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Old 11-25-2013, 11:58 PM   #21
cfellows
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Originally Posted by LSEW View Post
Chuck, that is good placement for your "Y"motor. Good thinking. On my conversion the pulley for the "Y" limits the travel a little, making parts with just over 8" in the "Y" impossible.

You may want to also check out the pulley size for the "Y" so this doesn't happen to you. You will want all the "Y" you can get.

maury
Thanks, Maury, the pulley on the Y-axis sticks out far enough that clearance isn't an issue.

Luc, thanks for the tip. I'll give that a try when I get the drivers and motors hooked up.

Shepdog, you're welcome to whatever drawings I have, although I don't know if they'll be any help to you unless your machine is substantially the same as mine...

The angular contact bearings came in the mail today so I spent the rest of the afternoon and evening getting those installed. Since I was installing the bearings in the original bearing block casting, I went very slowly and was very careful not to screw something up. I did have one close call... I was very near the final OD and decided to press the bearing in and see how it fit. It wasn't real tight, but getting it back out was a wooley booger! I did finally get it out and bored the opening a little bigger so it is a sliding fit with no slop.

I also installed a regular ball bearing on the motor end of the X-axis ball screw. All the feed thrust is on the other end of the table which has dual thrust bearings, so this end just needs to handle the radial force from the belt. Also, in addition to the set screw which holds the extension onto the Y-axis ball screw, I put some Loctite 620 on it and also pinned it with a roll pin.

So, I ordered some connectors like these:



to connect the motors to the cables. I'm currently planning on using 4 conductor , 18 gauge stranded wire for the cables. Is that what most folks use? I'd like to use coiled cable like they used to use on telephone handsets, but have no idea where to find anything like that in the gauge I need. The other end of the cables want DB9 connectors for the Gecko G540.

Chuck


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Old 11-26-2013, 12:36 AM   #22
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Chuck
here is the answer to your cable
http://www.cablescience.net/power-co...67b7905c1fc66b

enjoy


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Old 11-26-2013, 02:03 AM   #23
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Thanks, Steve. The motor inductance is 6.8 mh per phase, 1.6 ohms resistance and are rated at 3 amps. The holding torque is 280 N cm which converts to about 396 oz in. I bought a 24v, 15 amp power supply specifically for this application, but could buy a different if there would be a significant performance boost. The driver is a Gecko G540 and will handle up to 50 volts DC for the motors.

As you said, speed is of little consequence to me. I have 20 tooth pulleys for the motors and either 48 or 60 tooth pulleys for the ball screws.

Here's the Y-Axis motor mount. It will be attached to the mounting arm with two 5/16" bolts through the 1 5/8" long slot. The bolts will be 3/4" apart which will give me 3/4" belt adjustment.



I realize this could still slip, but with two bolts holding it, it should be much more secure.

Chuck
according to the math the drives would want 83 volts. The drives you selected max out at 50. You might be happier with a 48 volt power supply if you can find one.

Also something to think about. You probably bought one of those regulated power supplies. They try to maintain a constant output. The gecko drive is going to be taking an input voltage and trying to turn that into a constant current to the motors. Sometimes the two will try to fight each other and you might get some erratic behavior or some missed steps that are random. Best power supply for the geckos is a simple supply using a transformer, rectifier, and some capacitors.
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Old 11-26-2013, 06:30 AM   #24
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according to the math the drives would want 83 volts. The drives you selected max out at 50. You might be happier with a 48 volt power supply if you can find one.

Also something to think about. You probably bought one of those regulated power supplies. They try to maintain a constant output. The gecko drive is going to be taking an input voltage and trying to turn that into a constant current to the motors. Sometimes the two will try to fight each other and you might get some erratic behavior or some missed steps that are random. Best power supply for the geckos is a simple supply using a transformer, rectifier, and some capacitors.
Thanks, Steve. I do have a large Variac that I can dial anything from 0 - 140 volts at up to 30 amps. I've also got some pretty beefy bridge rectifiers that will handle up to around 25 amps. I guess all I need is a large capacitor and I'm set. Wonder if I'll have any problem with grounding?

