Jacknife trucks

Andrew McMillan

New Member
Hi again all. Further to my post about windows (thanks to those who responded!), I'm hoping there may be someone at CB with expertise either designing or constructing trucks.

Per my other post, the company I'm designing for will build these trucks and I'd like to provide quality plans to make their job a lot easier!

For context, the truck is preset center stage and needs to pivot to rest downstage parallel to the proscenium arch. It only gets moved once. It will have a desk, chair, easy chair, bookcase on top of the base shown below.
Approx truck weight: 470kg factoring in the weight of the frame, 18mm top, door/walls and actors. Actors won't be on the truck when it moves.

I've been advised that casters need to be fixed and mounted at right angles to the radius line.
How do I assess how many I may need, type and where best to draw the radial lines?
What type of pin/bolt do I need to anchor the frame to the stage floor and without putting a hole in the stage floor. I know there is professional iron mongory for this. I just don't know what I should be searching for! Weblinks welcome.


Below are some pics showing the frame design including overall dimensions. I'd welcome feedback re
- frame construction design below (Frame (35mmx70mm) sits below an 18mm chipboard top laid so a 2cm lip, and possibly 3mm plywood painted floorboards over the chipboard
- is there a standard size dimension for lips and facias?
- soundproofing options. (It is likely the company may choose to paint the chipboard top. I'm more inclined to paint plywood 3mm sheets, cut then lay over the top or over some sort of soundproofing material to deaden the sound of actors feet on the chipboard.

Lastly, if there are other design related forums other than Facebook where I could post these sorts of questions please do let me know.

Thanks
Andrew
Melbourne Australia
 

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Crisp image

Well-Known Member
For those playing in other parts of the world Trucks=Wagons.
Question 18" chipboard or 18mm.
I would also make the frame with the timbers that go horizontal in planview base frame about 400mm apart. This will allow for a 2400mm sheet to go on top and give 20mm overhang each side. Skirting/ facia boards come in 12mm, 16mm and 18mm thick. You would only need one strip of noggins going the other way just to hold it together while adding the top sheet. add the frame for the angled section as a second part to the first frame.
Paint the 3mm floorboards on top if using them no need to paint 2 items if you don't need to.
I once saw a touring group who had wadding stapled under the top deck and it seemed to work. Certainly took some of the drumming noise out.
Does any of this make sense?
Geoff
 
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jtweigandt

Well-Known Member
How many determined by what is stamped on your caster as to what it's load capacity will be. Then you factor in safety of at least 1/3 (just pulled that number out of my hat) so that you are not
ever "at capacity" As to the radius, assuming you have a fixed axis point... just run the string and draw the arc on your framing to figure likely mounting points and can estimate a tangent on the curve from there.

I will say that I have a shop full of swivel casters, and have done lots of free rollers and a few "pivot point" units. There may be some initial resistance as they swivel into place, but if the unit only moves once, you can
move it past it's spike point, and "pre swivel" the casters into alignment so they are ready to go with no resistance. Much easier than having to align to the curve, and you will be able to pick easy corners in your framing for the mounting blocks, without regard to obeying the curve.
 

JohnD

Well-Known Member
Fight Leukemia
Re: Terms is other parts of the world, I would like to point out that the thread title here COULD be a reference to what the Brits call "articulated lorries".
 

TimMc

Well-Known Member
Premium Member
What I love about this place: I can learn new stuff every day! @JohnD
 

almorton

Well-Known Member
Artics can jack-knife : it's that really bad thing where the tractor unit swings under the trailer, usually slicing the cab off in the process. Nowadays it's almost unheard of, as trucks have anti jack-knifing measures, but it was quite an issue in my youth (70s).
 

kicknargel

Well-Known Member
Premium Member
How many determined by what is stamped on your caster as to what it's load capacity will be.
This is true, but also determine by how far the frame can span without needing support. The freedom unit rule-of-thumb is if using 2x4 lumber (actually 1.5" x 3.5") framing on edge, you need to support every 48".

