Retrofitting a 1986 Maho MH400E

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21 Dec 2018 10:26 #122682 by Glemigobles
Thanks Mark for sending me your notes and diagrams!

I just wanted to share a thought I have after reading your file. I think that the reason Maho machines were so slow was because of the very high torque generated by the gearbox spindle. My machine has fine-pitched ball screws - 5mm in Y and Z, and 6mm in X (all are 50mm diameter). All axes have a 1:4 toothed pulley transmission and the Indramat motors are rated at 2000 rpm. This tanslates directly to the available rapid speeds:

X 2000*6 / 4 = 3000 mm/min
Y and Z 2000*5 / 4 = 2500 mm/min

You can see that later Maho models that had VFD spindles had twice those speeds. Likewise, Deckel didn't use gearboxes in the FPX NC series and their machines from that period had around 6 m/min per axis rapids; their VFD spindles had up to 6000 rpm IIRC which brought the torque down also (with the same overall design that was also used by Mikron and others).

Today, new tool room CNC machines with slide ways have around 10m/min rapids (at least those produced here in Poland). So in my opinion these differences between models are about torque and table load, rather than slide ways or machine castings (though those are obviously super important overall). The MH600E documents list an Md const. of 400 Nm and allow up to 400kg on the table.

If you changed the spindle to a modern high speed, direct drive model with a torque of 80Nm or less, I'm pretty sure the speeds could be cranked up without harm to the machine, especially with faster servos, like 3000 rpm (though the spindle would likely blow up a home fuse with its high Amperage).

Just some random tangential thoughts.

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21 Dec 2018 12:14 #122688 by RotarySMP
If you look at Stig over Ruud's retrofit, he ripped out everything and used modern servos, with much increased maximum speeds and acceleration.


I am a bit suprised at how lame the acceleration of the Indramat installation is. There is a obviously a lot of inertia in those large drive components, but there is also a lot of power to push it around. How did MAHO increase the rapids on the later machines? courser thread ballscrews, or higher speed motors?

If you want to do HSM tool pathes, you probably run a significant risk of galling the sliding ways of the MAHO. A linear rail machine is probably more suitable for such work.

Mark

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21 Dec 2018 12:26 #122689 by andypugh

RotarySMP wrote: If you want to do HSM tool pathes, you probably run a significant risk of galling the sliding ways of the MAHO. A linear rail machine is probably more suitable for such work.


I don't know the actual limits for sliding ways, but consider:

That did 200kph with crank pins at about 1/3 wheel radius.
So the peak speed of the cross-head was 1000 m/min....
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21 Dec 2018 12:29 - 21 Dec 2018 12:38 #122691 by RotarySMP
Wonder what the MTBR was :)

Maybe I am overreacting to seeing too many threads with way galling like this FP2:
forum.zerspanungsbude.net/viewtopic.php?...ilit=fresser#p429909

Mark
Last edit: 21 Dec 2018 12:38 by RotarySMP.

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21 Dec 2018 12:51 #122692 by andypugh

RotarySMP wrote: Wonder what the MTBR was :)


It would do London to Edinburgh and back in the same day, so at least 1 million linear feet.
That's a _lot_ of G-code path.
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21 Dec 2018 13:33 #122693 by RotarySMP
Pretty amazing when you considered the state of the art of oil technology and metallugy back then.

Is the tendancy to galling in machine slides acentuated by the extemely short moves used in HSM, not allowing the hydrostatic bearing to build? Or are we just seeing the machines which ran without way oil, and worn out wipers for years?
Mark

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21 Dec 2018 13:50 #122696 by Todd Zuercher
Without knowing how well the machines were maintained and used, I'd be inclined to say the latter.

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21 Dec 2018 14:38 #122702 by Glemigobles
Mark, I would tend to agree with Todd, in that I think you're being very conservative in terms of these machines' capabilities when they're properly tended to. You mentioned linear ways for HSM toolpaths, but DMG linear way machines reach 100 m/min in rapids:

en.dmgmori.com/products/machines/milling...near/dmc-80-h-linear

5-10 m/min is definitely not beyond the realm of slide ways, it's just that there's a lot of things to consider and a hobby modder can make a whole bunch of wrong choices that result in damages. Also, the machines are so old you never know how they were treated before.

Btw, I think Stig is fine with his Maho, though using a toolroom machine as a basis for a mill intended to cut aluminum seems sort of bizzare to me. My friend uses a 750 W 24000 rpm spindle on a 5000€ Chinese gantry-type machine (that's including transportation costs and taxes) with Mach3 to cut aluminum and he turns a tidy profit doing so. He bought a cast-iron machine and simply had the ways ground on a surface grinder to get the geometry right. Seems like far less work for a similar result (unless he's working on some large castings and needs the long Z travel).

All things considered, I think your retrofit is a much better idea. You can drill and tap in steel without worry and it's really easy to attach a fast spindle in the place of the vertical head to make short work of aluminum and plastics. To be honest, if you're cutting metals, the feeds are never all that high, especially with small endmills. Fast rapids, on the other hand, are always useful.
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23 Dec 2018 22:14 #122802 by Bernd

RotarySMP wrote: Thanks Bernd, how do change a tool if there is no program running, does the Gmoccapy tool change button activate this pin? For example if you are just setting up and want to mount a touch probe?
Mark


Hi Mark, sorry for my late answer, yes it is possible to do this without a program running.
You can use the Gmoccapy button "change to selected tool" (don't know the right name, it is a button under the tool list menu), or use the MDI and write a Tn M6.

As soon as the window appears with the request to "please change to Tool Nr.n and click OK" the button on the controlpanel goe`s hot.
during this request message the spindle can not turn, and you are safe for tool-change.
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25 Dec 2018 11:27 #122866 by RotarySMP
Merry Christmas to all. Hope you all had a nice family time yesterday or today, depending on tradition. I received a pair of AMF "Bulle" toes clamps, which are going to come in handy, along with a couple if other bits and pieces for the mill.



Thanks Bernd. I wanted to edit that into my HAL, but my chinese bellows arrived. I installed them (which is a real PITA) on the LH side, as the rear guard has to be installed at the same time, so you are working down in the gap between the transformers, and the guarding. This photo is from the RH side, and I had to take this back off a couple of times till I worked out the order of assembly of all the guards - the rear wall also gets sandwiched by the bellows mounts screws here.



But now all the guards are back on. Swarf tray and doors installed. The coolant which is in the machine is probably 20 years old and pretty gross, but I is working. I'll have to drain it and clean out the sludge and get some fresh coolant.

The replacement LH door which I bought from Ebay turned out to have the latch fittings 25mm away from mine (did MAHO ever make 2x the same thing?). Easy job to drill new holes for the lathe blocks and install them.
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