Chuck
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Old 11-26-2013, 10:14 AM   #25
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Thanks, Steve. I do have a large Variac that I can dial anything from 0 - 140 volts at up to 30 amps. I've also got some pretty beefy bridge rectifiers that will handle up to around 25 amps. I guess all I need is a large capacitor and I'm set. Wonder if I'll have any problem with grounding? Chuck
Whoa Chuck, you don't want to use a Variac here! Most variacs don't isolate from mains, I'd much prefer that you go with a regular step down transformer. That and an inadvertent adjustment would likely fry things. The trick here is to find the right voltage output to keep you comfortably under the drivers maximum voltage. You could also wind your own transformer if you are into that sort of thing. I know sourcing the correct transformers is a pain, that is one reason why buying a transformer from a CNC parts vendor is so popular.

Another issue, as DC voltages increase you need to be far more careful with respect to your safety. The possibility of electrical shock will become an issue at higher voltages. I mention this only because people are less cautious around the common 24 VDC and less supplies and often forget to be safe when higher voltages are present.
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Old 11-26-2013, 04:10 PM   #26
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according to the math the drives would want 83 volts
Steve--- how did you come out with this number
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Old 11-26-2013, 05:32 PM   #27
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Whoa Chuck, you don't want to use a Variac here! Most variacs don't isolate from mains, I'd much prefer that you go with a regular step down transformer. That and an inadvertent adjustment would likely fry things. The trick here is to find the right voltage output to keep you comfortably under the drivers maximum voltage. You could also wind your own transformer if you are into that sort of thing. I know sourcing the correct transformers is a pain, that is one reason why buying a transformer from a CNC parts vendor is so popular.

Another issue, as DC voltages increase you need to be far more careful with respect to your safety. The possibility of electrical shock will become an issue at higher voltages. I mention this only because people are less cautious around the common 24 VDC and less supplies and often forget to be safe when higher voltages are present.
Thanks for the warning, Wizard. I'm always a little concerned about using variac's to run anything other than a motor. Can you point me to any vendors who sell transformers?

Chuck
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Old 11-27-2013, 01:38 AM   #28
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Steve--- how did you come out with this number
You can read the whole story on the Gecko website but here are the highlights.



The voltage of your power supply is entirely dependent on the inductance rating of your motor, which we learned is translatable to the number of turns of wire in the stator. Every motor model will have a different inductance rating and will therefore have a different maximum voltage. To figure out what the maximum power supply voltage should be, use the following formula with the motorís inductance in millihenries (mH) used for the L value.

32 * VL = VMAX

If you are using several different models of motors on the same power supply use the lowest inductance rating in the above formula. This will ensure that your motors will not overheat due to the voltage being too high.


I think my drives are fed with some 60-65 volts but my drives max voltage is 80. Chucks is only 50 so cant exceed that ever. In his case I would go 48 if possible. To get 48 DC the ac input voltage needs to be about 34 volts. CNC suppliers have some wierd voltage transformers so its possible but not likely. At any rate he will need about 125Watt minimum if he uses the 4th. Also will need a 1500-2000MFD capacitor as close to the input of the drive as possible.
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Old 11-27-2013, 02:59 AM   #29
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Hi Chuck

I have been enjoying your CNC conversion; thanks for taking the time to post your progress.

I converted my kneed mill years ago with an AhHa system (long out of business);p about 3 years ago I started a project to upgrade to servos, MACH and a quill drive. Originally I only did the X and Y.
Things kind of got side tracked and well here I am 3 years later getting going on it again.

I was able to get my old controller interfaced with MACH using a break out board from Homan Designs; what a major improvement from the old DOS program both in functionality and speed. I was able to double my rapids using MACH.

I curious to see how you handle your operator interface control panel etc.

I have resurrected my project and hope to make some progress on it this winter.

Thanks again for keeping us updated on your CNC project.

Dave

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Old 11-27-2013, 05:01 PM   #30
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Thanks for the update, Steve. For the time being, I will plan on using my 24 volt switching power supply. I'll look to upgrading to a transformer system if I run into problems.

Another question, what are you CNC guys using for CAM? I'd like to keep my CAM cost under $300 if possible. Most of my work can probably be handled by 2.5D but might want full 3D from time to time.

Chuck


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