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IndustryArena Forum > MetalWorking Machines > EMCO CNC Machines > EMCO Mills > Seanano's Emco PC Mill 50 retrofit
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  1. #1
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    Seanano's Emco PC Mill 50 retrofit

    This thread is to describe my retrofit of an Emco PC Mill 50. I picked up the mill in February of '17 from an auction at a local university. The guy that ran the shop said he hadn't seen it run in the 10 years he had been there. It came with a bunch of tool holders, manuals, and even a CD and floppy disk that supposedly had the Emco software on it. No dongle or PC board to control it. They had it on a pallet so we used a pallet jack to roll the approximately 350 pound mill onto a tilt trailer.

    Attachment 390148 Attachment 390150

    Unloading at my end was easy... I don't know how I got along without a skid loader for so long. That thing is really handy.

    Attachment 390152

  2. #2
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    Seanano's Emco PC Mill 50 retrofit: Cleaning

    The mill was pretty dirty and had surface rust on various parts. I pulled the table and saddle and de-rusted them with naval jelly and #0000 steel wool. Then they were dunked in water to neutralize the acid, followed by a soak in WD40 to get rid of the water, then rubbed down with oil. The same process was done on the 6 tool holders (ER25 collet holders). The headstock was removed and the Z and Y ways were cleaned with WD40 and #0000 steel wool. I flushed the ballscrew nuts with spindle oil until they ran clean and then repacked them with new lithium grease. All axis use double nuts so I had to re-adjust since they were taken apart. I found a service manual pdf for the F1 CNC and followed the instructions they gave for getting the ballscrews aligned when re-assembling.

    Attachment 390154 Attachment 390156 Attachment 390158 Attachment 390160

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    Seanano's Emco PC Mill 50 retrofit: Lubrication

    The oiling ports require a fairly fine tip and none of my 5 oilers would work with it so I made an adapter out of a MIG welding tip. This made quite the mess just pushing an oiler into the back of the adapter so I made a threaded barrel for one of the oilers that would accept the M6 thread of the welding tip. This is less messy but the oiler still leaks pretty good when under pressure. I can see oil oozing out of the ways when I do this so it is definitely working. For oil I am using Mobil Vactra #2.

    Attachment 390162

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    Seanano's Emco PC Mill 50 retrofit: Axis motors

    Now on to the actual retrofit. First step was to determine what axis motors to use. The original stepper motors were 5 phase and pretty low torque. From the documents I have, the original max feed rate was around 30 inches per minute on each axis. This was with a 2.5mm pitch ballscrew and a 2:1 belt drive reduction. Given this, the original motors were driven to a max speed of 609.6 RPM ( ((30 ipm * 25.4 mm/inch) / 2.5 mm/rev) * 2). I wanted a bit more speed from the retrofit, around 70 IPM. To keep the original ballscrews and pulley ratio, that meant I would need the stepper to have sufficient power for rapids at a little over 1400 RPM. The recommendation I have seen from others that have done this conversion is around 2 NM (280 oz in) of holding torque.

    I decided to go with 276 oz inch NEMA 23 steppers from Automation Technologies (KL23H276-28-4B). These motors are wired for bipolar parallel and rated for 2.8 amps and 3.6 mH inductance. The torque curves showed that with 48 volts the motors should still have 90+ oz-in of torque at 1400 RPM which is about what the original motors were rated for holding torque. 48 volts and 2.8 amps falls within the range of the Gecko G540 so I went with that for the stepper drivers due to Gecko's reputation and the tiny package for 4 axis drivers. To power the G540, I bought a toroid transformer (Antec 5234) that outputs 34 VAC which when rectified and filtered should be close to 48 VDC. I used an 18000 uF 100 VDC electrolytic cap for the power supply filter. Installing the motors was mostly straight forward. The original motors were close to a NEMA 23 mounting but the holes for the mounting screws didn't quite fit so I rotated the motor slightly and drilled and tapped new mounting holes. The original motors have a 6mm output shaft but the new motors have a 1/4" (6.35mm) shaft. To fit the pulleys to the new motors I used a 1/4 inch chucking reamer and reamed each pulley on my lathe. Instead of drilling the motor shafts for a roll pin as was originally done, I used Loctite 609 retaining compound to glue the pulleys to the shafts. I did some calculations based on the surface area that would be wetted by the retaining compound and I think there should be plenty of margin to be able to support the full torque of the motors.

