Retrofitting a 1986 Maho MH400E

12 Mar 2023 03:28 #266465 by D Jensen
Hunting strategy for encoder index.

My machine had several sets of cams for the linear axes. The Heidenhain only uses two sets of them. I've removed the redundant ones.
There is a long metal cam. This must be positioned so somewhere in it's span lies the linear encoder index mark, (or home mark).
There is a second set of plastic cams, one cam at each end of travel, that tell the Heidenhain it must stop (end of allowable travel). Obviously these should be set inboard of the encoder travel limits, then the mechanical stops set inboard of that, which should be set inboard of the recirculating screw limits. This second set of cams are read by only one limit switch.
In addition to that the end of travel cam near the index cam must overlap the index cam.

The Heidenhain controller assumes the index is somewhere along the metal cam. At index search, if the axis is not on the metal index reference cam, the program knows to hunt in a certain direction for index (set in machine parameters).  If it is on the cam it hunts in the opposite direction for index. However, it's possible it could be on the wrong part of the metal index cam, so if it falls off the metal cam before finding index it simply reverses and goes back along the metal cam to find it. If it then reaches the plastic end of travel cam and still hasn't found the index it stops and flags a fault.
The attached image shows the index or home end of my X axis and the set of limit switches. Note all my Maho limit switches are in the same type housing, which has 5 switches in a row. It's only using two switches here as mentioned


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12 Mar 2023 10:18 #266479 by D Jensen
Back on page 114 of this string Glemigobles asked for pages 3.12 and 3.13 of the Maho manual in English. I've included them here in the zip file.

My Maho MH-C 700 takes an NT 40 tool holder. Yes it has the same taper as the BT 40. You are probably right about the M16 stud change for the ends to convert from one to the other. I've included photos in the zip file showing what I get ordering an NT 40. I've made my own setting tool for where to cut the groove in the extended end on the NT 40 tool holders I get. I simply fit it and scribe a line around the end then turn a groove up to that line with the dimensions on page 3.13 of the manual.

The M16 thread is further back on the NT style tool holder and it worries me a bit that there is not much meat between the thread root and the new groove. Fitting a solid NT stud to a BT  tool holder be better.

There are also photos of the tool retaining system sitting on my bench. It is easy to remove the tool holding clasps. Just undo the grub screw in the end while it is in the machine and unscrew the retainer nut (that thing with the slot) with a large screw driver. It would be relatively easy to machine the claws to change it to a different clasp type if you say had a lot of BT tool holders i think. That lone steel ball is pressed into the slotted thread end by the grub screw to expand the thread and lock the system. The bore in the end of the slotted thread is tapered where the ball sits. Setting the system in the correct position for it to properly draw the tool holder in is a simple matter of using the tail end of dial calipers to get the depth then locking the system with the grub screw. Although it is a blind assembly it's very quick to do.

The whole tool retaining system is shown on the bench. You can see the long stack of disk springs that retain the tool holder and the hydraulic ram that releases it, plus the rotary union. You can see the thread that screws the ram into the spindle quill at the end near the disk washers. Be aware that it is Loctited when assembled. I played my paint stripper fan onto it at low power as, the book says, while using a big spanner on the flats of the ram. It comes free suddenly when the Loctite melts.

Note also in the background my spindle disassembled. It has twin taper roller bearing like a spindle grinder. The rolling elements actually run straight on the hardened surface of the main housing which is the main quill (lying beside the spindle shaft). Early in my carrier the company I worked for bought 3 Deckel FP1 mills. But they came with precision grinder heads. I'm thinking my machine may have got a similar setup?
The special grease that I repacked it with has to go through a series of run ups at increasing speed using a thermocouple on the quill. The machine is limited to 1250 rpm even though the gearbox goes to 2500. I couldn't get it faster without it overheating, so the original commissioning engineer must have got it right. As well as that the spindle motor really sags at 3000 rpm switching from star to delta and it smells hot. The motor contactors also. So it's back at 1250rpm in the machine constants. So it misses it's top 3 speeds.

