Retrofitting a 1986 Maho MH400E

I now understand what the 7S1 switch is doing. When one terminal switch on an axis is triggered, the machine is disabled and the indramat can’t move the axis, but the L1 and L2 going into the Indramat with the 1.5mm² wires, gives the necessary power for the brake to release when the 7S1 is energized manually.

drimaropoylos wrote:

you probably have removed the maho pendant, and the estop on it is not closing the circuit to activate the K1. So the circuit for 7K1, 7K2, 7K3 can’t activate.
John

Thanks. Good call. I should have caught that, since I only just pulled that 19X5 terminal block a couple of days ago. Mine had no pendant, but that jumper was on the terminal block. Looks like I need a jumper between terminals 204 and 264 until I build a pendant.



Thanks also for the explanation of the 7S1 brake release circuit.
Mark

John, have you been following Stig's MH 400E conversion to Mach3? Very different approach in that he ripped everything out, and is not using the gearbox at all.

www.youtube.com/user/StigOveRuud/videos
Mark

I have seen the video, I have even made comment on the video

This approach makes sense if he is going to only mill aluminum with small cutters, and he don’t need the horizontal spindle. The spindle is rated at 1.5Kw, but this is what a true 1.5Kw spindle servo drive looks like.

www.aliexpress.com/item/Economical-1-5kw...arch0204.8.69.s9AoJl

This is one way to fit an encoder in the spindle.
John

Or even better mounted on top of the spindle fan, so I can keep the quill too

He has made a really nice control panel.
John

I respect his approach, he is much further along than I am. My thoughts to taking a different approach fall in four areas...

- I assume MAHO engineered everything very well. I assume they didn't just choose some Indramat and motors which fit, but designed the moments of inertia of the entire drive system, and ordered Indramat to build what they specifically needed. While the modern drives Stig using have very high speeds, they may result in lower stiffness in the system. Also, he is risking galling the ways, if he runs the machine for extended periods at those speeds.

- Dumping the gearbox for a 1.5kW belt drive is very limiting, as you said. Probably not an issue for aluminium, but these machines should be capable of so much more. I like your approach of combining the gearbox for torque, with a VFD on the spindle motor to allow spindle speed override and rigid tapping. I can see this being a future upgrade.

- In this video, you can see that Stig also gutted the control cabinet and replaced everything.

Given the quality of the big relays and electrical hardware MAHO used, and the nice layout of the 28A1 control relay board which is very easy to interface with, I didn't want to touch the main electrics. As an aircraft mechanic, "Never touch a working system" comes to mind. Seems like a lot of cost to redo something to get the same result. If you went into business retrofiting MAHO's for commercial use, you probably have to make some significant changes to the original electrical equipment, as they are probably not in in compliance with modern safety standards.

- Not using the glass scales. This might be tied in with the decision to use Mach3 which I don't think can support a closed loop system with glass scales, but it won't improve the machine by only closing the loop to drive encoders. I have the original Heidenhain test report for all three scales fitted, and none deviated more than a micron from it's indicated postion. Using MESA cards, interfacing with the Indramat and Heidenhain scales is trivial. I am hoping that getting them tuned in LinuxCNC is also trvial Watch this space.

I hadn't realised there is a fan mounted to the spindle. From Stig's video's it is plastic and has 12 blades.

You could install two optical sensors to read those blades passing, and use quadrature to give a 48 ppr spindle speed sensor. Not super accurate, but maybe enough for rigid tapping? If you ever want to implement an automatic tool changer, this should be enough for spindle positioning as well.