Newbie- Stepper torque/size question plus ebay CNC kits?

[AleG]

I've been wanting to make a CNC router for two or three years now, I've been reading related material since then, thinking over the best design approach, trying to find good sources for the parts, pondering over technicalities and finally came to the conclusion that I'm thinking too much about it and doing too little...

So, Today I bought the parts for the sliding and screw mechanisms, I'm going to use 8mm steel rod with linear bushings and 1mm pitch screws connected to the stepper motors for the motion. I'm planning on making an aluminium reinforced MDF structure with a base dimension of about 50cm long and 40cm wide (cutting area of 40 by 30 I think)
I plan to use two screws to move the X axis, interconnected with a timing belt, a moving YZ gantry and for the router itself for the moment I'll make use of my Proxxon IB/E drill/grinder and later I'll see about using something else.

Now the thing that has set me back the most is the decision about the stepper motor selection and driver board for them. Yesterday I saw this on Ebay: 4 aixs Nema 17 stepper motor & Driver board & Power CNC, well, bingo!, I said. A neat package of all I need to power up the router and a nice price too. Then the question is, is this package any good for what I want to do?
First practical matter is if 48oz.in of torque is enough for a router the size I intend to build, to be used cutting/milling balsa wood, MDF and aluminium.
Second practical matter is if these kits are worth buying or junk (I've seen similar kits from several Ebay vendors)

For the first point I could go for something like this with bigger motors 3 Axis Nema 23 stepper motor 287 oz.in CNC Router NEW. 287oz.in ought to be enough, no? On the other hand it may be too much force for a small table top router. Honestly, I have no idea.

[Hyrum R]

I personally wouldn't buy either kit. The motors on the first one are way too small, and the second kit, they are very poorly matched to the power supply voltage. I've had the very best experience with the Gecko G540. It's a lot pricier than what you'll find on eBay, but it does a much better job.

The motors that CNCRouterparts.com sells are matched pretty well with the G540, and with a 48v power supply (try to get an unregulated power supply) you couldn't go wrong. If you're on a tight budget, you may want to look at the kits that hobbycnc sells. But I personally feel that you'll feel like you got the best bang for your buck by going with the G540.

[AleG]

The Gecko driver looks nice, and I'm sure is top notch, but to get started it's a bit over budget for me. Probably down the road I'll upgrade to something like it but for the moment I'd prefer something cheaper. After all my first router is probably not going to be built to any high degree of accuracy so I think it would be a bit wasteful.

Anyway, thank you for pointing out about the power supply, that's the sort of thing I don't know. So I suppose I should go for a 48V power supply then? Stepper motor voltages are a bit arcane to me, I know the actual voltage to drive them is supposed to be higher than the motor's stated voltage, but I don't know how much. Let's say 48V and 5 Amps to be on the safe side? I have to admit it seems rather high power to me.
Perhaps then, I should opt for separate the components, get a board like the one on Ebay (I'm still assuming it's "usable" albeit not great) and get different stepper motors, perhaps Nema 23 and around 100, 150 oz.in torque?
On edit, I just realized the board takes up to 36 V input for the motors, so a 48V power source won't work.

[Hyrum R]

Mariss has come up with a formula for determining the optimum voltage for a stepper motor. You take the square root of the inductance (in mH) and multiply it by 32. Those 287 oz-in motors you were looking at have an inductance of 18 mH, which means they would run best at around 135v. Yikes! I've never seen a motor with that high of inductance. I'm not much of an electronics expert, but I can't imagine that running very well at all off a 24v power supply.

I'd recommend going with a hobbycnc package with their 185 oz-in motors if you're on a budget. They have a complete driver board/motor kit for a decent price, and it would do much better than these Chinese packages. You'd just need to find a transformer to complete your power supply. They have links to 24v transformers which would work, but a 36v would give better performance.

Then later on, you could upgrade to a Gecko drive. I started off with a Xylotex controller and 269 oz-in motors. It worked OK, but when I built my new machine, I reused the motors, but upgraded to a G540 (and a 48v power supply instead of the 24v they supplied). The difference was amazing.

[lukewarm]

I made the mistake of purchasing a cheap chinese driver/stepper kit with the same driver board as the ones you're looking at. The drive is just junk, honestly. Poorly designed circuit board, one channel blew a few hours into testing, and the board was unable to drive the motors at 1/10th of their potential. Very disappointing, and totally useless. If you'd like more information about these boards contact me and I can link you to other threads on this forum about that Toshiba based driver board.

I understand budgets but spend the time to research the driver you buy. If you have to save awhile longer to buy a better solution it may just be worth it in the long run. Gecko drivers are notoriously well built and come highly recommended. Three G251s will set you back $180 not including shipping and taxes.

Good luck

[JD_Mortal]

I have that same controller board and similar motors, by the specs of the nema-17 kit, except my motors are nema-23 form. (They have more torque and are super-quiet. Mini-stepper brand, I believe printer-feed motors from large-format printers. They are no speed deamons at about 20-in/min at 12v, should run better with 24v, but I need to limit the amps first.)