    Attachment 390166 Attachment 390168

  5. #5
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    Seanano's Emco PC Mill 50 retrofit: Spindle motor

    The original spindle motor is 3 three phase and rated a little over 1/2 horsepower and 1670 RPM at 60 Hz based on the voltage. The spindle is belt driven from the motor with a 1.7:1 reduction. The Emco docs I have show a max spindle speed of 2500 RPM which correlates to a max motor speed of 4250 RPM which correlates to approximately 150 Hz depending upon the voltage. I wanted to run the entire machine from 110 VAC to make it easier to sell when the time comes. Finding a 110 VAC VFD that actually outputs 200+ VAC was more challenging than expected since most of the no-name ones output the same voltage that is input (110VAC in this case). I went with a Hitachi WJ200-007SF which fully supports outputting the voltages necessary for the motor from 100 VAC. I went with the Hitachi in part because I already had another WJ200 for my lathe and used that one to test the motor and it worked well. The Hitachi supports a variety of input and output (10V analog, modbus) so I was confident I could hook it into whatever control I went with.

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    Seanano's Emco PC Mill 50 retrofit: Control

    As for the control, I had originally planned to use LinuxCNC with an ethernet connected Mesa card (7I92). However, while I was working on this I picked up another CNC mill that I want to retrofit that would be better suited to the configurability that LinuxCNC provides so I decided to get a different controller for the Emco. The Centroid Acorn had been getting good reviews since its release so I thought I would give it a try. It has specific requirements for the PC which my Linux box didn't meet, so I turned to eBay and found a used Lenovo M92Z All In One with an i3-3320, built in wired and wireless networking, and a 23 inch touchscreen for a good price. It didn't come with a hard drive so I picked up an 180GB Intel mSATA SSD. I loaded Windows 10 on it and followed the instructions on configuring it for CNC duty as per the Centroid site. Installing the CNC12 software went without a hitch.

    Attachment 390170

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    Seanano's Emco PC Mill 50 retrofit: Wiring

    Since I went through multiple control options and wiring options the control box layout isn't as clean as it perhaps could be. I reused the original grey wiring ducts, IEC power port, key switch, and DIN rail mounted fuses. To make sure I had enough space for everything I mounted the transformer, rectifier, and filter for the motor power supply on the horizontal part of the mounting plate. The G540 was mounted on a couple of right angle brackets I made out of the original card cage. It was positioned to be over one of the cooling fans. Speaking of cooling fans, the original fans were 220VAC but I didn't want to retain the original transformer or switch to 220VAC input power. Instead, I picked up a couple of 24 VDC ball bearing fans and used the 18V output of the Antec transformer along with the original rectifier and filter cap to supply the 24VDC for the fans.

    The machine already had home/limit switches, Emergency stop switch, and a door switch. The home/limit switches tested fine and could be used as is. The Emergency stop switch worked intermittently so I replaced the 2 internal contact switches (ZB2-BE102). The door switch tested fine but I doubt I'll be actually using it. All switches are wired as NC (normally closed) with one side tied to digital common.

    I originally wired the limit switches and emergency stop through the G540 but was getting some spurious triggers. By switching the inputs directly to the Acorn those triggers went away. The G540 now doesn't have the E-stop wired to it, but since it isn't a servo drive and has the charge pump enabled, I don't think this is much of a safety concern. The other E-stop circuit is wired to the GS1 and GS2 inputs on the Hitachi VFD. The VFD is using 2 digital outputs from the Acorn for forward and reverse and the 10VDC analog output from the Acorn is used for speed control. There are still a few inputs and outputs left on the Acorn to support additional functionality (coolant, air, probe, encoder for rigid tapping, etc...).

