Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

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RogueRose
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Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by RogueRose » Fri Sep 22, 2017 10:22 pm

So I need to make some moulds to cast spheres (or as close as possible - doesn't need to be exact/perfect). I'm using aluminum stock from 1/2" thick to 1.5 or 1.75 for the 2" spheres (need to do some calculations on heat transfer speeds).

This works the same as bullet moulds or fishing weight moulds - 2 pieces clamped together, metal poured in a hole in the top, release latch and dump out casting.

I've been told that I can do this by using a steel washer (placed vertically) that has a metal shaft welded to it at the top center, and then put in drill press and remove the metal/graphite. This sounds plausible but I'm wondering if there are more details missing like sharpening the cutting parts of the washer (the bottom 1/2) or at least squaring them off perfectly so the edges (circumference, of at least the bottom 1/2 of the washer) so they are perpendicular to the vertical, flat part of the washer. Other than that, I could see sharpening the edges on the bottom half either to a knife point (both sides are sharpened) or sharpening one side from the horizontal axis down to the bottom of the vertical axis - and then sharpen the opposite side on the bottom half. This way when it spins, there is always a sharp side turning in the same direction. IDK how this is supposed to work,

It seems a little unplausible that a setup like this would be able to drill out a hole 1" diam and 1/2" deep let alone a 2" diam and 1" deep.

My idea is to use a combo of drilling out the concave hole, removing as much as possible w/o going too deep and ruining the final shape. Do this around the entire 1/2 sphere and then use something like a Dremel (choose from many attachments to remove remaining material) to get maybe a total of 70-90% of total material removed - AND THEN, use the washer drill bit to do the final drilling and shaping of the 1/2 sphere.

I've also seen spherical burrs fromm 12mm to 50mmm which are 80 grit diamond. I would think this could be good for removing some material but I'm not sure if they could be used to remove all the material. the problem is that a 50mm (about 2") is listed at $30-35 + shipping from UK/EU so a little pricey compared to a $1 washer and a $.25 3" length of 1/4 drill shaft.

Can anyone add any light on this situation - if you see any potential issues, see better solutions (I DON"T have a lathe!!!) or have any other input I would greatly appreciate hearing your thoughts! Thanks for reading!

John Evans
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by John Evans » Fri Sep 22, 2017 10:49 pm

In a few words - Ain't gona happen !!! Get who ever told you this could be done this way to show you how. There are several ways of doing this but both need either a lathe or mill AND extra/special styles of tooling.
www.chaski.com

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WesHowe
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by WesHowe » Fri Sep 22, 2017 10:57 pm

If you have a vertical mill, using a rotary table (with the axis horizontal), a boring head will make any half-circle within the constraints of your boring head. You could mount stock on the rotary table and use the boring bar and head as a cutter (cutting edge pointed outward), moving the work into the cutter a bit at a time and rotating the table to get a 360-degree cut. When you get to depth you'll have your half shell.

If you don't already have the rotary table or boring head, they'll cost a lot more than $35 (particularly the table). You didn't say if you had a mill, you are probably really priced out of this; I don't think a drill press would take the side thrust for this or any method you described.

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Lew Hartswick
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by Lew Hartswick » Sat Sep 23, 2017 7:46 am

You'll need a lathe for sure and a "radius turner" . I've done this many times. It's even possible to make the hemisphere a bit deeper than the radius. The tool bit needs to be a bit different than the common one but it's no great problem . I'll be happy to send you some pix if wanted.
...lew...

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Bill Shields
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by Bill Shields » Sat Sep 23, 2017 8:17 am

If you do not have a radius turner, then a 2" BALL END MILL will get you very close for starters, if not to finish size, depending on the tolerances you require. Not cheap ($160 or so), but will get the job done....

Rough it out with a standard drills of various sizes / depths first.
Too many things going on to bother listing them.

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rudd
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by rudd » Sat Sep 23, 2017 9:46 am

What metal are you intending to use for your product? If a low temp metal (not steel) could you make a 2 part plaster mold from a plastic sphere? - Plastic spheres are cheap and available. There are special plasters intended for metal casting.
http://www.usg.com/content/dam/USG_Mark ... -IG538.pdf
Also: http://www.practicalmachinist.com/vb/ge ... ld-235089/

John Hasler
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by John Hasler » Sat Sep 23, 2017 10:07 am

RogueRose writes:
> Other than that, I could see sharpening the edges on the bottom half either to a knife point (both sides are sharpened) or sharpening one side from
> the horizontal axis down to the bottom of the vertical axis - and then sharpen the opposite side on the bottom half. This way when it spins, there is
> always a sharp side turning in the same direction. IDK how this is supposed to work,

