Introduction: How to Make an Ice Ball Maker

Picture of How to Make an Ice Ball Maker

Do you want an ice ball maker like those sold online, but don't have $800+ to spend?  Then make your own!

Don't know what an ice ball maker is, or how it works?  Then check out the last page of this Instructable for a video of it in action.

You'll need access to a machine shop, and specifically a CNC machine.  TechShop provides all the equipment you need for a monthy fee.  I made it at TechShop, and you can too.

Ice ball makers work by melting a large block of ice into the proper shape.  It accomplishes this by having two large blocks of aluminum (aluminum has high heat conductivity and capacity), each with a hemisphere carved into a side, slide together to form a single continuous chamber on the inside.  What's left is a perfect sphere.

Step 1: Materials and Equipment

Picture of Materials and Equipment

The basic material is two large blocks of aluminum.  You'll need to pick a size based on the size of the ice ball you want.

You'll need blocks that are in total at least 10 times the volume of your sphere.  This is so the aluminum properly melts away the rest of the block.  My ice ball maker produces 70 mm diameter ice balls, and the aluminum blocks are each 125x125x75 mm.  That's a 13-to-1 ratio, and works pretty well.

You'll also need stainless steel rod.  These serve as the bottom vertical guide shafts.  I used 3/8" SS rod.

Last, you'll need plastic rod of a larger diameter.  This piece slides over the stainless steel rod.  I used 3/4" teflon rod, but teflon turns out to be hard to machine.  I hear that Delrin machines well.

The only extra material is whatever you think will make the final product easy to use.  I added rubber feet and a cabinet knob for lifting the top.

For equipment, you'll need a CNC mill and a lathe, and basic tooling.  The inner hemispheres will be cut with a ball end mill, and you'll want as large a diameter here as possible.  I used a 1" ball end, but smaller diameters will work as well.  You'll also need a tap and die set.

Step 2: Cutting the Blocks Down to Size

Picture of Cutting the Blocks Down to Size

The first thing you'll want to do is to make sure you have perfectly square blocks of metal.  Extruded aluminum bar is not very square, so you'll have to do the last step.

I started with 5" square bar stock, which is 127x127 mm, and machined this down to 125x125 mm with a length of 75 mm.

You can do this on a CNC mill or just a normal one.  Get a large diameter end mill or, even better, a fly cutter, and machine down each face of the block.  For the final finishing step, you may wish to clamp together the two blocks so that even if there is a small amount of error, they still match together perfectly.  Make sure to mark a corner so that you know the right orientation!

Alternatively, you can use round bar stock instead of square, and do most of this step on a lathe.  You might like the round model better for aesthetic reasons anyway!  It's up to you.

Step 3: Machining the Hemispheres

Picture of Machining the Hemispheres

Next, you'll want to machine out the hemispheres.  This is the hardest step and will require you to learn how to use a CNC mill and the associated software.  If you use TechShop, take their classes and play around with some easier projects first to get a feel for how the machine works.  It's not too difficult, but it requires time to learn.

The basic model is easy: use AutoCAD or the equivalent to model the original block, make a sphere of the appropriate diameter, and subtract one from the other.  This leaves a block with a hemisphere cut out.

Then, you need to use CAM software to create the toolpaths.  You'll want at least two phases: a roughing pass with a large endmill to take away most of the material, and then a finishing pass with the ball end bill to leave a smooth inner surface.  Don't try to do the roughing pass with a ball end mill!  They don't like being "plunged" directly into metal.

Finally, use the CNC machine to cut the hemispheres.  Hopefully, you've learned by practice how to use edge finders, perform air passes, and so on so that you can perform this step safely and accurately.  If not, practice some more and find someone to help you!

Step 4: Stainless Steel Alignment Rods

Picture of Stainless Steel Alignment Rods

Next step is to make the steel alignment rods that come up from the bottom block of the ice ball maker.  As I said before, they are 3/8" diameter.

