Author Topic: CNC milling machine  (Read 15541 times)

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Offline akis

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CNC milling machine
« on: February 26, 2014, 10:01:49 am »
Hello, I am looking to cut out openings in PCB or aluminium panels and with the tools I have at home I can only manage small diameter holes. Larger holes are tricky because the drill bit jumps all over and the resultant hole is not round. Rectangular cut outs are also very hard to do especially small ones. I typically end up with something like in the picture.

I was looking on ebay at those CNC machines - there are some "cheap" ones eg
http://www.ebay.co.uk/itm/CNC-ROUTER-ENGRAVING-DRILLING-AND-MILLING-MACHINE-ENGRAVER-3040-BALLSCREW-a1-/261374026969?pt=LH_DefaultDomain_3&hash=item3cdb1b24d9

or
http://www.ebay.co.uk/itm/New-CNC-3040-Professional-4-AXIS-Router-H80mm-Engraver-PCBS-Routing-Machine-/290940824902?pt=UK_BOI_Metalworking_Milling_Welding_Metalworking_Supplies_ET&hash=item43bd6cad46

Has anyone ever used any of these machines at home? I have no idea how they work, but I suspect they use a router which they guide over a surface to cut out shapes? Does it make a lot of dust? Would it be able to work on a PCB and on aluminium? Would I need to change bits all the time?

Many thanks for any advice
 

Online trevwhite

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Re: CNC milling machine
« Reply #1 on: February 26, 2014, 10:22:22 am »
I heard from one user that some of those machines have really bad wiring - he ended up re-wiring the whole thing!

You could always make your own?

http://www.momuscnc.com/

The design looks really good but I have no actual experience with them.
 

Offline jeremy

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Re: CNC milling machine
« Reply #2 on: February 26, 2014, 12:59:56 pm »
PCB and aluminium are very different things. Fibreglass is an abrasive (like sandpaper) so you need to use extra hard bits to cut it. Conversely, aluminium is usually cut at different speeds with different shapes and materials in the cutter. All possible, but you gotta get the right bit! Just as important is how you hold the workpiece securely on the table.
 

Offline TorqueRanger

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Re: CNC milling machine
« Reply #3 on: February 26, 2014, 01:08:25 pm »
Hello, I am looking to cut out openings in PCB or aluminium panels and with the tools I have at home I can only manage small diameter holes. Larger holes are tricky because the drill bit jumps all over and the resultant hole is not round. Rectangular cut outs are also very hard to do especially small ones. I typically end up with something like in the picture.

I was looking on ebay at those CNC machines - there are some "cheap" ones eg
http://www.ebay.co.uk/itm/CNC-ROUTER-ENGRAVING-DRILLING-AND-MILLING-MACHINE-ENGRAVER-3040-BALLSCREW-a1-/261374026969?pt=LH_DefaultDomain_3&hash=item3cdb1b24d9

or
http://www.ebay.co.uk/itm/New-CNC-3040-Professional-4-AXIS-Router-H80mm-Engraver-PCBS-Routing-Machine-/290940824902?pt=UK_BOI_Metalworking_Milling_Welding_Metalworking_Supplies_ET&hash=item43bd6cad46

Has anyone ever used any of these machines at home? I have no idea how they work, but I suspect they use a router which they guide over a surface to cut out shapes? Does it make a lot of dust? Would it be able to work on a PCB and on aluminium? Would I need to change bits all the time?

Many thanks for any advice

When drilling always start with sharp bits then you will get a clean hole .. .. I use a drill doctor to sharpen my bits and keep them sharp... For the large hole ,Drill the 4 corners ,use a jigsaw to finish the hole  and then clean with a file .. Oh also use tape to cover the surface so you won't scratch it ..
 

Offline akis

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Re: CNC milling machine
« Reply #4 on: February 26, 2014, 02:04:13 pm »


When drilling always start with sharp bits then you will get a clean hole .. .. I use a drill doctor to sharpen my bits and keep them sharp... For the large hole ,Drill the 4 corners ,use a jigsaw to finish the hole  and then clean with a file .. Oh also use tape to cover the surface so you won't scratch it ..

The holes I am having trouble with are 6mm + , eg 8, 10, 12 - the bit jumps all over the place resulting in a weird shape hole (more like triangular). I might be able to achieve better holes if I were using a drill base and clamps to hold the PCB. Square cuts are very hard using the jigsaw, impossible even when the width is like 10mm or 15mm. The jigsaw is OK to use on longer cuts. Which however still leaves us with the problem of aluminium panels like those that come on plastic/metal enclosures.

