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How to increase FADAL drawbar tension (using shims)

triumph406

Diamond
Joined
Sep 14, 2008
Location
ca
I changed the belleville washers a while ago, 1 washer was broken, and maybe 8-10 were split. That gave me a drawbar tension of 900#

After changing the washers I measured a drawbar tension of 1200#.

According to a FADAL source the locking drawbar tension should be 1650#-2000#. I haven't seen this in any FADAL documentation, but I consider the source reliable (FADAL family member)

I called ITS who I got the washers from and asked if there was anything I was missing, changing to new bellevilles gave me 1200# (up from 900#) Was there a reason I wasn't getting in the range of 1650#-2000#? ITS had somebody in the FADAL spindle realm call me, and there is a method of increasing the drawbar tension.

To increase the drawbar tension requires .007" shims under the split retainers in the locking assembly.

Typically it might require (2) .007" shims, 2 didn't make any difference to mine. 5 shims bought the drawbar tension to 1700#, but it had a very distinct "thwack" when it was retaining a tool when I was manually loading the tool into the spindle.

I have 44 bellevilles installed, I added another belleville (for 45 total) and removed a .007" shim leaving 4 shims underneath the split retainer.This removed the "thwack" when the tool was being retained by the drawbar. That gave me a drawbar tension of 2000# Tool changes are smooth when using the ATC.

Hope this helps because as far as I can tell the procedure isn't in any manual, and I haven't seen it on line.

The shims are HDW-1204 and are availible from ITS. I made some from Mcmaster 98126A377, which I put on a mandrel and turned down the OD.

SPLIT REATINER.jpg
 
Enough room in there to add an extra belleville???

I think you might have something else weird going on in there...

You DID REPLACE THE FLOATER while you had the drawbar out??

For those that don't know, the floater is what the bearings ride on
as they are pulled upwards.. If the floater is beat, I don't care how
good your springs are, your tool retention is going to suck.

I'm going to keep the shims in mind for the next go around with the bellevilles.
 
Enough room in there to add an extra belleville???

I think you might have something else weird going on in there...

You DID REPLACE THE FLOATER while you had the drawbar out??

For those that don't know, the floater is what the bearings ride on
as they are pulled upwards.. If the floater is beat, I don't care how
good your springs are, your tool retention is going to suck.

I'm going to keep the shims in mind for the next go around with the bellevilles.

Nothing strange going on at all with 45 bellevilles.. At least with my drawbar it will do a toolchange OK with 100psi at the floater, 80psi is not enough pressure to compress the 45 washers to do a toolchange.

Floater was changed at the same time as the bellevilles.
 
Did you dress the new sharp edges of the cut washer with fine sandpaper to give it a corner radius? You may get faster fatigue cracking at these edges if that's not done.

What cut washer? I added shims and an extra bellevile that's all
 
Just responding to this thread for others having similar issue.

I had this exact situation today as OP. My drawbar pressure was testing around 900lb. Swapped in 44 new spring washers and only got up to 1200#. Frustrated I threw another washer making the total 45. Tested again to 1300#. I said screw it and left it. Just for giggles I swapped out the PULL STUD to a name brand one on my hydro gauge and yep got dead on 2000lb.

Point of the story. Make sure you only use high quality pull studs on all tools and test equipment. I'll be swapping all of my pull studs to Mari Tool for sure.
 
Just to trow a wrench into this
Belleville washers are a spring like no other the farther you compress the rate drops of and eventually the flip
I found out about this on some torque limiters that were tripping the more you tightened them the easier they tripped
 
Just responding to give Kudos to the original poster on this thread.

I, too, was having trouble getting enough drawbar tension. My machine has the 4.627" pocket and is supposed to take 44 springs. Well, 44 new bellevilles only brought it up to 850lbs or so. I eventually jammed 48 bellevilles into it but still only got 1250lbs, which settled to about 1100lbs within a few months.

I was scratching my head on this, until this thread got bumped to the top. Can't believe I never found this thread in my prior searching on the subject.

Anyway, I bought the suggested .007 shims from McMaster Carr, cut down the o.d. so they'd fit, and started experimenting with them. Four shims and 48 bellevilles gave a whopping 2400lbs, but the air pressure had to be really high to actuate the thing. Also, I had the big "thwack" that was mentioned when the drawbar grabbed the tool. After trying at least half a dozen different combinations of shims and bellevilles, I settled on 2 shims and 46 bellevilles, which gives 1800lbs and no "thwack".

