Help needed for small mill to cut molds for an injection molding machine

[gperkins]

Hello,

I've been trawling though the threads here, but it seems that my requirements might not fit the typical cnczone metal machine purpouses, so I'd appreciate some guidance.

Basically I would like to build a machine capable of cutting molds in aluminium billet for an injection molding machine.

Now I notice that most users are interested in cutting larger, thin material. My requirements are:
1) Smallish footprint, say 150mmx150mm
2) Deep Z cutting (up to 50mm)
3) 3 axis (no undercuts to worry about)
4) Fine surface finish for smooth molds ( I guess I'll need to switch to smaller bits after cutting the coarse form)
5) Don't care if the cutting time is very slow
6) Ideally desktop size(ish) mill. No need for a shop filling monster.

I feel like my requirement for small area, yet deep metal cutting leaves me stuck between weak desktop "engravers" and enormous door cutting machines.

I'd appreciate it if someone can point me towards some similar builds, kits or discussions. I have access to a shop for help and have built a decent 3D printer, but am by no means an expert machinist. Looking forward to learning.

Thanks!

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[speedtwin69]

I find mine on eBay

[probinson]

I can't point you to an off the shelf machine as I build my own stuff, but I do have some things to look for while shopping.

1) Surface finish is very important for this application. You want a sturdy machine that won't chatter which is going to be difficult to find in a small machine.
2) Stay away from anything with tubular construction. Hollow tubes will have lots of resonant frequencies that can cause chatter. A large solid rod is fine but never anything with hollow tubes.
3) Cast iron is better than aluminum. Mass and rigidity are the most important characteristics for good finish cutting.

If finding a compact, sturdy machine is a problem then choose a model you can easily bolster. i.e. Packing the hollow spaces with a sand/epoxy mix will work wonders on an light-weight machine.

[probinson]

Oh, and you said you have 3D print capability? I don't know what longevity you need from the molds but, if it's not more than a hundred or so, you can 3D print the molds and have them electroplated. It's a lot of hand sanding to get a good finish but it's perfect for small runs.

[gperkins]

speedtwin69, thanks, yes I've been quite tempted by the chinese 6040 machines on ebay (accepting they need the stepper wires chaanged and control unit upgraded). You can buy just the machine body without the crappy other parts, and add a g540 controller and decent spindle. I'm just a bit worried about the spindle mounting on the z axis being a bit loose.
To be honest I suspect it will fall far short of my requirements in terms of rigidity, but the price is just ridiculous!

probinson, thanks very much, that is great advice. I see what you mean about chattering spoiling the finish. The thing is it is impractical for me to get a large machine for these little jobs, so I might just try to get a small machine to be as rigid as I can. Filling the hollow voids with epoxy/sand mass is a brilliant idea. I'll take this into account when choosing. If I can't find anything iron based then fillable aluminium extrusion is a possibility.

What an interesting point about electroplating! I didn't realise it was possible with the PLA/ABS used in 3D printers. Do you have a link to where this is discussed. I'll try and read up more myself. It ccould be a fantastic solution!

[Tkamsker]

I Do have an proxxon cnc which I change in Winter to ballbearing spindle there is one Version which has a travel of 160 x 90 mm this May be best solution for you
I Do also molds ...

[gperkins]

Tkamsker, what a great little machine, that could be perfect. I'll look at it in more detail. Thanks!

probinson, I'm struggling to find any success stories of plating printed parts from diy 3d printers. But you did get me thinking, it might be possible to print a master part and press it into an epoxy resin mold, then disolve away the plastic part.

[wizard]

Tkamsker, what a great little machine, that could be perfect. I'll look at it in more detail. Thanks!

