CNC Build Advice, Motors and motion parts

[neo__04]

Hey all,

Looking for some advice on my upcoming cnc build because I just cant decide on so many things!

What i do know....
My aim is to build 1000x1500, ill buy the frame and support structure in that stock length, build area will end up smaller. Z-axis i dont have a set height in mind.
Looking to cut a bit of everything, mdf, perspex, aluminium.
Going to buy a 2.2kw watercooled spindle.

I cant decide on what to use for motion. Eg. SR20 linear rails on top of aluminium tube frame, or linear slides, rack and pinion, ball screws.
It's really quite confusing.

I dont't want to build anything rediculously cheap, but i also dont want to be unhappy with the results.

I was looking at 425oz nema 23s, but should i go for nema 34s?

Any advice would be great as im not sure what to do.

Thanks heaps

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[fretman_2]

Unfortunately...lots of configurations can do what you're wanting. I used Acme 1/2-10 5 start screws which seem to be a good and cost effective way to get accuracy, and motion per revolution. NEMA 23's should do most of what you're after. Get low inductance motors though. Read all the build threads here and you'll get a good idea of what will work. Most everyone has asked the same if not same kinds of questions. Here's my build thread...http://www.cnczone.com/forums/diy-cn...05340-cnc.html. I'm not saying mine's a good example of what to do, but I ask a lot of the questions you'll ask.

My machine is in the arena of 36"X24" cutting area with NEMA 23's. I used SBR16 rails...plenty rigid for this application. I build guitars so I cut a lot of hardwood with mine, plus I cut and engrave 6061 aluminum with it. Ultimately, you're going to have to be the one that decides on the oomponents to use. The advice given to me was just to go for it and I did. Good luck.

[ger21]

I dont't want to build anything rediculously cheap, but i also dont want to be unhappy with the results.

The issue is always that we don't know what you would be happy or unhappy with, so it's hard to give advice.

I would say to use profile rails like Hiwins. Either 2010 Ballscrews or rack and pinion.

I'd look at some 5-6 amp Nema 34's in the 400-450oz range, with high quality drives running at about 60V.

[wizard]

As others have already pointed out it is hard to offer help until you have zeroed in on needs first.

For example you defines a space upon which the machine must exist instead of cutting capacity. That might be because you have a fixed area in mind for setting yp the machine. The problem here is pretty simple will the resultant work area meet your needs.

The required work area is key to making a machine that fits your needs. You might build a beautiful machine that fits in a 1 x 1.5 meter space that ends up short in the work area by a couple of centimeters. So im going to suggest that you first put a lot of thought into what you need machining capacity wise. You want to do this to make sure the machine can tackle what you have in mind machining wise.

As for how you construct the machine it really depemds upon what you mean by machining aluminum. If this will be a fequent task i highly reccomend building a more robust machine than what is needed for wood. Id consider steel for the framework too as it is usually far cheaper in most locations.

[neo__04]

Thanks for the info guys.

Well I'll try and clarify as much as i can.

I can mainly see myself working with wood, I make home theater speakers on the side, so I was looking at a build size that would allow me to make a set of floor standing speakers. Eg. Around 1200mm long. 700 wide would be the largest I would need for this purpose.

I would like to get into cnc routing to make use of some waste products from my other work. Lots of hardwood offcuts. So doing some 3d carvings/signs etc to possibly sell.

I also make 3d printers, so i thought it would be nice to have the option to cad up 3d printer frames then cut them out of aluminium.

So basically the machine will be used to do a bit of everything.

Cost wise I though 1000x1500 build area would use stock lengths of rack/rails/ballscrews etc which may make it a bit more cost effective.
The resulting work area of maybe 700-800x1000-1200 would be more than fine for my purposes.

I have a mate who has just built a cnc router and he spared no expense, SR30 linear slides on top of 70x70 aluminium tube frame, rack and pinion on the side, massive nema 34 motors which require a power supply each, with drivers costing like $120 each. etc etc. He has probably gone way over the top for his needs, but it got me thinking about what I NEED vs what is recommended for the purpose.

I'm new to this and I'm trying to get as much advice before I start my build.

