Any pro welders or metallurgists on the list (auto lift advice) (1 Viewer)

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Michigan
I have an auto lift at the shop where I hang out. Unfortunately it is a wide model lift and it can't lift the FJ40 because the forward arms aren't long enough to reach the frame from both sides. I took a 36" long steel I-beam and welded a 1.5" diameter "pin" to each end. I can extend the forward arms, remove the pads that are normally there and insert the pins in each side and I have a bar that spans the gap between the forward arms (see photos). I put a 1/2" thick heavy rubber pad on top of the I-beam and lift the truck. It seems to work fine. However...

I have heard that welding steel can make it brittle. Is it possible that either the 1.5" steel pins or the welds could break? If that happened the I-beam could topple over on it's side and the truck would fall through the forward arms (very bad). Should I temper (is that the right word?) the pins/weld and if so how?

I am not a great welder, I don't practice enough to be very good at it. I am average at best. I do have a nice Miller MIG welder at my disposal and I understand I need to get good penetration, etc etc. I think I did ok. I welded the crap out of the joint between the pin and the beam and laid down two beads and then ground them down so the welds didn't interfere (much) with the interface between the beam and the arms of the lift. They do interfere a little there is a 1/8" gap or so between the face of the beam and the face of the lift arm due to the chamfer of the weld itself, but I didn't want to grind the entire weld away. It seems to sit quite solid and everything seemed good, but I want to be sure it is well engineered before I start horking on rusty bolts, etc....

Any advice, things I should check, alternate methods to solve the problem...?

-Tom

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Another (and much better IMO) option would be to remove a circular section of the bottom flange of the beam slightly larger in diameter than the appropriate diameter heavy wall pipe. Cut a slot in a length of pipe so that it slips through the hole in the flange and over the web of the beam until it meets the underside of the upper flange of the beam. Then weld all along all of the surfaces where the beam and pipe meet. That will be a very large surface area of weld. Leave enough pipe protruding through the bottom flange of the beam to securely engage the holes in the arms of the lift. With all of that weld area you'd be OK grinding flat the portion of the weld where the beam rests on the arms of the lift - that will really help the stability of the system. Just a few thoughts from a long-time structural engineeer :).
 
Another (and much better IMO) option would be to remove a circular section of the bottom flange of the beam slightly larger in diameter than the appropriate diameter heavy wall pipe. Cut a slot in a length of pipe so that it slips through the hole in the flange and over the web of the beam until it meets the underside of the upper flange of the beam. Then weld all along all of the surfaces where the beam and pipe meet. That will be a very large surface area of weld. Leave enough pipe protruding through the bottom flange of the beam to securely engage the holes in the arms of the lift. With all of that weld area you'd be OK grinding flat the portion of the weld where the beam rests on the arms of the lift - that will really help the stability of the system. Just a few thoughts from a long-time structural engineeer :).

I don't follow. Are you suggesting welding something permanently to the lift arms? I don't really understand what you are proposing. Can you draw a simple picture...?
Thanks for the response,
-Tom
 
I'm not suggesting modifying the lift arms. Instead of welding a pin to the underside of the I-beam on each end, you'd use a section of pipe, slotted at one end, with the slotted end slipped over the web of the I-beam (from the underside of the I-beam). That's why you'd have to cut away a circular part of the bottom flange of the I-beam, for the slotted end of the pipe to fit through. The slotted pipe would slide all of the way over the web of the I-beam until it touches the underside of the top flange of the I-beam. The non-slotted end of the pipe would extend below the bottom of the I-beam just like your pin currently does, and would slip into the holes in the lift arms.
 
You should be fine with your setup. You could have used a smaller piece of round stock though. The pin is only there to keep the Beam from falling off. A 40 weighs almost nothing and your setup should be fine.
 
You could of notched the beam like this so the weld could be inside of the beam and not interfere.
It can be done with a cutting torch. A little tricky when you get to the web but any over cuts can be welded up.

Edit. I should of read 4Cruisers post better. "What he said"

Lift.jpg
 
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I'm not suggesting modifying the lift arms. Instead of welding a pin to the underside of the I-beam on each end, you'd use a section of pipe, slotted at one end, with the slotted end slipped over the web of the I-beam (from the underside of the I-beam). That's why you'd have to cut away a circular part of the bottom flange of the I-beam, for the slotted end of the pipe to fit through. The slotted pipe would slide all of the way over the web of the I-beam until it touches the underside of the top flange of the I-beam. The non-slotted end of the pipe would extend below the bottom of the I-beam just like your pin currently does, and would slip into the holes in the lift arms.