Currently your part aren't big but the depths you are loping at could be a problem. Honestly I would suggest a far more robust machine. You make mo mention of the accuracies required nor surface finish but I would not suggest anything smaller than Tormachs small mill. As for the so called 60x40 machines from china there is no way those would be suitable. You may be able to get by with something smaller like a Tiag mill, but honestly I would thing you would want a mill large enough to place these billets on the table for surfacing and mold machining. Beyond that you will likely need more travel than the size of the billets imply.

probinson, I'm struggling to find any success stories of plating printed parts from diy 3d printers. But you did get me thinking, it might be possible to print a master part and press it into an epoxy resin mold, then disolve away the plastic part.

You could also 3D print a negative and then cast the mold in aluminum for plastic injection molding. There are many ways to skin a cat here. As for your actually mold making I'm not too sure it is advisable to get into mold making before you get some general machining experience. There are good reasons for the high pay mold makers get along with the guys that design the molds. With a little bit of experience, either formal education of DIY, you will quickly realize that going extremely small with your mold making machine will be a mistake.

- - - Updated - - -

Tkamsker, what a great little machine, that could be perfect. I'll look at it in more detail. Thanks!

Currently your part aren't big but the depths you are loping at could be a problem. Honestly I would suggest a far more robust machine. You make mo mention of the accuracies required nor surface finish but I would not suggest anything smaller than Tormachs small mill. As for the so called 60x40 machines from china there is no way those would be suitable. You may be able to get by with something smaller like a Tiag mill, but honestly I would thing you would want a mill large enough to place these billets on the table for surfacing and mold machining. Beyond that you will likely need more travel than the size of the billets imply.

probinson, I'm struggling to find any success stories of plating printed parts from diy 3d printers. But you did get me thinking, it might be possible to print a master part and press it into an epoxy resin mold, then disolve away the plastic part.

You could also 3D print a negative and then cast the mold in aluminum for plastic injection molding. There are many ways to skin a cat here. As for your actually mold making I'm not too sure it is advisable to get into mold making before you get some general machining experience. There are good reasons for the high pay mold makers get along with the guys that design the molds. With a little bit of experience, either formal education of DIY, you will quickly realize that going extremely small with your mold making machine will be a mistake.

[probinson]

Using chrome plated plastic for molds with high surface quality is nothing new. When I was a kid, I used chrome plated plastic parts from models and reflectors from flashlights as molds to make more. That was in the 1970's and 3D printing has been around since the 50's. The only thing that's new is the prevalence of 3D printing and materials that can handle the pressure and elevated temperatures of injection molding rather than having to cast the part.

<an hour or so later>

Well, I looked around for some info on 3D printing of injection molds and found this: Plastic Injection Molding and Custom Molds | Stratasys

At a quick skim, I didn't see any mention of electroplating for added durability but it just seems like a no brainer to me.

[gperkins]

Thanks wizard for your thoughts. To be honest, I think I've reluctantly realised that the Chinese mini mills will never get close to cutting acceptable molds for my injection molding, I was just tempted by the price.

I'm still left with the frustrating situation where I only need small (albeit deep) molds, but it seems that only a serious large and heavy machine will do the job, is a shame. Having said that, the small Tormach you mention looks pretty good value and isn't that much bigger shop floor footprint than a desktop machine.

I fully accept your points that mold making is a real skill and I can't expect to just reel them off. But theres no way I can afford to get the molds made for my short run hobby moldings, and the prices that molds go for, this machine could pay for itself if I can just get a few of the simpler ones built myself. Also I live to learn!

Thanks for your insight. I'm going to experiment with the various 3D printed pattern/negatives to see if I can get by for now, but I suspect that the layered deposit texture (even when sanded/soothed in acetone) of the 3D parts will mean I need to invest in a mill sooner or later.

Thanks for the advice.

[gperkins]

Fascinating thanks probinson. The stratasys example is shows some potential, although I'm still confused by how a mold can hold it's form when injected (with moderate pressure) by melted plastic with a similar melting temperature, even for a single run.

I guess the plastic is liquified in the melting chamber and by the time it passes the gate and reaches the mold cavity, it is cooled enough not to deform the mold surfaces.

I look forward to experimenting.

