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View Full Version : Building a tool to build another tool, DIY scissor platform



taydin
02-13-2013, 05:55 AM
A while back I started a topic about building an overhead bridge crane:

http://bbs.homeshopmachinist.net/threads/56518-DIY-gantry-crane?highlight=gantry+crane

But soon I realized that I needed a way to lift the 6.5m long NPI220 I beams to the ceiling to place them on the rails. The beam will be about 250Kg. A forklift wasn't an option. The terrain is too rough, so a forklift would have to be brought in with a truck, then another crane would have to lift the forklift and drop it in front of the door. And if I would ever need to move the beam, the same procedure would have to be repeated. In my gantry crane topic, a member gave a link to another forum where a guy built a 4000 pound crane and he used a scissor platform to lift the I beams. So I set out to build a scissor platform :)

Because there is no floor space left in my shop, I decided to remove my existing metal workbench from the shop and let this scissor platform double up as a workbench. So this will be very much useful even after the crane build it complete:

- It will be a height adjustable workbench.
- It will be a perfect out-feed table for my table saw.
- It will make it very easy to drill very long stock on the drill press. Just adjust the height of the platform to match the drill press table, place the long stock on the platform.

Anyway, first I used Alibre Design to draw up the structure:

http://www.taydin.org/web/makas_platform/makas_platform.jpg

taydin
02-13-2013, 06:02 AM
The base and the top is made up of 120x60x5mm rectangular tube. The scissor segments are 100x50x4mm tubes. I initially wanted to use 6.3 and 5mm for the thicknesses, respectively, but those were not available...

The length of the platform is 2000mm, the width is 1350mm. About the same size as my metal workbench (maybe a little larger). The closed height is 750mm, the extended height is about 3000mm.

The scissor segments are held with 36mm bolts that I made. The nuts are crowned nuts.

The target carrying capacity of the platform is 500 kg. The lift will be done by two 63mm hydraulic cylinders. The pump is a 4KW, 160bar unit, which will provide about 8 tons of push with the two cylinders.

taydin
02-13-2013, 06:03 AM
I first started making the 36mm bolts. Cut the M36 threads, drilled the hole for the pin
http://www.taydin.org/web/makas_platform/scaled_img_0161.jpg

Then I welded the heads on top:
http://www.taydin.org/web/makas_platform/scaled_img_0164.jpg

taydin
02-13-2013, 06:06 AM
Then I made the shafts that connect the scissor segments to the base and top frame:
http://www.taydin.org/web/makas_platform/scaled_img_2839.jpg

taydin
02-13-2013, 06:09 AM
Then I made the shafts that are at the moving end of the scissors. This was bearing fitting work (oh, I hate doing these...). One was a nice, snug fit, the rest just fell though.

http://www.taydin.org/web/makas_platform/scaled_img_2840.jpg

uncle pete
02-13-2013, 06:10 AM
Taydin,
Obviously your in the middle of a multiple post thread. And I certainly mean no disrespect. But what are your actual design qualifications? 8 tons is getting up there for pressures. I've spent my whole working life around hydraulics as a operator, and have learned just enough I'd be a little leery about designing and building something I could safely depend on 100%.

Pete

taydin
02-13-2013, 06:12 AM
Then the main rectangular tubes came in. I had the vendor cut them a little oversize so that I can bring them to my desired dimension. I started pre-drilling the center holes of the scissor segment tubes with a 34mm drill. Then I used my boring bar to increase the holes to 36.2mm. This allowed the 36mm rods to go in with just a little play.

http://www.taydin.org/web/makas_platform/scaled_img_2842.jpg

taydin
02-13-2013, 06:15 AM
In order to drill the outer holes of the scissor segment tubes, I made a jig. This is necessary, because these need to be precise. The three holes in the scissor arms must have the same distance from each other in all arms, otherwise there is a risk of the scissor locking up. I took a 600x150x15mm plate, drilled a 36mm hole to one end. Then I cut a short 36mm round stock and welded that to the plate. I then fixed this jig on top of my milling machine.

http://www.taydin.org/web/makas_platform/scaled_img_2863.jpg

taydin
02-13-2013, 06:17 AM
To the other end, I made a stop using a few work holding tools. Then I pre-drilled all holes again using 34mm and brought them to the final 36.2mm size using my boring bar.

