Servo draws too much current near edges of machine.

[CarbideBob]

Why okay in center and poopey near the outside?

 

[machina]

My theory is that the ways are worn more in the middle and therefore looser. Reasonable?

 

[barbter]

My theory is that the ways are worn more in the middle and therefore looser. Reasonable?

Yes - sounds reasonable.
Your lube pump activation time and duration, will probably be set in the PMC (timer) parameters. You need your specific machine maintenance manual to check.
For reference, my Robodrills (linear rail) were 15seconds on, with a duration between of 600 secs.
I'm pretty sure my Feeler drill/taps and Chevalier #40 machines, were very similar, as a squirt every 10 or 15 minutes, rings a bell.

Every 30 minutes....and on a box way machine....sounds to me like it's asking for trouble?

Edit - I just dug through my records to see if I still had any info regarding my 2x Siemens CNC lathes I had. They were both box way and I know I upped the activation time from standard, so the pumps were on longer.
I'm sure they were 30 secs squirt, every 15 minutes, and they were set that if the machine wasn't moving (so being setup or waiting first off) then no squirt.

The Robodrills had the same thing - no axis movement = no squirt.
I don't think the Feelers and the Chevaliers had that as a feature though (can't remember for sure).

 

[Ox]

I don't think that it matters how long the pump timer is on.
A Bijure unit will only fill a certain void in the metering stem (?) and once that is full - it's full.
Then it seemed that after the pressure cycled off, that the new volume of oil was shifted to the other side of the piston, and then was pushed out by the next pressure cycle.

So a shorter time between cycles would push more oil, but a longer pressure cycle should not change volume.
At least on Bijure.

If not, then the line with the most resistance (plugged?) wouldn't get any,and the most free flowing line would be flooded.

At least that is how it seemed to work when I was working on mine the other day, and also how it makes sense for the system.


I could be wrong, but I don't think so.


---------------------

Think Snow Eh!
Ox

 

[barbter]

Sounds logical Ox.
But on my Siemens lathes they definately used a lot more oil after me changing it.
Looking in the back the slides were always nice and wet and the machines stayed as accurate as the day i bought them.

 

[gustafson]

I don't think that it matters how long the pump timer is on.
A Bijure unit will only fill a certain void in the metering stem (?) and once that is full - it's full.
Then it seemed that after the pressure cycled off, that the new volume of oil was shifted to the other side of the piston, and then was pushed out by the next pressure cycle.

So a shorter time between cycles would push more oil, but a longer pressure cycle should not change volume.
At least on Bijure.

If not, then the line with the most resistance (plugged?) wouldn't get any,and the most free flowing line would be flooded.

At least that is how it seemed to work when I was working on mine the other day, and also how it makes sense for the system.


I could be wrong, but I don't think so.


---------------------

Think Snow Eh!
Ox

My VMC1000's had a rotary pump, rather than a displacement pump.

My older machines had a bijur with clockworks and a cam that only ran when the spindle ran, creating a pump once every x minutes of spindle time

 

[Ox]

Sounds logical Ox.
But on my Siemens lathes they definately used a lot more oil after me changing it.
Looking in the back the slides were always nice and wet and the machines stayed as accurate as the day i bought them.

Maybe your machine had orifices rather than metering valves?


-----------------

Think Snow Eh!
Ox

 

[machina]

UPDATE: I put a 0.002" shim between the underside pressure plate before reattaching. The servo current draw remains @ 30% when jogging X through most of its travel and worst case gets to about 70% at one end. I'm not sure if this is going to affect surface finish or chatter in my cuts if the table is a little looser but I'll find out soon.

In the meantime I can replace all the metering valves (24x) for $10 each from Dropsa USA in texas. If there is a lubrication issue that seem the most likely clogged point so I'll see if things improve after installing those.

Any other suggestions? Has anyone heard of the possibility of Turcite swelling a bit from absorption of oil or water? A tech I called mentioned that but it seems far fetched to me.

Aaron

 

[machina]

I attached a couple pictures. I pulled out the Gibb bar to inspect and I can see a little bit of damage to the turcite at one end. Its kind of smushed for about a 1/2" in length but I don't think it is a big problem ??? More interesting is all the red rusty sludge that came out with it. The rust seems to have embedded itself in the turcite, changing the color from blue to a muddy grey. This photo is after I cleaned it off several times, pulling more red stain on to the paper towel each time.

The turcite from the bottom pressure bars was similarly stained and reddish. I wonder if this is causing the extra friction I'
m seeing? What can be done?

Aaron

 

[machina]

 

[barbter]

View attachment 345968View attachment 345969

I looks like it was running fairly dry of oil?

 

[Ox]

Any chance that corner has gotten dinged somehow?
[from here] it just looks like that corner is pushing harder than the rest.


--------------------

Think Snow Eh!
Ox

 

[machina]

I looks like it was running fairly dry of oil?

There seemed to be plenty of oil on all the turcite (gibb + 2x pressure bars from underneath)that I inspected. The photo's are after I cleaned it well, but it remained stained reddish.

The damage to the corner does look like it got caught on a chip or smashed by something at some point. I think there was some bulging around that damage that may add to the pinching. I shaved it down very selectively and have reinstalled it. I'll see if it helps tomorrow.

Aaron

 

[guythatbrews]

Looks like fretting occurring which might indicate low lube.

Decrease lube interval and use a bigger metering device at the problem area. Sounds like this will be harder than it sounds.

Flaking the turcite will help. There might be plenty of oil in the gallery but if it can't spread out onto the sliding area almost might as well be none.

 

[guythatbrews]

Try posting your question about turcite swelling on machine rebuilding forum. Lots of knowledge there.