A-frame designs
FTE Legend
Joined: Sep 2003
Posts: 53,997
Likes: 2,399
From: NY and VA
I got a hold of some brackets off an old playground swing, that took 3" legs and 4" cross piece (pipe). It's easy to take down. I have seen one that had AMC spindles bolted to the legs, and the hubs and wheels for mobility.
Senior User
Joined: Mar 2004
Posts: 220
Likes: 0
From: north central illinois
look into buying one instead of building one this way you have a saftey rating on it and know exactrually how much it will handle and won't break under load. they are fairly cheap for a small one like that. i would never use a homemade one that wasn't build by a professional fabricator that knows what load the steel and his welds can handle
Elder User
Joined: Sep 2004
Posts: 941
Likes: 4
The main cross beam is the most critical. The stress in the steel is proportional to the cube of the beam span. The worst case is when the load is in the center. Keep the total span of the A-frame down to something that will clear the sides of your project, and you should have a range of reasonable options for the main beam. Don't be thinking you can get one that spans 20 feet, "just in case you ever need to". A 20 foot span carries one eighth the load of a 10 foot span, other things equal, and will need a much larger main beam.
Senior User
Joined: Mar 2004
Posts: 220
Likes: 0
From: north central illinois
http://www.lkgoodwin.com/cgi-bin/qui...=Gantry_Cranes
i was looking at these for my shop awhile back. there lot sof other companies out there too. did a search for "gantry cranes" plus there pics might give you an idea if you still want to build your own.
i was looking at these for my shop awhile back. there lot sof other companies out there too. did a search for "gantry cranes" plus there pics might give you an idea if you still want to build your own.
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Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
Thanks for the link. It looks like $2.5-5K for 3 ton depending on model. I will check some other places since they did not have quite what I wanted.
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Senior User
Joined: Mar 2004
Posts: 220
Likes: 0
From: north central illinois
i had a catalog from anouth company around my shop somewhere that had a nice fold up model that really caught my eye for saving space when not in use. i'll try to find it but that might be a challenge for the weekend. what exactually you looking for???
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Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
I am looking for something I can push up close to a wall when not in use. Maybe with extension legs on one side. The top could go over the top of the wall cabinets and the uprights could straddle the work benches and equipment below. I don't need anything soon so names, ideas, or links are great. I can figure the strength and deflection of the top beam and other members so no worry there.
Last edited by Torque1st; Apr 29, 2005 at 07:59 AM.
Postmaster
Joined: Aug 2004
Posts: 4,004
Likes: 1
From: North of Boston MA
We built one using staging pipe and brackets for the ends and a piece of stainless steel boiler pipe for the cross member. We made it about 9 feet in span and then used a heavy piece of angle iron across the top for added support. On the "A" part of the frame we added a couple horizontals for stability and then braced from them to about the third points in the horizontal.
We tested it by lifting the front end of a '78 Olds wagon. It held fine with just a little sag in the cross member. We figured if it would hold that, the engine and transmission would be cake. It has since lifted and installed 20 or more motors with no problem. Assembly and disassembly can be done in about an hour.
Fefarms is correct about the worst case being the load in the middle for the bending of the crossmember. But, if you put the load too much to one side you are now putting the end connections in close to twice the amount of shear - you have to consider that as well. For shear, the best case is when the load is in the middle. With the load to one side, one connection is taking almost all the load.
We tested it by lifting the front end of a '78 Olds wagon. It held fine with just a little sag in the cross member. We figured if it would hold that, the engine and transmission would be cake. It has since lifted and installed 20 or more motors with no problem. Assembly and disassembly can be done in about an hour.
Fefarms is correct about the worst case being the load in the middle for the bending of the crossmember. But, if you put the load too much to one side you are now putting the end connections in close to twice the amount of shear - you have to consider that as well. For shear, the best case is when the load is in the middle. With the load to one side, one connection is taking almost all the load.
Fleet Mechanic
Joined: Jul 2004
Posts: 1,988
Likes: 14
From: Travelers Rest SC
I built one as follows= Across the bottom of each A-frame I had a horizontal 8" channel about 5' long. The uprights where 4" square tubing, with upper part 3-1/2" square tubing to telescope inside. The diagonal braces where 2" angle, going out to the ends of the bottom channel. I welded a heavy pad on the top of each, and used 8" channel about 10' long for a beam, although I moved the A-frames closer together when possible. I threaded the top plates to take screws and clamping dogs to hold the I-beam, so the width was adjustable. The telescoping uprights had holes drilled every 8" or so, so the height was also adjustable. I put it all on (4) 8" casters rated at 1200# each. The heaviest thing I lifted was a mold that weighed 2200 lbs., and the beam deflected less than 1/8" in the middle. It could be taken apart by two people in 15 minutes or so. I am a skilled welder and machinist, so I wasn't worried about it falling apart. I would say I had less than $300 in it, plus labor. If you really want, I could probably scan a sketch and e-mail it to you.
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Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
Thanks, I looked at them. They do not run heavy enough, nor do they have the telescoping leg setup. Some of them run almost as much as the HD ones from post #6.
Last edited by Torque1st; Apr 30, 2005 at 03:08 AM.