G0704 Power Draw Bar Belleville springs 3000# holding force?

[ballistic42]

I have a G0704 with the 7/16" draw bar. I would like to have 3000# of holding force using the TTS holders. Can any one explain their Belleville stack for this setup. Here are the Belleville springs that I have purchased from McMaster Carr. 9712K436

McMaster-Carr

My air cylinder can support the 3,000#'s of force to pop the tool, so no problem. I just need how to stack them to get the 3000# TTS holding force.

Thanks,

Jeff

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[CS900]

Bellevilles are pretty easy.

Stack them nested to increase spring rate. ((((( each spring adds to the spring rate. So 5 stacked would be spring rate*5. Doing this does not increase the travel of the springs

stack them staggered to increase spring travel, but maintain spring rate ()()()(). The spring rate does not change but the travel is multiplied by the number of springs

And then you can make combinations of these to get the spring rate and travel that you need. (())(()).

for the springs you have, even nesting two together will get you 3600lbs. You may want to get some lower rate ones and stack them to get closer to 3000lbs. Or hope you can turn the air pressure up more!

[atomarc]

Jeff,

CS900 explained it pretty clearly. Every time you stack a washer on a washer, coolie hat fashion, you get double the spring rate of a single washer. To increase the travel of the washer you stack them coolie hat opposed. You asked about our setup on the Grizz and I referred you to post #73. That shows two 2050lb washers in nested-inverted stack of 12. This gets us 2 X 2050 lbs = 4100 lbs and the nested-inverted stack gives us the travel we needed, .132. Getting the spring rate out of the stack is only part of the equation, you need to work the formula so you get the travel you need that allows you to load the washers up yet leaves enough travel for your air cylinder to release the tool holder.

The Grizz has a pretty tall stack, but the washers are big strong fatties that don't flatten out much meaning we needed 12 of them so their combined 'mash' allowed the tool holder to release. I think this is how it works?

Stuart

[ballistic42]

Jeff,

CS900 explained it pretty clearly. Every time you stack a washer on a washer, coolie hat fashion, you get double the spring rate of a single washer. To increase the travel of the washer you stack them coolie hat opposed. You asked about our setup on the Grizz and I referred you to post #73. That shows two 2050lb washers in nested-inverted stack of 12. This gets us 2 X 2050 lbs = 4100 lbs and the nested-inverted stack gives us the travel we needed, .132. Getting the spring rate out of the stack is only part of the equation, you need to work the formula so you get the travel you need that allows you to load the washers up yet leaves enough travel for your air cylinder to release the tool holder.

The Grizz has a pretty tall stack, but the washers are big strong fatties that don't flatten out much meaning we needed 12 of them so their combined 'mash' allowed the tool holder to release. I think this is how it works?

Stuart

Guys, thanks for the input and I think I get it now. I am going to get this figured out as its the last thing I need to do. I will post pics of everything completed once its done.

Thanks,

Jeff

[CS900]

Jeff,

The Grizz has a pretty tall stack, but the washers are big strong fatties that don't flatten out much meaning we needed 12 of them so their combined 'mash' allowed the tool holder to release. I think this is how it works?

Stuart

I wouldn't sweat that. Commercial machining centers have stacks that can be several feet long. This is done to reduce fatigue on the springs thru the hundreds of thousands of tool changes that a VMC can do over the years.

[ballistic42]

I really appreciate the help and I think I have it figured out. I am going to stack them like this ()()()(). I have the room to adjust if need be. https://www.mcmaster.com/#9712k436/=1b70rh2 are the ones that I am using. My air cylinder will put out 3610lbs of force at 100PSI. I will run the system at 95 PSI which will give me 3430 lbs of force. The effective working area of my cylinder is 36.1 sq inches.

Jeff

[CS900]

Hey Jeff...
So that will only get you 1800lb on the drawbar then. You don't want to run the springs at the flat rate, they will fatigue very quickly. I'm not sure how much is enough, but this seems like one of those situations where more is better.

[ballistic42]

Well now maybe I don't get it because from my understanding for each spring it will give 1890 working load. From what I understand if I stacked them ()()()() it would be 7560 lbs of force, 4x1890. Is that not correct?

[CS900]

Well now maybe I don't get it because from my understanding for each spring it will give 1890 working load. From what I understand if I stacked them ()()()() it would be 7560 lbs of force, 4x1890. Is that not correct?

That is not correct. You have to nest them in order to gain spring rate. Furthermore you have to nest them in groups.

(())(()) will get you 2x spring rate and 2x displacement

(())() will get you 1x spring rate and 1x displacment (a little more in reality)

()()()() will get you 1x spring rate and 4x displacement

The system is only as strong as its weakest link.

[mikegiraud]

For my G0704 PDB, I use 8pcs of the Tormach belleville fully in series (no washers are nested). Configuration is ()()()(). Picture for reference. This has worked well for 1.5 years with TTS holders using up to a 1/2" end mill with no pull out or other issues. Not sure where I got this washer configuration, but it's from someone here on the Zone. It's worked perfectly, so I never had a need to do the math on the holding force. Also, for reference, I use a Tormach 770 drawbar as-is.

[ballistic42]

Thanks for the information. From all the advise and help teaching me how these work, I really this time got it figured out..lol. I will have to see how it works out when I start milling!

Jeff

[CS900]

Be sure to report back and let us know how it turns out for you!

And you're welcome.