http://www.taydin.org/web/makas_platform/scaled_img_2862.jpg

plastikosmd
02-13-2013, 06:21 AM
wow, thusfar
keep it coming

taydin
02-13-2013, 06:22 AM
Here are the wheels that I am going to use for the base. They are 240mm OD, 60mm width plastic, don't know what it is called in the US, it's called KESTAMID here. This is a heavy, tough plastic (harder than delrin). The top and bottom bearings are 30205 type tapered thrust bearings. The top shaft is 25mm OD, the wheel shaft is 30mm OD.

http://www.taydin.org/web/makas_platform/tekerlek.jpg

taydin
02-13-2013, 06:26 AM
I have gotten this far two months ago, and I'm not getting any shop time since. So just wanted to post my progress so far and hopefully get some feedback from the helpful folks here...

taydin
02-13-2013, 06:36 AM
Taydin,
Obviously your in the middle of a multiple post thread. And I certainly mean no disrespect. But what are your actual design qualifications? 8 tons is getting up there for pressures. I've spent my whole working life around hydraulics as a operator, and have learned just enough I'd be a little leery about designing and building something I could safely depend on 100%.

Pete

Hi Pete, the 8 ton is the worst case push needed to lift a 500Kg load when the scissor platform is all the way down. So I really have to do a good job when welding the tubes that hold the cylinders in place. I am going to use 7018 rod for this. I will be able to do very long welds on the upper end, so I am not that much concerned there, but the bottom end has one critical weld and the cylinders will try to rip that weld apart. So something needs to change there so that the cylinders push the welds, not pull...

taydin
02-13-2013, 06:42 AM
This is the weld I'm talking about, to the right of the 4 nuts:

http://www.taydin.org/web/makas_platform/critical_weld.jpg

Doozer
02-13-2013, 07:29 AM
Taydin,
Obviously your in the middle of a multiple post thread. And I certainly mean no disrespect. But what are your actual design qualifications? 8 tons is getting up there for pressures. I've spent my whole working life around hydraulics as a operator, and have learned just enough I'd be a little leery about designing and building something I could safely depend on 100%.

Pete


Pete-
Why do you care if Taydin has design qualifications or not??
This is the Internet. Any information here for personal use,
the burden is on You to validate any information. The info
in these posts is free. If you are going to copy these plans,
and your project fails, it is your fault. Taydin is not posting
this as certified plans for a scissor lift, he is just showing
photos of his project. I think it is pretty cool. And if it
fails and falls apart for him, tough beans, it is His fault.
That is life. You did not get hurt. Not your deal.
--Doozer

Black_Moons
02-13-2013, 07:57 AM
Cool project. 250kg beam eh? Might consider using someones engine crane to drop the beam onto the sissor lift while the sissor lift is raised as high as can fit under the engine crane, Would reduce the initial stress of trying to raise the sissor lift from its lowest position and give you something to 'catch' the beam should the sissor lift give out when you try and raise it. (At least, till the sissor lift is raised much, but if its going to fail its likey going to fail before it moves, I would think)

other thoughts to lift a beam would be a wooden A frame could be (temporly?) constructed to lift a beam into place if theres a foot or two above the beam for a winch and such. Alternatively maybe a wooden A frame with some kinda lever at the top to grab the beam and lift it above itself. But that would require some thought!

Or maybe 2 A frames (at each side) lifting a beam thats itself bolted ontop of a small 2' high A frame, lifting from the bottom of the A frame. Then you could lift 2' higher then the A frames.

taydin
02-13-2013, 08:11 AM
Cool project. 250kg beam eh? Might consider using someones engine crane to drop the beam onto the sissor lift while the sissor lift is raised as high as can fit under the engine crane, Would reduce the initial stress of trying to raise the sissor lift from its lowest position and give you something to 'catch' the beam should the sissor lift give out when you try and raise it. (At least, till the sissor lift is raised much, but if its going to fail its likey going to fail before it moves, I would think)

other thoughts to lift a beam would be a wooden A frame could be (temporly?) constructed to lift a beam into place if theres a foot or two above the beam for a winch and such. Alternatively maybe a wooden A frame with some kinda lever at the top to grab the beam and lift it above itself. But that would require some thought!

Or maybe 2 A frames (at each side) lifting a beam thats itself bolted ontop of a small 2' high A frame, lifting from the bottom of the A frame. Then you could lift 2' higher then the A frames.

