Frage Newbie: Stepcraft for carving a plastic box?

Hello, I'm a rookie about CNC milling, so I'm collecting any kind of information about... almost everything (machines, spindles, software, etc.)

Here my question: can a Stepcraft machine (i.e. the SC 300) be used to carve a little cube of PVC or POM material in order to make a potting box (ein Vergussgehäuse)?

I need to produce a little amount of small enveloping box (around 50x50x50mm) for a small electronic device with a display on the top.
As I understand there is no theoretical limit in doing so for a Stepcraft machine, I'm right?

Hi Julius!

POM an PVC is everydays business for our steppis.

So, I'd say the limit is whatever you can do in 2.5D and with milling cutters with a cutting depth of 10mm.

Maybe you should post some CAD images of the boxes you plan to build. When saying "Vergussgehäuse", do you mean that you want to mill the casting mold with the steppi?

Hello MagIO2,
so maybe I'm just dreaming in doing something like that?

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Obviously all internal corners will be rounded, they depends on the size of the bit.

I don't want to produce a casting mold, just a limited number (maybe 50) of the same carved box. The cube is small, so I have calculated around 40 minutes per box...
Furthermore, the metal-bit of the spindle should have no problems in milling for long time on plastic material. I mean, it should be not get "consumed" after long milling... or not?

It's just a dream?

First of all it is a waste. You have a block of material and want to turn >90% (guess) into waste.

I have to say, fortunately you won't find a tool long enough to do this.

Does it have to be POM or PVC? Or would ABS or PLA do as well?
This is a good job for 3D printing. If you really want to buy a machine yourself, then the steppi with 3D printhead would be an option.

But I guess it would be cheaper to order the parts at a 3D printing company. There you also have better quality and more choice of material.

PS: would it be an option to divide the box into separate walls and assemble the box by fixing the walls with screws?

Still did not get the Verguss-part. Is the plan to put the PCBs inside and then flood the box with epoxy?

MagIO2 schrieb: PS: would it be an option to divide the box into separate walls and assemble the box by fixing the walls with screws?

I think this idea makes much more sense ....
Maybe he could build a little jig to keep the parts in place and use an adequate adhesive instead of screws.

MagIO2 you make my heart bleeding...

So in your opinion I cannot carve more than 10mm with the Stepcraft machine? So why the documentation states 80mm of travel distance on Z-axis? If nobody can exploit this possibility then it has no sense...

I don't care about the waste of material, in any case there is no company that will produce for me the box-case for a so small amount of pieces. You need to make orders for 1000 or more pieces to get a reasonable price, otherwise you're going to pay even 9,- Euro per piece for that small ridiculous box.
ON the other hand here at Gemmel Metalle I can buy flat pieces of PVC at good price. By cutting and carving blocks I can get a reasonable price of 1,8 Eur per unit.
Furthermore, when I pay somebody else than nothing remains in my pocket. Using the Stepcraft machine I have almost the machine itself, it that stays mine.
Where I'm wrong?

Worldhusky schrieb: Maybe he could build a little jig to keep the parts in place and use an adequate adhesive instead of screws.

Well... that is a possibility, but I'm not sure if it will be enough robust and water cannot get in...

About the choice between POM and PVC I still haven't decided what material is more stable outside at open air.
Also, I have excluded 3 printers 'cause the quality of the flat surfaces is honestly horrible, seems like a sandwich prepared by a drunk man on a drunk horse
Yes, milling machines are not perfect too in that sense, but surfaces quality has no comparison with 3d printers.

MagIO2 schrieb: Still did not get the Verguss-part. Is the plan to put the PCBs inside and then flood the box with epoxy?

In my plan, the box will be closed by a little plexiglass window, screwed and sealed with a little amount of silicon around borders.
Maybe I should make a drawing of that too so you can give me your opinion.

Here the final idea: the same box together with the plexiglass window. The little transparent window should go down inside the box to be screwed at the four corners.