My board is a love-hate relationship so far... It does not operate correctly with my LPT/PP due to the ports "issue" (actually correct use), with the connections for the X-axis. (It uses the strobe-connection for x-move and line-feed for the x-enable. Thus, the strobe pin goes so fast that the average voltage isn't enough to trigger the optical circuit, and the line-feed voltage drops randomly because it is not designed to stay-on all the time. I need to reverse them, as they did in the later models of the boards. The 4 and 5 axis versions don't use those pins for driving the motors.)

As for power... if you stay under 28v, with a "Switched-mode" power supply, you are completely safe. Going near 30v, is pushing it. The smallest capacitors are only 30v caps, and the chip max voltage is is 40v (spike), 36v (normal).

Most users seem to be using linear power supplies, or variable power-supplies, which have a 45v spike surge on startup and have poor regulation, leading to spikes over 36v, which pops the driver chip, usually the middle one, due to the poor circuit setup that links the chips.

They are adequate, but buy from a reputable seller... You will pay more for the pre-tested and well matched setup, but not much more. I think I see them like $20 more expensive than the china-sellers. (If the seller sells USB plugs, tooth-brushes, lasers, and i-pad cases... stay away, they are just drop-shippers and have no idea where they are getting the stuff, or how to fix it.)

The "red" boards you see all over, 3-4-5 axis... are a better breed. I have one of those on the way also.

My setup will crush my finger and pull my bearings out of the mounts... (Don't ask)... They are strong, and function well. (I am running at 50% amps and 1/8th stepping on that board. Still playing with some settings.)

I can't say, "Bid with confidence"... because it has not earned that title... I say... "Bid with caution, and expect to return it, but be sure it can be returned."

You can NOT run these sensitive boards off a linear-power-supply, you will just kill them when your power fluctuates. It needs a power-supply that can adjust the amps and voltage, based on load... Linear power-supplies do not adjust anything, they just pour power as it is transformed, and flows out the capacitors.

[eddie3000]

I bought one of those chinese ebay kits too. The motors seem alright, maybe not the best, but the driver is pathetic. I wouldn't recommend it.
I have experienced many many problems, mainly missed steps. One or two missed steps in a project shouldn't be too much of a problem, but with this driver I have had one or two hundred missed steps in an aprox. 5000 line gcode project. I even had the motors running dead slow, at 3mm/s (as the driver, in my case, is very underrated for the motors that it came with).The final machined part was useless. Unless your projects are really simple, that driver is money down the drain. That's my opinion.
I am now looking for another driver, I should probably get at least the gecko g540.
Good luck!

[AleG]

Thank you very much for the advice. Now I'm thinking of buying either the Hobby CNC PRO 4 axis control board or the Easy CNC 4 axis board.

Besides one being an unassembled kit and the other plug and play is there any major differences between them? I really don't mind assembling the board, in fact I enjoy putting together circuit boards so that on itself is a non issue for me.
From a quick overview I think one of the mayor differences is that the Easy CNC board has opto couplers while the other doesn't.

This morning I bought 6 meters each of 2x1" and 3/4" square aluminium tubing plus some 3mm thick sheet to build the machine frame. I did a test of using MDF for the frame but although it seems to be rigid enough for my purposes I can't stand the mess working with MDF makes.

[Mike Ray]

If you are wanting to get a tested kit, take a look at some of these and heed the advise that the poor can't aford to be cheap. Shop and be frugal of course, but spend a lot of time understanding this purchase. You can read on many threads where folks end up buying the basic drives over and over becuase they do not understand all the pieces. Here are a few places to look for pieces for your drive system.

www.kelinginc.net
PMDX.COM - Products for CNC and motion control applications
Antek - Your reliable source of transformers, power supplies, and more.
Campbell Designs - CNC with Bob Campbell
Geckodrive - Quality American Made Stepper and Servo Motor Controls

Our CNC router is a larger unit using Nema34 motors running fron 400 to 640 oz in. Our inductance is typically giving us a final needed voltage of between 39 and 48 volts with a few exceptions.

You can build a lower end kit on the keling site and john has a good following with my folks.

Something like this,

4 - KL-6050 - $49.95 each
4 - KL23H276-30-8A (NEMA23) $39.00 each
1 - C10 Bidirectional Breakout Board $28.00

$383.80 plus shipping

Build your Own ps. You can surely find some info on that here. Switching PS are not really needed for a basic router.

If you want to buy one, John or John (Hee Hee) Keling or Antek can help you choose a unregulated toroidal ps with a power take off for the Motor Drivers and a Power take off for the BOB.

If budget is the name of the game look around for folks here that are changing up and have used parts. Ask but be aware they are selling for a reason. Most of the time is just because they are changing up . You can also dig around and find folks who got in neck deep and now want out or lost intrest in their builds.

The electrics are the heart of your machine, so knowing (not guessing) how these work is really important.

Also if you do not have a Parallel port on your PC , you don't have to do the Smooth Stepper or the like to goto USB. Parallel boards are available for about 15 bucks and they work fine with Mach3.

Also if you are new at this stay in the main stream like the items I have listed above. You get out in the weeds with these unknown suppliers us guys can't help you work out the bugs in your system that you WILL have.

Many ways to go about building a machine. Just read A LOT. You will see the trend of what people are doing.

[cut2spec]

I am having troubke find the post button I want to start a new thread but can not find where to do it?