[mcphill]

To get the surface finish you are looking for, a "desktop" mill won't do it. I would recommend a Tormach 770 (if you can swing the price, they have the BEST support!), or one of the smaller Novakon machines (if money is a big factor). I have a now out-of-business Mikinimech 1610L, and SO wish I had picked a Tormach instead....

[RICHARD ZASTROW]

What mcphill said.

Dick Z

[hjl4]

There's a lot more to injection mold making then just the machining aspect of it. Your probably aware of the most apparent ones, but surface finish and textured patterns can be quite challenging, and most mold makers prefer to keep those secrets hidden up their sleeves. It can get quite complicated, especially if you
have textured undercuts. Even the simplest job of a high quality polish can sometimes be a long process.
That's where the price of molds become prohibitive for the average diy.
In anycase, good luck.

[Tkamsker]

Hi i think it depends if the molds Need to make you Money then if you live in us buy an us machine like tormach if it is for Hobby you can Look in smaller machines like th proxxon but then the Mill paths will Make the difference you also Need to Choose Cam care

[wizard]

Thanks wizard for your thoughts. To be honest, I think I've reluctantly realised that the Chinese mini mills will never get close to cutting acceptable molds for my injection molding, I was just tempted by the price.

Plus a conversion to CNC blows the price up a bit. However that doesn't mean a larger machine converted to CNC won't work.

I'm still left with the frustrating situation where I only need small (albeit deep) molds, but it seems that only a serious large and heavy machine will do the job, is a shame. Having said that, the small Tormach you mention looks pretty good value and isn't that much bigger shop floor footprint than a desktop machine.

Just to point out that most of the Tormach comes from China. There are some very good machines coming out of China, it is just that they aren't cheap. Quality costs money every where.

As for floor space don't forget that any machine you have looked at so far will have a longish table moving around.

I fully accept your points that mold making is a real skill and I can't expect to just reel them off. But theres no way I can afford to get the molds made for my short run hobby moldings, and the prices that molds go for, this machine could pay for itself if I can just get a few of the simpler ones built myself. Also I live to learn!

I understand live to learn but just understand it will take time, possibly a long time, to become a tool and die maker specialized in molds for plastic. Engineering the mold itself is an art too.

Thanks for your insight. I'm going to experiment with the various 3D printed pattern/negatives to see if I can get by for now, but I suspect that the layered deposit texture (even when sanded/soothed in acetone) of the 3D parts will mean I need to invest in a mill sooner or later.

Thanks for the advice.

I was actually thinking here to use the 3D printer parts to make molds from which you would cast aluminum which after casting would need to be cleaned up for your parts. These would then be used in your injection mold machine after even more machining. Not the most elegant way to a mold but it would leverage a 3D printer.

You might be able to work the 3D texture into the products. if you need a Truely high quality finish, that is a polished mold, you will have a lot of work head of you to equipe yourself to make such molds.

[CAMAUTO]

I like you to tell me more of what exactly your trying to achieve here....with regards to what your requirements are for your plastic molded parts?

Like what type of tolerances does your finished molded part need to hold, what kind of surface finish does it need, how complex is the molded part, how small of a run does the mold need to make. A mold could be cheaper then you think to just get machined somewhere if aluminum and only needed for small run of simple parts with loose tolerances. Do you have the mold/molds designed that you want to make already?

[richardchris]

Well there are many methods, to skin a cat here. As for your actually pattern creating, i am not too sure you should get into pattern creating before you get some common machining experience. There are explanations for the great pay pattern creators get along with the people that style the shapes.

[richardchris]

Well there are many methods, to skin a cat here. As for your actually pattern creating, i am not too sure you should get into pattern creating before you get some common machining experience. There are explanations for the great pay pattern creators get along with the people that style the shapes.

Well there are many methods, to skin a cat here. As for your actually pattern creating, i am not too sure you should get into pattern creating before you get some common machining experience. There are explanations for the great pay pattern creators get along with the people that style the shapes.