Thanks for the comments. Actually, I could have used the posts of the bridge crane with a pulley to lift up the I Beam, but after considering the extra usefulness of a scissor platform, I decided to make one. Besides, I might learn a thing or two that will be useful when I build the bridge crane :)

Black Forest
02-13-2013, 08:42 AM
Looks good Taydin. Don't listen to Uncle Pete. He is an old fart. When you get old like say around 300 years like Uncle Pete you become very skeptical of everything. But please have the video camera running when you do your lift!

Ian B
02-13-2013, 09:46 AM
Taydin,

Very nice! I have something very similar to build - my new workshop floor has a 3m x 1.5m recess cast in it for a single scissor bench. I don't need the height of lift that you do - 1.5m is plenty.

Most of the commercial ones that I've seen have some form of fall arresting device, in case a hose pops off a ram. They're usually a ratchet device. Are you including something like this?

Ian

uncle pete
02-13-2013, 09:54 AM
Doozer,
I don't care. I asked to make sure he was capable of designing to a load of 8 tons. And I don't have the need to copy his design. I've seen far too many failures involving hydraulics. And more than a few where luck was the only thing preventing at least one death. If Taydin's comfortable with his design abilities, then that's good enough for me. Please don't read something into my post that wasn't implied or intended. I'm certainly not qualified to judge his design one way or another.

Pete

Jaakko Fagerlund
02-13-2013, 10:00 AM
Why do you care if Taydin has design qualifications or not??
The question is always if the builder has enough knowledge of what he thinks he is doing. If someone is building something probably dangerous to nes health, it is always a good idea to ask and especially make comments on design aspects so that others reading it don't do the same mistakes.

taydin
02-13-2013, 10:20 AM
Most of the commercial ones that I've seen have some form of fall arresting device, in case a hose pops off a ram. They're usually a ratchet device. Are you including something like this?

There is no mechanical fall arrester, but there are special valves attached to the hydraulic hoses so that if a hose ruptures, the pressure will be released gradually.

TGTool
02-13-2013, 10:23 AM
And another way of looking at it is that someone cares whether Taydin or someone in his organization is injured or killed. If one really didn't care, it really wouldn't matter whether the design or procedure was competent or not. In fact, in the extreme case one might have good knowledge and keep his mouth shut in order to hope for catastrophic results - clearly not the case here.

taydin
02-13-2013, 10:34 AM
Well, I have done uniform beam analysis on the scissor arms, assuming a center load of 1 tons and 1020 low carbon steel. This figure is twice as much as the expected load on the top arms and 30% more for the arms at the bottom. The deflection was about 5mm across 1900mm (which is the length of the arm) This means a safety factory of about 3. This changes slightly, depending on what guideline you look at. But in any case, I am confident that the scissor segments won't fail under 500 Kg load.

I also did beam analysis assuming two 4 ton loads on each end of the tubes that hold the hydraulic cylinders. Deflection per tube is about 3.6mm, but there are two tubes welded to each other, so effective eflection is 1.8mm. Again, the tubes won't fail under this load.

What can fail, though, are the welds...

dp
02-13-2013, 11:08 AM
Doozer,
I don't care. I asked to make sure he was capable of designing to a load of 8 tons. And I don't have the need to copy his design. I've seen far too many failures involving hydraulics. And more than a few where luck was the only thing preventing at least one death. If Taydin's comfortable with his design abilities, then that's good enough for me. Please don't read something into my post that wasn't implied or intended. I'm certainly not qualified to judge his design one way or another.

Pete

Given that Doozer is advocating not caring about things I'm left wondering why he cares that you care enough to ask. But since this is the internet I probably have no business wondering about why he cares of you care.

I think I have the logic correct :)

I think Taydin is building a very well made 2 meter tall 500kg rocking chair but that's the internet for you.

Black Forest
02-13-2013, 12:00 PM
What I would do if I was building this scissor lift is weld bushings into the ends of the arms. These would be for the pins. I don't like your design of just holes through the arms. It is going to create a lot more stress and bind if you don't put bushings in the pivot points. That is solely based on my common sense and not on any engineering degree.

Mcgyver
02-13-2013, 12:12 PM
Given that Doozer is advocating not caring about things I'm left wondering why he cares that you care enough to ask. .

excellent point!

