I need to put a 3/8" hole straight through the center of a 3/4" hardened steel ball. Tried the Bridgeport - leveled the top, centered and started to drill, and only dented it. Any advice from the D-Web brain trust?
Need help from a machinist
- Thread starter knewsom
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gracias man. Apparently the "low-range" on this particular mill is mislabled, as it is not in fact "low" but "reverse". 
Why not to mill/sand off a flat facet on the ball first, before drilling a hole? You only need it to be less than a quarter-inch in diameter.
p m said:
I think he did
Knewsom please dont say this is for some kind of a left coast prince albert.
crown14 said:
:rofl:
Oh man, that's genius... nah, not with THAT big a steel ball - my junk'd be stretched out the bottom of my kilt...
Yeah, we did mill off the top of the ball first so there would be more surface for the bit to bite. Tried carbide bits, went slow, etc, as per you guys' advice. The real trick was using a combination of a ball-tip and and endmill, but we typically needed two bits to do a ball, even moving slowly. They'd just build up too much heat once inside and burn out. I suppose we could have gone even slower, but as it was, it took about a half hour to do one.
Needless to say, we're looking into alternatives for this particular part. Thanks for the help, fellas.
Kris - go to Marshall's Industrial Hardware off Miramar and tell them what bit you need. I've left a small fortune there for drill bits.
Ok since I'm not a machinist, heres a stupid question. Why not drill an unhardened steel ball and then harden it when done?
first, you should be running faster on carbide compared to HSS, not slower
second, you have not mentioned coolant. Use it
third, if you are doing production quantities, look in to a coating. TiAlN on carbide works wonders for me, like doubling the volume between regrinds while increasing the cutting speeds. Its 20 bucks or so per tool, probably hard to justify on a 3/8" drill, but it will make a huge difference in longevity.
second, you have not mentioned coolant. Use it
third, if you are doing production quantities, look in to a coating. TiAlN on carbide works wonders for me, like doubling the volume between regrinds while increasing the cutting speeds. Its 20 bucks or so per tool, probably hard to justify on a 3/8" drill, but it will make a huge difference in longevity.
chris snell said:
What you saw was a prototype. We've made several revisions since, and are now using two kinds of bamboo plywood to build it instead of the solid oak, and some design changes. The ball is for the mechanism that rotates the iPad on top of the box. ...and every day we get emails from people trying to buy them. Needless to say, I'm going to be building boxes for quite some time. The real kicker is, I actually just landed a Color gig for Showtime too - I pendulum between having no work at all to having far more than I can handle. Hopefully the cashbox building gig will even things out a bit, as it's a bit more flexible.
I'll post pics of the mechanism when I get a chance. Have to go finish an episode, then head into the shop. Phew! Busy busy busy.
robertf said:
One of the bits we used was coated, and yes it DID make a big difference! As for coolant, we're just using oil, a squirt every time the bit is raised. Thanks for the speed advice!
Whatcha buildin?
It may be out there already.
http://www.grainger.com/Grainger/machining/ecatalog/N-big/Ntt-3~~~4+inch+ball?Ndr=textsearchesinbase%2Btrue&sst=subset
It may be out there already.
http://www.grainger.com/Grainger/machining/ecatalog/N-big/Ntt-3~~~4+inch+ball?Ndr=textsearchesinbase%2Btrue&sst=subset
I HATE PONIES said:
Thanks man - yeah, we're definitely looking for prefabricated balls, they kinda have to be a very specific size, as they're part of a mechanism. The prefab ones with holes through them are pricey, though those tapped ones may be promising. I'm starting to lean towards moulding and casting a ball in a tough plastic resin around a bearing instead of using a solid steel ball. I have concerns about longevity of steel-on-steel moving parts and possible bind issues with the head of the bolt going through it that acts as the shaft.
Here's a rough preview of what we're up to: http://www.happyowlstudio.com/pages/cashbox
The design has changed quite a bit since this, but it's the same general concept. I'm actually having a lot of fun with this - I love woodworking, and making money between film/TV gigs by doing this is pretty tantalizing.
For that, I can't possibly see why would you need a 3/4" hardened steel ball (something that can support a sizeable portion of an M415 tank turret).
It doesn't have to be hardened. Just steel, and a precise size.
LOL - "prariepunk". I like it. It's a new trend.
LOL - "prariepunk". I like it. It's a new trend.
