Retrofitting a 1986 Maho MH400E

I've been doing a bit more on the gear changing and some of it may help those updating older machines to LinuxCNC.

For these older machines the spindle motor is above the main gearbox making the gearbox hard to inspect. Following the explanation below may mean you don't have to.

The gearbox isn't as complicated as it seems at first glance. Without going inside the gearbox here are a few things to know:

There are 3 selectors each with it's own motor: 11M1, 11M2, and 11M3.

Each selector has 3 gear positions. That should give 3 x 3 x 3 =  27 gear ratios.
But the selector on the output end of the gearbox, on the 11M1 selector motor, has neutral at it's middle position.
So you get 2 x 3 x 3 = 18 gears.
Neutral is on the output end of the gearbox, presumably to eliminate one gear set at the high torque end where the gears need to be bigger, heavier and more expensive rather than elsewhere.

Each selector has 5 cams on it's shaft to monitor where the selector is. I've numbered the cams from the gearbox outward.
Every cam has a single lobe on it that sets a micro-switch for the controller to decode.
The lobes on the first three cams cover a small angle and tell you if it's in gear.
So, if a micro-switch is on the lobe of cam 1, 2 or 3 then it's in gear... or neutral if it's on the lobe of cam 3 of 11M1.

For all three selectors:
Cam 1 lobe will be on the micro-switch when the selector is fully counter clockwise
Cam 2 lobe will be on the micro-switch when the selector is fully clockwise.
Cam 3 lobe will be on the micro-switch when the selector is somewhere in the middle. (Odd order, but maybe the German mind works differently to mine.)

Cam 4 lobe covers a wide angle from full CCW to just short of the middle gear position.
Cam 5 lobe covers a wide angle from full CC to just short of the middle gear position.

If the selector isn't in gear, cams 4 and 5 can tell you which side of the middle gear position it is. In my case the PLC doesn't use cam 4, as you can assume that is where the selector is if it isn't in a gear or on cam 5.

All 3 selectors work in this way, but the "middle" is somewhat off middle on some of them. Presumably the selectors inside the gearbox differ in geometry.

If you have the older type 28A1 board like mine then cam 4 is hard wired into the motor circuit. But on mine it is always bypassed. I don't know how the older Philips controllers used that. On mine I've simply removed it from the circuit along with the 3 big resistors that limit the gear change motor speeds and added a wire shorting the gear change motors to the buss.

If you are converting to LinuxCNC then I think you will need to lift the terminals off X3 209 to X3 220 and redirect them to the LinuxCNC interface board. On mine they have been shifted to the inputs on my Izumi PLC that does gear changes on my machine.

Similarly you will have to drive some relays on the 28A1 board to make the gear change happen. Note the relay names on these older boards aren't the same as the later Schrack boards, but the schematics are similar enough to figure out.

David

A slight error on the Izumi outputs sketch in the previous submission. The 11d2 relay energizes the spindle motor brake to release it , not de-energizes it. I've added the corrected schematic.
Here is a comparison of the various gear change schematics. First Marks from page 1, then my original schematic and then my modified one.
I've drawn the schematic with the common buss down below rather than at the top. But originally mine was very similar, but for the resistor near the gear change motor.
11d9 on mine never activates. The equivalent on Marks is 11K3 or maybe 11S14.
Anyway, the 11K4, 5 and 6 contacts on Marks are shown normally closed. In that state they short the motor terminals and dynamically brake motors if it hey are spinning.
On my machine 11d9 normally closed contacts always shorted the speed trimming resistors, equivalent to 11R1, 2 and 3 on Marks drawing. Mine has no resistors 11R4, 5 and 6. So you can see in the last drawing I have removed all those upper components and simply shorted the equivalent of Marks 302, 303 and 306 to 301. That allowed me to remove 6 cores out of the door cable tray which went to the switches on the 3 cam 4's on the gear change selectors and stow them. In addition I removed the wires energizing 11d9's relay coil, removed the 3 big resistors off the board and the 11d9 relay. You can see that on the photo in the previous post.
It may be that the heavier gearbox on this machine, plus the older style windscreen wiper motors on the selectors allowed me to remove the speed trimming resistors.
All up there are so many redundant components on these old boards it may be better to just buy one of the Schrack 28A1 boards made by Maho specifically for these machines rather than mess with these old ones.

