# Attaching smart casters to a platform



## CLEFFEL (Oct 10, 2007)

Sorry about the simple questions recently, it's just been forever since I've done most of this, and now my wife is teaching high school tech theatre and guess who gets to help problem solve?

When attaching smart casters to a platform to create a wagon (both legged and legless) what is the best method?

Carriage bolt from the top down so as to not see a bolt head on top? If so, how do you prevent the bolt from getting in the way of the spin of the smart caster?

Carriage bolt from the bottom up so as to not interfere with the spin of the smart caster? If so, what do you do with the part of the bolt and nut protruding from the surface of the platform?

Chewing gum? If so, bubbalicious or bubble yum? Or perhaps some juicy fruit?

TIA!

-Chris


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## Van (Oct 10, 2007)

A technicque I've used in the past that works really well is this;
1. Attach the caster to a square of 3/4" plywood. I prefer to use an 
1-1/4" Stove bolt with the head counter-sunk into the top of the plywood. Be sure to use a split washer to lock the nut in place. 

2. You can now attach the wooden square to the bottom sie of the platform with Drywall screws. Again 1-1/4" work well, so you don't go all the way through the top. 

The nice thing about this system is it's really fast when you needto pull things apart and/or re-attach them.


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## Radman (Oct 10, 2007)

I'll second that, that's what I usually see done.


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## CLEFFEL (Oct 10, 2007)

Are drywall screws are beefy enough to deal with bumps and such that I have not doubt these wagons will incur?

Thanks again

-Chris


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## Van (Oct 10, 2007)

Aha! Good question! In this case the answer is usually yes. Since the forces at work here are shear < perpendicular to the shaft of the screw> rather than longitudinal. You could almost think of the screws as pins going into the bottom of the platform. the wieght of the platform itself is going to keep the caster from just falling off, the screws simple keep it from sliding away from where you want it placed. Now, if you were using particularly large diameter casters, so that the torque of rotational force incurred when running into an object, say a screw left on the deck or something like that, was enough that it might over come the down force of the mass of the platform, and transfer into longitudinal pull on the screw, it could become sufficient to overcome the "grip" of the screw making it necessary to use bolt through the top of the platform.

It's much easier to draw a picture of this than to explain it. :neutral:
I hope I didn't confuse with that little diatribe. 
Short Anwer- Yes screws are fine in most instances, unless you are planning on running the platfrom over rough surfaces really fast.


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## soundman (Oct 10, 2007)

The way I have seen it done is to make a bunch of caster plats with bolts and 3/4" ply. The casters never leave the plate after attachement. Then the caster plates get lagged scewed into the platform. thats for the low profile option but there are more ways to skin a cat.


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## Footer (Oct 10, 2007)

I usually do the 3/4 ply with stove bolts if possible, making a caster plate. Ya, making up caster plates sucks but after you get it done you don't have to do it again. If you build you platforming out of 1x6 (I don't like this method, but a lot of people do it) instead of 2x4 you don't even have to face the platform to hide the casters, depending on your caster size of course.


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## Van (Oct 10, 2007)

BTW, a good rule of thumb is to; measure from the midline of the caster <swivel point> to the outside edge of the wheel. Take that distance and multiply it by 2.25 this will give you the size of the caster plate you need to cut so that when you mount the plate tight to a corner the wheel won't rub on the framing.


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## gafftaper (Oct 10, 2007)

While I like the caster plates, if it's a one time deal and you just want to bolt them on, take your caster and wood and measure carefully how long the bolt has to be. Most casters I've seen have enough room for the bolt to hang down the thickness of the nut plus a little more no problem. Buy bolts that are the closest fit you can get. If the bolts are too long use little squares of luan as spacers to decrease the amount of bolt sticking through.


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## tenor_singer (Oct 11, 2007)

Van said:


> Aha! Good question! In this case the answer is usually yes. Since the forces at work here are shear < perpendicular to the shaft of the screw> rather than longitudinal. You could almost think of the screws as pins going into the bottom of the platform. the wieght of the platform itself is going to keep the caster from just falling off, the screws simple keep it from sliding away from where you want it placed. Now, if you were using particularly large diameter casters, so that the torque of rotational force incurred when running into an object, say a screw left on the deck or something like that, was enough that it might over come the down force of the mass of the platform, and transfer into longitudinal pull on the screw, it could become sufficient to overcome the "grip" of the screw making it necessary to use bolt through the top of the platform.
> It's much easier to draw a picture of this than to explain it. :neutral:
> I hope I didn't confuse with that little diatribe.
> Short Anwer- Yes screws are fine in most instances, unless you are planning on running the platfrom over rough surfaces really fast.



I've had dry-wall screws shear off during a performance. I'm not sure if it was just flaw of that particular batch, but I've learned the hard way to not really trust them when used in this capacity.


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## CLEFFEL (Oct 14, 2007)

As an extension of this (no pun intended) how do you all usually attach casters to legged platforms? We're not talking tall platforms, only 3' or so.


Thanks again for everyone's help.

-Chris


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## soundman (Oct 14, 2007)

I drew something up for you real quick. normaly I would run bracing on something this tall but it should give you a good idea of one option.


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## TimmyP1955 (Oct 15, 2007)

I mounted 4" Guitel casters on four 175 pound subwoofers (48"x22" base size). On the first two I used 1/4" bolts and tee nuts. On the second two I used 3/16" tapping screws. I had no trouble with either after many speedy trips over door thresholds and other nasty bumps.

Some drywall screws are overly hard and brittle, so I would not use them for something that is subject to side shock (such as caster mounting).


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## Van (Oct 15, 2007)

tenor_singer said:


> I've had dry-wall screws shear off during a performance. I'm not sure if it was just flaw of that particular batch, but I've learned the hard way to not really trust them when used in this capacity.


 
Oh sure it can happen. A couple of good things to keep in mind to alleviate this issue;
1. Don't re-use screws.... ever. Once a Drywall screw has been used to torque something together, it becomes extremely brittle and the chances that it will snap are extremely high. 

2. Don't over torque the screws when driving them in. Trying to bury the head of every screw you put in will put excessive stress on the shaft of the screw. 

3. Pre-drill, whenever possible.

All that aside, Tenorsinger is correct, drywall screws can fail in high stress or dynamic load situations. If you know a caster plated platform is going to be used in a high stress enviroment or over rough surfaces, then by all means use a standard wood screw, or even better bolt the plate to the platform. It's much easier to bolt a caster plate to a platform than it is to mount a caster directly to underside of the platform.


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## CLEFFEL (Oct 18, 2007)

Thank you for helping me with that. My wife just started a job as a technical theatre teacher at a high school. And while she's perfectly capable to teach this class, and an excellent designer, there were a few of the technical direction aspects that have escaped her since college (they've escaped me as well apparently.)

Ask me to pull together a lighting system, I'm great, ask me to build a platform and put it on wheels, then things get dicey. :-D


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## icewolf08 (Oct 18, 2007)

CLEFFEL said:


> As an extension of this (no pun intended) how do you all usually attach casters to legged platforms? We're not talking tall platforms, only 3' or so.
> Thanks again for everyone's help.
> -Chris



I think soundman's drawing is probably all the info you need, I would have said put the platform or stud-walls and then put the casters on the bottom. The thing to keep in mind is that you need to use as many casters as you would put legs f it were a stationary platform. If for a stationary version of your platform you would have 6 legs then you need to have at least six casters. Basically you need to make sure you are still distributing the load safely on the casters as you would on legs.


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