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View Full Version : Advice on type of CNC Machine to buy/build



GaryWilliams
24-04-2015, 03:39 PM
Hi All,

I need advice on what type/power of 4 axis CNC Machine to buy/build. I've looked at all the eBay offerings and various plans/kits for 3040 sized machines. There is plenty of choice but I have too little experience to make an informed decision, so I thought if I describe the most difficult jobs I want to do, the more experienced of you could prevent me wasting money on the wrong machine. These are the two most difficult jobs.

1. We want to use the 4th axis to cut/grind grooves in the stems of car engine valves. The material used is hardened steel, 6mm diameter. The grooves need to be upto 1mm in depth.

2. We also need to shape billet aluminium to form small con rods for a small petrol engine. The blank rectangle of aluminium we will start with will be 80mm long x 50mm wide x 20mm thick.

Will I need an industrial machine for these?

Regards

Gary

Boyan Silyavski
24-04-2015, 04:09 PM
You need Cnc mill, not router. And some very serious rotary axis. Forget about 3040 machines. And about routers.

JAZZCNC
24-04-2015, 07:22 PM
Ok well like Silyavski says ideally you need a milling machine. BUT because of your other need to mill aluminium it's actually not that straight forward.?

First to do the valves you will 99% need to grind them. This means you'll need some form of Grinding attachment to bolt to the Spindle column. The Forth axis will need to be quite ridged well setup and with good resolution. It will also need to be able to handle coolant which you will definatley need for grinding.

Now we get to one of the Less than ideals.? Milling aluminium ideally requires high spindle speeds and most common milling machines don't have the spindle speed for cutting aluminium correctly or with any decent feed rates.

The other less than ideal is the fact grinding is very messy and abrasive which plays havoc with milling machine slides and Ways. It basicly mixes with coolant and turns into grinding paste wearing the slides etc away in short order. At best this means very careful clean up before doing any other milling with some serious guards for coolant and at worst regular strip downs to properly clean.

Personally if I had your needs then I'd split the work between 2 purpose built machines.!!. .

First a Stiff fixed Gantry machine designed to mill aluminium correctly.

Then a purpose built 4th axis with grinder attachment to soley grind the valves which can handle the mess with sealed protected linearings etc.

One machine like a milling to do both will suffer badly IMO and be less than ideal at both.!!

GaryWilliams
27-04-2015, 10:36 AM
Hi silyavski and JAZZCNC,

Thanks for the replies. I forgot the grinding/coolant issue. Just shows how long it has been since I was last in a machine shop! I will forget the valves and look to outsource that job.

All the other jobs are milling/routing jobs. They will be 2D/3D shapes in MDF, plastic, PVC, Nylon, etc up to A4 size. All relatively soft materials. Do you think this Chinese 3040 machine will be adequate for these jobs - eBay item number:400882540881?

If I can find a machine that can also mill the con rod, I can then support my son with his Kart engine modifications, the con rod being the largest and most complex item. The other bits will be simple brackets, flanges, etc.

Can you suggest any particular make/model of machine that could handle this?

Cheers

Gary

JAZZCNC
27-04-2015, 04:02 PM
The 3040T version with watercolled spindle will work for the softer stuff but the machine it's self will struggle with aluminium due to lack of strength and low quality linear components.
The electronics on these machines are mostly cheap nasty items and will at some point cause you trouble. Often sooner rather than later.! Avoid any version that uses DC spindle.

These machines are great for cutting your teeth on and learning CNC but don't expect to much from them.!!. . . They are cheap low quality and it shows in what comes out the sharp end.

GaryWilliams
27-04-2015, 06:21 PM
Hi JazzCNC,

Thanks for this. What is the problem with DC motors for the spindle? I'm going to buy one of the 3040's to learn on, then look to build a serious one for milling con rods, etc. What type/size/power cnc do you use? Can you recommend a kit/spec that will handle aluminum blocks?

Cheers

Gary

JAZZCNC
27-04-2015, 06:56 PM
Hi JazzCNC,

Thanks for this. What is the problem with DC motors for the spindle? I'm going to buy one of the 3040's to learn on, then look to build a serious one for milling con rods, etc. What type/size/power cnc do you use? Can you recommend a kit/spec that will handle aluminum blocks?

Cheers

Gary

The use Carbon brushes and burnout in no time. Complete rubbish best avoided.!!

For milling aluminium you'll want a spindle that can run between 7000rpm and approx 18000 dependent on tool size. Water cooled 2.2Kw works fine for cutting aluminium and suits routing softer materials as well with it's 6000 to 24000rpm range.

Boyan Silyavski
27-04-2015, 07:53 PM
ebay item 400882540881

That is a toy, not a machine. Its a recipe for frustration. Plus buying it from people who sell tattoos... I wish i could forbid somehow that "machines" from selling :toot:

GaryWilliams
30-04-2015, 11:13 AM
Hi silyavski and JazzCNC,

I am definately looking at better quality machines now and increased my budget considerably.

Thanks

Gary