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Old 11-19-2014, 05:10 PM   #81
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Chuck,
Thanks for taking the time for such a detailed response. It was very helpful and I believe I have about figured out what to do. What started this is a friend gave me a couple of stepper motors and drivers and I have always been interested in cnc at home for my hobby projects. My used mill came with ball screws already installed so I have a little bit of a place to begin. Now to convince my wife to let me spend the money. I will probably just buy a piece at a time and work at it.
Also I want to be able to loosen the belts and back the cnc away and use manual if I need to. I liked the brackets you made for your steppers. I will do something like that.
Thanks again,
Mike


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Old 11-20-2014, 12:06 AM   #82
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Mike, I forgot to mention that Home Shop Machinist magazine featured a multi-part article on converting a mill / drill to CNC. I had found it to be interesting and helpful even though it was published starting in May 1990. Hardware hasn't really changed much since then although it has gotten cheaper, thanks to the Chinese!

I would definitely encourage you to move forward on the conversion. You'll be sooooo glad you did. It's really fun and interesting to see what you can do.

If you've already got your ball screws installed and stepper motors on hand, you've got a real good start. From a budgetary standpoint, this Stepper Controller is a lot cheaper than the Gecko G540:

http://www.ebay.com/itm/221464800449...%3AMEBIDX%3AIT

I'm starting a CNC Router Build and bought this controller to use with it. I've read mixed reviews on it, but at that price, I figured I'd give it a try. For the software, you can download a free version of Mach 3 and use it indefinitely as long as your g-code file doesn't exceed 500 lines. It also has some built in wizards that let you cut profiles, pockets and drill holes without the need for CAD or CAM software. And, if you can write your own g-code, you can do some pretty neat things in a lot less than 500 lines of code. All this will let you get started with your CNC machine and buy or upgrade the software later.

Chuck


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Old 11-20-2014, 08:13 PM   #83
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Chuck,
Thanks again for your time. I will keep you posted on my progress and may have a few more questions along the way.
Mike
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Old 11-25-2014, 08:50 PM   #84
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Default Timing sprockets and belts

Chuck,
I looked like you made your own timing gears/sprockets. Is there a certain type of belt that I need to use? Sources?
Thanks again, Mike
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Old 12-17-2014, 08:29 PM   #85
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Default Timing sprockets and belts

I have done some more research on my own and found several sources for belts and pulleys. They are quite expensive. I can see why you would machine your own. I may buy one for a sample and do the same.
I have purchased a breakout board and am building a power supply for the steppers. I will post some pictures when I have something to show.
Mike
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Old 12-17-2014, 10:51 PM   #86
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Give serious thought to using a direct shaft connect, no belts or pulleys. Look at a modern machine, like a Tormach and you will see that is what they did. Before the modern hi torque steppers pulleys were needed to get some torque boost, that is not the case now, particularly on a small machine. The only reason for using belts is when you need to get the motor into a position to keep it out of the way.

I would also stay away form those ebay driver boards, they are really poor drivers. When you are spending several hundred dollars on a project you will soon forget you saved a few bucks on a driver when you get less than the best performance.

Last edited by RonGinger; 12-18-2014 at 12:54 PM.
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Old 12-18-2014, 04:00 PM   #87
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Mike, sorry, I hadn't visited this thread for a while and didn't see your question regarding the pulleys. The pulleys and belts are the XL series which are 0.2" pitch. I've bought pulleys and belts on EBay when I could find them at a reasonable price and I've made them. The cutter is made froma 2" x 3/32" thick slitting saw.



If you do a Google search on XL timing pulley dimensions, you'll find lots of diagrams showing the tooth profiles, depth, and pitch diameter. I made this cutter a number of years ago and as I recall, I just mounted the cutter in the lathe and used a tool post grinder to bevel the sides of the teeth with the cutter spinning. There is no side rake or clearance on the teeth, which is not ideal, but it works OK for cutting aluminum pulleys. A suitable fly cutter with proper rake and clearances could be made quite easily and would also be fine for cutting aluminum. Belts are sometimes available in the right size from Ebay or you can get them from Mcmaster and Grainger. Stock Drive Products also has about any size you need, but their shipping costs tend to be prohibitive.

Ron, I used pulleys and belts on my machine because I didn't want the motors, which are pretty long, sticking out so far from the machine, particularly in my rather cramped workshop. I also felt like I needed the extra torque of gearing them down since my Nema 23 steppers may not be quite beefy enough for direct drive. It also makes it easier to use the machine manually by just removing the belts. Nema 34 would have been more suitable, but the jump in cost is considerable, not just for the motors, but the larger power supplies and stepper controllers needed for the higher amps.

Chuck

Last edited by cfellows; 12-18-2014 at 04:04 PM.
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Old 12-18-2014, 08:11 PM   #88
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Chuck,
No need to apologize, I realize people are taking their time to answer lots of questions from me, but it is appreciated. Thanks for your advice and the many threads we learn from. I will let you know once I make some progress worth reporting. Still in the parts collecting, learning stage.

Ron,
Thank you for you input. I agree with you completely that to have a quality system I will need to spend the money. I am having to experiment on the cheap for now, because of budget. What started me down this road is that a friend upgraded his Tormach mill and gave the the old style steppers and some micro step drivers. I believe they are probably powerful enough to direct couple and I believe I have figured out how to do that and still use my machine manually. I am putting these on a bridgeport size mill that I pieced together over the years and it also happens to already have ball screws installed. I my bother you folks with more questions as I go. I am building a 48v power supply right now.

Mike
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Old 12-19-2014, 10:14 AM   #89
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I don't know much about conversion to CNC, but I assume that most motors have minimum step of 1.8deg, which on a .200" per rev leadscrew is .001" per step. If you gear it down, say at 2:1 ratio, won't this allow a movement of .0005" per step, as well as help with more torque? I've been thinking about making a CNC mill, just seem to prefer direct drive.

Paul.
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Old 12-20-2014, 12:05 PM   #90
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Quote:
Originally Posted by Swifty View Post
I don't know much about conversion to CNC, but I assume that most motors have minimum step of 1.8deg, which on a .200" per rev leadscrew is .001" per step. If you gear it down, say at 2:1 ratio, won't this allow a movement of .0005" per step, as well as help with more torque? I've been thinking about making a CNC mill, just seem to prefer direct drive.

Paul.
all correct. but there are pros and cons to all.... i wouldn't go with belts on a stepper but i would for a servo. i wouldn't gear down a stepper but i would a servo and so on.

if you do gear down a stepper say 2:1 you would be right in saying you would double your torque and half your resolution, but you will also half your rapid speed. to get your resolution back..... most if not all drives have micro stepping, so the drive will split 1 step of a stepper (1.8deg) into 10 for e.g. now you have a stepper doing 2000 steps per rev or 0.18deg per step. this in turn opens up another can of worms over torque issues.

using belts is another place where backlash can creep in. if you do need to gear down to get more torque, put bigger steppers on it. then the cost will go up, but will the cost of a bigger stepper out way the cost of pulleys, belts, mounts and time and effort in making it all.

there are lots of options all depending in what YOU want out of YOUR cnc mill. you just need to find what you need to fit your requirements...... then add 30% to it.


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