Small home cnc machine advice

[nechaus]

Hello,

I have been looking at cnc machines, small ones, i wanted to know what these small ones on ebay can do for e.g.
http://www.ebay.com.au/itm/NEW-CNC-3020T-ROUTER-ENGRAVER-ENGRAVING-DRILLING-AND-MILLING-MACHINE-/280903984102?pt=LH_DefaultDomain_15&hash=item41672ea3e6#shId
$850 ish 3 axis

or a 4 axis is like just over $1100

I only really need a 3 axis one, i want to make drop outs, torque arms, make stuff out of aluminium...
What type of unit will i need .. some like the one above or does it need to be alot better...
I dont mind if it takes along time to do stuff...
Will it also cut steel?

 

[nechaus]

Can a machine like this also make hub motor covers?


Never had like this anything b4

 

[acuteaero]

Machines like that are not nearly rigid enough for any serious machining of any metal. The frame, bearings and spindle are all not rigid enough. The chinese benchtop mills like http://www.littlemachineshop.com sells, or Grizzly, or Harbor freight, etc, are a step up in rigidity, but less work envelope. They can cut metal but you must go very slow and won't get very great surface finishes. Look around on the CNC zone or Practical machinist forums for tons of information about machines and machining of all scales.

 

[nechaus]

is it possible to buy one that does metal that cost $1k or less?
new or newish, cheap Chinese one?

 

[nechaus]

expecting they would be $5k plus


really wanted to make custom drop outs and torque arms for my bikes myself..

So there is no chance a machine like this would work with a beefed up motor? like a large out runner

 

[nechaus]

[youtube]R2fgMPHAW4w[/youtube]

 

[Kin]

the guys who helped me CNC my torque arm said that it's better to get curly shavings, not powdery shavings [like in that video]. (which, incidentally, we were getting with the O1 steel.) He said it was just a general observation (he's only been doing it for several years.)

The right feed rate and rpm gets more curliness. Reportedly.

 

[acuteaero]

Feed and speed are important sure, power is good (it is not uncommon to use hobby outrunners to power a milling spindle, I know of a couple people here who do just that)...

The key is rigidity, which most small machines lack. Rigidity is how much a material deflects for an amount of force put on it. Cutting material with a milling tool generates a lot of cyclic forces, and harmonics- the less the tool and material you're cutting deflect while cutting the more power you will be able to actually effectively use and the more efficiently you'll actually be able to cut the material. Without enough rigidity the chips will come out fragmented or "powdery", the cut quality and accuracy will be absolutely crap, the cutters will scream and make a lot of noise, or break right off. It doesn't matter how much speed or power you have- in machining rigidity is the final word.

An RC motor is fine for powering a spindle, but it must (belt or other) drive a proper machine tool spindle with proper rigid bearings, balancing, concentricity. Otherwise it's not going to cut for crap.

How do you get rigidity? Big bearings, big iron castings, good design, and heavy iron parts to absorb vibrations.

A router motor spindle like on that ebay mill has a couple tiny bearings in it and a tiny collet- even a garden variety Bridgeport knee mill has dual taper-roller bearings of about 3" OD on the bottom of the spindle and a deep groove ball bearing at the top, and it's a dinky small machine, but the big bearings, dovetail ways and the weight of 2000+ Lbs allow it to machine most anything if you go slow enough. The VMC I run at work weighs 15 tons, has a 30hp spindle with massive ceramic bearings. I have never found the limits of the machine's rigidity, the rigidity of the tool or the part itself is always the limiting factor.

 

[nechaus]

ok im understanding more now..

So would it be possible to use a stock machine and program it to cut just fine layers off and let it take hours to make a small part?

just set it up and let it do its thing...
im going to join a cnc forum

 

[acuteaero]

Yes, that is the only way it will work. Small depth cuts reduce the rigidity required.

The machine you originally posted will never cut steel, and might cut aluminum at a depth of <.02" per pass, with a small diameter, good, sharp tool. The accuracy will be mediocre and the finish on the edges of the part will be very shitty. You will break tools like crazy until you get it figured out because you will not be able to use tougher larger diameter tools, because there is not enough rigidity. That machine is really only good for engraving and cutting out plastic bits.

The grizzly/HF/littlemachineshop mills are very well documented online, many CNC conversion kits, and they can perform much better, still nowhere close to an industrial machine. Work envelope is also quite small (4"x10" or something?)

 

[adrian_sm]

Do you really need CNC?

If you only have a $1k to spend, much better off going for a manual mill. $1k only get you a fairly basic manual chinese mill.
Sieg X2
TM16V
Machinery Warehouse

You can always convert it to CNC later, but don't compromise on stiffness now.

Oh and don't forget to budget for all the tools, clamps, etc.

 

[nechaus]

Well, i might just save for a big machine, maybe i could get a cheap cnc machine for 5k that will do steel..
5k is steep for me it would have to be good..


Id be interested in making a diy cnc machine... that i could make for cheaper..
The reason i liked the mini machines because im tight on space... and something small that takes ages but does the job would be ideal..

Maybe im just dreaming haha



Id like to get those manual milling tools..
I am slowly building up my tool shed...
Im really into cnc machine because i just got that plastic 3d printer...
I reckon my 3d printer with a cnc machine.. i could make some cool stuff and loads of ebike parts

 

[Arlo1]

[youtube]D4-p3ZGlThg[/youtube]

 

[acuteaero]

video

Eeeeeeew why on earth did he conventional-mill the outside contour.