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12 Mar 2023 10:21 #266480 by D Jensen
Sorry. one of those files was wrong

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13 Mar 2023 07:54 #266533 by D Jensen
Here is something for Oldtony on page 120. Maybe someone can alert him:
I see that you Maho has what appears to be a 28A1 board, but it is depleated of the older style relays.
During the rebuild of my machine I found that the previous update to a Heidenhain TNC 155 had made a lot of my relays redundant.
I've attached a couple of photos of them and how mine needed to be complimented to make it work on 4 axes. You can have as many as you want for free if you need them. We just need to figure out a way to get them to you from Sydney.
I'm only up to p124 on this thread and it seems like half the Kiwis in NZ were rebuilding Mahos during Covid lockdowns. Just a pity I found out so late or I could have helped.

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13 Mar 2023 08:03 - 14 Mar 2023 04:38 #266534 by D Jensen
Sorry the small files wont attach. I'll try later
The only way I can get these file to attach is by zipping them. Sorry for the inconvenience.
Anyway, if oldtony or anyone would like them they are yours. Note that some of the relays are smaller than the others. All have 4 off NC/C/NO contacts. Maybe they are different current ratings? The retaining clips in the background only fit the smaller relays.
Last edit: 14 Mar 2023 04:38 by D Jensen.

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14 Mar 2023 06:04 #266634 by D Jensen
I'm not sure who this is for. Maybe Brad or Chris on page 124. The photos of the MH-C 700 there are of the same build as my machine. I'm amazed! Never seen one the same as mine before
But there are differences: Mine has a CNC rotary table (4th axis). That is clamped by three hydraulic rams in the same manner as the tool holders. Springs hold the platen clamped and the hydraulic pump pressure releases it. Homing goes Z Y, X then B (set in machine parameters) . Since B is clamped initially, the pump hydraulic pump has to be up to pressure before homing. On my machine that happens immediately the main isolator is switched on. The pump makes quite a noise and runs about 5 seconds as the clamp rams are  big in diameter compared to the tool holder rams.The hydraulic pump is dumb and just switches off and on by the hysteresis in the pressure switch on top of the pump. When the pressure is up the NO contact illuminates a light in the "power" button on the main console to inform the operator the machine is ready. .After homing and the closed loop relay pulls in, the rotary table is held in position by the Indramat servo. So milling forces that might wiggle it are only held by the servo loop stiffness. Since I wont be using it much I have the rotary table defeated in the TNC 155 machine constants. Only a few seconds to change it back if I want it.The other mechanical difference is that mine is missing the hand wheel and Kipps clamp in the horizontal quill. It would be nice to source those parts if anyone knows where. To shift the horizontal quill in and out I have to remove the blanking plate, reach in with a socket wrench and unclamp it, then probably pull the quill forward by grabbing the tool holder. The rack teeth are there on the quill, as are the bearing mounts, so Maho wouldn't have saved much deleting it.
My Machine originally had a Philips controller but that was replaced in the late 80's with the Heidehain TNC 155. Most Mahos skipped that model and use the Philips instead.
You can see the differences in the breaker  panel photo and relay board on the door.
In the photo of the Indramat you can just see the top of the forth servo for the rotary table. Actually the transformer on the top of it. it's mounted on the other door.
I've replaced all the bottle fuses with contact breakers. These days they are going cheap as they don't meet Australia/ NZ RCD requirements. I thought of putting RCD ones in, but that requires a lot of additional neutral wires and there is much room in the cable trays now.
The incoming 3 phase 415VAC has an RCD. But all the secondary transformer wirings are earthed so I suspect I could get a belt off them.
I replace the old servo loop closing relays with much nice contactors.
Also added a couple more timers. The 2 old timers it had for the star/delta and a gear change delay (now done by an Izumi PLC) were dead. The new 2 allow a delay time for the first lubrication cycle, so it doesn't lubricate if you turn it on briefly during a commissioning test and to shorten the run time of the lube pump. I went through a lot of lube oil before that, which ends up everywhere. Now I understand how the metering works (see elsewhere) I'm going to remove that one.
I've added the TNC 155 back plane wiring to show that it has similarities your earlier model. I've modified it from the Heidenhain manual so that it shows where the I/O goes to. Hope that helps.
Note also that this particular model of TNC 155 is the one where the Heidenhain encoders plug straight into the back of the TNC so it doesn't have the separate connector board.

