Fadal Hi/Lo Shift Cylinders

RC Mech · May 23, 2021

Going through the quirks with my Fadal VMC 15XT, the shift cylinders are leaking fiercely. Initially thought it was the solenoid manifold at the back, but it sounds like air is getting past the piston seals.

The high shift cylinder will engage, and the low cylinder will leak until it creeps forward and tries to engage the low belt. My work around for yesterday was to pop the air lines off the cylinder and send it.

The FadalCNC Pros website lists PN Cyl 0006 as the shift cylinders- but it’s single port. Mine has 2 ports, one 1/4” line and the other 1/8” or so, both air. I read about the “hydraulic” shift cylinders. On my mill they are not hydraulic.

Anyone know what gives?

RC Mech · May 23, 2021

So it appears the hydraulic gear shift cylinders are on machines with the High Torque option.

With that solved, the twin plumbed air cylinder replacement parts are the issue. Fadal CNC looks to only have the spring return version.

triumph406 · May 23, 2021

RC Mech said:
So it appears the hydraulic gear shift cylinders are on machines with the High Torque option.

With that solved, the twin plumbed air cylinder replacement parts are the issue. Fadal CNC looks to only have the spring return version.

I thought it was hydraulic for all fadals.

Delw · May 23, 2021

what year is your machine? if you have 2 ports on your org cylinders its a air over hydraulic system.
to fill them you need to take the air blocks off and fill the resivour they sit on with oil. it also helps to fill the lines with oil using a syringe

they have them I buy them there all the time its a cyl-0005 if I recall.

look for these (pictured Parts) on top of the bridge over the spindle
take the 2 7/16 screws off lift the part off and pour oil down the big hole, then do the other one. dont loose the orings on the bottom of the parts pictures and DONT over tighten the bolts.

mmurray70 · May 23, 2021

VMC15XT with shift cylinders? I thought VMC15 was 7500 rpm single speed?

The standard hp 10k rpm machines came with single acting (single port) air cylinders with a spring return. Not uncommon for these to stick a little and not fully retract. Simple fix was to install the same cylinder except double acting and couple extra fittings/hoses to make them retract with air power. Sounds like this is already done on your machine. This works fine. I have this done on my machine and running fine for 4-5 years now. The cylinders are dirt cheap but looks to be out of stock right now. P/N you need is mcmaster 6498K654. If you want to see more details on conversion google "Air Belt Changer not Changing, Mechanical Issue" and it will take you right to the thread. I cant post link here as this forum blocks it.

The 15hp HT and 20hp VHT machines use the same double acting cylinders but use an air/hydraulic booster for more tension on the belt. I just bought the whole air/hydraulic system to install on my machine so I would have more grip on large taps, but the whole system seems like a cobble up. Think I will just leave it as it is and stick with threadmilling larger holes.

Vancbiker · May 23, 2021

mmurray70 said:
........The 15hp HT and 20hp VHT machines use the same double acting cylinders but use an air/hydraulic booster for more tension on the belt........

That’s part of the reason. The other part was to keep the belts from slipping in reverse rotation. In reverse, the belt tension is forcing the tensioner pulley back which creates slack on the opposite side of the belt and it will then slip pretty easy. When the HT machines first came out they did not have the air/oil setup and we had a few users that were trying to tap larger threads have problems with the spindle stopping with the tap stuck in the hole.

The air/oil system had a pilot operated check valve in the upper block on the extend line to prevent oil from being pushed back if the tensioner pulley was trying to be pushed back by belt tension when in reverse rotation.

And yes, it was a complete cobbled up add on. Pretty much like the entire machine was designed and built as a high school shop project.

The cylinders were made by Bimba when I had to work on Fadals. I doubt if they were specials though Fadal claimed they had special seals. I’d bet a little time looking through their catalog would let one find a match that could be ordered from any Bimba distributor.

RC Mech · May 23, 2021

Thank you all. They are Bimba cylinders. I ran the machine today nursing it along in D2 and just hand tapped the single 1/3”-13 hole I had to do.

The cylinders are two port, no oil in either line. The low cylinder leaks like the Dickens. I’ll order PN Cyl 0005 (and confirm with Fadal CNC), change the belts and fill the accumulator with oil.

The machine is a 1998. 10,000 rpm spindle with 2 belts & hi/low range around 2500 rpm. Someone else has been in this head before but it doesn’t look non-factory. I can move the (check valve/spool?) with the 1/4” line in and out of the accumulator blocks about 1/4”. Is this normal?

mmurray70 · May 23, 2021

Vancbiker said:
That’s part of the reason. The other part was to keep the belts from slipping in reverse rotation. In reverse, the belt tension is forcing the tensioner pulley back which creates slack on the opposite side of the belt and it will then slip pretty easy. When the HT machines first came out they did not have the air/oil setup and we had a few users that were trying to tap larger threads have problems with the spindle stopping with the tap stuck in the hole.

The air/oil system had a pilot operated check valve in the upper block on the extend line to prevent oil from being pushed back if the tensioner pulley was trying to be pushed back by belt tension when in reverse rotation.

Yeah I guess the check valves will help a little too. Any extra flex in belt from applied torque would move tensioner in further, and check valves would hold it there. The extra pressure will make huge difference on its own. I had trouble with belt slipping when reversing a big tap once and I connected a nitrogen tank to the low speed cylinder set at 200 psi for the whole job and it worked great, just had to stay in low range.

