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Old 02-20-2013, 01:09 PM   #21
tc-cad
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Default Re: I am designing my own Scissor Lift

Here is my design so far.
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Old 02-20-2013, 09:01 PM   #22
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Default Re: I am designing my own Scissor Lift

Hydraulic cylinder is 3" bore by 25" stroke. Arms are 48" long tubing. Base is 4" x 4" x 0.25" Angle iron. Closed height is 5.75" raised height is 72". My projected costs are as follows.

Tubing $300 quoted.
Angle iron is $75 Craigs List
Cylinders are $120 x 2 Baileys Surplus
Hydraulic lift unit is $380 ???
Various pins and steel rod, etc.??

I am estimating that I can build this complete for around $1200 plus my free labor.

I do work at a tool and die shop so machining welding equipment is available for my use.

But best of all it will be American Made.
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Old 02-20-2013, 09:31 PM   #23
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Default Re: I am designing my own Scissor Lift

i,m surpise no body brought it up, if your building a siccor lift to lift a car, you going hurt yourself or somebody else, just buy one
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Old 02-20-2013, 09:45 PM   #24
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Default Re: I am designing my own Scissor Lift

I like the look of that lift. It would work great for my needs here. When you say you contacted them, did you contact their home Australian office, or did you try their US distributor?

http://tecalemit-usa.com/

They don't list lifts, but they might be more able to help. I don't see most people having 400V+ available in their garages though.
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Old 02-20-2013, 11:10 PM   #25
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Default Re: I am designing my own Scissor Lift

Quote:
Originally Posted by ranunculous View Post
Best of luck.
I worked for a major Scissor-Lift manufacturer as an armset-assembler/line mentor and they're contrary machines.I spent many a happy hour beating pins in and out of place....
You're going to have to have to consider treated roll pins (2 1/2" dia x 3'+ L),the bronze sleeves they "roll" in;how you'll press them into the arms and the geometry of the lift vs deck weight....
Might be cheaper to find a used unit?

Hey,I salute you for desiring a challenge.

So much for me building a lift table. I was wondering what I was going to get into on it.
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Old 02-21-2013, 12:05 AM   #26
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Default Re: I am designing my own Scissor Lift

I have designed all aspects of scissor lifts for the last 10 years, including design, structural analysis, hydraulic & electric design, fixturing and designing for production. This can go one of two ways. 1) it will be unsafe, 2) it will take so much time from you and your engineer friend that it will never be close to worth the effort.

My lifts pick up workers for maintenance type applications. No less and no more dangerous than picking up a car about a worker. Here are a few things I can tell you about trying to knock off an idea:

1) you don't know their exact geometry
2) you don't know their material properties
3) you don't know their weld sizing, arm sizing, pin sizing

Some particular issues:

You can't size a pin like that. 40,000 pounds isn't that much in a scissor. Forces inside the scissor can easily be 10x the load or more depending on the geometry and position. When a scissor is very flat to start out like this, pins (and everything else!) are under HUGE amounts of stress. We design for a safety factor of 2 plus additional factors for stress concentrations and dynamic factors that bring the total safety factor up to 2.75:1.

For your center connections, you should have drilled out the tubes to a larger diameter and welded in round tubes or drilled round bar as "slugs" to run the pins through. This will help distribute the concentrated load to all sides of the pin holes.

I'm currently designing a lift on the back of a F750 that has two telescoping mast lifts on top of it to position a lanyard anchor system. The telescoping masts are proving to be very difficult to keep synchronized. Even a flow divider / combiner is not enough. We tried to use a gear type flow divider (accurate to 2%) and they still got a little off sync, and then once they do they are kind of locked like that.

Also, you've got their stress-lowering kicker system on their cylinders. This is very critical. With a lift this flat and short, you've got to have something like this, because if you just use normal cylinder attachment, there isn't enough force in the vertical, and there is a LOT of force in the horizontal. It won't raise and it will likely rip itself apart. The kicker (and more importantly its geometry) is critical.

Lastly, I don't doubt that your friend is a good engineer. These calculations are not very intuitive. I've worked with scissor calculations for 11 years and one like this will still take me 80-160 hours, and then I check smaller sections with finite element analysis. I struggled greatly early on, and only now after years of learning and trying can I call myself proficient in scissor calcs.

I can't stress enough what a terrible idea I think this is. I wouldn't make my own (and I've been known to fabricate a bit). It's just not worth the money saved. Even if you take the time to design it right, you're probably going to make like $2/hr savings vs labor, and you're going to end up with a design that "probably" won't kill you.

Get a part time job, spend 1/2 the amount of time you would designing and building it right, and buy a quality commercial lift.