These rods need to be nearly--but not quite--the full height of the ice ball maker.  I have chosen 138 mm out of the total 150 mm.  The rods start from the very bottom of the bottom block, but do not poke all the way out of the top block.  I have left 10 mm of solid aluminum above the top block, and then gave the rods another 2 mm of "slack".

The bottom part of these rods needs to be threaded.  I used a 3/8" die, pitch 24 for the threads.  I did the threading in a lathe, but you can also do it in a mill or just freehand.  The rods need to be as straight as possible, but you can always put some slack in the system later if you need.

I also used a lathe to bevel the edges a bit so as not to leave sharp edges, and make it easier to thread.

Last, I mounted the rods in a drill press, and sanded them (ultimately using 1000 grit) for a very smooth surface.  Remember that the plastic pieces slide on these, so the smoother the better.

Step 5: Hole Drilling

Picture of Hole Drilling

Before moving onto the plastic sliders, we'll want to drill the holes that the rods slide into.

Since the plastic has a diameter of 3/4", I chose to drill the slightly smaller diameter of 23/32".  This meant that I could machine down the plastic pieces to exactly fit the way I wanted.

It's very crucial that the holes on the top and bottom pieces are exactly aligned.  After you choose your hole positions, make sure to cut both of them at the same time per block--don't remove it from the vise in-between.  Doing so will add measurement error.

Because the holes are so big, you'll want to drill them progressively.  Start with a center drill to make the starter hole.  Then, use a smaller diameter drill, and only cut a fraction of an inch at a time before lifting it to remove the chips.  Do the same with the final size drill.

The top piece has holes of depth 65 mm (leaving 10 mm above), while the bottom piece has depth 60 mm.  I left the larger 15 mm on the bottom because we'll be threading holes, and we want a bit more strength here.

Step 6: Drilling and Threading the Alignment Rod Holes

Picture of Drilling and Threading the Alignment Rod Holes

Now, we work exclusively on the bottom block.  We need to make the threaded holes that the alignment rods screw into.

Find the tap you need (3/8"-24 in my case) and the drill you need (make sure to look it up in a table!).  This should be pretty straightforward: drill the holes in the same location as you did on the top side.  As before, make sure you start with a center drill!

Then, tap the hole all the way through.  If you use lubricant, this should be very easy since it is not a blind bottom, and the chips can fall all the way through.

When done, you should be able to thread the rods into the holes as shown in the left block in the picture.

You can see in the other picture that I have added rubber feet on the corner; this protects my countertop.

Step 7: Plastic Sliders

Picture of Plastic Sliders

These pieces slide into the top block, as well as over the bottom rods.  You'll mostly be using a lathe for this step.

I started with 3/4" teflon, but as I said you can use other plastics.  Approximately half the rod needs to be machined do to *just fit* in the holes you've created.  When you get close to the right diameter, only machine off about 2/1000" at a time, and check to see if they fit snugly via friction.

Next, you'll need to drill a hole all the way through of the same diameter as the metal rods--3/8" in my case.  Again, use a center drill to start with.  You may need to drill from both ends to get the length you need.

Next, you'll want to use a reamer to smoothen and enlarge the hole.  Reamers are made with very slightly larger diameters than common sizes: a 3/8" drill is 0.3750", and a common reamer size is 0.3760".  This is perfect for us since it gives us just enough gap for a smooth slide.

The other half of the rod should be machined down to a smaller diameter; one that fits freely in the hole.  Mine ended up as 0.68" diameter; you may need more or less depending on how precise you are with the other measurements.  Constantly try sliding the rod down the metal rods to make sure they enter the hole freely.

Last, you'll want to bevel the end so that it is guided down if there is any misalignment at all.  If your measurements are perfect, you may not need this, but I did.

Step 8:

Picture of

You're almost done! You should be able to assemble the pieces as the picture shows.