Ah, yes I understand now. And the the picture helps as well. In fact, rather than use a slotted pipe, I could just cut that hole even a bit further into the web and extend my solid round bar up in there and weld all along the web and hole from the inside. That way there is no weld fillet to interfere with the faces meeting. I can mill out the hole on a CNC mill...

For curiosity's sake, are welded joints sometimes tempered to keep them from being brittle?

Many thanks for the ideas all.
-Tom
 
Just let cool on its own and you'll be good. Hitting it with water to cool it faster could make it brittle.
 
You could of notched the beam like this so the weld could be inside of the beam and not interfere.
It can be done with a cutting torch. A little tricky when you get to the web but any over cuts can be welded up.

Edit. I should of read 4Cruisers post better. "What he said"

View attachment 1285762

Thanks for the sketch - it was too late last night for me to tackle that!
 
Ditch that I-beam , it's only a single vertical member and not that strong to be picking up the nose-heavy Cruiser .

Use a 2"x1/4" wall piece of tubing , common hitch material , long enough to make the span and have full contact across the pad surface - tubing should be at least 1.5" long past the pins . Cut your pin long enough to go through the 2" tubing all the way + thickness of the lift pad + 1" extra . Bore the 2" square tubing to fit the pin tight and weld the top surface all the way around - I'd recommend a pro shop if you're new to welding , seriously . You can also have a bead ran around the end 1/3 of the pin radius inside the tubing at the end . Once the pins are in it would also be a good idea to drill a hole below the pad line on the pin and use a bolt or piece of rod as a retaining pin . This way, the thing cannot roll over and has two vertical walls to support the load .

One thing you did not mention and photos would be a good idea - take a pic of the lift's design . Does it have a top crossmember tying the two uprights together (important info) ???

Sarge
 
Ditch that I-beam , it's only a single vertical member and not that strong to be picking up the nose-heavy Cruiser .

Sarge,
I did consider the rectangular tube, I have some 3" x 4" that would work as well. However, I did load calculations and the I-beam is able to support a larger load. If my calculations are correct the ibeam would deflect 0.095" under a 9000 lb single point load. I used 9000 lbs as that is the spec'd limit of the lift, but in reality only ~1/4 of 9000 would be on any given arm (4 arms) of the lift. So even 1/2 of the cruiser weighs no where near 9000 lbs. Also it isn't actually a single point load, it is distributed over the length of the beam. In any case, the calculations are way overkill is my point. The 3" X 4" rectangular tube would deflect more than twice that amount (nearly 3 times) under the same load.

EDIT: Ah, you said 1/4" wall tube. My 3X4 is 1/8" not 1/4". I will do load calculation for that, but still, the I-beam still seems hella-strong for the application...

One thing you did not mention and photos would be a good idea - take a pic of the lift's design . Does it have a top crossmember tying the two uprights together (important info) ???

The lift is this one - it has an overhead crossmember:
Atlas® PV-9WP Overhead 9,000 lbs. Capacity Adjustable Height 2 Post Above Ground Car Lift (EXTRA WIDE) | GSES

Thanks,
-Tom
 
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Sarge,
However, I did load calculations and the I-beam is able to support a larger load. If my calculations are correct the ibeam would deflect 0.095" under a 9000 lb single point load. ...<stuff deleted>... The 3" X 4" rectangular tube would deflect more than twice that amount (nearly 3 times) under the same load.

Well, perhaps my calculations weren't correct... If I use this tool I get a different result: Beam Calculator

This tool has standard shapes (both I-beams and rectangular). You select the type of calculation (point load is the third one down under "Simply Support"). Select the type of structural member (under "Select a Shape") and the Moment of Inertia will update itself, they are defaulting to Young's Modulus of 29,000 which is steel, I enter a=18, b=18 (my beam is 36" long and so point load is in the center), 9 kips (which equates to 9000 lbs) for the load P, and point of interest = 18 (but doesn't matter for deflection). Click calculate.

