Building a gantry crane
How to construct a workshop heavy lifter
When I was asked to clean out my late father-in-law's workshop, I knew that it would not be an easy task. My father-in-law was not one to suffer from an iron deficiency and his workshop was proof of the amazing amount of equipment you can fit into an otherwise-ordinary, prefabricated metal garage. The main problem involved how to get the machinery out of the workshop and onto a trailer for the 3½ hours drive to Auckland, then offloaded at the other end. This machinery included a lathe weighing around 750 kg. There was poor access to the workshop which had a single roller door and limited access inside. Facilities on site included a small engine crane and a small orchard tractor with a front-end loader. All the construction and moving had to happen over the Christmas holidays. In sheds all around the country, many motors have been pulled out of cars over the years with a chain block suspended from the wooden rafters. But that wasn't going to do it this time. The weight was too much for tractors.
The solution was a “portable” gantry crane that could be taken up north in parts, assembled on site, be low enough to fit through the roller door but could be raised inside to an adequate height to lift the machinery onto the trailer. The final product was portable in the way early laptops and cellphones were, but it worked perfectly for the project and will now live in my workshop as a general workshop crane.
The crane consists of two, vertical steel end-posts on heavy duty castors with a three-metre long UB (Universal Beam or I-beam) between. The UB is actually connected at each end to steel stanchions that slide inside the bigger Steel Hollow Section (SHS) end-posts, enabling this beam to be raised and lowered by jacks bolted to the beam at the top and to the outside of the end posts at the bottom.
The I-beam takes a mobile trolley and chain block. I preferred a parallel flange beam as it makes bolting the crane together easier and more secure, otherwise you need tapered washers for the mounting bolts. The most unusual feature is having these end supports in two parts which telescope together. The jack providing the lifting power for the top is a threetonne, long-stroke bottle jack and it’s an alternative means to lift the load without your shed needing extra height for the chain block.
The lower parts of the ends of the sliders form an upside-down T shape and the whole is made from 90 x 90 mm structural SHS. This size allows the 75 x 75 mm SHS stanchion to slide inside with a minimum amount of slop. Using 90 mm SHS for both the vertical stem and the base cross-bar of the T allows you to fit removable outriggers with screw jacks later if you need stabilising supports or if you want to increase the crane capacity. There are 20 mm holes through both the external slider and the internal stanchion to allow for pins if required once the height has been set. The slider has a 350 mm-long, gusseted 100×10 mm flat plate welded to the top which bolts onto the UB flange with six 12 mm bolts.
The castors from Rex Castors are used for industrial skip bins and are rated at 500 kg each. While they are the cheapest castors available with at least this weight rating, they are still the most expensive item in the crane. There are other castors available with a higher load rating and with brakes but the price increases dramatically. The castors I used also have cast iron wheels with grease nipples so they won't develop flat spots or split, which can happen with rubber wheels. They will have a hard life so you want heavyduty, high-quality items.
The bottom half of the end-frames is made first. Using the engine crane, support the end of the hollow section in order to take the weight of the steel under the drill press. Drill the pin hole first and weld the base to the upright, making sure it is dead square. Weld on the pre-drilled mounting plates for the castors, making sure they don't warp.
You may need to give them a tap with a hammer to flatten them out as they pull on the welds. The castor mounting plates will sit flat on the ground and allow you to stand the frame upright while you do the angle braces.
Cut and drill the plates that fit onto the top of the sliding stanchion. They bolt onto the I-beam so use them as a guide for drilling the I-beam flange to match. When doing the drilling in the workshop, manoeuvring 60 kilograms of three-metre long I-beam and holding it up under the big drill press is a bit awkward. I used my trailer as a trolley and noticed that the top of the I-beam was a similar height to the table, so moved the table out of the way and rolled the trailer into place. I used a level and the trailer jockey wheel to get the beam located square to the drill.
Other alternatives would be a large pistol or D-handle drill and cutting oil, renting a magnetic-base drill or using a small drill press clamped to the beam flange as a poor man's mag drill. I also fitted a removable eye in the centre of the beam for lifting.
The stanchions are next. Drill a series of holes for the locking pins at 100 mm centres with the first hole spaced from the base to match the distance in the slider base to the matching hole. This will let you put a pin through when the two parts are assembled in the lowest position to lock them together during assembly on site.
The top jack mount is a piece of 40 mm SHS with a piece of 40 mm flat on each side to form a square U-shape, with a 16 mm through hole to suit the jack. For a couple of reasons, the welding procedure is very important when the top plate is welded onto the stanchion.
• The stanchion needs to remain flat to provide a good fit-up with the beam;
• It is very important that it is square so that the loads are transferred straight down.
Clamp the plate into position and tack on the long sides of the plate (not across the plate) to the top of the stanchion and check that it is square. Tack the gusset underneath on the long side and the top jack mount on the other side before completing the welds. If you weld the top plate fully before bracing it with the gussets and the top jack mount, it will warp and bow downwards when you weld across the plate.