If you want to install a lifting knob, you can do so now.  Find a nice cabinet knob at the hardware store, and figure out what diameter screw it takes (mine was 8-32).  Find the appropriate tap, and the drill that you use with that tap.  Drill in the center of the upper block (again, use a center drill!), making sure not to go so deep that you plunge into the hemisphere.  Now tap the hole, cut off the head of the screw (so that you have a short threaded rod), and tighten it up.

Step 9:

Picture of

When you're all done, the ice ball maker should operate like shown above.  Perfect ice balls!

Wondering how I got such clear ice to start with?  Then check out my other Instructable, how to make crystal clear blocks of ice.

Attached are some very basic AutoCAD files of my design.  They contain the original 125x125x75 mm block and the same block with a hemisphere carved into it.  You should be able to import these into your CAM program (like SprutCAM), but I recommend starting from scratch to understand the whole process flow.


maliamalia (author)2017-09-06

Hey, is there any possibility to bye one of your selfmade ice mould maker??

Thanks for answering!


didgitalpunk (author)2012-01-19

would it not work better if it was copper?
just wondering cause it has a better heat conductivity than aluminum

spcutler (author)didgitalpunk2012-01-20

Copper would definitely beat aluminum in the heat conduction department, and be beautiful to boot--the main trouble is that it's so expensive! I also can't find it in the sizes I'd need; 5" square or round bar. I'm sure it exists but not at the places I've looked at so far.

I did make a nice copper cylinder on the lathe as part of a mini element collection. It's the prettiest element of the ones I have to far, and nice and dense too--although tungsten beats it there!

JimS26 (author)spcutler2015-06-28

spcutler, you said: "Copper would definitely beat aluminum in the heat conduction department", but in your explanation about how the device works, you said the aluminum has high heat capacity. Indeed it does, and it has three times as much as copper. Is heat capacity or heat conductance the dominant factor?

spcutler (author)JimS262015-06-29

You need some of each. Regarding capacity, the main thing is that you have *enough* of it--it needs to be enough to melt away all the parts of your ice block that aren't the sphere. If you had a material with twice the heat capacity as aluminum, it could be half the volume.

Too much capacity could be a minor problem. My device got noticeably frosty at the end of a run. This was an advantage because it meant the ice ball wouldn't melt any further (since it was at the same temperature). A device with much larger capacity would continue to melt the ice and the ball would become deformed unless you took it out quickly.

Regarding conductivity, my intuition is that it should be high but not too high. Something like plastic would take way too long. However, with aluminum I found that the balls would sometimes crack if they were too cold (well below freezing) and the aluminum was warm. The crack was caused by thermal shock. Something like copper with even higher conductivity would be even more prone to thermal shock, so I think aluminum ends up being just right.

Skymeat (author)spcutler2012-01-22

I think you might have nailed it on the aluminum...Copper is a pain in the ass to keep clean. Tarnished Aluminum just looks a bit dull..

didgitalpunk (author)Skymeat2012-01-23

true enough XD copper is so anoying to keep clean but you can plate it with zinc and it won't oxide anymore and the heat transfer won't be much affected by the microscopic coat of zinc.
at least i think so.

didgitalpunk (author)spcutler2012-01-20

Tungsten conducts heat better than copper?
That I did not know!
Anyway nice instructables man!

nickmh (author)didgitalpunk2012-01-22

It doesn't, he meant it's much denser than copper. Tungsten is nearly twice as dense as lead.

didgitalpunk (author)nickmh2012-01-23

hoo yeah i misread there ^^ thx!

praylax (author)2014-12-06

Can u sell me one of these please

Franzplanz123 (author)2014-09-01

waste of aluminum

have you ever tried freezing waterballoons?

mikejs (author)2012-02-06

New goal: get a 3D scan of my head, and then mill that into some aluminum. Perfect ice faces, every time. Thank you!

Franzplanz123 (author)mikejs2014-09-01

theres an idea

Brian996 (author)2013-06-19

How long do you have to wait between moulds?

