Newbie looking at 6040 (China CNC) for polypropylene 15mm sheet

[JOGARA]

Doing an order from TME already, saw they sold toroidals.
http://www.tme.eu/gb/details/tst600w...del/tst600008/

Though it is 600VA not 650VA.
That extra few watts going to make much difference?

[Clive S]

Doing an order from TME already, saw they did toroidals.
http://www.tme.eu/gb/details/tst600w...del/tst600008/

Though it is 600VA not 650VA.
That extra few watts going to make much difference?

That will be fine

[JOGARA]

That will be fine

Awesome! Thanks.

And my caps came yesterday.
https://www.aliexpress.com/item/Free...030086709.html

Might as well shove all 5 on?

[A_Camera]

My idea is to then use 15mm polypropylene sheet instead to get the same sort of light wight properties and strength (small sized case, about 100x45mm).

In my opinion Acetal (Delrin, POM) is the best material. It is not cheap, but it is stable, keeping it's form even in varying temperature and humidity, machinable and you can handle it as you would handle soft metal, yet it is very strong, you can tap it and use ordinary screws for metal. It is not melting easily and the chips produced are nice. I am using it and in my opinion it is the best for milled plastic cases, though it is not light.

Are these China CNC milling machines okay for this?
I have seen them eat 10mm aluminium so this should be fine right?

Can't speak about "China CNC milling machines" in general since I never had one (built and designed my own) but I am pretty sure they can handle Acetal, as well as aluminium, assuming you are using the right feed rate and spindle speed. My first spindle was a cheap 400W DC motor with the maximum RPM of 12000. I used that one for two years on PCB, acrylic and Acetal and is still working, though now replaced with a 1.5kW 24kRPM brushless 3 phase spindle which is of course better. Never the less, it shows that even cheap motors can be used, but you need to adjust the feed rate accordingly. Anyway, with the DC motor I never really dared to work on aluminium, the new one on the other had cuts aluminium just fine.

My understanding of milling plastic is speed and sharp tools to reduce heat and thus the plastic melting.
There is less horse power needed as it is more speed than anything, though I still want a powerful spindle for future proofing..

It doesn't matter which material you work on, speeds and good tools are always critical. Even aluminium melts if you are not doing it right or use bad tools. Anyway, how fast you have to spin the spindle depends on the type of tool and the material, as well as the feed rate. Use a feed rate calculator, practice and learn. Different plastics behave differently, there are even different material qualities, just like there are different grades of aluminium and other material.

I cut everything dry, not using mist and the only air which is blown around the cutter is the one which is sucked in by the dust shoe, so there is not much cooling. Melting is only an issue if you are using the wrong speeds and feeds, or cut too lightly and the chips are far too small. If you must shave material you must be more careful, it is better to produce chips than dust.

[CrazeUK]

In my opinion Acetal (Delrin, POM) is the best material. It is not cheap, but it is stable, keeping it's form even in varying temperature and humidity, machinable and you can handle it as you would handle soft metal, yet it is very strong, you can tap it and use ordinary screws for metal. It is not melting easily and the chips produced are nice. I am using it and in my opinion it is the best for milled plastic cases, though it is not light.



Can't speak about "China CNC milling machines" in general since I never had one (built and designed my own) but I am pretty sure they can handle Acetal, as well as aluminium, assuming you are using the right feed rate and spindle speed. My first spindle was a cheap 400W DC motor with the maximum RPM of 12000. I used that one for two years on PCB, acrylic and Acetal and is still working, though now replaced with a 1.5kW 24kRPM brushless 3 phase spindle which is of course better. Never the less, it shows that even cheap motors can be used, but you need to adjust the feed rate accordingly. Anyway, with the DC motor I never really dared to work on aluminium, the new one on the other had cuts aluminium just fine.



