round bottomed deep hole drilling

[pete boa]

can anyone please help. i need to drill/bore /ream. a 10.900 deep hole through 300 series stainless.blind hole .7875 dia. .3937 radius at the bottom. i would like a very high surface finish /straight bore hole.yes this is the start of a 1/6 scale napolean 12lbr. cannon. i have priced a custom reamer thru "clymer reamers" and they want $350.00 can. for this item. please don`t tell me to make my own reamer,i have neither the skill,heat treating equipment, nor the desire to try and build cutting tools that right now are far beyound my abilitys. right now ,the best way to do this job that i can figure out ,is to use a 19.5mm long series drill to full depth,then a 19.75mm ball nosed end mill with a welded extension, then a custom reamer. add up the tooling costs and this would be one expensive hole. i may not have any choice but to do it this way, but maybe the " GOD`S", "SAINTS" and or "wizord`s"of machine tool manipulation can explain a easier way to do this than my simpleton,vapour-locked brain can figure out! P.S. if anyone want's to build a very accurate napolean 12lbr. cannon try LARRY VAN SYOC in EMPORIA KANSAS, no affilliation but 100000% better than WILLAM F. GREEN'S PLANS not cheap, but well worth the $60.00 U.S i payed! nice to work with drawing's done by a machinist instead of an art school drop out/ draftsman/#@@%!&$)*/injin-eer!

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"TOOL SLUT"

[Dave Opincarne]

I hate to say it but make your own.

Calm down, I'm not talking about making a fluted reamer. Turn a piece of drill rod to .7875 dia. Turn the radius on the end. Mill half the material off the fist half inch (.3937" deep) Harden and hone. Drill a 3/4" hole just shy of the finished depth and finish with the reamer you just made.

[Dave Opincarne]

Hardening shoulden't need to be any more than heating to red hot until it is no longer magnetic (check with a cheep magnet) and quenching in oil. Polish and heat gently until a straw colored oxide appears and quickly quench again.

[Oso]

If you decide to drill, get a drill with only a short (2 or 3 diameters) fluted area. With more flutes, they tend to cut on the side, do not go straight, and drill oversize/bellmouth. The reamer may not correct that.

In thinner drills they will go seriously off-line, but with that size, I don't think there is much problem. I have drilled 1/4 inch holes 7 or 8 inches deep with short-fluted long drills OK, 0.006 error. Not for ordnance though.

They call the right tool a gun drill for a reason.

[This message has been edited by Oso (edited 03-18-2003).]

[JCHannum]

Why does it need to be 0.7875", and have a round bottom?
There is no real need for extreme accuracy in making a model cannon, and dimensions are probably what the maker had available to him, or what the bore ended up after he was done worrying it in.
Step drill, and finish ream to any convenient size between 3/4" and 13/16", and results will be just as good.
If you must have round bottom, the reamer or drill bit can be hand ground to produce acceptable results.
I have found William Green's plans quite acceptable. He made many museum quality and shootable cannon models from them. With appropriate care and attention to detail, others can as well. Many other plans I have seen bear a remarkable resemblance to his originals, but appear to be redrawn.

[kap pullen]

Tool Slut,

You don't need a perfect radius.
Just can't have any sharp inside corners that will hold burning embers to set off the next load.
I drill with a spade drill, redrill with a flat bottom drill with the corners rounded to say, 25% the bore diameter.
The worm should be able to clean out the bottom of the hole so a flatter bottom rather than spherical hole is better.

Don't believe the origionals were spherical anyway.

Swab out generously, and allow extra time for embers to go out ( should there be any).

You should mark your ram rod at full bore depth, charge depth, and charge, and ball depth so you know where your at.

Also should hear a solid metalic clunk when putting the ram in the wormed and swabbed bore.

Don't put body parts in front of your bore in any case.

kap

[Thrud]

Pete aka "tool Slut"

Listen to Kap - he is a cannon fan too, but he makes real big models...

I would avoid 304 Stailess like the plague - it is the worst work hardening alloy and hardest to work with normal tools. 316L is much more civilized and shinier!

[JCHannum]

If concern is for an accurate model, materials should be cast iron or cast bronze. Very few Napoleon cannon were made of stainless. In fact, none were.

[Al Messer]

I agree with the others: don't use stainless, use Naval Bronze or even common Brass. Don't worry about having a hole with the bottom shaped like the drill bit. Mark your rammer, and always keep the muzzle pointed away from you. Good luck!!

[Al Messer]

Oh, I forgot--someone mentioned "Gun Drills". Don't they have only one flute/cutting edge??