I agree about Bellevilles, which is why I gave up on that whole approach.  I expect for your sub-1000 pound target tension, you *might* could find a valve spring or die spring that would suffice.  For the 2500# I was aiming for on my attempt, I couldn't find anything close that wasn't really huge OD.  Even at 1000#, most seem to up in the 2-3" diameter range.  Up to about 5000 RPM, balance will be fairly forgiving.  Above that, I think despite a perhaps small-ish diameter, you'd need to at least provide very positive centering for the spring to prevent vibration.

Regards,
Ray L.

MIGHT work, But the closer to coil bind you take the spring the more unreliable it gets. I also build race engines. I would definatly suggest a screw down threaded adjuster as you WILL have to readjust the height over time to keep the pressures correct.

Compressing the dual spring packs up to 1000 lbs to install can be a scary deal even with a air/hydraulic spring compressor design to do it safely.

Would not be my first choice but could work.

Bevel spring packs are used around the world every day for CNC machines why reinvent the wheel?  WITH your number of tool changes I don't think spring changeouts will be a concern. The choice of spring is that for a reason. Might want to ask a manf WHY they use it.

(;-) TP

I already mentioned that the spring would be in a pocket machined in the top of the spindle and and held by a valve spring keeper. I would thread the top of the rod and run threaded nut/flange down onto the valve keeper so there is no need for a spring compres or at all and adjustability would be provided simply by turning that nut/flange. The spring pressure could actually be measured/monitored  by the air cylinder, but that's another topic.

If everything was done 'the way they always have been done', we would still be riding horses to work every day . .  or worse . . . we'd still be lion food. Edison said something like "I have not failed, I have simply  eliminated 10,000 material candidates so far" . Education, experiece, research . . only take you so far, and eventually, like the movie says, you just gotta go 'WTF' and give it a try.

One of my favorite sayings, which I had framed in my offices years ago was "A ship is safe in port, but that is not what ships are built for." But I digress . . .

http://www.summitracing.com/parts/SCC-SRP1363-1/Application/?prefilter=1

This guy seems like a perfect candidate. This spring exceeds the spec. I am leaning this way unless a 'game changer' that I have not though of comes up. I am not concerned with easily solvable retention or installation issues. This spring would only need to be compressed about an inch. I have not done the math on a belleville stack so I don't know at this point how much you would need to compress that stack, but the inch or so required by the coil spring is acceptable in my view. Changing to a lighter or heavier coil spring or replacing the spring would be very simple. The stack designes I have seen so far have no provision for changing the stack without removing the spindle and I am not keen on that idea. I am performance oriented and if the coil arrangement will perform with out the disadvantages of a long stack of springs, then I would be inclined to look at it more carefully. I have more to learn about this, but you guys have been a big help, and I appreciate all of the comments.

Thanks everyone!

I have the same 4 ball gripper setup and BT30 as you on a BP clone. ( I was the one who emailed you about grinding my spindle). My quill is locked and I drive the knee for the Z axis so my spring choices were better than If I was using the quill. I settled into these Belleville springs from mcmaster 9712K84. I'm running 30 springs. This gives me 1000 lbs working pressure and leaves me about .375" of travel before my air cyl won't move it. I only need .225” for release. I made a sleeve  that goes 1.5" into the drawbar bolt hole and then steps out to the bore size of the top step pulley. then the sleeve is turned down to accommodate the springs. I’ve been running this setup at 6000 rpm the last couple of day’s with no real vibration issues. In fact it seems to be better than my stock drawbar. I’ve got a job I need to get through but unless someone chimes in why that valve spring won’t work I’m going to give it a whack. My working height is around 2.5” of spring so If I can reduce that with a valve spring I’m all for it.
As a side note I’m running drive dog adapter on the spindle nose but I wanted to see how much grip the BT30 had. I removed the dogs and put a piece of .625 cold rolled in a set screw holder. I cranked the screw down fairly hard and tried to turn the rod with vise grips. The rod spun in the holder after a lot of pressure but the holder never turned in the spindle. Not scientific but gave me a little more confidence in my rig.
I have 100 pieces to machine with 4 setups with 4 tool changes each setup so that should be a nice test.

Derek

Derek, thanks for the replay. What you have is exactly what I was referring to in that you have a much smaller stack of much larger springs. Your stack is under 3" and arranged on top of the spindle instead of being 12" long and extending thru the spindle. Very good to have a working confirmation of my theory.

Coincidentally, I was slogging thru some numbers on the BV springs here this morning on similar springs and your selection produces the best numbers I have so far. Great choice!

Your finding without the dogs also reinforces the 600# spec I have for under 6k. drawbar tension. That test needed only a torque wrench to be 'scientific'.  

There was a comment about re-venting the wheel which I have pondered further. It occurs to me that if BV had some distinct advantage over coils, valve springs would have been replaced long ago. Now strictly to speculate; it seems to me that based on the manner in which Bellvilles flex, they would have a very short fatigue life. That notion is reinforced by another comment about the frequency of replacement, however, by primary objection is the containment issue which is made more complicated by the BV spring OD changing as it flexes.

I think the reason the industry uses Bellevilles is the high drawbar forces they need to hit. I was seeing numbers in the 5000 lb range. I also realized early in my design the the more washers you have the less movement each washer needs to make and the less overall pressure applied to the equipment. Also like you said working bellevilles will tend to fatigue them so the more you have the better.
One thought I had before your valve spring idea was to reduce the length of the splined section on my spindle and replace that area with bellevilles. I would have to reduce the diameter to fit in the bore of the step pulley but I think there are some washers in that size range that would work. The math looks good on the valve spring so I'm going to go that direction first and see how it plays out.
A car running that spring probably works it more in one 1/4 mile pass than I would in a year or two of tool changes

HEY guys go for it. Just a note the referenced spring is a triple set of springs not a single stack.

When you implied using a auto retainer setup I assumed you meant using the keepers as well.

When you do a static rotational grip test it is NOT the same as a running ,cutting spindle. The vibration and side force of cutting effect the holding power of the taper.

You can spend a lifetime inventing new ways to do old things with little improved outcome of the results OR a life time making new parts and gizmos. I am with the patent people 99.9% of everything important has already been invented.

Sling some chips, (;-) TP

You can spend a lifetime inventing new ways to do old things with little improved outcome of the results OR a life time making new parts and gizmos. I am with the patent people 99.9% of everything important has already been invented.

Sling some chips, (;-) TP

Yea but where's the fun in that
Seriously if I was running normal low RPM spindle speeds I would stick with my current setup. The lower overall height is appealing enough for me to make a stab at it.

The only reason I'm running it without the drive lugs is I have an opportunity to do this 100 piece job and I don't have my indexable VFD yet. I'm just doing light cuts in aluminum so slipping won't be a problem. I'm cobbing up a quick 6 position tray type holder and I'll auto tool changing!

I'm cobbing up a quick 6 position tray type holder and I'll auto tool changing!

What are you using to hold the BT30 adapters in yout tool tray?

right now they are just sitting in holes I pocketed. I'm designing a really quick and dirty cover with an air cylinder that pops open to expose the tools.

The end game is to have a 10 tool carousel. I'll be using a traditional spring loaded fork arrangement on that. It's all designed and ready to build I just don't have the time. I'm using an old servo motor and spare drive I have to run it. Trying to keep it as simple as I can and work with stuff I have on hand.