Im tempted to try fitting a larger air cylinder on low range and stick with air. Should get most of the benefits without all the headaches of the oil system. Should be enough for my 10hp anyway. There is a 1.5" bore cylinder thats just smidge longer. Thread is different but could machine shaft smaller, or try and find another rod end bearing that fits.

RC Mech · May 24, 2021

Significant Leak

Looking at this again today. I filled the reservoirs with ISO 68 Hyd oil, careful not to disrupt the O-rings.

Machine will shift to high range, no air leak. On the low range shift it hangs up, only recoverable by disconnecting the port shown to allow the High cylinder to retract, and constant leaking air in Low. Shifting from Low to High works as intended.

Adding oil only stopped the slamming it did from Low to High.

It’s as though the high cylinder check valve(?) is not releasing pressure to allow retraction.

Does this need new check valves rather than cylinders?

Delw · May 24, 2021

RC Mech said:
Looking at this again today. I filled the reservoirs with ISO 68 Hyd oil, careful not to disrupt the O-rings.

Machine will shift to high range, no air leak. On the low range shift it hangs up, only recoverable by disconnecting the port shown to allow the High cylinder to retract, and constant leaking air in Low. Shifting from Low to High works as intended.

Adding oil only stopped the slamming it did from Low to High.

It’s as though the high cylinder check valve(?) is not releasing pressure to allow retraction.

Does this need new check valves rather than cylinders?

View attachment 321728
View attachment 321729

Yes and no
1st take it apart and clean it all up inside, you may have to replace orings. they used to sell a kit I dont think they do anymore. orings are avail at mc master car. look for Burrs
make sure the piston slides in and out easy and smooth. Theres a ball bearing in the piston that gets gummed up from time to time. also the pin that pushes the ball bearing maybe damaged, never seen one damaged but heard it happens. usually a simple cleaning with fix it.

I an guessing you put oil in both the cylinders? if not you need too.

sometimes you can hit the piston witha screwdriver ie push in push out. better just to disconnect air then see if you can move it in and out by hand.
the release of air generally comes from the mack valve, howevere if a piston is stuck it will simulate the same thing

RC Mech · May 24, 2021

To confirm, there should be oil on both sides of the pistons in the cylinders? There is currently oil on the 1/4” (larger) sides only.

Delw · May 24, 2021

Delw said:
what year is your machine? if you have 2 ports on your org cylinders its a air over hydraulic system.
to fill them you need to take the air blocks off and fill the resivour they sit on with oil. it also helps to fill the lines with oil using a syringe

they have them I buy them there all the time its a cyl-0005 if I recall.

look for these (pictured Parts) on top of the bridge over the spindle
take the 2 7/16 screws off lift the part off and pour oil down the big hole, then do the other one. dont loose the orings on the bottom of the parts pictures and DONT over tighten the bolts.
View attachment 321652

RC Mech said:
To confirm, there should be oil on both sides of the pistons in the cylinders? There is currently oil on the 1/4” (larger) sides only.

Read above.
BOTH piston assemblies should have oil in the housing below them.
I looked for my pics and couldn't find them
you take each piston assemble off with 2 7/16 screws the middle hole of each for each assemble in the housing that there screwed too is 3 holes (with o-rings) fill the middle hole on each side with oil)
one piston assembly runs high the other runs the low range.
also fill the 1/4" tube that goes to each cylinder with oil I use a syringe . I been doing it this way for years and dont have any issues UNLESS you have a BAD CYLINDER Or piston assembly
Make sure your air is DISCONNECTED

Delw · May 24, 2021

heres the pic
the bottom piston assembly already has been removed, fill oil where red arrow is, then put it back together and do the same for the other piston assembly.

in2glamisgirl · May 24, 2021

RC Mech said:
To confirm, there should be oil on both sides of the pistons in the cylinders? There is currently oil on the 1/4” (larger) sides only.

The VMC 15 was available with the 10,000 RPM hi/low option, this was Fadal's lowest cost machine and most were the low torque y-delta 1-1 drive.

If you have oil on the return side (small rear line)or out the air valve exhaust, the piston is by passing oil and the cylinder needs to be replaced.

The reason they went with air over oil is that oil is not compressible like air, when the spindle reverses the idler will stay on location and not introduce backlash into the feedback loop during rigid tapping.

mmurray70 · May 24, 2021

I have the whole package here brand new if you need it. Everything except cylinders.

RC Mech · May 28, 2021

Installed 2 new shift cylinders, put oil in the 1/4” lines and topped up reservoirs. Sounds slightly better but still hangs up on Low shift, “Waiting on air valve”.

Murray, I’ll PM you. That’s a generous offer.

Tedger · May 28, 2021

https://www.fadalcnc.com/media/pdf/Waiting_on_Air_Valve_Alarm.pdf

RC Mech · Dec 28, 2021

Updating this thread:

Mill still will not shift into low by itself. Oil, cylinders, pneu solenoids replaced with no change.

Now we’re at the idler prox switches. How do you see the state of these switches in the diag?

RC Mech · Dec 28, 2021

Solved this.

The air line for the Spindle Air Seal was swapped with the air line for the Low Range shift cylinder at the solenoids.

No idea how/why that was the case. Thing still leaks oil like a sieve but at least it shifts.

Fadal Hi/Lo Shift Cylinders

Stainless

Stainless

Diamond

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Diamond

Stainless

Stainless

Stainless

Stainless

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Stainless

Stainless

Cast Iron

Stainless

Stainless

Aluminum

Stainless

Stainless

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