[kwyrbndr]

Good day, All,
I have been using my cnc ready 4400 and 5400 Sherline machines on my jewelry bench for a few years,now. I've pretty much worked out work holding issues and have been cranking the dials long enough. I NEED to go CNC.
I'm at the place where it's time to choose which upgrade path to commit too.
The Sherline package with 5 motors and their drive box appears to be the easiest and softest entry. I've already been exploring the Linix and EMC software from Sherline, as well as familiarizing myself with Mach3. I have basic skills on Bobcad ver20.
There are other several prominent providers of packaged systems which retrofit Sherline machines to cnc. How does one make an initial choice?
I would be most pleased to hear from others who might be at this same space in time.

Thanks,
Ken

[Stepper Monkey]

It depends on how much you want to get into doing some of it yourself. The kits that Sherline and the many others sell are nothing particularly special, and in fact can even somewhat underperform a package you assemble yourself. In any case they usually cost a couple of hundred dollars more than the parts that make them up, parts you can just buy directly if you desire.

If you are at all familiar with even the rudiments of basic electrical and electronic work you should not be worried about the technical aspects of assembling your own kit. It's pretty straightforward. It should be primarily just a value judgement as to whether or not the hours saved and the peace of mind to have someone else pre-assemble your setup outweighs the extra cost, or perhaps of you just having a desire to do it yourself.

After that it is a question of budget and desired performance.

After you have made those two decisions we can suggest options to best fit, there are a lot of them.

BTW, I'm a jeweler as well, and you won't regret going CNC. It changes the way you will look at the business, your designs, everything in fact. Just get damned good software, its the best investment you can make by far. Artcam, 3Design, Matrix, etc. The cheaper stuff just doesn't cut it, costs you a lot more money and grief in the end, just like bad bench tools do.

[Crevice Reamer]

Hi Ken. Welcome to CNCzone! It's about time you posted something, hehe.

I'm wondering if you are a good candidate for a CNC conversion--Especially a DIY one. You obviously use these machines for business, so down time while you convert might be a problem. Also, I imagine you have long since depleted their depreciation.

Before converting the old machines, you will want to refurbish them a little--at least new gibb strips and possibly lead screws, to withstand the more rigorous use.

Also, if you are doing jewelry, you may want to do fine cnc engraving. This would mean an emphasis on fine resolution and repeatability--Especially if you are thinking of Laser engraving.

Taking all that into consideration, you might be better off to buy a NEW CNC ready mill, keeping your old ones at the ready until all the startup finagling is accomplished, and then when you are well up and running, sell the old ones on ebay. This way, you would get to fully depreciate your new investment.

A SERVO system would give you the finest and most repeatable resolution. IMSERV has a good Sherline mill/lathe system--Just try not to go with the Deskcnc software:

http://www.imsrv.com/sherlinemachines/

Good luck!

CR.

[kwyrbndr]

Thanks to both of you.
I am leaning toward using a package for a few reasons.
Down time is certainly one.
Learning to match motors, drivers, power supplies, and wiring the box is not a task I care to invest my time in right now. Perhaps once I learn the limitations of whatever I end up using, I'll have to spend more time learning to make those choices, to better equip the machines to do what I want.
This time, unless it's real simple, I'd just as soon buy plug and play...
But, which way to go? I haven't a clue that's based on any solid knowlege.
I've seen the products at the imsrv site, as well as Flash-cut, and all the rest.
What makes one more desirable than another? What makes the choice of system more obvious?
Thanks again
Ken
Ken

[Crevice Reamer]

Two questions for you:

1) What do you want to do with the machine? (or have the machine do for you.)

2) How much is your budget?

CR.

[kwyrbndr]

Initially, I'll be setting up drilling cycles and faceting/texturing routines. Sometime later, I'll begin using BobCad to create small parts and pieces.
Nothing larger than perhaps 1.5" x 1.5" x 1.5"
Materials will be precious metals, wax, some hardwoods, aluminum, plastics and steel for tooling.
Beyond that?...
So, any and all advice and sources from more experienced craftsmen will be enthusiastically received!