David

in original,
the resistors had been switched in series of the motor, for speed reducing if the control wants to set the middle (center) position, to prevent for overshooting the middle (center)cam . At these days the plc cycle times had been around 50ms or more ...

The Philips controller on my machine was refitted with a Heidenhain TNC 155 controller and an Izumi PLC FA1 Junior for gear changing  around 1990 so they are a little faster.
Yes. I agree. The middle lobe is very short and could easily be over run. I had a quick look at the Izumi execution times for it and it looks like it is roughly 15ms per scan. So that may be why I can get away with removing the resistors.I gear changed a lot before I got the confidence to move those bits off the 28A1 board.
 I think that is why the guys commissioning it again wired the 11d9 relay to the Izumi where it was, to allow them to use the resistor if needed. But it seems that they didn't need to use it on my particular machine. It's nowhere in the ladder program and the gear change works nicely. It may be on these bigger machines the gear ratio has a bigger reduction and doesn't reflect the inertia to the motor as much? The rotating inertia reflects as the square of the gear ratio. I'm not sure if the older Bosch wiper motor they used is lower power and slower also.
But I agree to proceed with caution when commissioning any other Maho. There are myriad versions, all a bit different.They may need that those resistors. But go for the later 29A1 board if you can. Mine has masses of other redundant stuff on it that was difficult to debug and prove so.
Thanks for the reply.

David

Hi David,

Sorry, I had my eye off this thread for a while.

All my MAHO Gearbox knowledge is stored in the github repository with the COMP my friend wrote.
github.com/jin-eld/mh400e-linuxcnc/wiki

I would agree with Tommy. It is better to separate this excellent information into a separate MH700C thread, rather than burying it in page 164+ of a MH400E thread. Someone looking for this information would really struggle to find it located here.  I would suggest you start a new thread and cut / paste each of your excellent posts into it David, as you have done a real service to anyone else with a 700C.

It seens that Maho's were pretty rare down under. I live in Austria, so mine is closer to it's home, not mine
Cheers,
Mark

Hi Mark,
Thanks for the reply.
I came across your site by accident. It would have been helpful if I had found it earlier, but that's how it goes.
I've never posted anything like this before so I didn't have a clue what I was doing. The LinuxCNC site doesn't seem to have a beginners help about getting started. I had a lot of trouble getting attachment to work to start with, like some others, even when they were much smaller than 1.6MB.
I started out thinking you were in Auckland because of some of the early comments about arriving there, and with the Kiwi accent I jumped to conclusions. Soon realized you were in Austria and fluent in German.Unlikely for a Kiwi.
I took me a couple of weeks to get through all the 164+ page and the many videos you've posted. So much that I started writing notes on what I could comment on. Then I just decided to post replies to things as I went so they were still fresh in my memory. In a way it was nice to get the whole lot out without interruption. Part of the inspiration was some of the guys attempting to upgrade older machines than mine an struggling with the wiring and whether to upgrade to LinuxCNC or stick with the Philips. For them I think it would be better to go with LinuxCNC, but I doubt they will have the good experience that you had. Mine needed a lot of wire tracing to understand. There were components dead and bad wiring. I disassembled almost everything mechanical and cleaned and fixed it. Most had something wrong. I can see why this machine changed hands often. I suspect it caused a fair amount of financial distress for it previous owners.
Having commissioned a lot of PLC's running machines during the 80's a key thing to know is that they are very dead until all the I/O is all correct and working properly. It can take a very long time before that happens, and then the machine bursts into life. it often takes a lot of persistence and patience to get to that point.
I was amazed to see a Maho identical to mine on your site, in Christchurch as I recall. I've never seen one the same before out of hundreds of MH-C 700's I've searched for online.
When I worked in Australia as an engineer I mostly came across Deckels. Plenty of them, but all non CNC. I hadn't found any Maho's until later when some of my mates introduced me to them. They are so similar I wouldn't know how to chose one or the other. Mine came up on eBay.
I think I've posted all I want to for now. but there is plenty more that I could help with, not necessarily to do with upgrading to LinuxCNC. But a lot of mechanical stuff that guys upgrading might need to know. That might be better done face to face individually on Skype so I pan a camera on the machine live. But I'm happy to answer questions from anyone.
My feeling is your site is like a magnet for guys messing with these machines, not just with LinuxCNC.
I'm a novice at setting up a separate site for this, But if you guys want to paste my stuff to where it would be more useful, go for it.

Cheers,
David