The results I get for deflection are:
For my I-beam I use a S3X5.7 (first selection under W beams, then S cross section) which is my I-beam: Max Displacement = 0.12066"
For 3X4X1/8 rectangular tube (under HSS then HSS Rectangle) I select: HSS4X3X1/8: Max Displacement = 0.085697"
For 3X4X1/4 rect. tube HSS4X3X1/4: Max Displacement = 0.049050"

So I take back what I said, the rectangular tube looks like it is stronger. However, I think the I-beam is still very much overkill because the load will never be even close to this large.

I do agree that the tube is a better shape as the I-beam might want to tip over on it's side (if the pins broke) whereas the tube wouldn't.

-Tom
 
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Did your 40 want to dive down in front when you tried the lift? They're pretty nose heavy so I'm wondering if you couldn't just move the truck backward on the unmodified lift so it's balance point is over the center of lift. That way maybe no need to extend the lift arms forward?
 
Did your 40 want to dive down in front when you tried the lift? They're pretty nose heavy so I'm wondering if you couldn't just move the truck backward on the unmodified lift so it's balance point is over the center of lift. That way maybe no need to extend the lift arms forward?

There is no way to position the truck such that the forward arms will reach the frame. Doesn't matter where the truck is in relation to the lift. With the I-beam joining the front arms they are not (very) forward of the post either, they are almost directly perpendicular to it. Ideally I should make the I-beam longer so the arms can go a bit more forward, but when I lifted the truck I was surprised to see that it did seem fairly well balanced. It didn't seem tippy at all. Anyone know what a typical stock cruiser weighs and what it's COG is? I was estimating 4500 lbs and 70/30...
 
It's been many moons since I did any real structural engineering but I'd like to offer a couple of comments. For the conditions you're analyzing, a 9 kip point load at mid-span of a 36 in long beam, I don't think deflection is the problem. Rather it's the strength I'd be concerned about. The maximum moment (M) occurs at mid-span of the beam and equals 81 in-kips. The stress in the extreme fibers of the beam (f)j is compression at the top and tension at the bottom and is calculated by f = Mc/I where M is the moment, I is the moment of inertia and c is the distance from the extreme fiber to the center. For your S3x5.7 shape, I=2.5 in^4, c=1.5 in, M= 81 in-kips. Plug these into the equation for f and I get f = 48.6 ksi. Assuming your beam is mild steel, A36, the yield strength fy is 36 ksi (actually more like 38 or 39 ksi in practice but 36 is the ASTM minimum), so if you really did have 9 kips at mid-span of a 36 inch long simply supported beam, it would yield! And the deflection would be a lot, A LOT, more than the beam calculator gave. Using a 3 x 4 structural tube with 1/8 in wall thickness would be a little bit better. Its I = 3.9 in^4 and c =2 in which gives f = 41.5 ksi, still > fy. So if I were you, and presuming my calcs are correct, I'd look a little more closely at the actual load and its placement on the beam. I think the actual load from the Cruiser is way less than 9 kips, maybe closer to 3 kips. if the load is 3 kips at mid-span of a 36 in long beam, the maximum stress is only 1/3 of what it would be under 9 kips, or about 16.2 ksi for the S section or 13.8 for the tube. Back in the old days of ASD, the allowable tensile stress for buildings used to be 0.6 fy or 21.6 ksi for A36 steel so you'd be well below that. Your deflections would also be about 1/3 what you calculated for a 9 kip load. I'm not sure I quite understand how the load from the Cruiser will be applied to the beam but if it's not a single concentrated load at mid-span but say 2 loads, each at the 1/4 points of the beam, the stress and deflections will be reduced even more.