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As I understand the main limitation, in my case, is that there is no tool of 43mm length (cutter length + shank length). So carving 43mm deep inside the box is impossible, or have I misunderstood?

The longest tool I know so far is 30mm with 3mm diameter. But it is only good for milling foam. Anything harder and it will bend, which means you won't get straight inner walls. Maybe there are better/longer tools available for the stepcraft spindle with ER11 tool support?

If you go for separate walls and glue, POM is out of scope, because it is hard to glue.

Can't you cut the box in 2 pieces? If I understand you correct, only the bottom part will be housing the PCB/display. You can add some mounting holes to the upper ring and mount it with the same screws which hold the plexiglass.

MagIO2 schrieb: Can't you cut the box in 2 pieces? If I understand you correct, only the bottom part will be housing the PCB/display. You can add some mounting holes to the upper ring and mount it with the same screws which hold the plexiglass.

Nice suggestion MagIO2, I have to admit that I didn't think about this
I could mill the bottom part (around 23mm depth) and then the top part (25mm). As you can imagine, the top part it's just a sun-coverage useful at open air.

There is a little bit more work (more screws, more holes, etc.) but maybe that is the only way

MagIO2 schrieb: The longest tool I know so far is 30mm with 3mm diameter. But it is only good for milling foam. Anything harder and it will bend, which means you won't get straight inner walls. Maybe there are better/longer tools available for the stepcraft spindle with ER11 tool support?

I have to investigate about longer milling cutter...

Anyway, as I understand (remember: I'm a newbie) the collect is a piece of hardware clamping the spindle to the axis (shank) of the milling cutter. So an ER11 collect should allow to clamp a shank with a max diameter of 11mmm (!!!)
That would be enough rigid and stiff, yes?
(mmmmh.... but by using a "fat" shank I will be not able to carve the detailed internal corners... mmmmh...)

As I see, the Stepcraft HF 350/500 spindle allows a standard max shaft diameter of 8mm. If equipped with the ER11 nut it can be augmented to 11mm (I suppose).
But even an 8mm shaft seems quite rigid to my eyes

(but the HF 350 costs a lot! wow! And maybe it makes a lot of noise too? )

Cutting deep is difficult. Even on our professional routers up to 7-8,000 euro cutting 50mm deep is a challenge. We did this recently for a guy cutting stock timber for furniture. 50mm tool at 10mm diam cost 80£. As you increase the cutting diameter you increase the material removal rate. Which requires more power.

Anything up to 6mm IMO is max cutter for STEPCRAFT - and even at that thats a large cutter.

With extra cutter stick out - comes more leverage. The point of contact between the bottom of the cutter and the spindle is then large - 50mm and this is a large lever. Its almost too much for out larger routers - and then ask to mill with SC? No way... if the machine can do it - you will not get clean lines on the passes as the machine moves down.

Only in foam maybe.


The travel of the machine is completely different to the cutting envelope. Just because the machine can move 80mm does not mean the machine can "machine 80mm"... our larger routers travel up to 125mm but the max cutting thickness is 40-50mm and even this is a challenge.

Travel of Z axis is for access to the cutting surface. The cutting depth is dependant on the cutter, machine setup, machine stiffness, material and machine parameters..


You have too much waste from your process. The way you wish to manufacture requires special tooling - and lots of machining and a heavy machine - therefore the cost of your process - because of the way you have chosen to make it - is too high.

you need to approach this differently - 3D print. Or build up in 2 edges. limit the X axis cutting height to the thickness of the edges.


Or - find someone with a router that can do this for you. We can cut this for you.

Rory schrieb: With extra cutter stick out - comes more leverage. The point of contact between the bottom of the cutter and the spindle is then large - 50mm and this is a large lever. Its almost too much for out larger routers - and then ask to mill with SC? No way... if the machine can do it - you will not get clean lines on the passes as the machine moves down.