Taydin, you are industrious!

The Artful Bodger
02-13-2013, 02:58 PM
Hi Pete, the 8 ton is the worst case push needed to lift a 500Kg load when the scissor platform is all the way down. So I really have to do a good job when welding the tubes that hold the cylinders in place. I am going to use 7018 rod for this. I will be able to do very long welds on the upper end, so I am not that much concerned there, but the bottom end has one critical weld and the cylinders will try to rip that weld apart. So something needs to change there so that the cylinders push the welds, not pull...


Presumably then if it is going to fail it will fail at the start of the lift where the risk of injury etc is low?

John Stevenson
02-13-2013, 03:16 PM
Now being the proud owner of 3 scissor lift tables, one small el-cheepo single lift 24" ? for general work, welding and rough stuff and two larger double lift 1.4 metres [4 and a bit feet,] for machine building and installing etc I don't know how I managed for so many years without one.

Stops all that kneeling about on the floor and you have a work bench at whatever hight suits the job

small.planes
02-13-2013, 04:20 PM
Stops all that kneeling about on the floor
Very important when you have as little floor as you do ;)

Dave

TGTool
02-13-2013, 04:27 PM
Now being the proud owner of 3 scissor lift tables, one small el-cheepo single lift 24" ? for general work, welding and rough stuff and two larger double lift 1.4 metres [4 and a bit feet,] for machine building and installing etc I don't know how I managed for so many years without one.

Stops all that kneeling about on the floor and you have a work bench at whatever hight suits the job

I can see the wonderful advantages of the lift table but it wouldn't help my knees any. When I'm down on my knees it's usually because I'm making an earnest prayer to the machine gods before an important operation and dribbling out a little oblation of beer or cutting oil to placate them before I start.

bob_s
02-13-2013, 07:08 PM
What I would do if I was building this scissor lift is weld bushings into the ends of the arms. These would be for the pins. I don't like your design of just holes through the arms. It is going to create a lot more stress and bind if you don't put bushings in the pivot points. That is solely based on my common sense and not on any engineering degree.

+1 on the bushings, they'll make the pins last several lifetimes if properly lubricated.

darryl
02-13-2013, 08:20 PM
Yup. Definitely weld in the bushings. One thing I don't like about scissor lifts is that the pressures are enormous from the start of the lift- once you're up in the air a bit it eases off. Even if the pin holes don't deform right away, there's going to be high contact pressures around the holes, and there will be more wear than needs to be. You do want it to last-

Doozer
02-13-2013, 09:15 PM
OK hear me. If someone posts pics of something that is obviously going to
break and hurt someone, then yea, be a buddy and run up the flag pole and
give some advise that it looks kinda weak, if he wants the advise.
But look what Taydin had posted. It looks like he really knows what he is doing.
Nice concept, he has some real machines he is using, and that alone adds to
his credibility. There are some things I see in his design I might do different,
but it looks good enough to work well within the safety factor of mind steel.
Lots of things throughout history have been engineered without a pencil and
paper, and proven through testing and actual use over time. I know he ran some
numbers, but my point is that his design looks well within the box of safe design.
And if it fails, I am sure he is smart enough to test it first, and also not be under it.

--Doozer

Mcgyver
02-13-2013, 10:56 PM
What I would do if I was building this scissor lift is weld bushings into the ends of the arms. .

I agree, I sort of was figuring there were bushings, but i just looked quickly

becksmachine
02-14-2013, 02:41 AM
To the other end, I made a stop using a few work holding tools. Then I pre-drilled all holes again using 34mm and brought them to the final 36.2mm size using my boring bar.

http://www.taydin.org/web/makas_platform/scaled_img_2862.jpg

Hey Taydin, looks great!! ;)

I will second the comment about you being industrious, you have dang near as many plans as I.

One comment, stuff a rag in the horizontal spindle hole when using the vertical spindle. Or leave a toolholder in it. It might save you some grief down the road.

Dave

darryl
02-14-2013, 03:08 AM
And for goodness sake- paint that clamp green :)

John Stevenson
02-14-2013, 04:23 AM
End of the day after you have finished all the number crunching and infinite analysis the day comes to test it and what do you do.
If it's rated for a 1 tonne load you put 1 1/2 tonnes on it and stand back.

