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where to get this chuck from?

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mopen

mopen

Mechanical
Joined
Feb 14, 2003
Messages
14
Location
EG
Hi,

I am trying to attach a square bar about 2 m long to a face plate at the root " fixed support". I need to reduce the deflection of this bar as much as i can as there is a distributed force applied close to the free end of the bar. I thought that using 4 jaw chuck would solve this issue, also i thought that the jaws should be long enough say 10 cm long to accommodate the bar root inside tightly. Also i need this chuck to be mounted in a rotary table to be able to change the angle of the bar. So i come up with the device in the attached photo. My question is:

Is there a similar piece that has 4 jaws instead of 3 and the jaws length is around 10 cm or closer and can accommodate 2 cm bar to 0.5 cm bar side length?

I appreciate your help

mopen
 
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Rotary tables typically do not come with 4 jaw chucks. You probably can get one equipped that way but it will be hard to find. Why do you need the chuck? Can you not just clamp the bar to a standard rotary table using the existing clamping slots? It will allow you to clamp a longer length than a 4 jaw chuck will. If you don't know what I mean, just go ask a machinist to show you.

Timelord
 
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Thanks Timelord,

the point of using a chuck is that the gripping force of the jaws and the worm gear mechanism of the chuck allow appropriate alignment to the bar and strong support at the same time.

mopen
 
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Also i need to clamp bars of different sizes so the jaws can hold different sizes.
 
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The search term you want to use is
{ large "4-jaw" scroll chuck }
without the braces.

Common 4 jaw chucks have independent jaws so that one can chuck rectangular pieces.
A chuck that moves all jaws at once is a 'scroll chuck' or a 'self-centering' chuck; they are commonly made with three jaws, but four jaw versions are produced.

You may have to buy a chuck with demountable jaws, and make some extra long sub-jaws or grippers.




Mike Halloran
Pembroke Pines, FL, USA
 
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You do realize that 4 jaw chucks aren't self centering? Each jaw is individually moved. How big a bar is it? They do make square collets.
 
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Brian E22,
That as Mike explained is the difference between a scroll chuck, and a 4 jaw independent chuck.
Here is a link to a 4 jaw scroll chuck.
B.E.

You are judged not by what you know, but by what you can do.
 
 http://www.amazon.com/dp/B005LPZWCU/ref=asc_df_B005LPZWCU2899249?tag=thefind0101213-20&creative=395261&creativeASIN=B005LPZWCU&linkCode=asn
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Thanks guys for your help.

BrianE22

The bar is rectangle of 2 *1.5 cm and the size goes down to 1*0.4 cm. I think square collets is good idea. But is there a collet with a flanged bottom so i can mount it to a face plate. Also , as i understand how it works is that the size of the collet centre should match the smallest bar size i am using. But by how much the bar size can get bigger to fit them in the collet?. Also how you increases the collet size, like what toll is used for this? Also can the collet accommodate a rectangular sections or just square?

Thanks

mopen

 
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You need a rectangular collet, 15 x 20 mm, and
a collet closer, and
a rotary table.

I don't think the most common collet series, 5C, can hold a rectangle quite that big. Larger collets exist, but are harder to find.

Typical collets have a grip length of only a cm or two. The length of your workpiece suggests you may be better off with a custom chuck, or a double collet and closer so you grip the bar in two places.

I suggest you prepare a nice drawing of your workpiece and whatever you want to affix the rotary table to, call Hardinge, and fax or email the drawing when you get a sales engineer on the line.

How fast you need to change the bar, how fast you're going to spin it, what you're going to do to the bar while it's held, and how much the bars vary in dimension, and how precisely you need them located, radially, angularly, and axially, will all affect the price of your fixture.


As Timelord said, a generic rotary table with crossed T-slots could serve as the substrate for a custom chuck/fixture made by a local machinist who can more easily gather and evaluate the sum total of your actual requirements, in person, than we here could do by continuing to interrogate you remotely.


Mike Halloran
Pembroke Pines, FL, USA
 
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Why the OP would think that any type of clamping is going to affect the opposite "free" end, 2 m away, is still left unaddressed.
 
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Ok, I am actually learning from what you post. I do not think that a technician would help me with my problem.

Actually this bar is gonna be used to mount an airfoil wing to a face-plate force transducer in a wind tunnel experiment. The bar will be a cantilever beam with free tip. and the wing will be mounted at the most top 50 cm length of the bar.I have tried a cylindrical aluminium bar which is attached to the force transducer through an adapter of flange with 5 cm protruding neck and i used set screw for tightening the bar inside the neck.The adapting piece is screwed to a rotary stage and the rotary stage is screwed to the force transducer through another adapting flange.

using this setup i got appreciable deflection of the bar at high wing'force. Also it was hard to align the bar vertically using set screws. This is why i thought of using a chuck/collet arrangement to fix the bar tightly and ensure vertical alignment at the same time.

Thank you

mopen
 
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There are 4 jaw self-centering chucks, by the way. Any kind of chuck may be mounted to a rotary table or faceplate, as they generally do not come as an integrally manufactured piece. A sketch of your set up would help greatly to offer the best advice.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
 
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I posted a link to a 4 jaw self centering chuck earlier , but based on your latest post, I am not sure you want to invest that kind of money for a short term project.
B.E.

You are judged not by what you know, but by what you can do.
 
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Sorry Berkshire, I do see that now. A simple fixture with a degree wheel may very well do the trick, with a fraction of the cash outlay.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
 
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Sure would like to see a sketch of your setup. It sounds like you will try to measure lift/drag forces from a 50-cm span wing section via a horizontal cantilevered strut measuring less than 1/4" thick? "Appreciable deflection" may be the least of your worries, I think you may find aeroelasticity (flutter) problems to be bigger issues.
 
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Thank you.

Yes i think now that using a chuck would be too much. But what is the alternative for this?

btrueblood

Yes you got it right, this is what i want to do. I used a cylindrical strut but it deflects significantly. I do not know if flutter is gonna be an issue,as i am doing the tests now on steady wind stream. I used a rotary-stage from edmund optics as my rotary table :


But i think it is not strong enough for holding the forces.
I am trying to draw the setup in solid works and attach it.
I appreciate any further suggestions about this wing attachment mechanism.

mopen
 
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I'll bring it up again. Why can you not just clamp or screw the bar to a standard rotary table? You will be able to clamp or screw in two places at the perimeter of the chuck which will support your bar better than a four jaw chuck which will only grab it near the center of the chuck. If you really need more support, clamp or screw a short support bar to your long bar.

Timelord
 
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A couple of years ago I picked up a second hand 16" four jaw chuck scroll chuck where each jaw was individually adjustable via a separate worm drive, from a machine tool dealer for £50.
Unbelievably handy piece of kit.
It was a sweet deal, as the kids of today (probably don't) say.

"I love deadlines. I love the whooshing noise they make as they go past." Douglas Adams
 
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That's a 4-jaw independent chuck, not a 4-jaw scroll. The latter are much less common. Still a bargain if it was a decent brand - I paid twice that for a 12" independent.
 
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