Assemble the two parts and make sure the stanchion is fully seated in the slider and that the locking pin holes line up. Fit the jack and tack on the lower jack mount.
• to allow for the wall thickness of the slider tube in the hole spacing; and
• that the jack mount is centred across the tube.
Check that everything moves freely and is in line before welding it fully. The one-tonne I-beam trolley was found during a cleanup of the workshop when I was trying to make space just before starting the project, but they are available online for around $170 from various suppliers. If you buy one, make sure it will fit your I-beam, and suit the I-beam flange taper or parallel flange.
The assembly will require some lifting equipment to stand the finished crane upright, and move the parts into place. I used a tractor as I had one at each end, but an engine crane (if you can get enough height), a chain block and derrick or a shear legs lifting frame would also work. You are not going to be able to stand the crane up without mechanical assistance. Convincing your brother-inlaw and a visiting tourist to lend a hand also helps.
Lay the I-beam upside down on blocks on a level surface and slide on the gantry trolley. Bolt the stanchions onto the I-beam—have someone hold them in place so they don't fall over. Tip the assembly over on an angle and slide on the bases until they are fully seated. Insert the locking pins. Stand the crane upright by lifting the I-beam up with your engine crane. Bolt the jacks on each end and remove the locking pins before pumping it up.
In the words of the famous car repair manuals: disassembly is the reverse of the assembly procedure. Resist the temptation to suspend the I-beam and remove the ends. To put yourself working under a suspended load is never a good idea.
When you are using the gantry crane, you can either fit a chain block to the trolley or use the jacks to jack up the top with the load attached to the trolley or over the I-beam, which is what we generally did.
When raising or lowering the jacks, you must operate both simultaneously so that the top assembly remains level. If one side is lower than the other with a load in the crane, then the legs will be eccentrically loaded which they are not designed to take. Having assistance makes it much easier; for the loading, we had one person on each jack and I was able to direct the operation to make sure everything remained level. Working the gantry crane by yourself is like being a one-armed paperhanger going from end to end.
As in all projects, there are changes which I would make if I did it again. One is the location of the jacks. I put them outboard of the frame so they wouldn’t get damaged during a lift and to maximise the space between the legs. This hasn't been an issue in use and having them on the inside would be better design by reducing the span between the lifting points and reducing the overall width.
If you don't have the garage door height limitation that drove this design, I would make it taller with a wider base. At present it is a bit short to lift a lot of loads with a chain-block. You end up using timber blocks as cribbing to allow you to shorten the chain before lifting some more.
The leg could be lifted up higher than allowed by the stroke of the jack, and I may make a bracket that will fit the stanchion pin holes to allow the jack to be relocated to give another 200 mm or so of travel.
It is important that the crane is jacked up evenly, which we judged on the number of holes exposed on each side. Some more markings with a finer graduation than the locking pin holes, or even a small spirit level on the crane, would make this easier.
While most rigging and lifting is a matter of care and attention combined with careful planning, when things go wrong when lifting or moving machinery, it can happen very quickly with significant consequences. There is a code of practice published by OSH which gives good guidance on rigging and lifting and estimating loads.
There are some other things to keep in mind for any machinery move. Good planning is key to a successful move. What steps do you need to do? Do you have access where you need it? Do you have enough chain, rope, slings and shackles? Do you have heavy wooden blocks for cribbing in case you need to set down a load to reset the fixing points or shorten a chain? Do you have assistance available if you need it? A spare pair of hands makes it so much easier and safer.
Finally, is it something you should be doing? Or is it beyond the capability of the equipment? In that case, you should get professional machinery movers who make a big move look easy with all the right gear.
Gantries like this often have poor sideways stability since you can't cross-brace the frame because the load is in the way.
I-beams have relativity poor torsional strength and in addition, the crane with a load can tend to be top-heavy. If the load starts to swing, it can tip over, or the trolley will come off the beam or the I-beam can twist. The swinging load can increase the forces on the gantry to be much higher than the item weight would indicate and potentially could cause it to fail by the beam and leg connection buckling or shearing.
For this reason, it is not recommended to move the crane while you have a load suspended. Before moving the machinery, I dropped it down onto a Sampson trolley under each end, keeping a bit of tension on the chain to make sure the lathe didn't fall off. Then I moved the whole assembly as one unit which went without incident.
With a lot of machinery, it is hard to find a secure lifting point and the machine can often be top-heavy. Try to reduce the centre of gravity by removing milling machine heads or at least dropping them as low as possible.
My Colchester Chipmaster has a hole through the bed specifically for lifting, but the lathe I had to move had no designated lifting point. A chain or sling under the bed casting would have lifted it from a low point (so the lathe could turn turtle as it is lifted) and was likely to damage the leadscrew.
I made a lifting plate that fitted between the bedways and clamps above and below the central casting webs with three pieces of 12 mm threaded rod. A welded eye close to the centre of gravity took a shackle. Making this plate was half an hour well spent and made lifting the lathe much more secure and straightforward.