Thanks,
Ken

[kwyrbndr]

... and I'd like to keep the initial investment under $1000.

[Crevice Reamer]

Hi Ken! Your $1000 budget, (I assume that is for the mill only) relegates you to converting your present mill. The Sherline conversion mounts for $250 are a start.

In about one month, the new Gecko 540 quad driver board will be released. This will revolutionize CNC conversion as we know it, and offer more value, performance and protection then anything that has been available.

The G540 contains 4 mini-gecko drives incorporated into a total protection break-out board. This means that all you have to do is plug in the computer parallel cable, 6 or 8 wires from power supply, and your stepper cables.

I advise you to wait for this, and buy whatever kind of packaged enclosure/power supply/motor & cables Tom Caudle of http://candcnc.com/ builds around it. This will probably cost about $500. He will also sell you the Mach3 license very reasonably.

If you need a computer, Tiger Direct has off lease values for $250 w/1 yr warranty.

http://www.tigerdirect.com/applicati...415&CatId=2646

You may also be interested in this very nice ready-to-go 4th axis:

http://kdntool.com/_sgt/m3m1s1_1.htm

That will give you a bolt up and play system with very little effort or investment.

You can go the same route with the lathe if necessary.

CR.

[kwyrbndr]

Thanks, CR.
The mill and lathe are "cnc-ready" from sherline. The motor mounts have temporary covers and are fitted with the original cranks, so that pretty much leaves the choice of motors. There must be variables, galore here. What should I be looking for in a quality motor?
The Sherline box and 5 motors is on special for $735, til the end of the month. I am assuming the new Gecko will outperform this older design. Am I correct in this?
Thanks, again.

Ken

[Crevice Reamer]

I would assume so. Firstly, you DO realize that the sherline 4 drive box only powers EITHER the mill OR the lathe? You would have to transfer the box between mill and lathe.

The Sherline motors are fairly small. I know you don't need HUGE motors, but.... To get full power from the Sherline motors would require 50 or 60 volts. I doubt the Sherline board or PS is rated at even 36 volts.

The G540 definitely will provide more fault protection, power cability and compact size. You MIGHT be able to get two separate systems for mill and lathe for not much more than what Sherline wants for 1 1/4 systems.

But the Sherline system has the advantage of being available right now.

CR.

[Crevice Reamer]

Motors in this weight range are relatively cheap. I would imagine that Tom Caudle will package high quality motors.

To get an idea of stepper motor cost in the Nema 23 < 200 Oz. class:

http://kelinginc.net/NEMA23Motor.htm

I think the Sherline kit includes 135 Oz motors.

CR.

[Crevice Reamer]

That link doesn't work. try THIS one:

http://kelinginc.net

CR.

[kwyrbndr]

...I'm more concerned with making the "righter" decision than getting it right now. After looking at the options you mentioned, CR, and following an extrodinary numbrer of links to related information, I see that I have really, two purchases to make.
Firstly, steppers/servos... then, someone's driver box ( and a power supply). Mach3, being a given.
Will servo's actually translate to usable differences in precision for my application?
Are they any quieter than steppers? For the light loads I see myself using this mill for
It's becoming clearer to me, that choosing the drivers and power supply is the decision which will define the performance of the machine.
The Sherline box comes with a 24 volt supply. That's what I see with most of these small retrofit packages. Need I be concerned with using a higher voltage?
Am I on target?
I have a Sherline cnc rotary table already, but that cute little a-axis could make an interesting trunnion setup for working domed wedding rings.

Thanks for all your help
Ken

[Crevice Reamer]

Stepper motors work by pulses of current, not constant current. They work BEST when powered by up to 20 times their rated voltage. (Provided the DRIVERS are rated this high. The Sherline driver is probably only rated for 24 volts.