I was thinking a machine would be able to cut any shape quite accurately. However I am not sure how those ebay machines work, and in addition my son told me that at his school they are using a machine with a laser cutter, so now I am even more confused.
 

Offline Frost

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Re: CNC milling machine
« Reply #5 on: February 26, 2014, 02:14:14 pm »
The holes I am having trouble with are 6mm + , eg 8, 10, 12 - the bit jumps all over the place resulting in a weird shape hole (more like triangular).

But you use a punch bevor you drill?
And for the larger diameters 10, 12 mm a center drill?
 

Offline mos6502

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Re: CNC milling machine
« Reply #6 on: February 26, 2014, 02:28:31 pm »
The holes I am having trouble with are 6mm + , eg 8, 10, 12 - the bit jumps all over the place resulting in a weird shape hole (more like triangular).

Are you using a standard drill bit? Those are completely useless for sheet metal. Use either a cone drill bit, like this:



Or a step drill bit like this:



With those you can make perfect holes in sheet metal, even with a handheld drill. A standard drill bit should never be used in material that is thinner than half the diameter of the bit.
for(;;);
 

Online Kjelt

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Re: CNC milling machine
« Reply #7 on: February 26, 2014, 03:26:35 pm »
Has anyone ever used any of these machines at home? I have no idea how they work, but I suspect they use a router which they guide over a surface to cut out shapes? Does it make a lot of dust? Would it be able to work on a PCB and on aluminium? Would I need to change bits all the time?
Yeah I got one at home but it was a steep learning curve (cost me a few bits) before I understood the principles. Also you need some software, one is a cad program and the other one the driver software that drives the steppermotor driver. There are a lot of things to learn, the speed which to route, the depth at each pass, entry and exit strategy ect. Also you need or a processor in the steppermotor driver that buffers the commands or a real clean lean and mean dedicated pc which does not stutter.

Aluminium is quite difficult in that sense that there is a lot of power involved so you need a good heavy cnc machine that is bolted to a table or marble plate or something. Then you want to cool your bits with aluminium and this gives some mess (water with coolant and alu chips/dust) not something you like to do in home but in a garage.

Change bits: depends on what you want to route, if you only want special openings in a aluminium frontplate then a 3mm routerbit will suffice, your minimum radius is then also 3mm so you have to take care of that in your cad program.

My only advice is buy a decent cnc machine or don't buy one and outsource the work.
 

Online Kjelt

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Re: CNC milling machine
« Reply #8 on: February 26, 2014, 03:29:46 pm »
Here some pictures from two years ago. You can see in the work there are still some mistakes made. It really is not something you learn in a weekend or from a friend on an evening, you need to understand how all works and being able to read G codes.
 

Offline stuartk

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Re: CNC milling machine
« Reply #9 on: February 26, 2014, 03:50:45 pm »
Cutting a rectangular hole is a major problem. I've had modest success using a Dremel router table and following a metal guide clamped to the workpiece.

I've also found that plastic is much more forgiving then aluminum. No matter what, every time I try to drill or cut out a rectangular hole for an LCD display in my expensive enclosure, I'm sweating bullets. On slip and the case is ruined. It happens very easily as the rotational torque jitters the bit depending on the direction and speed of the cut.

I'm resolved that the next enclosure I make, I will avoid the headache and will send my design to a enclosure manufacturer, essentially renting out their $100,000 machine and pay to have professional results.

No matter how clever your design and programming is, people only see your enclosure.

Cheers,

Stuart
 

Offline PaulAm

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Re: CNC milling machine
« Reply #10 on: February 26, 2014, 04:13:03 pm »
Ditto on the step drill for drilling round holes in thin materials.

You can actually use this odd behavior to drill triangular and square holes using specially adapted drill bits.  This was quite common in the bad old days before CNC.  Here's a youtube link for a square drill.
     
 They do leave a small radius in the corners.  It's still used today because it's fast and the tooling costs are low.

Good layout along with a saw and files plus care can produce nice square cutouts.  But if you want professional looking results, it's probably better to send it out.  You can do it yourself, but it will probably take more time than it took to build the electronics.
 

Offline akis

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Re: CNC milling machine
« Reply #11 on: February 26, 2014, 04:16:35 pm »
The holes I am having trouble with are 6mm + , eg 8, 10, 12 - the bit jumps all over the place resulting in a weird shape hole (more like triangular).

Are you using a standard drill bit? Those are completely useless for sheet metal. Use either a cone drill bit, like this:



Or a step drill bit like this:



With those you can make perfect holes in sheet metal, even with a handheld drill. A standard drill bit should never be used in material that is thinner than half the diameter of the bit.

