Sorry for the frustration folks. It's quite a lot to swallow, especially being in a rush to get the parts. Suddenly not being able to post for help and advice, with exception to this solitary thread of mine, makes the whole project feel quite daunting, sort of being restricted to a small raft in an ocean of unfamiliar territory. To me, this is a considerable investment for not being quite sure of my ability to produce the end product. My lack of confidence has me feeling for the for the walls a bit more than usual. So I apologize for the frustration, and for asking too many questions.

Thank you for the support.
Chris.

Well Chris amny feel that way at first and once they do dive in they just do the work in pieces and look up one day and they are cutting :)

Chris, I felt intimidated when I started. But I had read some post "Not enough" but what I found reading the post is if you ask the questions you will have everyone trying their best to help. I have made some changes to my setup by adding a 4th axis, changing the operating voltage of my motors and the addition of a removable sections of my table to allow Vacuum hold down or the Tee slots I original installed. Most if not all of this information is contained in the Forum. Some of the people answering the questions are also found on throw out the web doing the same thing, helping others. Trust me I did not complete my machine without help and every time I asked for assistance someone stepped up and answered the question at hand.

A lot of us also subscribe to specific threads, including build threads, so get email notifications that you have posted, and can see your question immediately there. Posting a new thread only gets noticed by checking the forums for new threads.
Good luck on your build!

A lot of us check last day and it is frustrating to open a "new" post, wait for the whole thread to load, and then see at the bottom it is a duplicate post.

If a particular user becomes irritating, some would put that user on ignore, and make sure time is not wasted with irritations.

Ok no worries. Thanks for the reassurance. Just don't want to start building this and get stuck, which being so far from the US tends to happen with parts especially.

Still just trying to figure out what motors will make the finest cuts that require little sanding, the OM geared, or the ungeared. Anyways, thanks again everyone for the help.
Chris.

It is my understanding that the direct drive motors with the belt drive reduction offers the best resolution,but someone may chime in to dispute that.

To be very specific. Direct drive motor with a belt reduction is the most cost effective mean to increase mechanical transmission resolution on top of the electronics means e.g. micro-stepping.
A stock gear box with the right specification will achieve the same performance but the cost is a lot higher.
BTW, even with home made belt reduction, the cost is definitively more than a few dozen of hot dogs, timing belt pulleys don't come cheap especially when you have to make 4 set of them. but will still be cheaper than buying a single OM with 7.2 gearbox.

Thanks Ken,

I'd be happy with whatever option delivers the cleanest cut, which requires least sanding, despite the price, within reason of course.
Chris

"Cleanest cut" is such a general, subjective & illusive goal...

In all three groups of users (those with gearboxes, those with belt-drives and those with direct drives) some will get good cut quality and some will get poor cut quality, with swings between good/poor happening from day to day. There is generally consensus that direct drives can be improved by gearboxes/belts. But there is no hard evidence that a belt always beats a gearbox, or vice versa.

And there are those (yours truly) who are too lazy to "upgrade" their direct drive even after 2～3 years...
"You gotta sand anyway..." Is one's excuse...

Thanks.

I think I get it now. One last question, does it hurt performance to have too much torque? In other words, would it be too big to go with an OM 299 vs a 296 OM? Then put a gearbox or belt drive on it? Also, is there any benefit to going with .72 degree or .90 degree motors to get finer edges?

Almost there with motors.
Thanks,
Chris

see here: http://www.mechmate.com/forums/showthread.php?t=255

Thanks, I read that one, and was staying away from the larger 1200+ oz motors. But did wonder about them. Really interesting and informative post though.:)

Thanks,
Chris

Chris,
I assume that you have decided whether to wire half-coil or bipolar? Because that affects your torque. You must have, because you've decided your power supply, right?
Just thinking...

Chris, let's do some math. A stepper motor driven by a Gecko stepper driver makes 2,000 steps per revolution. Finding how "fine" or "small" each step is, on an ungeared motor is simply knowing the diameter of the spur gear and then dividing that by 2,000.