It doesn't matter which material you work on, speeds and good tools are always critical. Even aluminium melts if you are not doing it right or use bad tools. Anyway, how fast you have to spin the spindle depends on the type of tool and the material, as well as the feed rate. Use a feed rate calculator, practice and learn. Different plastics behave differently, there are even different material qualities, just like there are different grades of aluminium and other material.

I cut everything dry, not using mist and the only air which is blown around the cutter is the one which is sucked in by the dust shoe, so there is not much cooling. Melting is only an issue if you are using the wrong speeds and feeds, or cut too lightly and the chips are far too small. If you must shave material you must be more careful, it is better to produce chips than dust.

Would that mean one should do fewer slower deeper passes, as opposed to faster more shallow passes?

Sent from my SM-G930F using Tapatalk

[A_Camera]

Would that mean one should do fewer slower deeper passes, as opposed to faster more shallow passes?

Sent from my SM-G930F using Tapatalk

I don't think there is a simple answer to that, since it depends on the material, but in general terms it is better if the material is not shaved or rubbed off because that generates too much heat and causes melting. So, some times increasing the depth may help, other times increasing the feed rate, or the spindle speed, and again, some times all three. I am not afraid of doing shallow cuts if needed, but in that case I do it with very high feed rate and the spindle speed, feed rate and the quality of the cutter is more critical there.

When I notice melting (mostly when different acrylic qualities are used) then I try to guess if the feed rate is too slow or if spindle speed increase can be a solution, or if deeper plunge would help. I am by far an expert but normally I can guess pretty well based on my experience, adjust and do it right next time. In my experience it is not always working to have pre-calculated parameters, and one which works this time may not work next time if the material is not exactly the same batch. Never the less, when starting with new material or cutter which I don't have experience with, using a feed rate calculator is a good idea because it gives me a good reference to start from. If the calculated values work then I use it or play with different values in the calculator if I intend to change something, for example if I want to increase feed rate to finish a job faster.

[njhussey]

Would that mean one should do fewer slower deeper passes, as opposed to faster more shallow passes?

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It also depends on your machine, in fact it's mostly about your machine and how stiff it is and what type of cut you're doing. If you're slotting then you have to go slower or shallower than if you're doing a 60% width stepover pocketing pass.

I'm about to cut some more samples (see photos below) at work in Acetal and I'll be doing 20mm deep cuts with a 6mm 2 flute uncoated carbide mill, I'm using Trochoidal milling mind so don't try to take that deep a cut normally!!

[JOGARA]

Getting close to the point where I want to buy.

Am I better off just trying to buy a VMC like a Tormach 1100?
I have been looking around for one for a few weeks but they are a bit rare over here.

Also trying to find other options though they are at least £10,000 :/


Might it be worth spending a bit more trying to get a decent 6040 like frame rather than messing with a China frame?
The thing is the part I want to make is not that tricky I don't think. Looks like we will be using 15mm thick aluminium.

Surface finish needs to be at a point where I can just sand it down to a fine grit for anodising.

Thoughts?

[edit]
Looking at some videos, it looks to do fine with pretty deep stuff...

[Zeeflyboy]

Again within reasonable bounds, the depth of the material really isn't hugely relevant to the machine's ability to cut it... as long as a tool in an appropriate diameter and length can be found then it really just becomes a question of number of passes.

That last piece must have taken ages to machine at that speed and depth, but as you can see most of these things will have a stab at alu.

If going the chinese router path, I do recommend you avoid any round or unsupported rails if alu is on your to-do list, having owned both I can say you will have much less frustration if you get one that at least has proper HG20 rails... take a look at omioCNC - they make some of the better chinese routers imo (I own an X6-2200L at the moment, building myself a new bigger badder one mostly for fun). If you wanted to go sans-electronics they would probably sell a bare frame if asked.

This is an example of a 20mm plate cut on my X6-2200L:

[JOGARA]

Ill check them out. I get what you are saying and from the looks of the video it is totally worth it.

Where do you get your cutting bits?
Not really looked into that yet.