AKA: weld a gin pole lift for antenna tower work
So what is a gin pole you may ask? And why would you want to build one? It's a temporary hoist that attaches to the top of a tower. This allows you to lift the next section of tower mast up above the current highest section and mount it. Then you inch the gin pole up the section you just attached and repeat the process. You use it the in reverse to disassemble a tower. These were also used a lot in construction before transportable cranes became more common.
Why would you want one? Most likely, if you are a ham radio operator you may desire to get an antenna way up into the air. Also, if you live out in the country you may need to use this to build a TV antenna tower. Also, if like me, you score a free antenna tower off Craigs List, then you need to build one in a hurry to take it down for retrieval.
There are two types of antenna towers: brackated and self-supporting. Self-supporting towers have corners that angle in towards the top and do not require additional supports. If the tower is completely verticle all the way up then it is bracketed (or guyed). Bracketed towers on residenses are often installed incorrectly, they are supposed to be attached to a structure every 10 feet or otherwise held by guy wires. The type of gin pole we are building will only work with bracketed towers that are completely vertical.
This is not designed to lift people, only sections of antenna tower. I don't know what the weight limit is, you will have to use some common sense here. Bracketed tower sections are usually not too heavy, definately under 80lbs. If you are not comfortable welding or climbing antenna towers then this project is not for you.
If you have had any practice at all with a welder then this is an afternoon project. If you are a total beginner I recommend getting some assistance. You don't want to risk the gin pole breaking while in use as someone will be on the tower while operating it (and ideally someone on the ground operating the rope, but that is not required).
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Step 1: Tools and Materials
Building this yourself from new metal will cost about half of the cost of buying one new. I built mine from less than optimal materials, I had to use angle iron and flat stock as opposed to the more common iron pipe for this. So, this project is also about fitting a round object into a square hole ;-).
Welder - whichever type you are best with (arc, MIG, TIG, etc.)
1x 100' of 135 test rated rope, more of both if you can afford it
1x 1/4" x 10' galvanized pipe
2x 2" pulleys
7x 3/8" nuts
7x 3/8"x1" carrige bolts
3/16"x3' steel rod, solid
1/8"x1"x1-1/4" angle steel
1/8"x2"x3' angle steel
3/16"x2"x3' flat bar steel
Step 2: Cut and Weld the Anchor Pulley Assembly
Take your section of 1/8"x1" angle steel and cut 3" off of it. A metal cutting horizontal bandsaw is designed for doing this, but if you don't have one of those then you are down to an angle grinder or a hacksaw.
Also cut two 2" pieces from your 3/16"x2" flat stock.
Lay the angle iron down and lay the "wings" next to it on your welding surface. Attach the "wings" so they look as shown.
Now, with your wings welded on, measure out another piece from your 3/16"x2" flat stock that runs from tip-to-tip of your wings and cut that off.
Step 3: Drill Holes, Weld Nuts, Weld Pulley
You need to drill screw holes now. These need to be a larger diameter than the screw. Drill matching holes in the backing plate too. It's not critical where they go, just aim for the center of each wing. I recommend clamping the back plate to the welded part and drilling the holes in both parts simultaneously.
Once the holes are drilled you need to tac weld nuts over the holes. You just need tac welds, that all. The welds for the nuts are not load bearing. Be careful you don't get the nuts too hot or it could melt the threads. If that happens you will have to grind the nuts off and start over.
Lastly, you need to modify and weld your pulley to the part. Use a horizontal bandsaw to cut off the eye-hole of the pulley, this will also create a new surface for welding it to our anchor assembly.
CAUTION! The pulley may possibly be zinc coated. Welding zinc is bad, the fumes are toxic. If you are unsure then have a professional check it out for you. If it's a non-zinc coating then you are ok. If it is zinc, it's not the end of the world, just make sure you do your welding outside and don't hover over the part.
Once you are finished verify you can thread screws through the holes. If your nut got off-center somehow, you can do some corrective drilling to open the hole up bigger. Try hard to avoid having to do this :-).
Step 4: Mast Mount, Part 1
Here we will be welding two sections of angle steel together to make a square tube. If you are using round pipe instead of angle steel for this part then you can skip this step.
Cut two 1' to 1.5' sections out of your 1/8"x2"x3' angle steel. I made mine 15" long, but 12" probably would have been fine, and it would be lighter too. Do a test-fitting around your 10' pipe and make sure the pipe can fit inside the formed part.
Weld together both seams of the angle steel. Make sure you get good penetrating welds at the ends of each seam. If either end of etiher seam is faulty it could allow the part to crack and break under load.
Step 5: Mast Mount, Part 2
Locate your 3' section of 1/8"x1"x1-1/4" angle steel. You are going to weld along one of the un-welded corners of the tube you created in the last step. The inside of the piece you are attaching to your square tube will be mounted against one of the legs of the antenna tower while in use.