Common spur gear sizes in the United States are 20-tooth (1" diameter), 25-tooth (1.25" diameter) and 30-tooth (1.5" diameter). So, minimum (finest) per step movement on an ungeared motor would be 0.0015708" for a 20-tooth, 0.0019635" for the 25-tooth, and 0.0023562" for the 30-tooth.

Using a 4:1 belt-drive would reduce that distance by 4X, for a minimum per step movement would be 0.0003927", 0.000490875" and 0.00058905".

Mechanical "wobble" or flexing or "slop" in the machine will keep you from getting that resolution unless everything on your machine is tuned perfectly. A MechMate is much "stiffer" than my Shopbot PRT-Alpha was, but I think that if you ran a CNC router back and forth about 10" several times with dial-indicators on both ends of the travel that you would see several thousandths of an inch variation with each move. That would show you the "repeatability" of the machine.

We all know that wood changes dimensions because of humidity, so cutting multiple parts that have a few thousandths of an inch variation is not a problem because next week or next month, the wood will be a slightly different size anyway.

Metals and plastics are highly resistance to humidity, but they still are affected by temperature. Even the best machinist can't guarantee that a precisely cut piece of metal will have the correct size if that piece of metal is measured at different temperatures.

What I'm trying to say is that you shouldn't just do the math and then expect your cuts to be as "fine" as the math tells you that they will be. Machine "looseness", chip load, cutter flexing and all the other little "gotchas" will affect the quality of your cuts. I was extremely disappointed with the cuts that I got with my Shopbot, especially on curves; however, when I learned that each type of wood seems to have a sweet spot with feeds and speeds and cutters, things improved, i.e., operator inexperience was causing a lot of problems. After I built and installed 3:1 belt-drives on the Shopbot, cut quality improved dramatically. You'll probably find the same thing with your machine. Operator inexperience will give you poorer quality than you expect, but things will get better as you learn and gain experience.

On my best days, I was happy to get cuts where the gap in any joint was less than the thickness of a piece of copy paper (about 0.003"). When that happened, I knew that all the flexing was working in my favor.

Now, to your question about the PK296 vs the PK299. If you're going to add a belt-drive, the PK296 is plenty of motor. If you study the electrical specs on the Oriental Motor website and compare the PK296-03, the PK296-F4.5 and the PK296A2A-SGxx, you'll see that the motors are the same electrically. The F4.5 has eight leads and the other two motors have six leads, so the F4.5 can be wired either half-coil or parallel. The F4.5, with a belt-drive, can be driven harder than the SGxx motor with a gearbox. That's because the gearbox is not as mechanically robust as a belt drive, i.e., if you drive it harder than Oriental Motor recommends, it will wear out sooner than expected.

The Keiling motor that Mike (Metalhead) sells is an excellent motor. I tested one for him a while back and ran it side-by-side on my test bench with a PK296-F4.5, a PK299-F4.5 and a PK296B2A-SG3.6. ALL of the motors were excellent. ALL of the motors (when used with the proper power supply) were more than adequate for a typical CNC machine.

Build your machine. Learn how to use it. Make some money with it and then, after you know exactly what needs improving, you can modify it by adding different motors, linear rails, or anything else that allows you to make the cuts that you need to make.

Wow, thanks for that incredible information Mike. That really helped a lot. No I haven't figured out the half coil thing yet either Red. When the gearbox wears out on the SG7.2 version, is it easily replaced, or does one have to toss the motor out and start from the beginning? Also, can you upgrade the gearbox to a belt drive later (take off the gear box)?

Linear rails/motion bearings sound really good on the Z axis at least. I looked at the carriage design and am not sure I can reproduce the amount of accuracy you guys have on it. We'll see.

Thanks for the info guys.
Chris

I know it is intimidating, i had the same concerns going in. But the reality is that if you follow the instructions here, and go about it carefully, you will get the same results others have. I want sure going in, and i am really happy with where my build is right now.

