Problem- Belleville spring washer replacement

[Fadal Error]

I am starting a new thread after finding that the "Waiting on air valve" error message seemed to be caused by a drawbar with no retention. When I pulled it apart, I found 13 of the 42 washers were broken. I had no tension on the drawbar at all.

I will try to document my adventures for future reference.

[Fadal Error]

I could not clamp a tool in the spindle. I though the drawbar was stuck in the clamped position. It turned out that it was actually open and couldn't clamp on the tool. There was no tension.

What I found along the way.

"Waiting on air valve"
The piston would just cycle over and over.
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Drawbar up


Drawbar down


Lots of cracked washers

The floater was dinged up on the ID where the bearings ride.

[Fadal Error]

The piston that was working fine.

[Fadal Error]

The drawbar tool from cncpros.net
I don't really know what to do with it. It's not what I expected. There was no picture of it on the website. It is not a complete tool and I did not receive any instructions. It's more like a socket without the ratchet.

[Bwana Don]

We replace our bellville washers yearly. It's part of the PM program here. It just needs to be done on occasion. They make a tool to check the tension of the springs. Command makes one, a bit pricey though. I found one significantly cheaper somewhere. If I find it I will add it to this post. Of course it's too expensive for us to own one. Spindles are cheap though (sorry I've been surly lately).

I take a pry bar and periodically try to leverage the toolholder while in the spindle. I insert the bar between the spindle nose and the flange on the toolholder.This checks for a loose condition before it gets catastrophic. Don't ask me how I finally figured this all out.

Found it; http://www.clamprite.com/productinfo.asp
Don't know anything about it, just ran across it.

[Dyad1]

Has anyone ever tried to gauge the condition of their belleville springs by lowering the air pressure way down and then slowly raising it until the tool will release? Maybe when you replace them record a baseline pressure it takes when new and as time goes on how much lower pressure it takes when some washers are broken. Maybe there is a rule of thumb as too how much pressure is required to be safe and below which they should be changed. I know this sounds very imprecise but it's a lot cheaper than a gauge and may be okay for a go/nogo range. Barring friction in the system we know that pressure on the piston equals force on the draw bar release. Maybe if someone out there has a retention gauge you could take some readings and post an equivalence chart.

[carbidecraters]

I think you can check the condition of the belleville's. I think one of our 6030's needs replacing because we are getting marks in circles....nto axis marks but vertical marks around the radius.

[underthetire]

Get a drawbar gauge from Clamprite. Well worth checking them yearly to avoid blowing up a spindle taper. Key Bellville is the place to get springs.

[bl409]

Would someone post the procedure for changing out the belleville washers. I know mine have been in their a long time and probibly need replacing.
Thanks, BL

[Fadal Error]

I should point out that this is a 1994 VMC 4020 with 10k RPM spindle equipped with rigid tapping.
First you need to pull the top piston assembly off.
.
Note that there are six screws (You will need a 7/16" socket). Four in front. Two long ones going through the smaller block on the right as seen here. Do not mess with the smaller block on the left unless you want to bleed your hydraulic system. That block stays attached to the big block underneath.

There are two more shorter screws going through the bigger block in front on the right side and two in the back of the big block.
I set plywood across the back right corner of the machine to set the assembly on while I worked.
You can see the unanodized piston plate here. This is evidently prone to failure. cncpros.com has this part if yours is cracked. It's the first thing that the Fadal tech (not from the factory) suspected.


Here you see the bridge that straddles the pulley. It is held on with four long 3/8" allen screws. Nothing tricky to removal of this piece.

[Fadal Error]

Put a box on the table under the spindle to catch parts that will fall out when you get everything loose. The drawbar itself should fall out, so pad its fall.

Now you see the low-gear pulley. It stays in place. Remove the four small screws(8-32?) in the drawbar cap. Underneath is a four-legged spider. It is held on with two half-moon retainers that fit in a groove in the drawbar. You need to smash the spider. It and the part it fits into are holding the Belleville washers in. There are four 3/16" ball bearings between these parts. Each one supports a leg of the spider.

Mine actually had no tension because so many washers had broken. I guess they came out when I warmed the mill up with no tool in the spindle.



There are three 5/16-18 screws on a 3" bolt hole circle. They have plugs in them that you can remove with a flat screwdriver. These holes can be use to pull against if you make a tool to compress the drawbar. (This picture is out of order as the drawbar is already removed here.)




This is the tool that cncpros.net sells. IT DOES NOT WORK ON THIS MACHINE. I don't know which one it is made for. The OD is too big. The tech support guy told me to just smash it down in a vise until it fit. I thus destroyed a $26 tool that would have been useful to somebody else.


This is a similar tool that I made to fit my machine.
OD not critical. I had 1.5" thick-wall tubing. You need a hole in the top for the gear puller to center in. Picture shows the tool upside down. .870" ID and 1.050" ID for the small tabs that stick up .260". The slot is .850" wide and .900" deep. The slot is just to give you access to the half moon retainers.


I used a heavy-duty gear puller that had a round split plate that went under the pulley. I had to shift to low gear so I could move the high gear belt out of the way.

With this big gear puller I didn't need to hold the pulley in place, but the first gear puller I tried was smaller. I anchored the pulley with a piece of aluminum that bolted to a 3/8 hole that the bridge's long allen screws go into. The other end screwed into one of the pulley's 5/16 holes. It was hokey, but I think it might have worked. I'm sure there is a better way, but I didn't get very far before the first gear puller exploded under pressure.

Some people make a tool that screws to the 5/16 threaded holes in the pulley with spacers to allow access to the retainers and screws to push down on the legs of the spider. That is what I would do if I could start over. If you go this route, use steel and the biggest screws you can get to press on the spider legs. I think I would use 3/8 or bigger fine thread and turn down the ends to fit in the slots where the spider legs are.

[Fadal Error]

That last part was really hard. You are actually looking at pics of the reassembly. I didn't take any during disassembly because I didn't know what I was doing.

After you get the drawbar compressed enough, the half-moon retainers should come out. The drawbar and its eight ball bearings should have come out.

Now you see the washers. These have nice clean anti-seize because they are actually the new ones I put in.


Pull the old washers out. I used a magnet on a stick that mechanics use to get bolts that they drop in the unreachable depths of an engine compartment. My washers were ugly. I only had 29 intact.


I replaced the floater because mine was beat up. You access it from underneath where the spindle taper is. I put cardboard down and worked lying on my back on the table. The floater is held in with two bearings that go in a groove inside the spindle. If it's not too beat, the bearings should come out with a magnet. I magnetized a long screwdriver.