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Old September 26th, 2006, 09:39 AM   #1
Inner Circle
Join Date: Dec 2003
Posts: 4,299
Rods and Mattebox support construction.

I seek some advice on wordstuff, better known as terminology relating to support rods and matteboxes, also some best methods for fixing the bits together.

I'm putting together a rod arrangment to support 500mm and 1000mm lenses attached to an Agus35 arrangement for ground to air videography. I have had a piece of pine decking and scraps of alloy and wooden blocks cobbled together for a while but it is not very good.

Rods? - self explanatory.

Crosspieces? - correct name of single bars which join two rods?

Bridge plate? - Is this the piece with the camera mount on it or the tripod mount or is the same name used for both?

Piece which supports a heavy lens?

Piece which supports a filter holder/hood assembly?

Methods of construction.

None of my components conform to a standard. I have determined that 12.7mm, 15m and 19mm are apparently standards and 60mm between centres of rods is one other.

My arrangement is custom to support my own Agus design which is a bit bulky. I also could not get hold of material in standard sizes and have not the means of skimming wider rods down to standard size.

I have used aluminium tube which is a bit over 19mm and used a 20mm slugger bit to drill straight sided holes with an intention to fit fibre bushes into the holes for smoother adjustment.

Drilling and threading holes in the cross-pieces and fitting thumbscrews to lock them to the rods, is going to cause crush damage to the rods which will no longer want to slide freely when I need them to.

Slotting the crosspiece ends back and then fitting clamping screws is another method but my material was chosen to be thick for solid support as I am using a long lens. By the time I slot this material back far enough to get enough bend for a bolt to clamp the ends shut on the rods, there is going to be too much flex there and I don't want the thing to flop about.

I thought about using cycle pedal collet pins but these will also cause crush damage.

Does anyone know of any other fixing method in existing use which does not injure the surface of the rods?

Any advice will be appreciated.
Bob Hart is offline   Reply With Quote
Old September 26th, 2006, 07:02 PM   #2
Join Date: Nov 2005
Location: Honolulu, HI
Posts: 1,961
I think I know what you mean. Tell me if this makes sense.

When you slot the crosspiece ends, make the slot somewhat "T" shaped instead of just a straight line. Since this part of your crosspiece is only to prevent the piece from sliding on the rod, it does not need to be as strong as the rest. If you make the "T" cut, it decreases the material that needs to bend and also makes the material remaining have less overall curvature. You could just cut away almost all the material and just leave two tabs protruding to achieve the same effect, but the clamp would then be clamping directly touching the rails. By leaving the material, you leave a sleave that keeps the clamp from scratching the rails. I don't think the "T" cut needs to be long, I would probably leave half the original material in place to support the rest.

Also, when you cut a slot in any material, drill out the end of the slot to prevent cleavage that can crack through the remaining structure. A circle at the end of any crack or slot causes the energy applied to the material to go around in circles instead of spreading the crack. The hole doesn't need to be large. If you are having trouble imagining this procedure, picture a silhouette of a lollipop as the shape you should make a straight slot. The "T" slot would have small circles drilled at the end of the top crossbar of the "T".
Marcus Marchesseault is offline   Reply With Quote
Old September 27th, 2006, 07:36 AM   #3
Inner Circle
Join Date: Dec 2003
Posts: 4,299

Thank you for your response.

I hadn't thought of "T" cuts but I am familiar with drilling holes and radial fillets to eliminate stress risers or to stop cracks from travelling. The method as I understand it is to drill the hole then cut into the side of it.

I gave the assembly a try out at Jandakot airport today without any clamping on the frame. As is, it is heaps better than the piece of timber I was using, firm enough for the 1000mm with no bending when focus and aperture are adjusted. It cuts a lot more wind when the sea breeze gets up though.

I tried 1/150th sec through the glass disk to strobe the props on the aircraft. There was only about one stop left before the disk artifacts came in at f8 on the SLR aperture. Things look a lot better at 1/50th sec through a groundglass.

I think I'll be going back to no GG for the aviation footage with long lenses.
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