The higher voltage allows the motor coils to charge much more quickly--Hence more power & speed. Sherline motors are rated 3.2V. 20 times that is 64 volt. Running these motors at 24 volts seriously underpowers them. An underpowered stepper motor will stall and lose steps more easily. Now a motor rated at 1.2 volts would perform best with a 24 volt power supply.

Since your machines are already CNC ready, The new G540 packages should allow you to CNC them with steppers for the most reasonable cost. It will be up to YOU though to verify the power supply voltage/stepper rating ratio and get the best performance.

Steppers VS Servos:

http://www.arrickrobotics.com/motors.html

http://www.woodweb.com/knowledge_bas...er_motors.html

http://www.cnczone.com/forums/archiv...p/t-17419.html

http://www.torchmate.com/motors/elec..._selection.htm

This is heavily biased for servos:

http://www.imsrv.com/deskcnc/steppers_vs_servos.htm

CR.

[kwyrbndr]

WOW!! THANK YOU!
So concise! Now, I'm getting a grip.
I learned my basic electronics as a young man, so I've long been confident with building small projects and repairing stuff around the house... but motors? Never been there. Thanks, CR!

I'll keep you posted as the project proceeds. (...and I will most certainly wait for June.)
Ken

[Crevice Reamer]

You may already know all this, but here is a basic CNC primer of sorts:

MACH3 is the hobbiest defacto best computer software for machine control. It can control either Steppers or Servos. Mach operates by sending out pulses to to the drivers that control the motors. The NUMBER of pulses is limited by the speed of the computer and by an upper limit. 35 to 50 thousand pulses is an average amount.

BREAK OUT BOARDS: Mach3 uses the many wires in a parallel port (printer) cable to send control from the computer to the drives. Rather than fastening each tiny wire in the cable to its destination, the breakout board accepts the cable plug and then puts each wire on an accessable screw terminal.

BACKLASH: When reversing direction, any handle movement that does not also move the axis (or table or head/quill) is backlash. It is measurable directly by the dial on the handwheel. For CNC, backlash must be checked and adjusted often. Backlash will turn a circle into a vague blob.

RAPIDS: Non-cutter axis moves to get quickly from one point to another. These are cumulative, so if they are slow it slows down the whole job.

ACME SCREWS are the standard for most manual mills. They are just a relatively close tolerance screw thread and give fairly high precision and backlash while the adjustment lasts.

Acme screws and nuts wear quickly. Usually the screw wears most in the middle and less on the ends. After a while, you can't use the ends because it's too tight.

Even relatively cheap ballscrews, which HAVE some backlash, are better because the backlash does not vary so often. Mach3 can compensate for backlash that doesn't keep getting worse

BALLSCREWS have large threads that allow a ball bearing to roll IN them. The ballscrew nut contains many small steel balls that recirculate inside to reduce friction. The ball nuts can be extremely tight to eliminate backlash--yet still have little friction.

Once ballscrews are installed, manual control is lost. Because ballscrews turn so easily, the table or head will not hold a position, but is free to move on its own. So while you COULD install hand cranks on double shaft motors, you would have to constantly lock the gibs on the other axes and it's just not practical.

Ballscrews come in two types: Rolled and ground. Ground ballscrews are best, but can cost thousands of dollars for just one screw. We small-time automators usually can't afford them.

Rolled ballscrews come in several grades. The better they are for accuracy and low backlash per length, the more they cost. We usually use a medium grade.

If you buy say a six foot length of ballscrew, it needs to first be cut to axis lengths. It is hardened material, so this is usually best done with an abrasive cutting disk.

After they are cut, each end is turned down on a lathe. Because they are hardened, this is difficult to do. One end is usually turned to one diameter to fit a bearing. The other end may be turned to several decreasing diameters to accomodate thrust bearings, threaded for clamp nuts, and turned at the end to fit stepper coupling or pulley.

Once you have determined the LENGTH of the screws you need, there are companies who will make your ballscrews to order.