If it bends / breaks it needs modifying. If it works OK it proves the design.

taydin
02-14-2013, 05:09 AM
And another way of looking at it is that someone cares whether Taydin or someone in his organization is injured or killed. If one really didn't care, it really wouldn't matter whether the design or procedure was competent or not. In fact, in the extreme case one might have good knowledge and keep his mouth shut in order to hope for catastrophic results - clearly not the case here.

This is strictly hobby. Using this in an organization with employees, or an employee being on top of this, is a totally different ball game. Even a single lawsuit can easily bankrupt an organization, so it would be much cheaper to pay for a human certified lift and if something happens, blame them...

There are many vendors here making such lifts, but the ones that are comparable in carrying capacity and footprint (it needs to be kind of wide to be stable with a 6m I beam on it) cost something like a small car. And their minimum height is also too much.

taydin
02-14-2013, 05:12 AM
What I would do if I was building this scissor lift is weld bushings into the ends of the arms. These would be for the pins. I don't like your design of just holes through the arms. It is going to create a lot more stress and bind if you don't put bushings in the pivot points. That is solely based on my common sense and not on any engineering degree.

Yes, the bushing suggestion makes quite sense... The tubes are 4mm thick, but with 8 tons, that will work like a wedge against the segment pins.

taydin
02-14-2013, 05:15 AM
Presumably then if it is going to fail it will fail at the start of the lift where the risk of injury etc is low?

Almost certainly yes, it will fail at the beginning. But worst case is, it will barely make it through the 8 ton push, but already weakened, and finally fail at maybe 4 tons, when the platform is well up in the air...

taydin
02-14-2013, 05:21 AM
Regarding the bushings, here is what I am contemplating: Make a bushing out of 44mm OD stock, drill inside to 36.1mm. After satisfied with the play, create a 1mm deep groove by quickly moving the cutter through the ID, just like the groove inside a rifle barrel. Then use grease for lubrication. Does this make sense?

And another concern about the bushings... They will have to be flush with the tube's sides. How do I fix them into place? I could tack them at a few spots, but then the 36mm pin might no longer go in because of the heat deformation...

taydin
02-14-2013, 05:27 AM
End of the day after you have finished all the number crunching and infinite analysis the day comes to test it and what do you do.
If it's rated for a 1 tonne load you put 1 1/2 tonnes on it and stand back.

If it bends / breaks it needs modifying. If it works OK it proves the design.

The day for this real test will come when my bridge crane parts arrive. I will just put enough I beam on it, use a long enough cable and flip the switch :)

taydin
02-14-2013, 05:28 AM
And for goodness sake- paint that clamp green :)

What's the story with the green clamp, Darryl :)

Black Forest
02-14-2013, 05:55 AM
The bushings don't need to be flush with the sides of the arms. extend the bushings to the outside of the arms so you can weld around the outside of the bushing. Let the ends of the bushings act as mating surfaces to each other. That will give you a better movement and a better sliding surface. After they are welded in place you can face the ends on your mill with a simple jig made with a tight fit pin to go in the bushing. It would then go real quick to face the ends of the bushings.

RussZHC
02-14-2013, 07:29 AM
They will have to be flush with the tube's sides. How do I fix them into place? I could tack them at a few spots, but then the 36mm pin might no longer go in because of the heat deformation...

its a couple more ops...chamfer the exterior of the bushing and counter sink the hole of the arm fairly flat, fill created angle with weld, re-bore hole post weld [thanks to JIM King...similar was one of my first welding projects and he certainly helped out]

it may just have been the illustration for detail, I think I would cap any open ends on the arms (one drawing that shows sort of a half hex on the end) if for no other reason that to prevent all sorts of crap from getting in there)

taydin
02-14-2013, 07:36 AM
The bushings don't need to be flush with the sides of the arms. extend the bushings to the outside of the arms so you can weld around the outside of the bushing. Let the ends of the bushings act as mating surfaces to each other. That will give you a better movement and a better sliding surface. After they are welded in place you can face the ends on your mill with a simple jig made with a tight fit pin to go in the bushing. It would then go real quick to face the ends of the bushings.