For the pivot, you can find two sizes of iron pipe that sleeve together. Using flanges, attach one to the unit and one to the floor. Or, given that this only turns once in the show, if you set the angles of the casters accurately, you may not need a pivot at all.
 

TimMc

Well-Known Member
Premium Member
This is true, but also determine by how far the frame can span without needing support. The freedom unit rule-of-thumb is if using 2x4 lumber (actually 1.5" x 3.5") framing on edge, you need to support every 48".

For the pivot, you can find two sizes of iron pipe that sleeve together. Using flanges, attach one to the unit and one to the floor. Or, given that this only turns once in the show, if you set the angles of the casters accurately, you may not need a pivot at all.
^^ What Nick said, plus be certain to attach your casters in a way that fastening hardware cannot pull through wood.

{brief, related anecdote}
This proved to be a problem back in 1969 at the first Woodstock. Stage was built with 24ft (ish) revolve. Assembled without washers or other load-spreading hardware, fasteners pulled through after the revolve was loaded with 2 band's gear and stagehands valiantly attempted to turn it. Schedules were created based on being able to pre-set the backline for the next act; the result was at around 6am Sunday, the last Saturday night band was starting their set. {/brief, related anecdote}
 

Andrew McMillan

New Member
This is true, but also determine by how far the frame can span without needing support. The freedom unit rule-of-thumb is if using 2x4 lumber (actually 1.5" x 3.5") framing on edge, you need to support every 48".

For the pivot, you can find two sizes of iron pipe that sleeve together. Using flanges, attach one to the unit and one to the floor. Or, given that this only turns once in the show, if you set the angles of the casters accurately, you may not need a pivot at all.
Thanks Nick. The company use 70mm x 35mm timber for their frames so as long as I put noggins every 600mm I believe this should be ok.

Re iron pipe, do you mean welding them to the ‘flange’? By flange do you mean a hinge? A pic would be helpful if possible as I’m not clear what you mean. Thanks.
 

RonHebbard

Well-Known Member
Premium Member
Thanks Nick. The company use 70mm x 35mm timber for their frames so as long as I put noggins every 600mm I believe this should be ok.

Re iron pipe, do you mean welding them to the ‘flange’? By flange do you mean a hinge? A pic would be helpful if possible as I’m not clear what you mean. Thanks.
@Andrew McMillan Up here on the top side we have mounting flanges commonly available with three or four holes to accommodate large wood screws or lag anchors. Iron schedule 40 pipe threads into the flanges. Tightening the threaded pipe into the threaded flanges is usually sufficient. Grease applied inside the larger diameter pipe permits noise free rotation.
Toodleoo from one of the other colonies.
Ron Hebbard
 

Crisp image

Well-Known Member
@Andrew McMillan Up here on the top side we have mounting flanges commonly available with three or four holes to accommodate large wood screws or lag anchors. Iron schedule 40 pipe threads into the flanges. Tightening the threaded pipe into the threaded flanges is usually sufficient. Grease applied inside the larger diameter pipe permits noise free rotation.
Toodleoo from one of the other colonies.
Ron Hebbard
@Andrew McMillan I think Ron is referring to something like this flange
Flange.JPG
which is available at Bunnings. you then screw a pipe in to it and fix it to the stage then have another pipe that goes over it which is connected to the truck to form the pivot.
 

bobgaggle

Well-Known Member
I push back against the swivel casters unless you happen to have them lying around. fixed casters are cheaper and better suited for rotational movement. (no 'drag' when you change direction) is there a term for that? like, caster back-lash? Anyway unless you want to drop a bunch of money on triple swivel/zero throws, go for the rigid wheels, with a rectangle plate. mark center on each end of the plate and line up those marks with the arc you swing like @jtweigandt said, and you've got your wheels mounted tangent to the arc. also for just one move during the show, like @kicknargel said you might not need a center pivot. but then you run the risk of the whole unit creeping across the stage after a week of tech rehearsal then you've gotta try to shove it around with brute force...
 

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