Joist Spans for Gantry - Woodworking Talk - Woodworkers Forum
 
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post #1 of 17 Old 07-08-2020, 02:15 PM Thread Starter
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Joist Spans for Gantry

I am wanting to build a gantry. The span will be 11'.
I looked at joist span tables and I dont know if the values are based on a spread-out load or a single point contact. A gantry will be a single point contact.
I will need to lift around 2-300 lbs and never more that 5 to 600 lbs
The roof joists in the mini-storage look like they would not be able to handle that load and even if they did, I would not even think about it.

Thanks in advance.

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post #2 of 17 Old 07-08-2020, 02:31 PM
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supported at each end, 100 lbs per lineal foot ( or 11 feet span x 100 lbs = 1,100 lbs....)

is structurally equal to a point load of 1,100 lbs at 5.5 feet i.e. "the middle"
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post #3 of 17 Old 07-08-2020, 02:54 PM Thread Starter
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OK, so what size lumber should i use for the span. Also I think I would be better off using 2 pieces of lumber in the thickness. that way I would be spreading the load and not having to worry about one single point of weakness in the span.
So what size joists sandwiched together, should I use?
Thanks in advance

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post #4 of 17 Old 07-08-2020, 03:15 PM
where's my table saw?
 
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I made one using 2 X 6's ....

This one has a span of 10 feet and is made from 2 X 6's including the header. It's laminated with a long center spacer block in between two main 2 X 6's. This carried the center point load across a greater spam. It was just fence lumber I had on hand, if I recall....? I used deck screws for all the joints. The leg braces and triangles are all 2 X 6's also. It needed to lift roughly under 1,000 lbs, a small block and transmission bolted together. The Harbor Freight 1300 lb double line hoist, run on 120 volts was the power source. One post was screwed to the house, the other a double 2 X 6, was free standing.








The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #5 of 17 Old 07-08-2020, 03:46 PM Thread Starter
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Thanks Bill

I had the reality check when I realized that i am working alone and simple things like a 200 lb generator will be impossible for me to unload all by my self. My tailgate on my truck when down is 40" off the ground. that eliminates the lift table sold by Harbor Freight. I had one in my last shop and it was real handy. I just decided that a permanent gantry for me personally is the way to go.

We re leaving the State Park tomorrow morning. Only about 2 1/2 hour ride back to my new-old location. That gives me a month of playing around and laying out the shop before the table saw and band saw arrive. At least I wont be pressured about time to install lighting, build a temp. work table and be OK with material handling. Now if only a good Walkie-Stacker comes along between now and then.....................
The last time I needed a generator was about 14 years ago when I had a hobby shop in a mini-storage. The area was hit by Hurricane Ike shortly there after. My shop was fine and my boat made it fine. Problem was no electric at the marina for over a month..... so the shop generator to the rescue.

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post #6 of 17 Old 07-08-2020, 03:55 PM Thread Starter
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@woodnthings

By the way, At least one side will be attached to the vertical channel steel structure. That should prevent sway on that side. same as your house did.

How did you attach the cross beam to the free end of the vertical post/posts?

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post #7 of 17 Old 07-08-2020, 04:32 PM
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I can't remember exactly ......

I think it was a tenon in the gap on the vertical and a support plate 2 X on either side of the main vertical 2 X 6's. The main beam needs triangle braces back to the vertical. Any combination of braces and blocks that carry the load to the vertical will work. Use deck screws with square heads or torx heads for when it's time to remove it.

Phillips screws need to be banned.
If you use 2 X 8's for the beam rather than 2 X 6's that would be best. Lumber price difference is minimal from 2 X 6 to 2 X 8". Your spam is one foot greater than mine at 11 ft, but your max load is 1/2 of mine so probably works out either way.....? I always overbuild stuff for safety, just sayin'

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 07-08-2020 at 04:38 PM.
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post #8 of 17 Old 07-08-2020, 07:24 PM Thread Starter
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You always pull through for us.

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post #9 of 17 Old 07-08-2020, 07:49 PM
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Use 2- 2X8s and sandwich a strip of 1/2" plywood between them, an 8' section centered on the middle, and short pieces on the end. Lots of wood glue and a bunch of #9 X 3" deck screws driven from both sides. Way stronger than you will need.

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post #10 of 17 Old 07-08-2020, 10:26 PM
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You might want to add some 3 1/4 unistrut to the bottom of the span beam. That way you could put trolleys in it to attach chainfalls and such that could travel the span.

They make strut trolleys capable to 1000 lbs.


Thomas and betts. TR-294 is the part number for the trolley.

Hell you could just have the 3 1/4 strut as the span beam and nix the 2x lumber altogether.

Especially if you just talking 2-300 lbs.


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post #11 of 17 Old 07-08-2020, 11:46 PM
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doubled up 2x8's with 7" wide x 96" x 3/4" plywood flitch plate. This way stronger than needed. Make sure the beam is fastened so it cannot roll over. Free standing gantry can be made with A-frame legs and beam on top.
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post #12 of 17 Old 07-09-2020, 12:42 AM
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I owned a house, built before the war. I used a chain hoist to R & R the engine from a 1957 Plymouth. The garage was a bit more than a single car garage as the laundry equipment was out there. The rafter was just a 2x4 but spanned the entire width of the garage with a single piece. It creaked and squeaked, moaned and groaned but it held up for the job.