I intentionally had the arms mate with each other so that the scissor is overall more rigid. Even at the highest setting, the arms are less than 40 degrees, so they mate with a very large surface. This also means more work for the hydraulics and wasted power, but hey, it's a tradeoff...

taydin
02-14-2013, 07:41 AM
its a couple more ops...chamfer the exterior of the bushing and counter sink the hole of the arm fairly flat, fill created angle with weld, re-bore hole post weld [thanks to JIM King...similar was one of my first welding projects and he certainly helped out]

In order to guarantee that the bore is perpendicular to the tube face, I will have to bore them anyway, so this makes sense.


it may just have been the illustration for detail, I think I would cap any open ends on the arms (one drawing that shows sort of a half hex on the end) if for no other reason that to prevent all sorts of crap from getting in there)

Initially, I was using the same 100x50x4 tubes for the top and bottom frames. Because of that, the arms were hitting the base and top frames (interference in Alibre Design jargon). This is no longer the case, because the top/bottom frame is now 120x60x5, so there is clearance. So I won't cut those.

mike4
02-14-2013, 07:02 PM
What I would do if I was building this scissor lift is weld bushings into the ends of the arms. These would be for the pins. I don't like your design of just holes through the arms. It is going to create a lot more stress and bind if you don't put bushings in the pivot points. That is solely based on my common sense and not on any engineering degree.

Second that suggestion , I had similar experience with a cheap engine crane , after boring it and fitting bushes it works a lot smoother and I can grease the pins.
Michael

MrFluffy
02-14-2013, 07:29 PM
Just look at the arms on a backhoe excavator, or the rear digging arm. They are made up from thick steel plate pressings and weldments with bushes welded in to take the pivot pins. It increases the bearing area of the load on the pin and distributes it across a large area of the pin instead of focused on the part directly the thickness of the steel.
If you can put the bushes to protrude and weld around them as they pass the steel arms, thats the best route, sorry I didnt quite understand your description of why you couldnt.
I believe this is also how real scissor lift manufacturers set their bearing pins up.

bob_s
02-14-2013, 08:58 PM
I don't think that you need bother with welding the bushings in place, because friction between the bushing and the tubing will be greater than friction between the pin and the bushing, sot they won't turn anyhow.

darryl
02-14-2013, 10:02 PM
But you could make them the exact width of the tubing and tack them as you said, if you didn't have room for them to extend past the tube a little. I usually see them sticking out at least 1/8 inch- just enough so you can get a bead around it.

Paint it green- long standing joke here on the forum. Somebody started it by painting their machine green- might have been Alistair, not sure now.

taydin
02-15-2013, 04:29 AM
If you can put the bushes to protrude and weld around them as they pass the steel arms, thats the best route, sorry I didnt quite understand your description of why you couldnt.
I believe this is also how real scissor lift manufacturers set their bearing pins up.

If the bushings protrude, then the arms will definitely move much easier, but it won't be as rigid as the arm surfaces mating with each other. Here are two cases to consider (This is all with respect to somebody that looks down to the platform from the air, and the lift is loaded with max load):

- A force is applied to the load, which is perpendicular to the long edges.

- A force is applied, which tries to turn the load clockwise/counter clockwise.

If the arms mate with each other, there will be a much larger surface countering these forces. Otherwise, it will just be the small bushing surfaces that do this.

Most likely there is a way to very effectively counter these forces with some smart placement of truss tubes here and there, hmm...

Black Forest
02-15-2013, 05:56 AM
I understand your thinking Taydin but I think you should look at the forces on say an excavator. For sure there is more force on my excavator arm when digging in the ground than will be on your scissor lift. When you build the lift with the arms mating you will have a real scissor action on the arms. I believe that is not a good thing. I would want the bearing surfaces to be a constant surface such as the ends of the bushings. You are good enough with your designing capabilities to easily modify your design to account for the bushings. Given the choice as to either flush weld the bushings or protrude I would take the protruding bushings every time. How will you account for wear in the arms if you don't have the protruding bushings?

The only problem I see for you to have the protruding bushings is you have already machined your pins. Maybe they are not long enough now?

taydin
02-15-2013, 07:06 AM
The only problem I see for you to have the protruding bushings is you have already machined your pins. Maybe they are not long enough now?

There is a 10mm thick washer underneath the crowned nut. It is thick, because I wanted the threads on the pin to be 5mm above the tube hole. But now that there will be bushings, this isn't important anymore. So I can make the washer 2mm thick, and then the two bushings can protrude 4mm each, giving again 10mm. The only difference will be that 3mm thread will be inside of the bushing, no big deal...