This will work for a low-quality hole in soft material. Use a hardened washer. Don't sharpen the edges to a knife edge. Make the leading side flat and give the edge about a 15 degree relief. Drill a pilot hole to full depth: this tool will cut poorly or not at all at the center.

jcfx
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by jcfx » Sat Sep 23, 2017 5:54 pm

How about a core box router bit ?
https://www.mlcswoodworking.com/shopsit ... _core.html

At $30 bucks it's a heck of a lot cheaper than a 2" ball end mill, and with the end mill you're probably
going to have problems holding the shank unless it's a reduced shank type.
That router bit should cut thru graphite easy peasy, but I'd use caution with aluminum especially
if you don't have a milling machine.

RogueRose
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by RogueRose » Sat Sep 23, 2017 11:25 pm

As for what I am going to be making the moulds out of, I'm not sure of the alloy of Al as it is blocks I've had around for a while. I do have lots of Al ingots from melting and casting various Al components like heat sinks, tabs from soda cans, shells from large electrolytic capacitors, Al pipe/tubing and lots of other stuff (also have some ingots of soda cans melted down).

As for tools, I have LOTS of hand tools but no real drill press (ShipSmith, but that is for wood, maybe it could be slowed down and a vert& horizontal metal bandsaw + lots of shop tools, forge, welders, mig, oxy/act, plasma cutter, routers)


First off, the size and perfection of the final product spheres (cylinders might also be adequate, I'm not sure on that) is not of major concern as these are going to be used as grinding material in a ball mill.

As for the metal I'm planning on casting it is a zinc allow, one is called ZA-27 (MP of about 806F and then another called AcuZinc5 MP 826F) the Brinell Hardness for the ZA-27 is 119 while AcuZinc5 is 115 and densities are 5.1g/cc vs 6.96g/cc respectively - so I'd much prefer the more dense and the slightly less hardness isn't much of an issue for grinding soft metals and salts. I'd also like to be able to cast lead as well if possible and maybe some unique alloys I'm going to be toying around with to get the density up as I really only need a Brinell HB rating of ~50

I am curious as to what you think about using cylinders vs spheres as the cylinders would be easier to make. So for a cylinder of 2" diameter I was thinking of maybe 2.5-3" length and having the ends curved to whatever can be made without a lot of work. IDK if there is benefit to rounded ends on cylinders for the milling media or not - I could always grind the ends down later after casting/moulding cylinders (or longer rods & cut them).


As far as the plaster mould, I have a lot of CaSO4 (plaster), clays and other things which I could make a mould, but I don't think it would be reuseable like I need.


Finally, does anyone know where a good supply of Zinc as the AcuZinc5 is about 90% zinc and it is almost impossible to buy anything from salvage yards around here and it may be difficult to tell how pure it is. I'm not keen on spending $10 for 1lb on ebay...

spro
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by spro » Sun Sep 24, 2017 12:16 am

Broken gears from Atlas lathes and mill are of little use. Look up Zamak (sp) may be useful.

Harold_V
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by Harold_V » Sun Sep 24, 2017 1:47 am

RogueRose wrote:I am curious as to what you think about using cylinders vs spheres as the cylinders would be easier to make.
I have limited experience with ball mills, having built one to reduce ½"- crushed gold ore to less than 200 mesh. For that process, I used a combination of balls and rollers, all steel. Ball size varied from about 1½" to about 5/8", and rollers were no larger than 3/4" diameter and about an inch long, no longer. For me, it worked exceedingly well.
Ball mill.jpg
You're going to get considerable wear with soft materials, perhaps contaminating the substances you wish to mill. You might be well served to explore other options if that would be troublesome.

H
Wise people talk because they have something to say. Fools talk because they have to say something.

earlgo
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Re: Need to drill 1/2 sphere hole in aluminium and/or graphite - 1/2" - 2" diameter

Post by earlgo » Sun Sep 24, 2017 9:13 am

Harold has the right of this one.

All the ball mills that the Norton Co. (Chemical Process Products Division) made used hardened steel balls and the drums were covered in Tungsten Carbide 'tiles'. They were used to grind a ceramic slurry from which Chemical process equipment was made.
I can't imagine a ZN alloy that would stay together and still make a good ball mill.

Amazon or E-bay might have a supply of steel balls.
Or you might try these folks: https://www.mcmaster.com/#standard-steel-balls/=19iu8jr

--earlgo
Before you do anything, you must do something else first. - Washington's principle.

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