Absolutely amazing that a couple of shims could make such a huge difference. Looking at how the whole thing works, I don't fully understand why. But I saw it with my own eyes.
 
Do guys own your Force guage, or is there a place to rent?


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I bought this one a couple years ago. It's priced quite a bit better than most of them and it works good. Still pricey, but drawbar tension is an important thing to keep up on, and you've got to be able to measure it, so I bit the bullet.

Between my business partner and I, we have three Fadals, plus I've loaned it out to another local shop that has a 4020. Out of our four machines, three of them were showing 600lbs or less. The only one showing a good number was a 1991 VMC40 that had a whole new spindle and drawbar assembly installed a few years ago. It was showing about 1600.

All the machines are showing north of 1500 now. Only one of the machines, a 2001 4020, needed the shims to get there. The others got there with new bellevilles alone.

I would've had no idea about the shims without this thread. It totally solved the problem for me. Took me most of the day, trying different combinations of belleville and shim counts, but worth it to see 1800lbs of tension and quiet, reliable tool changes.
 
Thanks for the link, I ordered one up, hopefully there is some science behind it, and that it closely displays actual drawbar force :)


Sent from my iPhone using Tapatalk Pro
 
I would've had no idea about the shims without this thread. It totally solved the problem for me. Took me most of the day, trying different combinations of belleville and shim counts, but worth it to see 1800lbs of tension and quiet, reliable tool changes.

It took me a few combinations to get the drawbar tension to where I wanted it to be. The Fadal spindle rebuilder who told me about the shims said that sometimes they had to try a few combinations to get the correct tension.
 
Thanks for the link, I ordered one up, hopefully there is some science behind it, and that it closely displays actual drawbar force :)

Well, I've got no way to prove that it is or isn't accurate. But the numbers seem reasonable, within the range of expectation. One of our machines was literally showing 300 some lbs. But after replacing the bellevilles it jumped to 1500. That seemed reasonable. Likewise the machine that had a new spindle/drawbar assembly a few years prior showed 1600, which also seemed reasonable. And with those machines showing good numbers, I knew something wasn't right on the machine that only showed 1200 despite 48 new bellevilles in a machine made for 44.

It took me a few combinations to get the drawbar tension to where I wanted it to be. The Fadal spindle rebuilder who told me about the shims said that sometimes they had to try a few combinations to get the correct tension.

Thanks so much for creating this thread, I had never heard of this.

Thinking back on it, the first time I disassembled the thing, there were remnants of a shim in there. Basically just slivers at that point, but now I realize what it was. So the factory probably shimmed mine. I didn't see any shims on any of the drawings for the assembly, so I didn't think too much of it, and put it back together with no shims. Now I understand how critical it was.

It seems odd to me that .014 of shim in that spot could make such a dramatic difference. I mean, if I understand the mechanism correctly, the only thing the shims do is to preload the spring stack ever so slightly more. Yet they make much more difference than adding an additional belleville, which would seem to me to add much more preload. I don't get it. But there's no arguing with the tension gauge. It solved the problem.
 
Thanks so much for creating this thread, I had never heard of this.

My pleasure.

It's not mentioned in any Fadal manual, and even where it's listed on say Fadalcnc (HDW-1204), there's no explanation in the description to what it does. strange

Thinking back on it, the first time I disassembled the thing, there were remnants of a shim in there. Basically just slivers at that point, but now I realize what it was. So the factory probably shimmed mine. I didn't see any shims on any of the drawings for the assembly, so I didn't think too much of it, and put it back together with no shims. Now I understand how critical it was.

It seems odd to me that .014 of shim in that spot could make such a dramatic difference. I mean, if I understand the mechanism correctly, the only thing the shims do is to preload the spring stack ever so slightly more. Yet they make much more difference than adding an additional belleville, which would seem to me to add much more preload. I don't get it. But there's no arguing with the tension gauge. It solved the problem.

How it worked was explained to me, but I've forgotten the explanation.

Since I added the shims I've experienced no fretting on toolholders, but that may be because I've retired any tool holders that fretted in the past. Plus I put a thin layer of moly grease on a toolholder once in a while. Especially if machining 4340
 








 
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