Use the half-coil wiring.

The SG7.2 is essentially a single, non-serviceable unit - the motor shaft itself is cut into a helical gear, so you cannot remove the gearbox and use the motor. You can check with OM, but I'm pretty sure you can't replace the gears either.

The Z axis, in the modern six wheel version, with the offset bushings is not difficult to make accurate. Might even be easier to get plumb and square than linear bearing rails, which will only be as accurate as your mounting of them - which you'll have to design.

I will say that I have owned Multicam units with linear slide z axis and my MechMates.
Each require their own little secrets to set up square and true.
By far, because the mass is less on the MM, it is the easier of the two types.

The slides required a lot of m4 m6 hex head cap screws to play with. The MM....6 jam nuts, bur really only 4, because you use the top and bottom to set it all up, then match the middle.

Last time I squared up #28 during it's annual checkup, it took 2 framing squares and socket wrench to reset the plumb in about 15 minutes.

Brad brings up a really good point. Replacing a geared motor vs replacing a belt drive motor are two very different costs. I think, as far as accuracy goes, you'll get roughly equal results with either one, potentially better with the belt drive.

The z axis, while it took me a full day to complete, was no harder than any other part of the machine.
I doubt that using linear rails/motion bearings will result in a noticeable increase in machine accuracy.
Having completed a machine, I can say, every time I thought I had a better idea, I ended up back on the proven path for one reason or another.

Ball Screw + Square linear guide is actually easier than it look; as long as you have a reasonable knee mill at your disposal. I have to get base plate milled.
The difficult part is the cost. It cost me around 600~700US$ to get one built. Still going strong.
The plus side is that mechanical reduction is naturally built in (no worries over weak gas spring & loosing steps when carving texture with big diameter (2") ball nose bits). The down side is you can't move Z-axis by hand when power is down.

All really interesting points. I mean, I really know very little about any of this, but for some reason, linear motion bearings keeps popping up in various conversations I've read, which caused me to question that. But you are right, I should jut try to get the first one finished as it is currently, then maybe alter it later, as it would require a new design altogether.

The gearbox vs belt drive is a tough decision. On one hand, if you go with a gearbox, it seems much easier to complete the machine, plus very accurate from what Ive seen on other people's builds, on the other, the serviceability seems less with a gearbox. The belt reduction seems like it would be higher torque, but maybe accuracy depends on the drive construction?

How frequently do motors go out? Has anyone here had to replace motors on their machine much?

Chris

Chris,

I dont use my machine to foten (unfortunatly) but i had a motionking (9801) motor going out.it felt stuck... I opened it and cleaned it out, put it back together and voila, it worked perfect again. I dont read much they go out, sometimes do. I have a spare in the shop just in case, also because i am in a country where import is very differcult.

Thanks Ries,

I understand that about import. It's tight in NZ also.

Chris

Hi guys,

I'm back in NZ, and looking to get some laser cut pieces done, and have a vendor. Should I just trace the plans or is there a set of DXF files for me to take to the cutter to get an estimate? They do one off cutting and folding for great rates.

Thanks!
Chris

Going shopping for an enclosure today, and Din rail, wire/cable. Read the posts about the wiring and electronics, very informative stuff. Still not sure about the power supply, but will read that tonight and see what they have at the electronics outfits here in Auckland. Started gutting my old G5 for it's case to install my new Hackintosh, which will be a dual boot PC/Mac OS based off of an Asus Rampage IV Gene board, which is micro-ATX going to the BOB.

Stuffed my shoulder, and received 6 stitches in my head after falling on the rocks out at the beach a few days ago, so waiting for that to heal before I start with the table steel. Hopefully, my arm can move by then and lift some of it (it sounds fairly heavy from what all of you say)

Ciao
Chris

So what was the beer to fall height ratio? :)

Just kidding - Hope your better soon !!!

