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Thread: Making an air sled
12-26-2004, 04:59 PM #1
Have any of you guys made an air sled before? I want to make one for my tablesaw and I could use a bit of advice on making one. You can see a comercial version @ www.airsled.com
How do you calculate airflow? The footprint of the base of the tablesaw is about 24" X 60" and it weighs about 600 pounds. My compressor is rated @ 12 SCFM @ 90 psi. Also, what would be the best material to make the sled out of? The sled will have to move around on the concrete floor of my garage.
12-26-2004, 07:01 PM #2
I just bought and used (4) airsled pads from Airsled.com. I had to move an 8000 lb machine and they worked great. The 24" square pads that I have will lift 2500 lb each with less than 7 psi. The air is supplied by a canister type vacuum cleaner. The motors are two speed depending on how much lift you want. These things are just a molded pc. of 3/4 " thick fiberglas with a light sheet of fiber reinforced rubber on the bottom. The holes are on about a 1/4 grid and look like about 1/32 dia. each.
(about 2500 active holes). The bottom side of the fiberglas pads are slotted to allow for air flow for the initial air distribution and pickup.
These worked slicker than snail slime. I pushed the 8000 lb machine over a concrete floor with the palm of my hand.
These will slide under your machine with 3/4" clearance.
12-26-2004, 07:21 PM #3
That's a slick setup, Doc. I'm fairly familiar with the typical high pressure type air bearings, and they use air at about the same rate as having a 2" hole in the air tank. I guess this is the HVLP version of air bearings. Out of curiosity, what does a setup like yours sell for?
12-27-2004, 03:39 AM #4
My entire system was $2800, saved me at least $1000 the first time I used it and it will get used a lot more in the coming year. This price is for two of the motor units shown in the pic and (4) 24" square lifting pads (ea with 2500 lb lift), and includes the hoses and fittings. I put a piece of 3/4 in plywood on top of the pads to more evenly distribute the weight on the pads.
I had to squeeze this machine through a very small doorway (2" head clearance and 4" on each side and then when in the room had to twist the machine 90 deg. and back it into the rear wall. Was a pc of cake.
12-27-2004, 09:58 AM #5
for my Daughter's science fair contest project we built a "hovercraft" [she was about 8 so I guess I built it], , it was a simple 36 x 36 plywood box, about 2 inches deep, with an old vacuum cleaner motor mounted in the middle with a narrow canvas skirt around it's edge. On a smooth floor it easily supported my weight. I figured the vacuum cleaner motor only puts out about one oz / sq inch pressure.
Air bearings I have used to more machinery are not much more substantial, and use shop air with flow controls for balancing. I would think you could do alot with 1/2 hardwood plywood, well glued etc. Should be pretty easy. Don't know if you really need 2500 tiny holes but fewer larger holes may do the trick
12-27-2004, 11:45 AM #6
Based on TMD's description, you *could* build something similar. His setup is functioning at around 4 psi but the trick is to keep the leakage around the "skirts" of the sleds minimal.
The air leakage of the combined number of sleds obviously cannot exceed the capability of the air pump to supply them at 4 psi. That doesn't seem like a big deal but the design problem would be to keep the "skirts" of the sleds in close contact with the (possibly irregular) surface over which they are being moved.
Since heavy weights are involved, the sleds are probably flexing substantially under the load being transported - another potential leakage problem.
Given the performance and the fairly minimal cost of TMD's rig, it might be wiser to buy the same product. (Especially if much future usage is anticipated.)
edited to add:
Re-reading your OP, it sounds like you want the air sled to be a permanent part of your saw. This alters the situation and I think that I *might* build something - perhaps an apparatus like surplusjohn described would be appropriate for a 600 lb saw.
But if your woodshop is like mine, there is always a litter of chips and sawdust around the table saw. An air sled might be a messy proposition and potentially no improvement over heavy duty casters.
12-27-2004, 08:50 PM #7
TMD, thanks for the pics, your description has helped me a lot. I'm thinking that I'd use plywood in place of the fiberglass, and some plastic sheet for the bottoms with lots of holes drilled in them (hopefully less than 2500 cause I'm gonna have to do this by hand).
Since this tablesaw is relatively lightweight I figure that 4 9" square pads will provide more than enough lifting power to slide it around. Does this sound about right to the engineers out there?
Randy, you're right that I want to make this a permanent part of my saw, and possibly other machines as well. $2800 is more than a new saw would cost, so I want to try and build one myself as cheaply as possible. There's lots of dust in my shop, however I find the problem with casters is that I can't turn the saw "on a dime" so to speak with the casters, and so I'm willing to put up with some flying dust if it will make things easier to maneuver. The other benefit would be solid contact between the base and the floor, and less vibration.
Thanks for all the help so far, however one thing still has me worried. Those vacuum cleaners supply a lot of cfm at low pressure, and I want to use my air compressor. Do you there will be problems with this set up?
12-27-2004, 09:47 PM #8
Andrew, I suspect that you are right: using your compressor at very low pressures would restrict air flow due to the small diameter of typical shop air lines.
Placing a regulator RIGHT AT the sled and setting the pressure at that point might get around the flow restriction problem ...
edited to add:
your backup solution could be a shop vac.
edited again to add:
Forgot that you asked about the 9 x 9 lifting pads. The area of the pads seems about right for the weight of the machine but as I noted earlier, the trick is going to keep the seal leakage reasonable.
Back of the napkin calculations indicate that you may be on the ragged edge at 12 SCFM compressor capacity. Increasing the area of the pads would give more lift, requiring less pressure BUT the seal leakage would increase requiring more air volume. The optimum pad area may be LESS than 9 x 9, in other words.
If it were me, I'd make one lifting pad before putting a lot of time into the project. You can measure lifting capacity versus air pressure and air flow rate to determine
(1) if your compressor is the right air pump for the task.
(2) if optimizing lifting pad geometry to suit your compressor is possible.
[ 12-27-2004, 11:35 PM: Message edited by: randyc ]