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

[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?

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[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:

[Zeeflyboy]

Okay so you pretty much sold me the omioCNC...
Few other threads on it show that it is pretty good.

Question is, do you still use the stock components like the controller, steppers, drivers etc?

And what accessories to get?

Ta

Hah I'm not trying to sell you on it - just that if you are going the Chinese router direction, that is one of the better ones. It still has it's issues but you pay your money and you take your choices...

I am not using many of the stock components anymore, although there was nothing wrong with them. I changed the motion card mostly because I wanted to try out mach4 and also because I prefer Ethernet to USB... the stock card worked fine with Mach3 though and I didn't run into any obvious interference issues. I also changed the motors over to leadshine closed loop easyservos, the rest of the electronics I kept (PSU, VFD, Spindle) although I'd like to change to a toroidal at some point.

The biggest issue for me is that they (like seemingly all Chinese routers) don't ground the spindle. When I mentioned it they said grounding the spindle can cause interference issues with the USB card, but it's a point of safety so to my mind it needed to be done.

I changed to a 4 core shielded cable for the spindle, and re-wired the box into a star point earth... doing it that way I never had interference issues.

Accessories wise you just need to figure out what you need or want for work holding (vise, clamps, spoil board, vacuum board etc), and a good set of high precision ER collets in the sizes you want is a sound investment. Beyond that just a few cheap cutters to get started with as you will probably break some while getting to grips with it.

[JOGARA]

Just one more question for everyone. I need to basically set up multiple stations on the CNC to do different operations.

What is the best way to get positional accuracy with the drill bit and workpiece?

I have seen John over at NYCCNC on his Tormach and HASS use a device that sits inside the collect to get XYZ positions as well as a little cube that gets the drill bit position.
Is that an option with Mach3 and this sort of CNC?

Was going to mill a 10mm plate to put vices on that can then be squared and made repeatable. But it is that first setup each time I want to make sure I am a 0.01mm accurate.

Thanks
Jack,

[Zeeflyboy]

I just recently got one of these... I think it's pretty good for the money and certainly the only one I'm aware of in this sort of price range that uses contacts submerged in di-electric oil to avoid the oxidation problem.

http://www.kurokesu.com/shop/TPA2

[A_Camera]

Just one more question for everyone. I need to basically set up multiple stations on the CNC to do different operations.

What is the best way to get positional accuracy with the drill bit and workpiece?

I have seen John over at NYCCNC on his Tormach and HASS use a device that sits inside the collect to get XYZ positions as well as a little cube that gets the drill bit position.
Is that an option with Mach3 and this sort of CNC?

Was going to mill a 10mm plate to put vices on that can then be squared and made repeatable. But it is that first setup each time I want to make sure I am a 0.01mm accurate.

Thanks
Jack,

I just googled "touch probe mach3" and I get 83,400 hits... :)

...along with pictures, and build instructions of everything, from simple touch plate to complex 3-D probes.

A simple conductive material works fine and will give you the accuracy, but remember that your accuracy depends on what you calibrating with as well. A touch probe is connected to one of the free inputs and you configure that input in Mach3 as "Probe". The thing is that you need a macro to get it working as well, but there are plenty of those available freely if you don't want to write one. Once you have the macro you have to attach that to a button and call it every time you intend to use it. It is pretty simple but maybe you need to spend some more time if you have never done it before.

I am using a simple PCB piece most of the time, it works just fine, but have plans on making something more advanced, but it isn't highest on my priority list.

[Neale]

Repeatable accuracy to 0.01 mm is pretty demanding. I know that on my own machine I can get repeatability to +-0.003mm - one microstep, in other words. However, accuracy is another thing, and apart from anything else you are going to need a decent set of collets. As already said, you can do this kind of probing with a simple accurate block plus a straight plain shank in a collet, or spend hundreds or more. For ease of use, you might also want to look at an upgraded Mach3 screenset. Gerry"s 2010 screen set is widely recommended and includes probing functions - a Google search will find it.