    Attachment 390172 Attachment 390174 Attachment 390176 Attachment 390178 Attachment 390180

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    Seanano's Emco PC Mill 50 retrofit: Initial Testing

    Initial testing has gone well. I was able to easily hit the 70 IPM I was shooting for on all axis. I kept turning up the max jog speed waiting for the motors to stall but stopped when I hit 200 IPM with no stalls. That seems way too fast for normal use (ballscrews turning 2000+ RPM) so I set it at 80 IPM max speed per axis. I currently have the limits set at 7.25" for X, 4.25" for Y, and 7" for Z. To get the 4.25" from Y I had to remove the two hex stop bolts. More travel could be had but that would require modifying the Y axis covers (front cover would need to be cut or extended, rear cover would need some changes around the limit switch trigger point). Spindle control works well both forward and reverse up to max speed. I have done some basic cuts using manual code entry. My next steps will be to continue tuning (G540 motor tuning, accel settings) and to start learning Fusion 360 so I can actually start making some parts.

    Attachment 390182

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    Seanano's Emco PC Mill 50 retrofit: Original parts

    If anyone is interested in parts that were removed please PM me. I've got the main transformer, all axis motors, and the control boards. I can't guarantee they will work, but before tearing it apart to clean and retrofit I powered it up and verified motors had holding torque and the home/limit switches would change the LED states.

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    Re: Seanano's Emco PC Mill 50 retrofit

    I got some more done on the mill this past weekend. I added some cable clamps to provide some strain relief of various cables. These were 3D printed and then stuck down with double sided tape. I also added a panel mount RJ45 pass through port so I don't have to run the ethernet cable directly from the PC to the Acorn. The terminal is shielded as is the new short cable running from it to the Acorn. I used a step drill starting in the hole left by the original DB9 connector.

    Attachment 391062 Attachment 391064

  11. #11
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    1st Part

    I attempted a first part last weekend on the mill. I used Fusion 360 for the CAD and CAM. Here is the part on the fixture plate:

    Attachment 391296

    This stock is 1" x 1.574" x 4.074" 6061 Aluminum. The odd dimensions are so it can be clamped on the fixture plate. The fixture plate has holes every half inch. Some are reamed 0.250 and most are tapped 1/4"-20. There are three pins that hold the part for reference and 3 MiteeBite clamps with 1/4" screws to keep it from moving. The clamps specify 0.301 from the center of the hole to the edge of the clamp and the pins are 0.125 from center of the hole to the edge. MiteeBite says shims can be used but this being my first attempt I didn't want to deal with another variable. Milling and spot drilling went well. The drilling not so much. This was the third op which was drilling with a #9 drill bit to a depth of 0.7". I used the Rapid Out Drill cycle. Should have used Deep Drilling (Peck Drilling) cycle. Here is why:



    The bit made it 0.6" before the spindle ran out of power and stalled. Then during the retract cycle it yanked the part out of the fixture clamps and the spindle started spinning again heading back to 2500 RPM. The part was very imbalanced and the rotation quickly caused the drill bit to snap and the part to get thrown. It made a nice dent in the Z axis ballscrew cover...

    Attachment 391292

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    1st successful part

    Learning from the failed attempt, I tried again this weekend. For reference, here is a picture of the part:

    Attachment 391298

    It is a fixture for another part. I made some minor changes to the part from the first attempt. Obviously I changed the drill cycle for the two holes. In addition I added a chamfer and messed around with the strategies for the milling. Here is another piece of stock ready to go. Note I added an additional clamp as well.

    Attachment 391300

    Here is the machining:



    I definitely need to work on the machining strategies, but it did work!