PULLEYS are used to increase torque by gearing down the motor RPM. However, stepper motors get weaker as speed increases, (To a limit of 800-1500 RPM depending on PS voltage--up to 20-25 times motor rated voltage if the drivers can handle it.) so most of the gain in torque results in lost speed. That's why most stepper motors are connected direct drive.

IPM: Inch Per Minute is the speed rating for the X, Y & Z axis motion. Cutting in a mill usually happens below 30 IPM. But rapids may need to be as fast as possible.

MICROSTEPPING: Some drivers are designed to artificially reduce the distance the motor will turn by electronics. A full step is hardwired at 1.8 degrees and with 200 computer pulses it will complete one revolution. With microstepping set at 10 (Or one tenth) The motor will theoretically take 2000 steps (And computer pulses) to complete a revolution. I say theoretically because microsteps get just a little more vague in size as their number increases. Micro stepping operates at the expense of speed, and promises extremely high accuracy by increasing steps per revolution, but practically 8 or 10 microsteps are the limit. The computer and software can only put out just so many pulses, and the higher the step count, the slower the motor will run.

CONTROL DRIVES:

Stepper drives are the electronics that translate the pulses from the computer into useable current for the motors. They are fairly expensive and many are easily damaged. Wiring the drive wrong or disconnecting it during use will destroy most drives. Generally, the more expensive drives (Like the Gecko G203 Vampires) offer the best features like overheat protection, micro stepping and speed morphing. Steppers tend to get hottest standing still. Overheat protection will 1. Cut the current down, and 2. Put the motor in "sleep" mode after a short wait. Both will drastically reduce heat buildup. Morphing changes the speed to micro step at low speed accuracy, but jump to full steps for high speed rapids.

PID: A Proportional–Integral–derivative controller (PID controller) is a generic control loop feedback mechanism widely used in servo control systems.

Servo Drives that WE can afford, use basically the same pulse system as stepper drives. Actual expensive commercial servo drives use a different, more expensive system.

GECKO DRIVES are generally acknowledged as the best. Gecko "Vampire" drives are virtually unkillable.

The new low-cost Gecko G540 board (Accepts up to 50 volt power supply) will combine four axes of tiny cheap drives with a "Vampire" morphing breakout board so that all you need to connect is the parallel cable, power wires, and motor cables. In a short while, CNC conversion is going to be a LOT easier and less expensive.

SERVO MOTORS, which are more expensive, do not have the starting torque that steppers have, but they maintain what torque they have into high rpms. They are usually geared down 2 or 3 to 1 to gain starting torque. Even geared down, they can still attain thousands of RPM, so speed is not a problem with pulleys. Servo motors are also equipped to tell the computer (through encoder feedback) exactly where the motor is at any given time so there are no missed steps. Stepper motors can stall and miss steps unbenownst to the operator until the finished part is measured.

CPR: Count Per Revolution.

PPS: Pulse Per Second.

Encoders: These send position and speed feedback to the controller and are rated in CPR. They are quadrature devices that require 4 times the PPS per revolution. For example: An encoder rated at 250 CPR, will require 1000 drive Pulses Per Second.

Each system has its pros and cons. Steppers used with proper power supplies are reliable, consistent and cost effective--That's why most hobby applications use steppers.

POWER SUPPLY: Both types of motors run on DC Voltage. The power supply simply converts ordinary alternating current into this direct current. Stepper motors need around 20 times their rated voltage to perform at their best. For example, a motor rated at 2 volts will perform best, without stalling or losing steps, with a 40 volt power supply.

NEMA SIZES: Both steppers and servos may come in different Nema flange sizes. We usually use either the smaller Nema 23 or the somewhat larger Nema 34. The torque may overlap between the sizes, but generally the larger motor has an easier time.

For example, a 500 oz Nema 23 stepper motor will be working hard (and getting hotter) to attain the torque at which a 500 oz Nema 34 will be easily cruising. Generally, power is added by extending the length (stack) of the motor.