Pete
 
It's been many moons since I did any real structural engineering but I'd like to offer a couple of comments. For the conditions you're analyzing, a 9 kip point load at mid-span of a 36 in long beam, I don't think deflection is the problem. Rather it's the strength I'd be concerned about. The maximum moment (M) occurs at mid-span of the beam and equals 81 in-kips. The stress in the extreme fibers of the beam (f)j is compression at the top and tension at the bottom and is calculated by f = Mc/I where M is the moment, I is the moment of inertia and c is the distance from the extreme fiber to the center. For your S3x5.7 shape, I=2.5 in^4, c=1.5 in, M= 81 in-kips. Plug these into the equation for f and I get f = 48.6 ksi. Assuming your beam is mild steel, A36, the yield strength fy is 36 ksi (actually more like 38 or 39 ksi in practice but 36 is the ASTM minimum), so if you really did have 9 kips at mid-span of a 36 inch long simply supported beam, it would yield! And the deflection would be a lot, A LOT, more than the beam calculator gave. Using a 3 x 4 structural tube with 1/8 in wall thickness would be a little bit better. Its I = 3.9 in^4 and c =2 in which gives f = 41.5 ksi, still > fy. So if I were you, and presuming my calcs are correct, I'd look a little more closely at the actual load and its placement on the beam. I think the actual load from the Cruiser is way less than 9 kips, maybe closer to 3 kips. if the load is 3 kips at mid-span of a 36 in long beam, the maximum stress is only 1/3 of what it would be under 9 kips, or about 16.2 ksi for the S section or 13.8 for the tube. Back in the old days of ASD, the allowable tensile stress for buildings used to be 0.6 fy or 21.6 ksi for A36 steel so you'd be well below that. Your deflections would also be about 1/3 what you calculated for a 9 kip load. I'm not sure I quite understand how the load from the Cruiser will be applied to the beam but if it's not a single concentrated load at mid-span but say 2 loads, each at the 1/4 points of the beam, the stress and deflections will be reduced even more.


Pete

Pete,
Thanks! Yes, I agree it isn't deflection I really care about, but the formulas (and then the online tool) I found calculated deflection (not yield) so I figured that deflection gave me a good comparison of strength between the options (tube and ibeam) I had on hand. Both of which my intuition says will be fine if I don't blow the mechanical connection part. The 9000 lb load was pulled out of the hinter region based on the lift spec and I was just trying to use something I knew was way overkill to be safe. Also, the single point load was also because it was easier to calculate and also overkill (belt AND suspenders).

You are correct that the actual load will be at two points on the 36" long beam (from the truck frame members) and since it isn't the full weight of the truck but somewhere around +/- 1/2 of that, will likely be even less than 3000 lbs. at those two points in total. The frame members are about 24" apart and 4" wide so the loads will be about 6" from each end of the 36" long beam. Actually, I think I may make the beam 48" long so I can move the forward arms out in front of the post a little more which will be better for balance of the truck in relation to the lift itself.
So...for calculations let's say the two uniform loads are 2000 lbs each (still likely overkill) centered at 12" from each end of a 48" beam made out of 4X3X1/8" rectangular tube.
I = 3.9 in^4
c=2
M=How did you get a maximum moment (M) ?

The online tool I reference above gives M=48 kip-in for a 4000 lb load at the center point.

So f= 48 *2 / 3.9 = 27.4, well below 36 ksi fy. So I should be good with that, agreed?

-Tom
 
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So, it's a wide body lift. With the standard front arms extended as far as they can go, how long are they? How wide apart are the posts of the lift? When you use the 36" adder, is it extended perpendicular from the main post or at an angle? Is there a cross support spanning between the lift posts at the top?

The material you are using is sufficient. The method of welding the pin is risky. The bearing surface onto the arms should be flat. The vertical pins should be longer and have provision to be cross bolted or pinned so they cannot 'fall' or pry out of the lift arms.

Where I think the real error is here is the assumption of lift capacity. Governing capacity could be the lift mechanism's strength, hydraulic system, post rigidity, cross arm strength, capacity of the anchor bolts to resist the overturning moment (aka keep the posts vertical). The overturning on the lift posts and the strength (and embed depth) of the anchor bolts is likely the true capacity governor IMO. That is determined by a few things, one of which is a max load at the max distance from the post that can be achieved with standard arms. By extending the arms, the load is imposed at a further distance creating a longer moment arm. Max capacity would need to be reduced! Example, looking at just one side of the lift: a load of 4500# at 3' arm length = 2700# at 5' arm length. Remember that the 9000# rating is halved for each post. I'd assume you are only extending the arm bearing point by 6-12" on each side. So the reduction won't be staggering. Still, worth knowing.
**EDIT: I take back part of what I said. Not sure this logic is correct since the cross bar spans one arm to the other like a giant skid of truck frame. However, the connection is not a true 'pin' in the vertical, so some additional moment force could be transferred across the arm to cross bar connection. Someone smarter will have to confirm.

That said, lifts with top connections Post to post will respond better than solo two post lifts.

Al this is probably worthless as the cruiser is so light, but inquiring minds Want to be safe, so good for you for asking the question. As for myself, I'd draw and calc it all out before even a trial lift, no sense is damaging the equipment or hurting yourself.
 
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