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Unread postAuthor: inonickname » Sun Jul 19, 2009 8:19 am

Ok for reasons I will not mention, I need to make a veeeery big hole.

Lets say that I have a 3" piece of solid steel bar about 1.5m long.. And I turn it round, cut a taper and so on. Basically think of a cannon..

Now lets pretend I want to bore a hole the whole way through (and make a bolt-on breech) that is around 43mm in diameter to fit a golf ball.

I have no idea how I'm going to go about this, it's fairly high carbon steel and extremely strong. With a lathe and 4 jaw chuck what's the best way to go about this? (bar may be cut down to 90cm to fit within the confines of the lathe)

By the way, this is the lathe it will probably be done on:
https://www.machineryhouse.com.au/Produ ... kCode=L183
Or if I'm unlucky then it may be on a 600, but hopefully not. I'd like to have the barrel as long as possible.

I'm aiming for at least mach 2.. :twisted:
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Unread postAuthor: jrrdw » Sun Jul 19, 2009 8:46 am

You will simple need the right drill bit for the job. For a exact size use a adjustable reemer. Kinda costly to do one hole if your buying.
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Unread postAuthor: inonickname » Sun Jul 19, 2009 9:21 am

jrrdw wrote:You will simple need the right drill bit for the job. For a exact size use a adjustable reemer. Kinda costly to do one hole if your buying.


I can buy 1 meter drillbits where? :shock:

I was thinking more along the lines of an extension. I could be happy to sacrifice the drillbit for it. (will probably be knackered after anyway). I don't mind if it's a bit large, I don't mind wadding. Time will be insignificant given the loading time of my propellant.

Perhaps a reduced shank drillbit, and a turned holder for it? The problem is starting the hole, and then extending the drillbit continuously into it.

The bit of metal is a little heavy to cart around elsewhere..
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Unread postAuthor: velocity3x » Sun Jul 19, 2009 12:21 pm

inonickname wrote:I can buy 1 meter drillbits where?


Welcome to the wonderful world of "Endless Expense"......Machine tools and tooling. For tooling, try:
MSC Industrial Supply
http://www1.mscdirect.com/CGI/NNSRHM
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Unread postAuthor: jrrdw » Sun Jul 19, 2009 4:13 pm

https://www.use-enco.com/CGI/INSRHM :wink: The lathe turns the work and the bit is chucked into a tailstock drill chuck, then pushed into the work piece, if the lathe is set up right you will get a parfect center, (well close to perfect).

Link fixed.
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Last edited by jrrdw on Mon Jul 20, 2009 7:32 am, edited 1 time in total.
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Unread postAuthor: Technician1002 » Sun Jul 19, 2009 4:16 pm

For what you are trying to do, more expertise, tooling, etc will be needed. The basic problem is with long bits, the end is free to wander. As soon as there is any wobble in the bit, it will keep drilling off center and if the work is long enough, break through the side.

Study methods used for boring cannons. Often the initial bore is cast in the metal so just a finish cut needs done.

Long drill bits are made, but they are not built for that application. I have a couple 3 foot and 5 foot bits. They are for drilling down a length of wall to install cable tv or telephone wire. The shaft is flexible so drilling a hole in the floor inside the wall is possible.

Unfortunately, they are made for wood, not high carbon steel. They are flexible, not rigid. Page below has bits up to 72 inch long.

http://www.lashen.com/vendors/BES/Fish_Bits.asp
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Unread postAuthor: john bunsenburner » Sun Jul 19, 2009 4:37 pm

Well really if you find a 50cm drill bit you are done, as you can simply turn the work piece around half way. I have found long drill bits called blacksmith's drill bits

The seller has long drill bits up to 9.5mm, perhaps an email to the guy might help you out. Really you could try and have a gun smith make a small bore hole, and you can then use this hole as a pilot. Eitherway, i wish you lots of luck, this one will be hard...

Have a look on here http://www.backyardmetalcasting.com/forums, they have quite a bit of know how, and iv found it very helpful!
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Unread postAuthor: far_cry » Sun Jul 19, 2009 5:56 pm

but in this case you will need a 3 meter long lathe
if the spindle hole is 3" this will demand a shorter lathe

and 3500$ you want to pay !!!!!

take the part to machinist to this for you less effort and less mony
or just search for barrel in the same numbers you want
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Unread postAuthor: inonickname » Sun Jul 19, 2009 8:37 pm

The lathe is for other things as well, not buying it specifically for this.

I guess I could turn the stock round, cut it into sections, or whatever, sleeve them with a piece of stainless pipe and then weld it all back together, then turn the welds nice and smooth.

I can see this being slightly time consuming.
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Unread postAuthor: Gippeto » Mon Jul 20, 2009 12:13 am

Call your local purveyor of metal and inquire about seamless mechanical tubing.

Metal Supermarket handles 3" with .750" wall... 1.5" bore. Might be a better starting point depending on expected pressures.
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Unread postAuthor: inonickname » Mon Jul 20, 2009 12:36 am

Gippeto wrote:Call your local purveyor of metal and inquire about seamless mechanical tubing.

Metal Supermarket handles 3" with .750" wall... 1.5" bore. Might be a better starting point depending on expected pressures.


think higher than traditional firearm pressures.. I think creating the cannon in bits and then sleeving the pieces over stainless steel tube is the way to go, unless I can get a 4m long lathe..
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Unread postAuthor: Gippeto » Mon Jul 20, 2009 1:11 am

Any idea what the mechanical properties (tensile strength) of your steel bar are?

Some quick calculations, indicate a requirement for ~200000psi tensile strength for a safety factor of 3. (working pressure of 66700psi)

That's a pretty stout requirement to meet.
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Unread postAuthor: inonickname » Mon Jul 20, 2009 1:19 am

Gippeto wrote:Any idea what the mechanical properties (tensile strength) of your steel bar are?

Some quick calculations, indicate a requirement for ~200000psi tensile strength for a safety factor of 3. (working pressure of 66700psi)

That's a pretty stout requirement to meet.


No, but I'm gonna get it checked first. I just measuer, and it's actually larger than 3" - the walls will be almost 1" thick.

Propellant will not be smokeless powder...
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