Looks like depth-cuts of .050" with maybe a .125 tool, running a very high speed router spindle. Note the roughness of the finish on the walls of the cuts, and the typical chatter-marks in the inside corners. Once you've had your hands on real industrial CNC milling equipment it's really hard to want to play with this stuff...

If it's an option I would always advocate taking some machine shop classes at a local community college or technical school- to really learn the skills on real equipment. For this sort of stuff you don't really need to own the tools yourself, having limited access to really good tools is often better than owning dinky janky ones. The bulk, weight, cost and 3 phase power requirements of real tools are huge barriers to entry for home use.

 

[bigmoose]

Well, i might just save for a big machine, maybe i could get a cheap cnc machine for 5k that will do steel... 5k is steep for me it would have to be good..

I went through this 20 years ago... I bought a worn out Bridgeport vertical mill for under $1,000 US. Disassembled it all and had the ways reground for $600. Realigned everything, repainted it. Add zero backlash ball screws for $800 and added stepper motor drives. I designed and built the drivers and wrote the control software... I had a lot more time back then! It has sure been a workhorse ever since.

 

[nechaus]

very nice!!

That's a healthy amount of knowledge !
Wish i could make mine right now

 

[heathyoung]

Looking at a lot of the conversion information, the cheapest to convert would be the Sieg X1

http://www.flickr.com/photos/60552763@N00/475947347/

Available locally for $700 or so (vs. $900 for the X2) - the x1 is cheaper to mod since you don't replace the lead-screws, but as a result the backlash is worse.

There is a conversion kit for the X1 for $350 (overpriced) from CNCFusion (http://www.cncfusion.com/micromill1.html)

or the X2 http://www.cncfusion.com/micromill1.html

A lot of people make up some cheap brackets to fit steppers to these (X1), and use Roman black's PIC stepper set-up (or use a gecko 540).

Those cheap Chinese machines could be fixed with some electrical know-how, but as others have said, they have poor rigidity - even the X1 can mill mild steel in its standard configuration.

Now the only way to make the cheapies more rigid would be to replace the deck with 10 or 12mm steel plate - heavy, but probably would (if tied to the standard deck, or placed under the standard deck to keep the mounts in place. There is a a lot of room for improvement.

 

[amberwolf]

I've gotta say that unless bling and spiffiness are super important, you might be better off saving up slowly for the machines you really need, and just using "hand tools", including the good old drill and angle grinder, as well as files, to make simple things like torque arms and dropouts, which generally have very little "3D" work to do--most everything is on a single flat plane and simply needs to be cut thru a single plate of material, with perhaps some lips or bevels here and there.

It is time-consuming, but could well be faster to produce a part this way than to use a machine that has to make a bajillion passes to be able to accurately make the part.


And it may also be possible to produce a higher-quality finish and more accurate part than with a cheap machine. Just look at some of AussieJester's work with trained beavers!


Of course, it does require you to spend the time actually doing it, and checking your measurements and fit along the way repeatedly so you don't over cut something, or file too deep, etc. And to have the time to do all the work yourself.

 

[Alan B]

I don't have CNC (yet) but having a lathe and mill have allowed me to hack out parts that I would never have had the patience or accuracy to make by hand.

I also found it is pretty easy to make enough doing some jobs for folks to pay for the machines. And that is a learning experience as well.

I have the Grizzly http://www.grizzly.com/products/Combo-Lathe-w-Milling-Attachment/G0516 which is a 10x24 lathe with a mini-mill mounted on it. The lathe has been pretty competent, but the mini-mill is marginal. I would go for the larger mills, preferably one with a square column like the http://www.grizzly.com/products/6-x-21-Mill-Drill/G0619.

I would add the CNC later.

 

[nechaus]

yeah it seems like the way to go, at least i can make stuff myself to begin with.

id be tempted at making some sprockets my self

 

[Dauntless]

The bigger the machine you buy, the more it will weight. Are you SURE you're staying right where you are for a long time? That's been holding me back. The smallest machines, as they say, mostly don't do what I want to do even if they do cost close to $1k. You get to say $1,200 and you have 1hp, some fair sturdiness, but you also have something heavy enough, say 300 pounds, that moving it is no casual feat. (I've spent my adult life wondering if I'll stay in this house much longer, but never find a permanent job to move close to, so here I am.) So if you go for this bigger unit, keep in mind it needs to find a PERMANENT home. And beyond 1hp is usually 220 volt in the U.S., not sure how that will work in Australia.

I notice your selection of used mills on eBay isn't good in Australia. It would kill you to look at the American selection. Probably doesn't really need work if you're not a precision machinist and only $500 for a large Bridgeport with a power feed, etc. But where would you put it? Would you have the power in your home it needs?

So darn, sitting here doing some research about what's available on eBay dow under, I was about to put my foot in my mouth. Found a cheap used mill.

http://www.ebay.com.au/itm/Verlinden-1-35-Panzerwerke-Milling-Machine-2708-/130628790448?_trksid=p4340.m263&_trkparms=algo%3DSI%26its%3DI%26itu%3DUCI%252BRTU%26otn%3D18%26pmod%3D190706903118%26ps%3D63%26clkid%3D1244216321959524321

Instead of spending a lot of money just yet, why not jump in with a cheap used machine? Say "Approximately AU $15.19." If I thought those would run on American power, I'd be working on getting one. Oh, wait, there seems to be a sale here, too. I admit, I'm wondering what the catch is. Until I hit google to try to figure out what sort of mill this REALLy was. Darn, it's a little scale model for a WWII German workshop simulation. If I wasn't the type to look things up, I wonder how many people here would have scrambled to buy one so cheap. Sure looks real, eh?