Nuclearpwr (author)2013-01-31

I am really on a mission to make these really cool ice balls...hope you can help me out here....

I do not have access to any machining equipment and even if I did, I am not a machinist...would you consider making one for me? I would of course pay you for the material, machine time and your time.

Thanks again,

Marko in Mass

Nuclearpwr (author)2013-01-31

You are my hero. I've been trying to make clear ice balls for a while and your post does it all...clear ice and the ice ball machine...and a whole lot cheaper than the on-line units.

Question : What size piece of clear ice do you need to use in the unit? Does the size of the clear block of ice matter...assuming it is big enough to fill the sphere...and does the shape of the clear block make any difference.

I found a small mini-version of the on-line model and when I use mine, sometime I get flat spots on the ball...and I think it might be because I am using irregular shapes of clear ice...pieces just broken off a larger pc of clear ice.

Thanks again and great instructional video.


ToolboxGuy (author)2012-11-11

Way cool ! Given that you have a CNC at your disposal, I am surprised that you didn't add any runoff channels/gates, to keep the countertop dry. Since you don't want to corrupt the shape, just make an outer ring around the shape, and an outlet channel.
I would love to make one of these for ice formed whiskey glasses, say four at a time, or perhaps shotglasses in quantity. Shape then freeze until the party. Have to make grips/indents so it doesn't become too slippery.

Perfect for pool parties - and very little to clean up, at least for those of us who drain our glasses.

spcutler (author)ToolboxGuy2012-11-12

That's a great idea! I was originally thinking in terms of having a small hole in the bottom that the water could flow through, but that would, as you say, corrupt the shape. And I'll admit, drilling tiny holes in a nearly-finished project always scares me! Your idea with the channels solves both problems. I was already planning on making some more, and I'll be sure to try that out if I do.

One thing to watch out for when refreezing--because there is still a film of water on the surface, you will tend to get marks corresponding to the container you put them in. So it looks a bit imperfect, though after 30 seconds in the glass the marks will melt away.

spcutler (author)ToolboxGuy2012-11-12

That's a great idea! I was originally thinking in terms of having a small hole in the bottom that the water could flow through, but that would, as you say, corrupt the shape. And I'll admit, drilling tiny holes in a nearly-finished project always scares me! Your idea with the channels solves both problems. I was already planning on making some more, and I'll be sure to try that out if I do.

One thing to watch out for when refreezing--because there is still a film of water on the surface, you will tend to get marks corresponding to the container you put them in. So it looks a bit imperfect, though after 30 seconds in the glass the marks will melt away.

jayhitek (author)2012-11-01

Can you post the G Code?

eyong2 (author)2012-10-30

Hi im from malaysia and Im trying to make an ice ball maker using your steps shown above. May i get more information from you like from "Step 3 Machining the Hemispheres", what sort of sizes of the end mill and ball end mill should i use for the cnc with the DFX file u attached?


spcutler (author)eyong22012-10-31

My opinion is that it doesn't matter too much, but the larger the better. I used a 3/4" end mill for the roughing and a 1" ball end mill for the final pass. These days, I would use a real roughing mill instead of a standard end mill since there is so much material to remove.

jayhitek (author)2012-10-22

I will buy one from you.

EpicCraftMan (author)2012-09-19

Well its awsome

EpicCraftMan (author)2012-09-19

what would happen if you tryed to use strofoam or somthing like that?

captain Jack (author)2012-09-17


superpositron (author)2012-09-14


Great stuff. You wrote that aluminum has high heat conductivity and capacity. I was considering milling this in Steel. Do you think steel is just wrong for this?

Many thanks.

spcutler (author)superpositron2012-09-14

I would avoid steel for a few reasons. The two big ones are, as you said, heat capacity and conductivity. Per gram, steel has about half the heat capacity as aluminum, so the unit would need to weigh at least twice as much to work as well (it could be a little smaller, though). It also has only a fifth of the heat conduction, so it would work very slowly.

