough that cranking the tailstock out is too much, just pull the entire tailstock out to clear chips, then return it to where the carriage is, and continue drilling. You can drill holes far deeper than the available travel on the tailstock.
Author:  Big Bore Bart [ Sat May 24, 2014 5:59 pm ]
Post subject:  Re: Advice on drilling a 5" hole?
Why are you even using the tailstock when drilling a deep hole? :? Lock a piece of stock in the tool holder, and drill it with the drill you intend to use for the hole, add a setscrew, and viola, instant, power fed, reversible, deep hole drill. :mrgreen:
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