RESOLUTION: The measured (In mm. or inch) amount of accuracy possible in an axis move. This is a combination of number of steps per motor revolution and number of turns per inch of the lead screw. For example: A direct-drive Stepper motor with driver set for full step will take 200 steps for one full revolution. If that revolution turns a ballscrew with 5 turns per inch, then there will be 1000 steps per inch or a resolution of one thousanth of an inch. (.001) If that same motor was turning a 20 turn per inch Acme screw, the resolution would be 4000 steps per inch, or 4 thousanths of an inch. (.0004) Pulley or gear ratios add to the resolution.

CR.

[kwyrbndr]

You are UNbelievable!

This should be a "Sticky" at the top of the forum.

Thank you thank you thank you!

Ken

[Jaime128]

I was reading up on the ball screws last night and others because I'm thinking of making my own cnc setup someday. I want to have the Z axis ball screw behind the column though, just to keep all chips off. Kind of like what the new x2 will be. I have no idea what their setup is, but I've been playing around with the design in my head since I started reading about the DIY cnc. I then saw your posting today and well, your info just added to the little of what I have read. I'm just a little torn now because I like to have the manual access on the machine. I don't want to have a computer on all the time, and well, it's something to think about newbies and I'm glad I'm doing my homework before I even do or buy anything. You either have one or the other, but just due to the way both system work, manual vs. cnc you can't have it both way...hehe. When people tell me that it can't be, that's when I like to see if I can prove them wrong, but I think this one has been tried and true so darn...might be out of luck on it now...

[Stepper Monkey]

There is a lot of good advice on what is best, like for example ballscrews over acme, or servos over steppers, but for you newbs you have to remember there is a big difference between "better" and "unacceptable". We don't make that distinction enough here, and while debating finer technical points of things people get the idea one or the other is actually bad or undesirable. In many cases the differences are so slight when dealing with a small machine, especially one that isn't run continuous production duty. Things like wear will usually take years to appear on the nut for an acme screw setup, and the nuts are trivial and a few dollars to replace. Running proper nuts, actual screw wear is unheard of in any reasonable time scale. Even then IT is trivial to replace and only costs ten bucks. I'm not about to argue that ballscrews aren't nicer to have, I use them too, but are they really a big deal to insist on for a first hobby mill? Usually not, which is why most hobby mills don't have them. Most of their advantages don't even apply on small CNC mills, while their problems still do.
I guess my point is that while debating some of those differences, a newb looking for a first machine can get very confused and get scared away from options that are perfectly safe and reasonable ones. Sometimes even optimal choices for them, simply through the magnified fear of one of its style of part. Especially with the commonly seen fear ingrained by misleading (to be polite) servo sales literature of buying anything that doesn't have servos. This often drives newbs to spend way more money than they needed to on the drive system and be able to afford less of an actual mill in the end because of it. As well as they often don't even wind up with a true servo system in the first place, or even worse a cheap brushed system inferior to steppers in the first place. In any case a more fragile and complex system, usually the last thing they needed.
Take most of this stuff with a grain of salt. There is a solid reason the lower tech systems are still out there, so don't fear them. Quality of the system and its suitability to you needs are far more important for you to focus on than some specific type of part, regardless of how many buzzwords get thrown in.
It's Cost/Benefit you should be looking at, and just like with tuning cars, its the last couple horsepower that cost more than all the rest combined...

[kwyrbndr]

Yes, Steppermonkey! I have to agree. Even at 62, I still unconsciously am drawn to seek out and include the coolest design feature or function when evaluating any given purchase, Boys and toys syndrome, I guess... built right in us.
So, with a clear morning mind, I have composed the following statement:

>What I want to accomplish here, plain and simple, is to retrofit of my existing mill and lathe, to include a level of automation needed to be able to machine tool steel, aluminum, precious metals and wax. It should be capable of enough resolution and "finesse", to be able to draw a .5mm circle in any plane, which looks circular, and, to accomplish the action at a rate that will initially make me giddy.<

Steppermonkey, since we work on similar sizes and materials and you've covered more ground, please feel free to contribute to the above.

Thanks, all.
Ken