The other big problem, as you might expect, is corrosion. Even without anodization, aluminum doesn't corrode in any significant way in the presence of water. Steel will of course rust if you have no protection on it.

Steel is also harder to work with, and isn't necessarily cheaper when you take the heat capacity into account.

You could use stainless of course, but that's far more expensive, even harder to machine, and only fixes the corrosion problem.

The only other material that I would really consider is copper, and that would be a situation where cost isn't the dominant factor. It's impossible to beat aluminum in bang-for-the-buck terms.

illusionistpro (author)2012-09-11

Is there a reason you specify a 10:1 ratio of metal to ice?

spcutler (author)illusionistpro2012-09-11

Warning: geek out alert.

The short answer is that you need enough thermal mass to melt through all the ice, and 10:1 is about the right amount.

Long answer:
To melt ice, you need to get through what's called the latent heat of fusion. For ice/water, this is 334 joules/gram. The density of ice is 0.917 g/cm^3, so this comes to 306 J/cm^3

This heat comes from the aluminum (in the short term). Aluminum has a heat capacity of 0.9 J/K-g, so at a density of 2.7 g/cm^3 we have 2.43 J/K-cm^3. Room temperature is 25 C, and we can only go down to 0 C before it stops being able to melt ice. Therefore, the aluminum can supply 61 J/cm^3 of heat energy to melt the ice.

306 J/cm^3/61 J/cm^3 is just about a 5:1 ratio. But that's a bare minimum: the ice ball maker works very slowly when it gets close to 0 C, and the ice will start at a temperature <0 C (depending on how cold the freezer is), and there are some extra holes and such that take away some capacity. So in practice we need a little extra leeway, and 10:1 makes for a nice round number.

firesirt (author)2012-06-23

this is awesome. I think I might try something like this, only casting the aluminum rather than cutting it.

spcutler (author)firesirt2012-06-24

Good luck, and let me know how it turns out! My first thought is that the surface wouldn't be smooth enough. But on the other hand, the surface of the ice ball melts fairly quickly and would probably leave a nice surface in short order. So it might actually work really well. Have fun!

r_harris2 (author)2012-04-12

Very interesting project. You know, this could be done on a lathe, even a manual one. You could either make a custom cutter, or build a radius-cutting attachment. Then mount the block on the lathe faceplate (or 4-jaw if you have a big enough one). I think a block of this size could just barely be mounted on a mini-lathe's faceplate.

blastin06 (author)2012-01-19

I think this is an awesome project and I commend you on all the work and learning you did. With that being said, for future possibly since you have to use a CNC anyways why not use a CNC lathe and turn multiple steps into two or three. Using a three jaw chuck you could use a round stock, shave the sides, face off the front and also cut the sphere shape. This all could be done in one step and most likely with out the use of a CAM package. Leaving the guides to be drilled on a knee mill.

spcutler (author)blastin062012-01-19

Unfortunately, I don't have access to a CNC lathe. TechShop has several CNC machines, but a lathe is not one of them--they just have manual lathes (with DRO displays).

If I make another I may try out using round stock. It's actually pretty hard to make a perfectly square block, even on a good mill!

Thanks for the support!

imatoymaker (author)spcutler2012-01-19

My compliments on an excellently designed and well made part... but actually making a "perfectly square block" is rather easy. I have been a machinist for 30 years and can do it on even the most humble mill. Good setup and one little trick is all you need. As long as your vise is flat to the table travel in the x & y axis, it's solid jaw parallel x axis, and the spindle & solid jaw are perpendicular to the table it can be done in 7 steps with 3/4 ball with a flat on it and a parallel. I have won many drinks proving it. Maybe I should do an instructable on it if there is any interest. Or maybe just for the fun of it. Just not sure this is the right forum to post on.

