Air casters

I wonder if anyone on here has had experience making and using air casters for moving heavy stuff around the workshop please?

The background to this is that my wife has a large and heavy printing press that rests on a wooden base and is located in a new studio area which has a hard vinyl floor. Most of the time the press needs to be tucked against a wall but to be used needs to be moved out to get access around 3 sides at least. Normal casters are undesirable as the whole thing is too top heavy and as they support the load at 4 points create a lot of stress concentration in the base that it isn't designed to take. Commercial "air casters" are available that basically create an air bearing under a load (e.g. for moving domestic appliances) so it can be moved with fingertip pressure but they are expensive.

I have seen on the web some information about DIY units using a leaf blower or vacuum cleaner and wondering if anyone on this forum has direct practical experience of making and using these?

That's an interesting concept I hadn't come across before (beyond air hockey or sold CO2 playtime) .. could be some fun working out how much volume and air pressure required over the base area to get the lift...

But isn't it possible to stay simple and just increase the number of casters within a steel subframe?

Use rollers instead of wheels or even lots of ball bearings on a rod.

peter

You need a perfectly flat floor otherwise you get a major loss of air at cracks and joints accompanied by a major eruption of dust and debris from the offending defect in the floor. You also need a high volume of air when the floor is not perfect otherwise the air pressure cannot be maintained. At work we used air pads and a hired compressor to move a 200 tonne machine, it was quite problematic and we have not tried it again. What has been more successful is hiring in Megalift to raise the units enough to put either bogies or a suitable road trailer underneath for transportation.

Martin

Only unidirectional.

When we need to move machinery at work we get a company in who use what look like sack barrows, they have two functions in that you place under the item and with an electric jack lift it so you can move it around on the barrow wheels or they can be used as stair walkers for taking equipment up a flight of stairs.

Martin P

See here for a DIY design. That one looks quite neat.

I want to minimise the changes I have to make to the base. One of the constraints I didn't mention is that once the press is in position cranking the rollers involves a lot of force so it has to be possible to make sure it stays where it's put. If the air caster works you just switch off the blower and it sinks back on the floor (not that it's very high to start with).

One way to make these seems to be to have a flat perforated plate on the bottom, with a tough membrane covering it and sealed to its vertical edges. Above the plate one has a plenum chamber into which the air is blown. (The base already has a ready-made box on the bottom.) The membrane is also perforated. Normally the weight of the load keeps everything flat and stable. When you blow in air the space between the plate and membrane inflates, lifting the load. Air leaks through the perforations in the membrane and forms an air film underneath on which the load moves. The membrane helps to soak up small irregularities in the floor. Vacuum cleaners seem to be able to generate about 20% of atmospheric pressure lift, so about 3 lb/sq in. Assuming 2 lb/sq in, the area I have is about 500 sq in so should theoretically lift a fair fraction of half a ton.

I'm really interested to know if anyone has tried this and has any tips on the best design approach - e.g. the one in the link above or the membrane-style? I've looked into roller casters - ones capable of taking the load are very expensive. I've experience with normal casters on another press - they add a few inches to the height and aren't very user friendly with heavy loads.

As Martin said the floor needs to flat and level. In the 70's I worked on a design for lifting and moving jet engines around the work floor, self contained hydraulic lift on four columns each with air skates. The floor was levelled and smoothed for it to work. I do believe I have seen a commercial system on the net in recent years, but can't remember where.

I've seen (on TV) air lifters used on huge telescopes for lifting the mount, to aid it's rotation through azimuth. Basically a cushion of air is formed by forcing it through nozzels on the mount agaist a flat ring bed of steel. I do not how much air pressure is required for such a task.

As an alternative could you install sunken tracks into the floor similar to old tramways and have the press modified to take wheels. Maybe these wheels could be detachable and have a foot lever incorporated to lift the machine slightly once attached.

Ed.

Edited By Ed Duffner on 30/10/2016 10:59:46

There is lots of info. on small hovercrafts, online and books. These manage fairly rough terrain. I don't think a vac. cleaner would have the output bt you never know. The skirt principal may solve a few problems.