Hey Mike,

No beer, just stepped onto the rocks and had my camera in one hand, backpack on, rocks were wet, so legs just went right out from underneath. Smacked my head on the rocks in an effort to save my lens. Shattered my filters, but lens was ok, so it was worth the 6 stitches:) Was just a trip standing up and seeing everyone freak out about the blood gushing from my skull.

Am I correct in assuming that if I go with the PK296 A2a SG7.2, wiring Full Coil, that my PS voltage would need to be 78.38vDC at 500va? Mh = 6 at bipolar series? Is there a way to build a switch to toggle half or full coil for different uses? Would that even be nessesary?

Wire the motors half-coil and use a PS with 35VDC to 45VDC. The gearbox on the PK296A2A-SG7.2 limits the usable torque, so wiring the motor half-coil still gives you all the torque that the gearbox can handle. The bonus is that your top speed is much higher when you wire the motor half-coil.

The only time that I would wire one of those motors full-coil is if I knew that I would never need more than 100 RPM.

To put it another way, if you use 1.25" pitch diameter spur gears with your rack, a 7.2 geared motor running at 100 RPM would move the axis about 55" per minute. That same motor wired half-coil can go 10X faster, or about 550" per minute. Actual speeds depend on ramping, the load (jogging or cutting), and the pulse generator (Mach 3).

Chris,
Mike Richards has posted quite a few comments on why, with that motor, wiring half coil is better. Lower voltage requirements, and mostly that in that configuration, you will produce more torque than the gearbox is rated for. Unless you have a power supply already at that voltage, I would suggest half coil wiring for that motor.

Mike you beat me to it. :)

Half coil huh? Others here have said full coil is better, but ok I'll do it half coil then. Would be much cheaper on the PS, that's for sure.

Thanks,
Chris

So in Nz we have 230v 50hz, the only toroidals I can find in stock are
50v+50v 500va
50v 50v 300va
40v 40v 300va
Then 18v 18v 300va
Then it goes down to 160va, I can't find a 25v 25v 300va. Any thoughts? Also, should I wire them series being in a 50hz country?
Thanks,
Chris

I'm living in a 230V 50Hz country too, that isn't an issue at all when using tranny built for 60Hz.
Check this out

Awesome Ken, thanks for that link. RS components is huge, and they are in Auckland. I will go there to get the toroidal. I just thought that it needed to be wired in Series for a 50hz country is all. I'll keep on researching it tonight and get out there tomorrow.

Cheers,
Chris

Chris,
Series or parallel has no bearing on the line frequency.

You wire your primary for the line voltage you have, It might be two windings in series or one winding or two windings in parallel, depending on how they built the transformer.

The secondary is wired to give you the voltage and current you need. For the transformer Ken suggested, if you wanted 35VDC you would wire the two secondary windings in parallel to give you 25VAC(35VDC after rectifying and filtering) and you will get double the current of one winding. If you wanted a 50VAC secondary then you would wire the secondaries in series to give you a 50VAC secondary at a current rating of one winding. (You will want the parallel setup for the a2asg7.2)

Thanks Heath,

It all makes sense to me now. All the gist of the motor power threads to me is 32x sqroot of inductance (1.5)= the voltage, but with the PK296A2A-SG7.2 it can be pushed to 4.5 amps just fine without overheating because they are rated lower for some reason? Only need 67% total amperage. The transformer should be 1.4x less before rectifier, as it pushes it 1.4x higher voltage.

Here is the part that is confusing, do Parallel windings on the secondary gives me half the voltage, half amperage, and series gives me twice the voltage, twice the amperage right? I can only wire in series if they are the same correct?

Thanks for the help everyone. It's a great educational process learning how to make your own PS and everything else on this machine. I really love it. Should I regulate the power to smooth the ripples, do I need a breaking resistor on the cap, and last question, is it more preferable to use multiple capacitors to 1 giant one and I bought a rectifier rated at 400v 35a, spade type, is that ok?

Chris