Retrofitting a 1986 Maho MH400E

Yesterday used the MAHO all afternoon, and towards the end there were signs that Y axis creeps, losing position slowly. I need to write a program which simulates what I was doing, with a dozen or so moves per hour, and let it run for hours and see if I can localise the issue.

We took a first stab at altering the gearbox.comp to ignore the S0 commands which LinuxCNC sends when a stop is commanded. It will need a little more tweaking.


Yesterday was a pretty bad day to be a milling cutter.
My big 100mm six insert face mill pulled work out of the vise, smashing three inserts and putting nasty gouges in the work.
Burnt up a 10mm HSS end mill on a lathe tool holder again, as the coolant wasn't full enough and wasn't flowing back fast enough to feed the pump.
Drove a lovely 10mm carbide into the work during touch off, as I mistook the rabbit and the hare. Broke off all three cutting edges.
Removing an 8mm carbide end mill from the spindle, touch it on the vise (I didn't even notice I'd done, it, Sergey pointed it out), sure enough, chipped off one corner.

Along with the other end mills I had already offended, it was time to crank up the Clarkson T&C grinder today. I need more practice with end mill sharpening, but the way I use the MAHO that is guaranteed.
Mark

Hi Mark,

That's a nasty run you've had with the cutters! Mistakes are unavoidable when learning (on my mill I crashed the spindle into the table hard enough that I needed to replace the bearings, which it turned out are quite expensive on these machines!). That kind of goes back to the issue of speed, many operators never jog their machines at full rapid speed because they're afraid - there's not enough time to react when you see things are going south.

Do you know the manufacturers of the cutters you use? One of the best practices for operating a CNC machine is to use the manufacturer's catalog to determine the proper feeds and speeds for specific materials using the standard formulas. I pretty much never guess my parameters and always calculate them beforehand.

The lathe tool holder is likely to be hardened to around 32 Rockwell C. It would probably be a good idea to cut it using a carbide endmill, but without knowing what alloy it is it's hard to say what the material resistance is. In general, when cutting harder materials with carbide cutters, it's not advisable to use coolant during roughing. That's because milling is an intermittent process where the blades enter and leave the material at short intervals and using coolant increases the temperature difference between the short periods when the cutter is engaging the material and when it's not. Large temperature swings coupled with the cutting forces can damage the carbide tool.

Carbide has very high heat resistance and will withstand the high temperature generated during cutting without undergoing chemical changes if you select the cutter adequate to your application. When cutting most steels, the chips break easily and tend not to stick to the edges of the tool. Unless you're machining in deep grooves or pockets and want to flush the chips out to improve surface finish (and in some other cases, such as machining cast iron to flush out the toxic particles), you don't need to use coolant for roughing steel. On the other hand, you should always use coolant, and preferably at a reasonable pressure, to cut aluminum because that metal tends to build up in layers on the cutter, which dulls the edge and will lead to breakage if left unchecked.

So, in general, it's good you used coolant on the HSS tool, but it's not a good idea to use HSS tools on steel that might have been hardened to some degree, especially if you don't really know what said steel actually is. Remember that machining hardened materials used to be accomplished mainly through EDM and grinding before the advent of advanced carbide tooling and fast spindles.

Sorry if I come across as a smart-a$$, I'm just trying to help you a little since your experience with the mill seems to be rather underwhelming considering the amount of planning and work you put into it and I know for sure you can get it to do what you want without much grief. I think one of the best online resources for learning about modern machining is maintained by Sandvik:

www.sandvik.coromant.com/en-gb/knowledge...g/Pages/default.aspx

You can change the language to German and it will tell you much more than most people online will. I actually don't have any Sandvik tools, but I have to say that their knowledge base is rather comprehensive.

Also, do you have the larger coolant tank and pump attachment, or is your coolant stored in the basin at the bottom of the machine?

I have the former, and in order to keep pressure adequate on my machine I always have to make sure there's enough coolant in the tank while the everything's running, usually by nudging the attached tube to get all the liquid out of it and back in the tank.

In the beginning, when the tank is topped off that's not an issue, but later on it kind of becomes one as the level of liquid drops below the pump (which has a small stand), and no longer reaches the holes connecting the various compartments in the tank.

The coolant tank attachment is probably the most poorly thought out thing on my machine and I'm really glad I don't have to use it often. The pump cable is too short to put it anywhere reasonable, and the tank's resulting placement near the machine has led to damages to the left splash cover when it was open.

Thanks Glemigobles. I appreciate your advice.

I had the rapid turned down to about 350 mm/min, which is what I use to approach, and then I switch to the turtle, to touch off. Just a dumb mistake, I misunderstood which setting I was on. I want to make up a tool setter and touch probe to both speed up this process, and not have to touch tools on a piece of paper on the work. For edges I currently use an edge finder.

I have a mixed variety of cutters, and use the feed and speed calculator from here...
littlemachineshop.com/mobile/speeds_feeds.php

It generally worked well for the lathe, and most of my errors on the mill have been dumb concentration errors like choosing mild steel for a lathe tool holder. I only tried HSS, as I had already damaged my limited selection of carbide.

My MH400E has the coolant in the foot of the main casting. It is still mostly the old coolant which has been in there since I got it (probably 20 years old). Draining it, cleaning it, and replacing the coolant is also on my to do list, but for now I just topped it up. I turned down the coolant flow, so now it runs back faster enough to maintain continuous flow to the tool. I also have a mist cooling system to be installed (also on the to do list.)

My Intro to CNC was a little 7x lathe conversion I did years ago. With the lathe, I didn't really bother using CAM, but just did most stuff using the MDI, or hand written programs. While that is fine for a lathe, I really need to take the time to design parts in CAD and finish learning to create the tool paths in CAM, as it would be a waste of the LinuxCNC/MAHO's capabilities to only uses it as like an old single axis at a time machine.
Mark

Hello,

i am back at home and have no tour job for the next two months....
I have started to work on the Maho again removing the dust from a 2,5 year pause, mounting the new ballscrews (X,Y) and attached the servos again.

I have an question:

After switching power on, the servos are loud humming and have some oscilations(no turning, fast vibrations). This is also with control input connected to 0Vm and adjusted drift to stand still.
I can't remember if this has been souch load 3 years ago. I think it is not normal.
The humming is about 100hz (switching rate of the thyristors, but so heavy that you can feel it on the machine).

I have measured the whole control electronics from the Indramat 3trm2, all signals are clean and look like the pictures in the manual. Have done all adjustments descripted in the manual. Checked Brushes and clean Motors, no changes.

Only the 24V Volt in the indramt is about 31.3V. Ok, line Voltage has increased over the years, but theoretical this should be 26-27 Volts. But there is no regulation in the Indramat for this, only rectifier -> capacitor, so i think this is ok.

Do your servos are humming to?

Cool that you are back working on the MAHO.

Yes my servos also hum. Gets pretty annoying over time. NOt loud enough to hurt the ears, but annoying.

If you are interested, a friend of mine programmed a gearbox.comp. My programmer didn't want to start with reverse engineering yours, as it isn't really commented, so he started from scratch. If you wonden't mind taking a look at it:
github.com/jin-eld/mh400e-linuxcnc

I would be interested to hear what things you did differently. We are still working on a solution for LinuxCNC resetting motion.spindle.speed.out-ABS to S0 whenever a spindle stop is ordered. We are tending to give complete spindle control to our gearbox.comp, and just have LinuxCNC's output spindle commands as gearbox.comp inputs.
Mark