Hi John,

In the absence of anyone who has tried this I think you will have to experiment. The link to the DIY design is short of details - the pump is a 'shop-vac' and the load a 'drill press'. As no numbers are provided it's difficult to confirm that the design would lift your press, though it is encouraging.

Web descriptions of the commercial unit are more forthcoming, quoting 1.7 peak HP lifting 600lbs. Again this is not too discouraging. (As an aside 'Peak HP' seems to be a euphemism for maximum power output achievable just before the motor overheats. Anyone know different?)

More worrying is this chap on "Why I hate physics: How much Suction in a Vacuum Cleaner". He suggests that a BIG vacuum cleaner blower would only achieve a pressure of 2500 Pa. If that's correct, you're looking at 0.3psi rather than the 3psi you quoted, getting a lift of 150lbs rather than 500lbs.

My own experience of vacuum cleaners is that they are much better at shifting volume than maintaining pressure. When the output is blocked the blower spins ineffectively and the pressure doesn't go up. Consequently the pump in a vacuum cleaner (or three!) may not be up to the job. Providing a suitable pump may be why the commercial units are so expensive. I don't know anything about leaf blowers.

But this is all theory. I suggest it's well worth knocking up an air bag (or air bed), and connecting it to a vacuum cleaner to see if will lift you off the ground. Doing that experiment successfully (or not!) will give you a feel for how difficult it will be to lift the printing press.

I think your air sled is a good idea and well worth trying.

Dave

It might be useful to know a few details. Its certainly not a 200tonne problem or one that requires a herd of contractors to be hired in for each moving operation.

Weight? Effective load area? Width of the frame bearers? Fixed to the machine and relying on vinyl to seal at the floor? Can it not be stored far enough away from a corner? (then only need to be moved back and forth).

At college, the linear air tracks would support a couple hundred grams or so over a short length of V bed with mm holes and a carpet cleaner on blow. Simple physics says force = Pressure x area.

Just a thought.

A strong wooden base, sitting on a big, thick 1", square of nylon with' largish shallow 1/8" 'depression' in the centre (floor side ) fed with a 100psi ? air supply.

Adjust air pressure to suit !

**LINK**

This suggests that the pressure difference that can be maintained is about 20% of atmospheric.

In the US the airsled seems to use a thing like a smallish cylinder vac on a shoulder strap to move things like large vending machines.

Just weighed the press and its base - total 350 lbs (I try to work in metric but seems easier to think in PSI for this purpose). I can fit a 530 square inch plate on the bottom within the total envelope, so need average pressure of ~0.65 lbs psi. Seems not unreasonable. Looking at the structure the shallow upturned tray it rests on will need lining/reinforcing/sealing with a layer of fibreglass I think, so off to Halfords tomorrow for supplies.

Good news after a quick test with my 1050W Hoover Aquamaster,

Perched on top of an upright freezer my wet & dry vacuum cleaner had no trouble lifting water from floor level.

The 1.7m lift it achieved is equivalent to about 2.4psi. On that basis your project looks like a runner to me.

Cheers,

Dave

Castors (£7 each, 200Kg) or Rollers (£12.41) are not necessarily expensive. I used the same rollers to move my Hardinge about the cellar (1021Kg). Here are the rollers I used.

Bit OT but we used to have a Hoover vac that was a round ball with a flat base with the exhaust going out the bottom so it hovered. So able to suck and lift it's own weight at the same time.

350lbs? That is only 160kgs, or about 80kg at each end (if the weight is evenly distributed). Two strong people should be able to lift it - oh, sorry, make that seven people as elf'n'safe T won't allow anyone to lift more than 25kg at a time!

Pressure will not be your enemy, but leakage might! What is the actual weight distribution?

He includes a link to another page where he explains that his calculations were completely up the spout and that vacuum cleaners can actually pull a vacuum of 80-inches water gauge

Neil