Kev's Stupid Macturn Tricks

In this trick we show how add heavy part capabilities on the sub-spindle and improve the hydraulic & lube systems.

Singing subspindle...

I machine some big heavy parts for our hydraulic motor/AC generator adapter kits that have enough inertia to cause the supspindle servo to resonate when the machine is in milling mode. An audible hum is clearly present and I can feel the vibration. The oscillation prevents the spindle clamp from coming on during drilling operations for example. As explained to me by Dave Bethell at Procam Automation, the control cannot stabalize on the set point so it will not clamp. The machine waits infinitely for a stable set point match.

To get through my first couple of batches (it took me 2 runs to figure out what was going on) I sought out the brake solenoid valves under a cover on the front of the machine. I found that if I actived the low pressure brake used for C-X contouring, via the manual override, the spindle would stabalize and the clamp would come on. To drill, chamfer, airblow and tap 16 holes per part, I got pretty tired of pushing the manual override.

Now, supposedly Okuma has a heavy spindle option for the Macturn subspindle but after 3 failed requests for a quote including a couple of unreturned calls from my Okuma dealer, I just got pissed off and said "Screw 'em, I'll do it myself".

The Technical Stuff...

The photo shows an Omron Zen PLC/smart relay that costs under $200 and is 96 line, ladder logic programmable. With 6 inputs (2 analog capable) and 4 contact outputs, it turned out to be perfect for my upgrade (Thanks Tak for finding this thing!). Note on the far left are the relays for the external M-Codes and their terminal blocks in between.

Basically how the system operates is:

  • M101 DISABLES the heavy sub option.
  • M102 ENABLES the heavy sub option.
  • when enabled the PLC watches the M-Spindle unclamp solenoid line:
    • originally, while the M-spindle is clamped, it does nothing but directly pass through requests for the subspindle clamp and low pressure brake.
    • when the M-spindle unclamps, the subspindle low pressure brake comes on unless a clamp is requested. In which case, it turns off the low pressure brake and turns on the clamp.
    • when the M-spindle re-clamps, the option gets disabled (same as M101). This prevents running the option through a tool change so it can't be left on.
One limitation is that the system does not actually verify if the M-spindle is working on the subspindle. I could not find a suitable signal to verify this status. I thought of using the indicator on the operator panel but it is dependent on which turret is selected for the display screen. Ditto this on why I used M-spindle unclamp as opposed to getting feedback that M110 is enabled. It also does not respond to a control reset. I am still looking for a signal I can tie into for this but the M-spindle clamp reset ensures that it can't go too far wrong. So it's not perfect but for under $200 in hardware and a couple of days to do the schematic, wire in the controller (note that every wire is identified) and learn & program the PLC, I figure we did all right!

Poor Hydraulic Reservoir Design...

The Macturn was giving intermittent hydraulic pressure fault alarms so I opened up the reservoir and found a few nasty surprises. There was probably an inch of silt in the bottom and the suction strainer was covered in cake. Not only that but all of the return fluid was being air dropped back into the reservoir which in my opinion causes frothing.

The inch of cake comes down to me and a former employee. Him for changing the oil and filter when we first got the machine but never inspected the reservoir; even though the filter showed signs of trouble. Me for not insisting the inspection be done.

Anyone who knows me, knows I hate suction strainers. Just like this case, they don't even really keep out the contamination. The silt was fine enough to go through the screen and the cake builds up and cavitates the pump: it's a lose-lose situation.

I gave the strainer a fling; the open female elbow is where it used to go. Since the chiller sucks from the bottom of the reservoir, I put a simple spin on hydraulic filter on its outlet. Nothing fancy but simple and cheap to replace: which are what I consider critical for routine maintenance. Then I added elbows to the coupling/ports to get the drains and returns below the oil level.

The other criticism I have is with the way they ported the tank. No consideration has been given to directing return flow. Returns are right next to the pump inlet so fluid will come in the port and go straight back into the pump. To shed contamination and heat, the oil should be coaxed, if not forced, to flow around the walls of the tank before making it to the inlet. I would have to say that I see too much oil that just sits in the reservior and never gets circulated into work.

Lube Repair & Upgrade...

When the Macturn started throwing lube system errors, Dave from Procam and I wound up tracking it down to a broken pressure switch in the lube pump. For a $5 microswitch that was nearly impossible to access even if I pulled the pump apart rendered the whole pump assembly useless. We decided instead to install a line mounted pressure switch. I believe the one I am using is 60 psi. It almost doesn't matter. The lube lines are so long on the Macturn, I can get full pressure at the pump long before some of the auto-lubes are charged and ready to fire. While troubleshooting the heavy part/subspindle resonance problem, I found auto-lube controls on my sub spindle seem to be the slowest to respond. Setting the pump on for 40 seconds seems adequate to preset them.

While I had the line apart for the switch I decided it would be a good idea to put a filter in. The only filtration the lube system has is the screen on the filler port. Keeps out small rodents and that's about all. It was an easy upgrade, I had the Arrow filters in stock. The electrical connection into the box is a SwitchCraft 2 pin Mini-Con sealed, box mount connector. Again, I had it in stock but you can get them from Digi-Key (my favorite electronic supplier for this type of work!).

Doors for Service Access...

The most obvious modification to our machine is the big, unpainted, aluminum panels on the back; with stainless hinges to boot! It is also a change that I appreciate weekly if not daily. If there is one area where I feel Okuma really did a poor job, it is service access for regular maintenance; and even our changes don't address all of the issues on the machine.

There are 3 air filters behind the big aluminum door that Okuma recommends blowing out weekly. It also gives access to oil filler caps, a reset for a thermal temperature switch that goes if one of the coolers is not blown out and is the only place to get a quick visual on the main tool belt without using a ladder. The stock, bolted panel was almost a 2 man job to remove and was forever being left off because it was just way too inconvenient. This made it a safety hazard. Note the aluminum step we built to reach access points deeper in the machine.

The aluminum panel below the door was changed with larger openings so we could actually fill the oil reservoirs without making a mess. I can't remember exactly now but I think the original panel even blocked viewing of one of the site levels.

On the back tool belt, we split the rear panel and put hinges and latches on it too. There are optical sensors to detect tool holders on belt to belt transfers and we found that they need to be cleaned regularly. In the picture with the open door, you can see an aluminum top cover (watch for clearance to large diameter tools if you do this), plus a back cover that blocks most of the vertical opening. We also hung heavy poly film over the back, grating panels to help keep the grime off the tool shanks. Magnets along the bottom keep the poly from floating in the breeze and let us conveniently lift it to get a quick visual of the tools.

I don't know whether to call this a simple mod or not since not every shop has a press brake. I think for Okuma is would have been simple to do something similar.

I hope any Macturn users (or any CNC users for that matter) that stumble across this page find the tips handy!