As an example..
2 x Hiwin 1500mm are about $450
2 x Rack 1500mm long - $150

There is a big price difference between the rack and hiwin setup.
This is where i was meaning that if you suggest that there is a big price difference but the Hiwin are MUCH better, then its worth the money.
If the difference is minute, then that's one place I could save some money.

Hope that clears things up a bit.

[ger21]

Sounds like your friend doesn't really know what he's doing. There's a lot of things very wrong with your description of his machine.

As an example..
2 x Hiwin 1500mm are about $450
2 x Rack 1500mm long - $150

Why are you comparing the hiwin rails to the gear rack? You need both.

This is where i was meaning that if you suggest that there is a big price difference but the Hiwin are MUCH better, then its worth the money.
If the difference is minute, then that's one place I could save some money.

With CNC, you definitely get what you pay for.

Imo, there's a big difference between 20mm round rails and 20mm Hiwins. Then again, many people would be happy with the round rails. It's all about expectations, and unfortunately, if you have no experience, then you don't really know what to expect.

$100-$120 per drive is the going rate for a good quality drive.

If you want a cheap machine, get some round linear rails, chinese 2010 ballscrews, a Gecko G540 or Leadshine MX4660 and appropriate sized motors.
Use it, learn about it, and upgrade if you think you need to.

[jahnj0584]

36V PSU 14A
TB6600 Drives
425 Ozin Nema 23, 4mH or less
2010 and 2510 ballscrews
20mm square linear rail (hiwin)
40120 and 80160 80/20

im selling the plans to my machine if you want that

[wizard]

First off id hardly call you friends machine sparing no expense. That said a friend with a CNC can do much to help with your build.

Second i would suggest reading the stickies and some of the build threads to bet a better idea of how everything works together. There are important aspects of machine design to grasp but perhaps the biggest area to wrap your head around is the need for stiffness in the machine to deliver high quality work.

Third working with aluminum, at least is a way that is money making, requires a much stiffer machine than a wood working machine and more importantly requires some sort of coolant / lubricant. I realize one can hand apply WD40 and get good results but on long runs or more than a few pieces it becomes a pain. Beyond that CNC routers are fast enough to really question the safety aspect of tending to coolant. So if you exoect to do a lot of aluminum an enclosed machine with a coolant system is in order. As a side note im not a big believer in the flat panel reprap designs, i dont see a huge future for such machines when extrusions, even small cross section ones deliver better mechanical results.

Forth Since aluminum requires a stiffer machine this moves you into the area of profile rails instead of round rails. Again it is a matter if expectations but the more aluminum you do the better iff you will be with profile rails.

Fifth all linear rails require supporting structures that allow them to work to spec. This is where i start to have problems with aluminum extrusions. In a nut shell there are so many manufactures out there that you cant just call out the cross sectional dimensions and call it good enough, many are so light weight as to be crap for CNC usage. Combine this with other issues and i have to say im not a big fan of T slotted extrusions for the major structural parts if a CNC. There are successful designs out there of course but id consider steel, especially for the gantry.

Sixth speaking of the gantry this is where many cut corners. You want a beam of suitable criss section to resist twisting and vibrations and is big enough to properly mount the linear rails to. Like wise the supports for that beam should be mechanically stiff. The longer the span the bigger the beam. A long Z clearance requires a bigger beam to resist twisting under load.

I didnt even get into controls above but what im trying to get at is the need to think about design a bit. However dont over think it. If you arent familiar with machine building or design it can be confusing at first. In any event the basic concept is that the more difficult a material is to machine the stiffer the machine must be. Increasing the size of a machine works aganst you when discussing stiffness. One if the advantages of a smaller machine is that for the same amount of cash laid out you can build a much stiffer machine or keep stiffness and lower costs.

So what everyone here runs into is balancing machine construction/design against the allocated budget. It is a big challenge but do consider sources for parts that arent new or at least discounted. For example large steel suplliers often have drops heavily discounted. If you can find junk yards that sell to the public you can often find good material deals there. Auctions at failed business are another possibilty. The point here is thatusing substantial materials doesnt mean paying list price.