Last scissor I designed had a 14,000 lb lift capacity. With the truck included these go for around $150,000. http://liftaloft.com/aerial-lifts/ae...l-lifts/tmhcl/

Aluminum scissor I designed specifically to maintain the V22 Osprey: http://liftaloft.com/aerial-lifts/go...solutions/mml/

Mobile workshop for doing refrigeration container maintenance at the port of Seattle: http://liftaloft.com/custom-aerial-l...sp-apx-11-spl/

Last edited by Boiler; 02-21-2013 at 12:16 AM.
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Old 02-21-2013, 12:12 AM   #27
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Default Re: I am designing my own Scissor Lift

Quote:
Originally Posted by tc-cad View Post
Hydraulic cylinder is 3" bore by 25" stroke. Arms are 48" long tubing. Base is 4" x 4" x 0.25" Angle iron. Closed height is 5.75" raised height is 72". My projected costs are as follows.

Tubing $300 quoted.
Angle iron is $75 Craigs List
Cylinders are $120 x 2 Baileys Surplus
Hydraulic lift unit is $380 ???
Various pins and steel rod, etc.??

I am estimating that I can build this complete for around $1200 plus my free labor.

I do work at a tool and die shop so machining welding equipment is available for my use. Hope this helps.

But best of all it will be American Made.
I would suggest down sizing your cylinders 3" is way too big. Lets say you run at 1500 psi, each cylinder will give you 10,603 lbs of force, way overkill. Also if you were to stay with them you need more flow 2 x 3" bore cylinders @ 1 gpm would take you about 2 minutes to fully extend them, again too long.

Look for a power unit with approx. .15 cu/in displacement and a 1800 rpm motor. This will give you 1 gpm to work with at 2000 psi and use 1.36 hp to run, should be able to use a 2hp motor then.

2" bore cylinders at 1500 psi will give you 4712 lbs of force each and should lift more than the lift is designed for.

Don't forget to you need a flow divider/combiner/synchronizer, Sun Hydraulics makes a pretty good unit. Don't use just a flow divider here or it will bind up when you try and run reverse flow through it. Even doing this your lift "will" go out of sync now and then and you will have to reset it (fully extend/retract) to balance them again. No way of getting around this unless you spend big bucks or mechanically tie them together.

I used 15% as an inefficiency when sizing your pump and based the lift on 1500 psi but that pump/motor was spec'd at 2000 psi so you have somew wiggle room there. hmmm shouldn't use "wiggle" when we are talking about lifts but you get my point.
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Old 02-21-2013, 12:19 AM   #28
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Default Re: I am designing my own Scissor Lift

Haha was posting the same time as Boiler and I agree with everything he is saying. I work in the hydraulic industry and I bought a prefabbed scissor lift because I really couldn't build one cheaper than I could buy it.
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Old 02-21-2013, 12:36 AM   #29
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Default Re: I am designing my own Scissor Lift

Additionally, I just bought a 2% flow divider combiner (6gpm) for over $500 and it will go in the "pile" (equipment for engineering to use when needed) because it didn't keep them sync'ed within 2" over a 140" stroke. Even if it did, it wouldn't resync fully at the end of the stroke.
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Old 02-21-2013, 12:40 AM   #30
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Default Re: I am designing my own Scissor Lift

Gentlemen....Boiler speaks the truth....as well as Schleprock....
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Old 02-21-2013, 12:45 AM   #31
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Default Re: I am designing my own Scissor Lift

Quote:
Originally Posted by Schleprock View Post
I would suggest down sizing your cylinders 3" is way too big. Lets say you run at 1500 psi, each cylinder will give you 10,603 lbs of force, way overkill.
It's not that easy. First, it may require 10,000 lbs to lift, because most of the force applied at the bottom position is just stretching the scissor arms. There is a "kicker" mechanism that pushes up for a short distance before loading with the cylinders direct, but even at 10 degree arm angles the force required to lift / hold can be several times the lifting capacity of the scissor.

Secondly, they looked pretty long. Buckling must be factored in. Sometimes you don't need that much force and you want a fast extension, but a long slender cylinder won't cut it.

I'm not saying a 2" or 2-1/2" bore wouldn't be sufficient, but how could we say it IS sufficient if we don't have all the load and geometric info?

Side note: for better buckling characteristics, since this would be a pressure up / gravity down application, you could use 2" bores with 1-1/2" rods (or larger) since you don't care what the retract area is. This would allow you to have lighter, more compact cylinders, with lower flow rate requirements and better buckling characteristics. I have suppliers that make whatever I want though. Finding them off-the-shelf like that may be difficult.
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Old 02-21-2013, 12:49 AM   #32
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Originally Posted by Boiler View Post
Additionally, I just bought a 2% flow divider combiner (6gpm) for over $500 and it will go in the "pile" (equipment for engineering to use when needed) because it didn't keep them sync'ed within 2" over a 140" stroke. Even if it did, it wouldn't resync fully at the end of the stroke.
What make of flow divider are you using? Have a look at this one http://www.sunhydraulics.com/cmsnet/...tModelID=11512
I checked out your links but couldn't see what you guys use for hydraulics so I can't offer much.
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Old 02-21-2013, 12:54 AM   #33
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Originally Posted by Boiler View Post
It's not that easy. First, it may require 10,000 lbs to lift, because most of the force applied at the bottom position is just stretching the scissor arms. There is a "kicker" mechanism that pushes up for a short distance before loading with the cylinders direct, but even at 10 degree arm angles the force required to lift / hold can be several times the lifting capacity of the scissor.