Ahhh it seems I have been foolish. I need to buy some new bits then! Thanks.
 

Offline mc

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Re: CNC milling machine
« Reply #12 on: February 26, 2014, 05:14:54 pm »
Step drills are the best option for thin metal. As you've discovered, larger drills and thin metal don't produce a consistent round hole. For square holes, a dremel and a selection of good files are the best options. For hand working square holes with minimal tools, some practice with a suitable file (flat + triangular fine files) should produce good holes.

As for the 3040 routers you looked at, they are pretty rubbish.
Woeful construction which leads to lots of flex/backlash which will cause issues in harder materials, and need a fair bit of rework to produce a good result. They may provide an acceptable finish out the box, but it depends on your level of acceptable.
The other issue is the usually supplied stepper drivers are mediocre. The TB<can't remember the number!> chips are notorious for popping at the slightest issue, especially since the control boxes are usually pushing them to their voltage limit with minimal safety margin, and as they use an all in one board, you've either got solder in new chips, or replace the entire board.
 

Offline PaulAm

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Re: CNC milling machine
« Reply #13 on: February 26, 2014, 05:31:28 pm »
Another option is a manual table top milling machine.  You don't need cnc to make square cutouts.

The downside is a machine with sufficient rigidity and table travel to be useful is still 4-600 pounds at a minimum (a full sized mill is over 1800).  Sometimes these show up pretty cheap on the used market.
 

Offline ajb

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Re: CNC milling machine
« Reply #14 on: February 26, 2014, 06:10:54 pm »
[quote autho0r=Kjelt link=topic=27430.msg395674#msg395674 date=1393428395]
Aluminium is quite difficult in that sense that there is a lot of power involved so you need a good heavy cnc machine that is bolted to a table or marble plate or something. Then you want to cool your bits with aluminium and this gives some mess (water with coolant and alu chips/dust) not something you like to do in home but in a garage.
[/quote]

With the right bit you can get away without liquid coolant on the harder aluminum alloys.  We regularly cut 6061 with Onsrud 63-600 series bits which are single "O" flute upcutting bits and nothing but air to cool and clear chips.  5052, which is slightly softer, does okay as long as the bit is relatively new and a smear of lubricant on the surface of the part helps keep burrs down.  Real soft stuff like 1100 cuts like taffy, though.  The 63-600 series are also pretty good on plastic. 
 

Offline mos6502

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Re: CNC milling machine
« Reply #15 on: February 27, 2014, 02:43:57 am »
Oh yeah, for making perfect square holes in sheet metal (or plastic), there's this little gem:



It's called a nibbler. What does it do? Every time you squeeze the handles, it cuts a little 5x1.5mm rectangle out of the metal. With a little time and effort, you can cut perfect rectangles. With this and a cone drill bit you can really do just about any type of case work.
for(;;);
 

Offline liquibyte

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Re: CNC milling machine
« Reply #16 on: February 27, 2014, 02:55:04 am »
Square holes in aluminum are dead easy with a smallish sharp drill bit and a nice flat file.  Mark out the borders with a pencil and drill holes as close as you can through the throw away part as close to the borders as possible.  Cut the rest of the pieces with good wire cutters around the perimeter.  Now file the leftovers down with the file to the border.  Takes time and patience but I can guarantee you I can make a perfectly square hole like this in no time.  I'm actually doing a project right now like this.  You can do large round holes this way too using a half round file and taking your time.  No CNC machining required, just a hand drill, wire cutters and a file.
 

Offline GeoffS

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Re: CNC milling machine
« Reply #17 on: February 27, 2014, 03:19:00 am »
If you need square holes then a punch is hard to beat. Not the cheapest option, especially if you need multiple sizes.

I have a 6040 CNC and have only cut aluminium a few times (4mm). If you take it slowly and use a coolant (WD40 or methylated spirits), results are quite good.

I also have a small mill (not CNC) and it does a much better job on aluminium, especially thicker sheets. Mill weight is around 150Kgs so small depth of cut is required.
 

Offline AlfBaz

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Re: CNC milling machine
« Reply #18 on: February 27, 2014, 03:54:03 am »
When drilling larger holes always start with a smaller bit and work your way up and make sure the hole is it least half the size of the bigger drill or it will grab the job and mess the hole up. Make sure the job is well secured. For small drill bits you use a fast drilling speed and for large ones slower speeds and very light pressure. If you are sharpening your own bits make sure you don't make the angle to steep or the leading edge too high in comparison to the trailing edge.