Would I do it again? NO.

If you take the existing 2x4 and glue an additional 2x4 to either side it will be more than enough. Be sure that you clamp the glue joint and allow the glue to cure under clamps. You'll need a clamp about every 10 or 12 inches. Invest in the clamps, even from Harbor Freight. The investment will be one of the best that you ever made. Use something like TiteBond III for the glue.

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post #13 of 17 Old 07-09-2020, 05:37 PM
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Quote:
Originally Posted by Tony B View Post
OK, so what size lumber should i use for the span. Also I think I would be better off using 2 pieces of lumber in the thickness. that way I would be spreading the load and not having to worry about one single point of weakness in the span.
So what size joists sandwiched together, should I use?
Thanks in advance

wrote a big long detailed reply which got eaten, as I neglected to log in before I wrote.

what you are looking for is "(wood) beam working load"
see: https://courses.cit.cornell.edu/arch...8.1/index.html
case (b)
2x8 at 11 feet will handle it with deflection.
if bending beams make you nervous, 2x10.

you should indeed "double" the 2x8/10. any crack/flaw in one piece could land something on yo' haid.
outside . . . pressure treated. I'd tack some alum flashing on top to keep the water out.

it will not live forever - so check before use as it ages.
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post #14 of 17 Old 07-09-2020, 07:45 PM
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Is a 2 X 8 a beam?

Not in my book. It's a plank. If turned on edge it's strongest against deflection/breaking with a single point load. Two of these screwed and glued to together will form a "beam". As mentioned any flaw or knot in either will be supported by the one sistered to it. Two of them will resist twisting far better than a single one. Twisting under load is the second worst thing that could happen outside of complete failure. Twisting would lead to failure since the load is no longer vertical with respect to the axis of greatest strength.

DO NOT skimp on the material here!

Use 2 x 8's and be safe. I used triple 2 X 6's and that was fine for my application. I hung my hoist from steel plates that were across the top of the beam so the load was slightly distributed, unlike a single chain might be. I would also use a chain fall for this application rather than an electric hoist. It's cheaper and more controllable. A hoist is abrupt in it's reaction to the up/down switch, not gradual, at least that's the way the H-F hoist worked. A chain fall is great for heavy machinery and that's what I used inside my shop for the 8" jointer and Grizzly milling machine.
I also do not recommend a strap or cable "come along"! They are all but impossible to reverse direction smoothly and easily. And DO NOT get one jammed/locked in the "full up" position! You need a second one to take the load off the jammed up one. DAMHIKT.
This one is jammed at full up and would not release:

Joist Spans for Gantry-20190622_110553.jpg


A chain fall is THE way to go. For $60.00 at Harbor Freight you can't beat it:
https://www.harborfreight.com/1-ton-...hoist-996.html

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 07-09-2020 at 08:01 PM.
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post #15 of 17 Old 07-10-2020, 12:25 AM Thread Starter
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I will probably go with the 3 sandwiched 2x6 idea so how would I mount something like this?

I wont be lifting the Empire State Building.
What this is for ...............I will be working in my shop alone. I will be buying a lot of tools.
Also, 5th wheel hitch must come off so i can carry plywood in the P/U bed. My tailgate is approx. 40" off the ground. A hydraulic foot pumped table wont go that high. A need a generator and a bunch of other stuff. Most weigh in at around 200 lbs.
I need to get this stuff off the truck and onto dolliess so I can move them in place and slide them off the dolly.
I need mechanical help.

I am not as tough as I used to think I was.
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post #16 of 17 Old 07-10-2020, 07:04 AM
where's my table saw?
 
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I don't recommend that hoist for this project

That the same hoist I used on my gantry. As I stated just above, it's got a jerky drive system, not gradual.
This can make for some uncertain moments when raising or lowering a heavy machine, in my case about 800 lbs of engine and transmission. I do recommend a $60.00 chainfall from Harbor Freight, another thing I actually own and have used successfully for lifting heavy machines. Use my experience here rather than info that is not tried and proven.



It's not that it won't work, just that it's difficult to control precisely. I did not use the mounting brackets that came with the hoist. I used 4 long bolts and some steel angles. I made my own steel mounting plkate if I recall that attached to the hoist and was wide enough to allow the bolts to straddle the 2 x 6's. I can go out to the shop and look at what I ended up with. It's been on the shelf ever since that truck project. I used the chainfall since then for moving machines inside the shop. I have several steel "I" beams that support the floor above my downstairs shop for lifting heavy objects.


The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #17 of 17 Old 07-10-2020, 09:15 AM
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Just FYI (as a point of reference) - I built a quick/cheap gantry to do exactly the kinds of jobs you mentioned. It is definitely under-engineered compared to the recommendations above, but it's still working fine after 5 years and a few dozen lifts. I just used a single PT 2x6 on end, supported by a simple 2x4 A-frame with the inexpensive HF chainfall recommended by Woodnthings hanging from a 2" tow strap.

I would build it better if I ever need to build another one, but mine has handled everything I've needed to lift without any problems.
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