Ok, I understand this. Bigger is the length bigger is the lever, so the radial force on the end mill increases when cutting the material.
But what happens if you decrease the DOC (Depth Of Cut) as the total length of the tool increases? I mean, you need more power if you want to carve/cut the same material as you do with a shorter tool. If you decrease the DOC then the force on the milling bit should not decrease too? So, even if the tool is more long than before by applying a reduced force it should not bend excessively.
(Please remember that I'm a rookie and I don't know what I say )

On the other hand how could this french guy cut for 9,6mm depth on an Alu 7075T aluminum plate???


He uses just a poor 100W Proxxon IBS spindel (!!!). So I could think that by buying a plutonium-cobaltium-titanium cutting mill (produced by the Kryptonit company) I could mill a PVC plate. I don't know the proportion between the hardness of aluminium and PVC (or ABS or POM), but plastic seems a lot softer...

Rory schrieb: The travel of the machine is completely different to the cutting envelope. Just because the machine can move 80mm does not mean the machine can "machine 80mm"... our larger routers travel up to 125mm but the max cutting thickness is 40-50mm and even this is a challenge.

Travel of Z axis is for access to the cutting surface. The cutting depth is dependant on the cutter, machine setup, machine stiffness, material and machine parameters..

Yes, I understand this. Anyway, I could carve an upside-down pyramid (with large large steps) for, let's say, 70mm depth with a short-short-supershort cutting tool, yes?
The problem is the rigidity of all the machine plus the cutting tool.

Rory schrieb: you need to approach this differently - 3D print.

I still cannot find data about the robustness of 3D printing artifacts... I'm quite skeptic on this, maybe I'm wrong.

Rory schrieb: Or build up in 2 edges. limit the X axis cutting height to the thickness of the edges.

Edges? Do you mean in 2 dimensions and to assembly every part with glue or screws?

Rory schrieb: Or - find someone with a router that can do this for you. We can cut this for you.

This is interesting

No question is a stupid question.


Yes - he does super nice work there in the Aluminium - but the process has to perfect. He uses some coolant to help with the ali cutting. His cutter choice has to be excellent and his machine parameters too.

I would be happier to try 10mm ali plate with a proxxon. Than 50mm deep in anything with the HF spindle. His is also at the top end of the envelope and does a super nice job. I would consider this Advanced CNC work and no-one should attempt this sort of work untill they are very experienced with their SC machine.

Watch this video for 50mm deep cutting with 100€ tool If someone can manage to get stable results from a SC to this depth I would very much like to see it.



Agree - 3D printing may not be best way to do. depends what your final output requirement is.


Yup 2D and assemble.

Rory, looking at the result of the french guy, do you think there is some chance of machining 25mm of PVC using a good quality and rigid cutting tool?
(I plan to divide my box in 2 parts: the upper and the lower part, both with height of 25mm)

Here are my 2 cents again

I think best way is to have the pieces well prepared. Meaning that the outer dimensions should already be perfect. So, I'd order the parts in size 50 x 50 x X.

The upper part is no big deal, as it's like a ring you can mill from both sides. (Using top brackets should give you the accuracy you need for that)

The problematic thing is the bottom part. If you divide this in 2 pieces it is easy again. One flat bottom part and a ring, which can also be milled from both sides. Of course then you'd need the same kind of sealing as for the plexiglas to make it waterproof.

If you want to have it in a single piece I would prefere to plan the piece in a way that it has a step. (Upper part of the wall is 2mm, lower part of the wall is for example 10mm). Mill ~10mm deep as in your drawing and mill another ~10mm deep but with a smaller outline boundary allowing the tool-holder to work in the area cut away in the first step.

(Hope it is somehow clear what I mean)
This might require to change the shape of the PCB or change the XY-size of the box.

MagIO2 schrieb: Here are my 2 cents again
................

I think that I've got perfectly your ideas MagIO2.... mmmmh... sehr interessant... I have to think about it.
Thanks!

Rory schrieb: We can cut this for you.

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