For very large holes 15, 18, 20, 25, 32mm etc buy some hole saws and a selection of half round second cut files. I have one who's radius exactly fits a 32mm hole, perfect for large industrial push buttons

For large rectangular holes mark out the opening with a scribe (nothing worse than getting half way through to find your pencil outline has rubbed off).
Drill 2 large holes in opposite corners large enough to fit a hacksaw blade. Make sure you don't get to close to the edges of the hole as its better to have to file some metal out than drilling over the edge.

Holding the hacksaw blade with your hand as close to the job as possible (you can actually buy special hacksaws that allow the blade to protrude out one end) and cut from each hole to the other corners, again, don't go to close to the desired edge.

With a nice sharp flat 2nd cut file, file off the very large lumps normally and get each edge as straight and parallel to the desired edge as possible. When you start getting close start using the "draw file" technique (see figure 6 here

When using files, hacksaws or pretty much any cutting tool on aluminium, stop often and clean the aluminium out of the tool. For files you can use a file card or a brush with hard bristles( see figure 5 in the above link)
 
« Last Edit: February 27, 2014, 03:55:49 am by AlfBaz »
 

Offline akis

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Re: CNC milling machine
« Reply #19 on: February 27, 2014, 10:20:55 am »
Thanks for all the replies. Even though most replies concern aluminium plates, I am currently using a fibreglass board as a panel. It is the right thickness and very rigid. In addition it is copper clad, and I can etch most the copper off, and leave just enough to allow me to weld/solder the panels together thereby making a box!

For the time being I will improve the quality of the round holes :

1) very small holes up to 4 mm are no problem I can use my Dremel Workstation (not the best workstation mind you).
2) for larger holes I have bought a good quality Sealey step drill, from 4mm to 22mm. I do not think I will ever need larger holes than this. I hope the step drill bit does not hget ruined on the PCB material.
3) For drilling those larger holes I will use a vertical drill base which I will steal from my in-law who has one in his garage. I will make sure the PCB plate is firmly secure first.
4) For square holes I will use very small holes around the perimeter and then a file.
5) For larger square holes I am not sure. I have used a jigsaw before and the blade got ruined in about 1 cm cut. Also it is hard to use unless the holes are quite large. I am thinking of buying a nibbler hand tool, except I am not sure it will work just as well on a fibreglass PCB.

 

Online Kjelt

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Re: CNC milling machine
« Reply #20 on: February 27, 2014, 10:45:32 am »
With the right bit you can get away without liquid coolant on the harder aluminum alloys.  We regularly cut 6061 with Onsrud 63-600 series bits which are single "O" flute upcutting bits and nothing but air to cool and clear chips.  5052, which is slightly softer, does okay as long as the bit is relatively new and a smear of lubricant on the surface of the part helps keep burrs down.  Real soft stuff like 1100 cuts like taffy, though.  The 63-600 series are also pretty good on plastic.
Absolutely. Unfortunately my cnc machine is not professional and the mill starts at 10000rpm. So instead of nice chips I get mostly dust.
 

Offline PaulAm

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Re: CNC milling machine
« Reply #21 on: February 27, 2014, 01:26:48 pm »
A nibbler will work fine on PCB material. 

When you hand gets tired, you can find electric and air driven versions as well.
 

Offline akis

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Re: CNC milling machine
« Reply #22 on: February 27, 2014, 03:07:08 pm »
A nibbler will work fine on PCB material. 

When you hand gets tired, you can find electric and air driven versions as well.

They sell nibbler attachments for ordinary drills, eg http://www.amazon.co.uk/Sealey-SNA9821-Drill-Nibbler-Attachment/dp/B003OXBPJA/ref=sr_1_4?ie=UTF8&qid=1393513540&sr=8-4&keywords=nibbler

Is that attachment going to be OK for small size precision cutouts or is it geared more towards cutting long straight lines?
 

Offline mos6502

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Re: CNC milling machine
« Reply #23 on: February 27, 2014, 05:32:53 pm »
I haven't used one, but I think a powered nibbler would be awkward to use, especially for smaller work like case stuff. Remember that you'd have to somehow clamp your work, while the hand nibbler can be used freehand. Also, the nibbler you linked cuts round holes, instead of rectangular like the hand nibbler.

Maybe this video will give you a better idea of how the nibbler works:

for(;;);
 

Offline akis

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Re: CNC milling machine
« Reply #24 on: February 28, 2014, 06:42:51 pm »
My son's school are willing to let me have an old Roland CNC router from the pictures it looks like a desktop inkject printer plus a control box - I am not sure of the model, neither of the method of operation but I am willing to give it a try. It seems there is a cable which moves the head and from the pictures it is frayed and half-broken, this seems to be the problem with it. I attack some pictures in case anyone here knows it.
 


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