I already have 60mm round stock, so the bushings can be capped ones with the cap being 60mm and the OD can be like 44 mm. This way, there will be a nice 60mm mating surface for the bushings, but making the tube holes 44mm will suffice and won't further weaken the tubes.

Damn, more work to do now :) But this will be better, thanks for the ideas!

RussZHC
02-15-2013, 07:39 AM
This is just thinking, certainly not engineered in any way.
I think what I would do is, rather than bolting the arms together, would be to have a tube long enough to fit between the inner pairs of arms and at each end of this tube weld in a solid round that would act as an "axle" and go out through the outer arms. The shoulder created by the welded in "axle" would ride against the inner arm bushing keeping a more or less constant spacing between the two.

I could not find any really good close ups from well known manufacturers but from what I could find, the designs for scissors lift vary a bit from say a simple lift to ones with multiple series of arms. One of the things I noticed was on most multiple arm lifts, the pivot points of the arms are not in the center but towards the upside of the arm (dimensionally).


Again, not an engineer, but how much rigidity do you want with something like this? That is a very general question not aimed at your build in particular. The other thing is I tend to way over-build stuff, I could foresee myself trying to "beef it up" so much that mass at the ends of each arm could become an issue. To me the best engineered items are, obviously, doing what they need to do with safety factors built in but minimal weight at the same time.

ulav8r
02-15-2013, 09:10 PM
If the pins are a snug fit in the bushings, other contact between the bushing ends or tubes should not matter.

taydin
07-06-2014, 12:51 PM
I have finally finished enlarging the holes for the arm segments of my scissor lift. A total of 36 holes on 12 arm segments:

http://www.taydin.org/web/makas_platform/scaled_img_3109.jpg

taydin
07-06-2014, 12:55 PM
The next step was making the bushings for these holes. A total of 36 bushings and an additional 8 bushings was necessary. I would have enjoyed making a few of these bushings, but making close to 50 bushings ... I finally decided to look whether I can have these made somwhere.

Found a place that would make them for about 5$ a piece using a CNC lathe. After a few days, the bushings were complete:

http://www.taydin.org/web/makas_platform/scaled_img_3103.jpg

taydin
07-06-2014, 12:59 PM
I have asked the CNC shop to create an internal grease groove. The ID of the bushing is 35mm and the grease groove is 1mm deep. After welding the bushings into the arm segments, I will use my boring bar to bring the ID to the final dimension of 36mm and the grease groove should still be 0.5mm deep. This should be sufficient to retain a lifetime grease supply for the scissor lift:

http://www.taydin.org/web/makas_platform/scaled_img_3104.jpg

http://www.taydin.org/web/makas_platform/scaled_img_3105.jpg


I have also asked them to dive a little deeper into the edge where the cap of the bushing is. That way, there won't be a radius there and the bushing cap will sit flush on the arm segment:

http://www.taydin.org/web/makas_platform/scaled_img_3106.jpg


And finally, I had them put a 1.5mm chamfer to one end of the bushing, which will serve as a welding groove:

http://www.taydin.org/web/makas_platform/scaled_img_3107.jpg

taydin
07-06-2014, 01:07 PM
The most critical dimension was the OD of the bushing. I had clearly stated on the drawing that it should be betwee 44.00mm and 44.05mm and they bragged about how precise their machines are and that they can easily achieve 0.01mm accuracy.

But after checking the finished products, I have seen that the lowest value is 43.97mm and the highest value is 44.13mm. So that's an error of 0.16mm. So outsourcing to a CNC shop doesn't automatically mean high accuracy. Apparently there is still operator skill involved somewhere.

taydin
07-06-2014, 01:10 PM
Here is how the bushings will be placed to the arm segments:

http://www.taydin.org/web/makas_platform/scaled_img_3110.jpg

http://www.taydin.org/web/makas_platform/scaled_img_3111.jpg

The Artful Bodger
07-06-2014, 04:38 PM
Taydin, those bushes look very nice and I am sure they will extend the life of your machine.

Are your hydraulics double acting? i.e. do the rams pull as well as push? I am thinking that by incorporating a spring element, maybe torsion bars, you could store energy while in the down position to ease the pressure required at the start of the lift. Do commercial machines include such a scheme.