    Attachment 391302 Attachment 391304

  13. #13
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    Centroid configuration

    Here is the setup for the Acorn in the mill wizard:

    Attachment 391696 Attachment 391698 Attachment 391700 Attachment 391702 Attachment 391704

  14. #14
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    Re: Seanano's Emco PC Mill 50 retrofit

    Are you still using the factory ballscrews on this machine? I am having terrible luck with mine. I have done the control retrofit using a Gecko G540 and Huanyang VFD. But twice now, the x-axis ball screw has blown up. I didn't blow it up the first time mind you, I got the machine that way. I tried to repack the balls into the nut but found the recirculating tube was damaged. I was able to buy a new nut off ebay. I had to machine back up and running just recently and I accidentally overstroked the x-axis because my limit switch wasn't set right. I was slowly jogging the table and the pulley end very slightly tapped the nut and blew out the balls again. I think I'm going to look into changing out the ball screw for something a little more robust. The trick is going to be finding something that will fit under the table, or I might have to modify the table.
    If there were no rewards to reap,
    No loving embrace to see me through
    This tedious path I've chosen here,
    I certainly would've walked away by now.

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    Re: Seanano's Emco PC Mill 50 retrofit

    I don't have the full history of the mill, but the ballscrews appear to be the original factory ones. They do look identical to the ones you have posted in your thread. I'm pretty sure I did slow jog (10 ipm) at least one axis into a hard limit without issue when I was configuring the limits and I have stalled the Z axis at low speed when machining (spindle stalled when drilling) so I'm pretty sure I've put the full motor torque on the screws. I'm running 2 NM (276 oz in) steppers at 48 volts with the original 2:1 reduction pulleys. Any chance you are running significantly higher torque motors? I haven't seen others complaining about these ballscrews blowing up like that.

  16. #16
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    Re: Seanano's Emco PC Mill 50 retrofit

    I am running higher torque motors. I have 381 oz. steppers. I have my doubts that it was due to that though. I have re-packed the ball nuts a couple times and came the conclusions that the 'catch' that is supposed to keep the balls from getting past the recirculating tube broke off. I don't see a way to fix it either. This 'catch' appears to be a little piece of the recirculating tube that they intentionally leave sticking up in the nut. So I can re-pack the nut, wind it back onto the screw but as soon as I reverse direction, all the balls spill out the other side.

    I have been hunting for a replacement but I have yet to find anything I can make fit without getting into significantly modifying the table.
    If there were no rewards to reap,
    No loving embrace to see me through
    This tedious path I've chosen here,
    I certainly would've walked away by now.

  17. #17
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    Re: Seanano's Emco PC Mill 50 retrofit

    Thanks for the build! I just picked one of these up myself and am doing some research before buying the stuff.

    I keep thinking of questions to ask but then see you've already provided most of the information! When I get closer to putting things together I'll be sure to have more questions about how the electrical stuff worked out, as I don't quite understand how all the voltage changes are exactly taking place.

    Anywho, Thanks again!

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    Re: Seanano's Emco PC Mill 50 retrofit

    Havoc, I'm glad you found my build log useful. Please feel free to post any questions and I'll answer as best as I can (I'm certainly no expert).

  19. #19
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    VFD model information incorrect

    By the way, I noticed I listed the wrong model of VFD that I used. I actually used the Hitachi WJ200-007MF which is the model that supports 110VAC single phase input. The WJ200-007SF only supports 220VAC single phase input. I can't edit the original post so this will have to do.

  20. #20

    Re: VFD model information incorrect

    I realize that this is a pretty old thread, so if you can't answer this no worries - would you happen to have a wiring diagram for the motor or how you wired the motor to the VFD? I'm using one of these spindles for a DIY epoxy granite mill I'm building, but I have next to no info on the motor.
    Attached Thumbnails Attached Thumbnails Screenshot 2021-02-22 103445.png  

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