cylinder stroke for grapple question

[/pine]

I'm planning a grapple/thumb for my FEL buckek...the length of the thumb arms is about 2' the same as the face (opening) of the bucket...

can someone give me a ballpark idea of what length cylinder stroke would work best for this application?

BTW...I would like the thumb to be straight up when not engaged

 

[kennyd]

Most grapples use 8" stroke cylinders...but you will need to figure out exactly what your design requires. One simple and effective way is two pieces of different sized PCV or CPVC pipe-like on 1/2" and the other 3/4" so the small one slides into the bigger one. You can then graduate the small one with marks to identify the stroke based on your mounting points. This is usually the most frustrating part of building home built grapple/thumb.

 

[/pine]

Thanks for the reply...
For some reason I was thinking I would need about a 12" stroke but heeding your reply I guess it would be prudent to take the time to mock it up with some cardboard or plywood scraps and get it at least close to right beforehand...

Thanks again

 

[Brad_Blazer]

Your grapple isn't very big - a 2 x 6" cylinder might be plenty. I'm pretty sure that's what was used for this grapple:
http://www.tractorbynet.com/forums/build-yourself/106141-front-end-loader-grapple-scratch-12.html

I used a 2x8" cylinder on my grapple that is about 30" long.

 

[JustGary]

Slash -

I just lost about an hour's worth of reply to you because the forum decided to log me off...

If you have trouble making a mockup, let me know and I'll try to recreate the post. It was basically what steps to take to easily figure out the actuating arm length and placement for your cylinder. One of the important things to note is that the cylinder ram and the actuating arm should make roughly a right angle when the grapple is half open. See the center image.

Other than that, it just needs to fit together without binding...

I used a 3" X 8" cylinder to get 100 degrees of throw on my root grapple. That equates to over 46" of movement at the grapple tips. I figure I have over 2200 pounds of closing force at the grapple tips worst case, so it's plenty strong.

Regards,

- Just Gary

 

[Brad_Blazer]

Gary - nice grapple - it looks like a beast!

Here is a link to my grapple thread with a force calculator spreadsheet attached.
http://www.tractorbynet.com/forums/...-grapple-cad-build-geometry-calculations.html
The geometry for your style of grapple is quite a bit different than mine but it shouldn't matter to the spreadsheet. Mine has force peaking at around 1100lb down to about 700lb fully closed. I used the spreadsheet to bias peak force closer to the closed position while allowing fairly high speed/low force approaching fully open over a 120 degree range of motion.

Brad

Edit: In that original spreadsheet the inputs did not match my drawing - here it is with matching numbers.

 

[beenthere]

/pine (in slash pine country? )

Any more progress on the thumb?

I'm interested too, for my forks on the FEL. Thinking outloud if a one-way (single) cylinder might work if the thumb was spring loaded (torsion spring maybe) so it would return to full open position. The single cyl would be plumbed into the curl hyd line of the FEL so it would only extend (close the thumb) after the forks were curled to the stop. Takes out some of the usefulness, but avoids any additional control valve plumbing.

Any thoughts anyone?

 

[/pine]

I have been accumulating parts and pieces...have everything but maybe a couple of hoses and a few fittings...

Between now and when I head back to NE GA (where my tractor is) the first of April I will be cutting out the actual grapple bars and mocking up a prototype...

I'm not sure I'd want a wound up spring out in front of me like that when the grappel was engaged...


BTW...
I hail from "Pinellas" county FL lots of slash pines (and spanish moss)