HERCUS Mill Retrofit
Posted: Wed Jan 03, 2018 6:01 am
Hi Gents,
I thought i would start a thread to show my side project. I picked up an old HERCUS DTM320 from a mate who is a high school tech teacher and has accumulated a bunch of old desktop mills and lathes from his school over the years.
The servo drivers were missing from the cabinet as apparently the machine has done very little work and kept blowing something. It had a breakout board with a serial plug and a bunch of IO and rectified and what not. It may have had the motor control imbedded in the board or the rectifiers may have just been to generate DC power for the DC motors. either way the tracks are fried.
It appears as though a manual mill/drill has been used as the basis for the milling machine as it a bunch of holes and unused cavities in the head which im assuming were for different gear ratios and quill feed.
I stripped it down to figure out how best to go about retrofitting new control gear. I have removed the old DC servo motors and have 2 leadshine AC servo motors and 3 servo drives spare from when we bought our plasma cutter for work. I will need to source a third servo motor but am surprised at how much they cost on ebay. I ordered my acorn board and it arrived just in time for Christmas. I have an old Z400 workstation which i have setup as my CNC PC and will eventually get a touchscreen monitor for it. I bought an omron 2000ppr encoder for the spindle and have wired it up and tested it to be functioning correctly. The shafts on the servos are 14mm and too big to fit the original pulleys so i orders larger ones and machined them to suit the servos. I have ordered longer belts which should arrive in the next day or two.
I have had some trouble getting the NC control to move the servos properly but after much searching online and on here i think my problem has been me trying to shortcut. It would only rotate one direction and very slowly, as soon as i bumped up the speed it would lock up. i thought it might have been set to double pulse but i eventually got a comm cable to work so i could access the drive with protuner and it seemed to be set right. i was too impatient to order the leadshine tuning cable so i used a db9 plug and cut up a rj11 phone plug to make a cable. it took a bit of experimenting but finally got it to work. I can share the wiring arrangement if anybody is interested. Weirdly the RX and TX in the leadshine manual for the drives means RX and TX on the db9 plug not inverse like most are.
Instead of using a separate power supply for the step and direction commands i used pin 19 on the drives which is a 5v output but after going back and reading the specs on the drives this output is only 10mA. I have ordered a dual voltage power supply and am waiting for that to arrive to see if it fixes it.
This is what my cabinet looks like so far.
Luckily as it was already a cnc machine it has the limit switches already in place so next job is to wire them up while i wait for my power supply and timing belts to arrive.
My main unknown has been the spindle motor. It has a 230VDC 600W motor which is what my post was about. Dickybird posted some interesting info and although i had come across a couple KB motor controller and got some pricing from some local suppliers none had suggested the KBCC. I have however already ordered a cheap 1.1kW VFD off eBay and will see how fast i can spin up some old 3ph motors i have laying around.
The other thing which is a bit strange is the Z axis arrangement. It has a ACME thread looking screw with what i would imagine is a rotating nut and worm drive arrangement. I guess this is so the head doesnt sag without power to the drives. At first look there is a tonne of backlash in this arrangement but a lot of that is axial play in the worm shaft and bearings and housing. It also looks like the ratio of rotations to travel is much greater than the ball screws so i would probably change the gear ratio to get a similar rotations to travel ratio as the ball screws so i have similar travel speeds. I would be thinking the servos are plenty big enough.
I thought i would start a thread to show my side project. I picked up an old HERCUS DTM320 from a mate who is a high school tech teacher and has accumulated a bunch of old desktop mills and lathes from his school over the years.
The servo drivers were missing from the cabinet as apparently the machine has done very little work and kept blowing something. It had a breakout board with a serial plug and a bunch of IO and rectified and what not. It may have had the motor control imbedded in the board or the rectifiers may have just been to generate DC power for the DC motors. either way the tracks are fried.
It appears as though a manual mill/drill has been used as the basis for the milling machine as it a bunch of holes and unused cavities in the head which im assuming were for different gear ratios and quill feed.
I stripped it down to figure out how best to go about retrofitting new control gear. I have removed the old DC servo motors and have 2 leadshine AC servo motors and 3 servo drives spare from when we bought our plasma cutter for work. I will need to source a third servo motor but am surprised at how much they cost on ebay. I ordered my acorn board and it arrived just in time for Christmas. I have an old Z400 workstation which i have setup as my CNC PC and will eventually get a touchscreen monitor for it. I bought an omron 2000ppr encoder for the spindle and have wired it up and tested it to be functioning correctly. The shafts on the servos are 14mm and too big to fit the original pulleys so i orders larger ones and machined them to suit the servos. I have ordered longer belts which should arrive in the next day or two.
I have had some trouble getting the NC control to move the servos properly but after much searching online and on here i think my problem has been me trying to shortcut. It would only rotate one direction and very slowly, as soon as i bumped up the speed it would lock up. i thought it might have been set to double pulse but i eventually got a comm cable to work so i could access the drive with protuner and it seemed to be set right. i was too impatient to order the leadshine tuning cable so i used a db9 plug and cut up a rj11 phone plug to make a cable. it took a bit of experimenting but finally got it to work. I can share the wiring arrangement if anybody is interested. Weirdly the RX and TX in the leadshine manual for the drives means RX and TX on the db9 plug not inverse like most are.
Instead of using a separate power supply for the step and direction commands i used pin 19 on the drives which is a 5v output but after going back and reading the specs on the drives this output is only 10mA. I have ordered a dual voltage power supply and am waiting for that to arrive to see if it fixes it.
This is what my cabinet looks like so far.
Luckily as it was already a cnc machine it has the limit switches already in place so next job is to wire them up while i wait for my power supply and timing belts to arrive.
My main unknown has been the spindle motor. It has a 230VDC 600W motor which is what my post was about. Dickybird posted some interesting info and although i had come across a couple KB motor controller and got some pricing from some local suppliers none had suggested the KBCC. I have however already ordered a cheap 1.1kW VFD off eBay and will see how fast i can spin up some old 3ph motors i have laying around.
The other thing which is a bit strange is the Z axis arrangement. It has a ACME thread looking screw with what i would imagine is a rotating nut and worm drive arrangement. I guess this is so the head doesnt sag without power to the drives. At first look there is a tonne of backlash in this arrangement but a lot of that is axial play in the worm shaft and bearings and housing. It also looks like the ratio of rotations to travel is much greater than the ball screws so i would probably change the gear ratio to get a similar rotations to travel ratio as the ball screws so i have similar travel speeds. I would be thinking the servos are plenty big enough.