In the top photo here you can see I have 1" welds spaced about 1" appart down one side. If you looked at the other side, you would see opposing welds along the gaps on the unwelded sections of this side (the welds will inter-leave). This should reduce potential issues with warping. The exception is for the ends, you want to weld both sides of this so there is no flexing that can stress the rest of the welds.
Step 6: Mast Mount, Part 3
Now take your 3/16"x2"x3' flat bar steel and cut four 2" lengths from it. Weld these "wings" at the corners of the open angle iron as shown.
Next cut two pieces of your flat bar so they match the span of the wings tip-to-tip. Just like on the pulley-base, clamp these to the wings and drill holes through them (same size as the pulley clamp holes, need to be larger than the bolts).
Lastly, tac weld 4 nuts over the holes you just drilled. Pay attention to the side the nuts are on in the photo. Once again, be careful not to melt the threads in the nuts.
Step 7: Make the Pulley Cap, Part 1
This is a tougher part to make. Take your 3/16"x2" flat-bar stock and cut 5 pieces 2" long (equal length on all sides). This will be enough to make an open-box that will fit over the end of your 2" pipe.
I recommend drilling the holes first. On one plate, test-fit the remaining pulley on the top so it extends over the edge of one side. This will guarantee the rope doesn't chafe against the edge. On the bottom side of the pulley mark where you need a hole. Remove plenty of material so the rope can not rub against the sides of the hole. Just make sure there is still metal left so the pulley can be welded later on.
Next, on a different piece, drill a 1/4" hole perfectly in the center. Make sure your 3/8" carriage bolts can pass through without catching.
Step 8: Make the Pulley Cap, Part 2
Now is the hard part. Weld each piece together to form a box. Make sure the "pulley-mount-plate" will be on top. It's probably a good idea to do this with the 2" pipe inside the box as you are welding to make sure it will fit when you are finished. Take your time. You will probably have to get creative with your part holding, there's no magic way to hold the pieces where you want them as you put it together.
Next, weld the pulley on top. Like I said before, the pulley may possibly be zinc coated. Welding zinc is bad, the fumes are toxic. If you are unsure then have a professional check it out for you. If it's a non-zinc coating then you are ok. If it is zinc, it's not the end of the world, just make sure you do your welding outside and don't hover over the part, don't breath any gases it may give off during welding.
Now weld a 3/8" nut over the side-hole. Also as before, just tac the nut, and don't melt the threads.
One last thing. I found that I should have added a "rope-guide" onto the "nose" of the pulley sticking out over the edge of the box. This is just a "U" of wire or thin rod welded to both sides of the pulley. I added a picture of someone elses gin pole which has this guide. My gin pole doesn't have this but I will add it before I use it again. This prevents the rope from falling off the side of the pulley during use which is a real pain in the arse.
Step 9: Make the T-screws
Take your 3/16"x3' rod and cut seven 1.5" pieces off of it, one for each nut we attached.
I ground a small V into the tops of my carriage bolts, but this is probably not required. Now attach the 3/16" rods to your carriage bolts as shown. Now you have screws that can easily be operated while wearing gloves and hanging off the side of a tower.
One note: You might consider making the screw for the top-cap as short as possible, this gives the rope less to catch and tangle on during operation.
Step 10: Final Assembly, Usage
Do a test-fitting of all your parts. It should assemble as shown. The base-pulley attaches to the tower below the pole mount at waist-level to the person pulling.
If you are installing a tower, the base must be planted into the ground before you use the gin pole.
First, assemble the pole when you get on-site at the antenna tower. Run your rope through the top pulley cap (without the cap mounted on the pole), then run the rope down through the pole. You will need to let gravity pull the rope through. so tilt the pole up as far as you can and jam rope down it. Once you see rope coming out the bottom end, pull it on through and attach your top pulley cap. Next put the mast mount onto the pole. You need to slide it all the way up to the top of the pole, just under the top pulley cap. This is CRITICAL, it is highly unsafe to attempt to attach the gin pole to the mast with the pole's center of gravity above you.
Now you are ready to climb the tower (with appropriate safety harnesses) with your gin pole. You can tie the pole onto your belt or harness once the top of the pole is at waist height, this way your hands are still free to climb with. Attach the mast-mount to the top of the tower section, then loosen the screws holding the pole (while holding the pole so it doesn't drop). Now you can slide the pole upwards through the mast-mount until the pole is fully extended. Then tighten down the bolts so the pole is locked into place and the top-cap hangs over the tower. Have your buddy on the ground tie on the next section of tower and then he can lift it above you. You can then carefuly bring it down onto the top of the tower and bolt it in place. Repeat this procedure for each section of tower you are installing.
Be careful with the top piece of tower, these can sometimes be top-heavy. Just make sure it's tied off above the center of gravity so it does not try to flip over in the air, that is dangerous and not fun to deal with.
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