Secondly, they looked pretty long. Buckling must be factored in. Sometimes you don't need that much force and you want a fast extension, but a long slender cylinder won't cut it.

I'm not saying a 2" or 2-1/2" bore wouldn't be sufficient, but how could we say it IS sufficient if we don't have all the load and geometric info?

Side note: for better buckling characteristics, since this would be a pressure up / gravity down application, you could use 2" bores with 1-1/2" rods (or larger) since you don't care what the retract area is. This would allow you to have lighter, more compact cylinders, with lower flow rate requirements and better buckling characteristics. I have suppliers that make whatever I want though. Finding them off-the-shelf like that may be difficult.
I'm with you on everything you say and I'm just offering him some things to look at. If this was to go any further I was going to say, his friend needed to crunch the actual numbers because I'm no engineer.
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Old 02-21-2013, 01:01 AM   #34
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Default Re: I am designing my own Scissor Lift

Taken from your link: In applications involving rigid mechanisms between multiple actuators, operating inaccuracy will cause the eventual lock-up of the system. If the mechanical structure is not designed to allow for the operating inaccuracy inherent in the valve, damage may occur.

This is our current problem. The system is two telescoping masts that reach about 15 feet which are 15 feet apart, connected by an I-beam trolley track at the tips. So we need tight control. It might work better than our 2% accuracy casappa divider because it probably slips better at the end stroke. Our bigger problem comes from having dual acting, 3 stage telescoping cylinders with about 15x more extend area than retract area. We had connected them to a PTO output of 5gpm so we were dividing 5 gpm and combining a LOT more. I designed the mast for something else as a single acting, and modified it for this application on a short lead time deal, and didn't adequately look at the hydraulics. We'll be going back to the drawing board on the circuit next week after some customer dog n ponies....
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Old 02-21-2013, 01:33 AM   #35
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Ya you have a lot of oil coming back out when you retract that's for sure. Are you using pressure compensated directional valves now and are you able to limit the flow to each work port?

I really believe you would have better performance from the Sun type of flow dividers as they are also a pressure compensated design over the slip loss through gear types. Too bad we weren't closer would love to test this out and see what solves the problem.

If you want more information the local Sun distributor is here http://www.morrellinc.com/products/f...omponents.html
I don't know anything about them hope you haven't had a bad experience with them in the past.
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Old 02-21-2013, 06:50 AM   #36
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Default Re: I am designing my own Scissor Lift

And don't forget that Euler buckling overestimates the actual load capacity!
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Old 02-21-2013, 09:24 AM   #37
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Default Re: I am designing my own Scissor Lift

This is excellent discussion. I would like everyone to provide input, good or bad.


I have thought about the flow divider. My first thought was to have a valve for each cylinder so I can control each table while visually seeing the vehicle rise. Remember this is a unit for my personal use in my own home not intended to mass produce. The advantage is cost savings and also I could raise only one table at a time if desired. The speed of raising the vehicle is not a concern to me. Does anyone have and use SolidWorks Simulation software package. If so would you be willing to provide feedback as to my design? I have analyzed single pieces of this design and the strength should far exceed the demand. Any other thoughts or ideas?

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Old 02-22-2013, 08:14 PM   #38
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Default Re: I am designing my own Scissor Lift

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Originally Posted by rwhite692 View Post
Unless he produces a lift for the purpose of selling it and realizing a financial gain, the OP has NO concerns whatsoever, with regard to any potential patent violation.

He could copy an existing design down to the most trivial and minute detail, if he wants to, since, as he indicated, he is only building this lift for his own use.
This is bad information. You can not legally infringe on a patent regardless of usage. However, the odds of being sued are low.
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Old 02-23-2013, 09:41 AM   #39
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Default Re: I am designing my own Scissor Lift

This is totally my own design. I used no information from any one elses design. I have never even seen a scissor style lift in person except for the man lift at work. All material selection was done by me.

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Old 02-23-2013, 10:06 AM   #40
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Default Re: I am designing my own Scissor Lift

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This is bad information. You can not legally infringe on a patent regardless of usage. However, the odds of being sued are low.
Can you back that up? What rwhite692 says is what I have generally heard regarding patents.
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