Ogredude (author)imatoymaker2012-04-08

I'd *LOVE* to see an instructable on this! The only mill I have access to at my friend's house is definitely a very humble mill.

spcutler (author)imatoymaker2012-01-20

I would love to see an instructable on it, and think it would be quite popular with folks like me who like to do machining as a hobby but don't have the decades of experience to pick up tricks like what you described.

I managed to do the first 4 sides without much trouble but the final 2 sides were more difficult. I ended up fiddling around with an L-block (is there some better name for that?) to get a side perpendicular to both axes, but I'm sure there's a better way.

skrubol (author)2012-01-26

Why is squareness of the material important? To me, the whole operation of milling the face flat, cutting the hemisphere and boring the alignment holes should be able to be performed without re-mounting the workpiece. As long as you can hold the piece down securely without interfering with any of the cuts, the shape of the piece shouldn't matter.

spcutler (author)skrubol2012-01-27

You are almost certainly correct, and I mostly blame my inexperience.

One small problem is that the CNC machine is only available in 4-hour increments. Although with an optimized process I probably could have finished a full block in that time, with me learning as I went it took much longer than that. Given this, and the fact that I needed the blocks to be square in the end anyway, I decided to make that the first step in the process.

If I do it again, I'll probably look into doing the squaring, planing, hemisphere boring, and drilling all in one pass.

skrubol (author)spcutler2012-01-27

Well that makes sense.. Making something square is challenging for a novice machinist, so it's a worthwhile thing to try to do even if it's not necessary.

big-jamie (author)2012-01-24

that is absolutely gorgeous, the mould and the finished ice ball. i really wish i had access to a cnc machine =(

rimar2000 (author)2012-01-18

Beautiful ice ball!

A doubt: the holes in the photo of step 5 seems out of phase. It is to say that joining the hemispheres, the holes don't match. Does you changed them?

spcutler (author)rimar20002012-01-18

Thanks! The holes are actually in perfect alignment, probably less than 0.0005" error. Getting this right was one of the most important steps so I drilled the holes for each half without removing anything from the vice. If the the holes look out of alignment, it is probably a matter of the photo's perspective.

koebwil (author)spcutler2012-01-19

To be fair you did tap the holes which gives you some intrinsic misalignment. If you do another I would suggest using a press fit. Also you mentioned using an edge finder, if you want better accuracy you can swing the block in with a dial indicator, this is commonly done in mold making. Lastly a spot drill will give you much better results than a center drill, center drills are typically just for lathes and due to their shape don't do well in CNC mills, granted your aren't drilling a lot of holes, but you break one of those suckers and it'll ruin your day. I was wondering if you drilled the holes in a separate op or if you were able to get them into your program, I know the tormach doesn't have too much z travel, but even just spotting them in the same setup can give you much better accuracy.

spcutler (author)koebwil2012-01-23

I forgot to get to your last question:
Although I didn't incorporate the hole drilling into the program, I was able to use the Tormach for both the hole drilling and tapping. I did this separately from the hemisphere cutting, but that is not a big deal--the hemispheres could be a couple thous off and no one would notice. But each pair of holes did need to be the correct distance apart and so I did those in one step.

If I do make another, I'll see if I can incorporate the drilling into the program. I was using peck drilling since the holes were so deep and there was a lot of volume to remove, and it became quite tedious (and error-prone) after a while.

You're right that there isn't a huge amount of Z travel on the Tormach, but it was sufficient for my purposes, even with my 2" height gauge.

spcutler (author)koebwil2012-01-20

True, the tapped holes seems to have some intrinsic amount of wobble. I didn't realize this going in because of my inexperience, but it seems you're right that a press fit would work better.

Thanks for the advice on the spotting drill. It seems that there is some debate as to whether center drills are appropriate for this application or not, but in any case spotting drills are a good choice here.

rimar2000 (author)spcutler2012-01-20

Pardon, I am an old fool man.

I saw the pieces simply rotating around a vertical axis, the holes do not match, but I realized now that as they are perfectly symmetrical, you also have to rotate them horizontally.

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