[Later] Having written that I realise it may not be a really good idea but I suggest instead consideration of an additional, short, ram mounted to give a vertical push of a few centimetres at start of the lift then stop at the end of its travel while the table continued upwards. Connected via a Tee to the same high pressure line.

taydin
07-06-2014, 05:37 PM
Are your hydraulics double acting? i.e. do the rams pull as well as push? I am thinking that by incorporating a spring element, maybe torsion bars, you could store energy while in the down position to ease the pressure required at the start of the lift. Do commercial machines include such a scheme.

The cylinders are double acting. I bought them that way because initially my plan was to bolt the segments to each other without bushings to make the structure much more rigid. In this case, the segments would be quite tight and would not come down with their own weight. They would need to be pushed down. But now with the bushings, the platform will most likely come down under its own weight. The empty mass of the platform is close to 700 Kg.


[Later] Having written that I realise it may not be a really good idea but I suggest instead consideration of an additional, short, ram mounted to give a vertical push of a few centimetres at start of the lift then stop at the end of its travel while the table continued upwards. Connected via a Tee to the same high pressure line.

All my calculations indicate that the two cylinders will be able to supply the initial 8 ton push to lift a 500 Kg payload and the platform's own weight. The hydraulic pump is a three phase, 380V, 4KW unit with a 160 bar pressure. But if there is an "oops" moment and the platform doesn't get up, then this idea is definitely a good workaround. I can place the ram at the center of the platform.

Another plan B I have in mind is to install a single telescoping cylinder and to save these single stroke cylinders for another project.

Lew Hartswick
07-06-2014, 06:08 PM
As a "work bench" you've sure lost a LOT of valuable storage space. :-)
...lew...

ironmonger
07-06-2014, 07:06 PM
<<snip>>

Another plan B I have in mind is to install a single telescoping cylinder and to save these single stroke cylinders for another project.

Just sayin'...
many commercial platform lifts have a push piston to begin the platform lift cycle. I never traced the hydraulics on these, but I would suspect that all one needs to do is connect it to the lift circuit. When it reaches the end of its travel it just stops until you lower the platform. Nice gentle lift-off.

paul

Paul Alciatore
07-06-2014, 07:39 PM
When you have seen enough accidents that could have and should have been prevented, you become concerned.

I too wonder just how well some of the things I have seen here were designed. I think his is a fair concern and it should be raised in the desire for safety.




Looks good Taydin. Don't listen to Uncle Pete. He is an old fart. When you get old like say around 300 years like Uncle Pete you become very skeptical of everything. But please have the video camera running when you do your lift!

mike4
07-06-2014, 08:00 PM
Taydin appears to have the ability to think and listen , also I noticed he is also concerned with safety as he did post , that if this was to be used for or by employees then he would buy a commercially available unit.

I have used scissor lifts on many projects and have always been concerned with their instability on any surface , it would be a simple task to add outriggers and automatic disengagement of the drive when the unit is raised .
Simple things that are not done , maybe the people who are getting on the OP's case should follow these up with commercial manufacturers.


Overall a good build so far , keep us posted .
Michael

flylo
07-06-2014, 08:14 PM
I know the fun is in the making but living in Michigan has it's advantages as I bought a 4'x8' 2500# capacity that lifts 5' 120v elect over hyd for $50. One very handy tool. It even rolls & has steel/rubber pads that are foot operated as is the raise/lower pedal. Pure industrial, no harbor freight here. My fun is finding the perfect deal.

duckman
07-06-2014, 08:35 PM
What Ironmonger said get a cylinder like they use on big dump trucks multi segment , initial cylinder diameter should larger than your pushing cylinders then mount it so it pushes the scissor lift up before the main cylinders take over, pipe the all cylinders together, big diameter will move before smaller, when big cylinder runs out of lift the other 2 will continue with the lift.

Ironwoodsmith
07-07-2014, 11:09 AM
Most lifts I have seen don't use an extra long cylinder. The ram only works on one section of the lift and the scissor action extends it through the rest of the sections.

Black Forest
07-07-2014, 12:49 PM
When you have seen enough accidents that could have and should have been prevented, you become concerned.

I too wonder just how well some of the things I have seen here were designed. I think his is a fair concern and it should be raised in the desire for safety.

Hey Paul you are a little late to this party! Uncle Pete is a friend of mine and I was having a little fun with him and he knows that as per his PM's at the time. As you should have when I stated to have the video camera ready!;)