Go well,

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15 Mar 2023 03:50 #266719 by D Jensen
I'm attempting to put all my MH-C 700 wiring schematics here. They are the result of several months of painstaking wire tracing. As they exceed the upload limit I'll have to do them in 2 submissions. As I mentioned they were done by sliding a loose cable tie from end to end on every wire in the machine. Lots of scraped knuckles, swearing and sweat etc. I had to cut loose all the existing cable ties first and pull the wiring out of cable trays. The bundles are quite convoluted and many the same color, so it's easy to lose which is which especially where the bundle goes through bulkheads. The cable tie idea cures that problem and even allows a rest now and again without losing you place
Although I've done a lot of plant commissioning in my time, my first glance at all this left me a bit overwhelmed.
I did have the schematics for a similar MH 400, so I had a general idea, but in many ways it was just as misleading as not having it, especially with my machine being refitted with an non standard controller. An all that shuffling between drawing sheets and in German with Google translate: a nightmare

I hope for many people this presentation will be helpful. The way the drawings are, you can see where you might put the Linux interface cards where my Izumi PLC is. Or you could rebuild an older Maho an see where you could put and equivalent PLC or see how the old system might be better rebuilt.
Each individual drawing has everything in one place, so you can print it out and sit beside the machine and go through each subsystem with just one printout.
Each cable is labeled with it's core number, where they are multi-cored (mostly).
Each wire has the terminal number at each end
Each contact has the name of what it does where appropriate and/or it's I/O number/name  etc.
The X1/ X2 terminals are usually found along the bottom of the cabinet: X1 on the left merging to X2 on the right
The X3 and X4 are the terminal strips along bottom and side of the 24 volt to 220 volt interface relay board. I think these might be called the 28A1 card on the Maho drawings. Mine are on the cabinet door and originally, for the Philips controller, there were 3 of then. Now only 2 any only partly complimented with relays. I've seen them placed elsewhere on other Mahos. On the schematic for these boards you will note that some of these relays have quite a lot of interlocking logic.That may not be suitable for the LinuxCNC implementation as you could do it just as well in the program logic.
Similarly you note on the motor contactors, there is wiring logic which wont allow the spindle motor to attempt operation in both directions at once etc.
Sorry they are just mud maps


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15 Mar 2023 03:57 #266720 by D Jensen
Here are the last of the schematics for my MH-C 700 rebuild.
Good luck
The following user(s) said Thank You: andypugh, tommylight

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15 Mar 2023 10:03 #266732 by tommylight
Probably should have started a new topic, but i might be wrong. :)
In talks to do a Maho 600 retrofit, from pictures paint looks quite good, but it was used as a grave for other stuff, so ...

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15 Mar 2023 10:24 #266734 by D Jensen
Thanks for replying.
Yes maybe Tommy. And probably not on LInuxCNC at all!
But I read a lot of comments here on similar rebuilds that talk about maybe resurrecting old non Linux controllers and the pros and cons.
I'm hoping to add stuff on the pitfalls with the common problems with this generation of Mahos that are the same for all of our rebuilds.
I see stuff on the servo loop closing and my schematic shows pretty much the one we will all have to use.
My PLC program for the gear change should help with the very long discussion on LinuxCNC logic for this and also what it needs to do mechanically.
The group of old Mahos being rebuilt is broader than I realized until I got into marks stuff.
It seems to have gone quiet lately without me knowing how many of them turned out.

Best Regards
The following user(s) said Thank You: tommylight

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