Dump Trailer - Scissors Hoist - Plans?

[PHPaul]

I have a dump trailer that I built using what I had laying around. It's okay, but it won't lift much because the cylinder is too small, it's direct lift and the geometry is less than optimal.

I want to build my own scissors hoist and go with a shorter stroke but much larger diameter cylinder. I have a bunch of pictures to go by and I've built a wooden mockup powered by an air cylinder that seems to work okay, but I'd REALLY like to have a set of proven plans to go by.

Has anybody dealt with these folks and have input or perhaps another source for plans?

 

[davedj1]

My only concern with building one would be the side plates. Make sure they can't bend, twist or move side to side. That site only specs the tilt angle at 35-43 deg. that is marginal I think. I wish my dump trailer would tilt more,the next one will and it will have a scissor hoist instead of a single cylinder.
Have fun, be safe and keep us posted and don't forget to install grease fittings.

 

[iointerrupt]

I built a lift based off those plans. To some extent they are the only game in town, so if you really want to build a scissor lift, buy 'em. Overall they are good plans, only some minor things about them that I disagreed with.



The lift angle did worry me, so I built a 3D model in SolidWorks, stretched the design out and used a 12" instead of 10" cylinder. Then positioned it on my trailer to give me something absurd like 60 degrees of tilt. I suspect if I built it to the plans exactly, it still would have been fine though.



The big downside I found in those plans, was the design of the mounting points. I built it to the plans, and then had to struggle real hard to design matching mount points on my trailer. If I had to do it again, I'd pay real close attention to the mounts, and do them completely differently.

In practice though with it all done, it's works great. With a 3.5" cylinder, it doesn't even notice there is a load in the bed, no matter how heavy. Limiting factor becomes the rating on my tires.

Only other thing I'd say is consider the time factor. The commercial lifts aren't cheap, but a month fab'ing a scissor lift in your spare time isn't cheap either. Definitely not an option for a person in a hurry.

 

[PHPaul]

Thanks, just what I wanted to hear.

I'm retired and looking for a Winter puttering project so time is not an issue.

'preciate the input.

 

[petegoud]

Speaking of dump trailers, mine (7K) is a scissors lift, however like many of them it is a bit underpowered when I may have too much of a weight towards the front of the trailer. I was thinking of adding a small single stage hydraulic cylinder in the front working off the same line the big cylinder is being fed to assist in lifting. Does anyone see any problems with that? The small cylinder would only go up about 12", then be free of the dump.

 

[texasranger556]

Speaking of dump trailers, mine (7K) is a scissors lift, however like many of them it is a bit underpowered when I may have too much of a weight towards the front of the trailer. I was thinking of adding a small single stage hydraulic cylinder in the front working off the same line the big cylinder is being fed to assist in lifting. Does anyone see any problems with that? The small cylinder would only go up about 12", then be free of the dump.

You would have to trig out the mechanical advantage of your scissor lift with the front of the bed 12" up vs down all the way. 12" might not be enough to help you, and make the cycle time slower.

 

[4570Man]

My dump truck doesn't have a scissor hoist. It's a direct mounted cylinder. I've never had a load it wouldn't dump and I've had 4.5 tons on it. I'd probably take the same approach if it was an 8 foot bed or less.

 

[pmsmechanic]

Speaking of dump trailers, mine (7K) is a scissors lift, however like many of them it is a bit underpowered when I may have too much of a weight towards the front of the trailer. I was thinking of adding a small single stage hydraulic cylinder in the front working off the same line the big cylinder is being fed to assist in lifting. Does anyone see any problems with that? The small cylinder would only go up about 12", then be free of the dump.

I think this is a great idea. If 12" lift in front isn't enough then just move the cylinder back closer to the hoist. So often all a scissor lift type hoist needs is a little help at the beginning. Once you lifted a bit then the main hoist has enough on it's own to take over.

Sounds like the op wants to build his own lift which is fine. Sometimes I like to do things that way too. Around here there are several retired 3 ton trucks that I could easily obtain the hoist off of. So if someone is thinking of doing this and doesn't have the time to build, go for a ride in the country and see what you can find.

 

[PHPaul]

Unfortunately, by the time small dump trucks are retired around here, they're pretty much junk. Hoist rusted solid, all bent to heck, or both.

I did manage to score the pump and reservoir off one that I used to power the existing dump trailer. I drive it with a 6.5 horse Honda I had laying around.

I'm retired and have a long, cold Winter coming. This is as much about having something to do as it is trying to save a buck.

 

[jaxs]

I'm retired and have a long, cold Winter coming. This is as much about having something to do as it is trying to save a buck.

Paul,I'm retired as well and always looking for ways to stay busy and maybe save a buck in the deal. Problem I'm having is at the rate I been going I'll have to live to be 101 to finish what I already have in the works. The bright side is with all the money saved, I'll be wealthy. :laughing:

 

[jaxs]

Speaking of dump trailers, mine (7K) is a scissors lift, however like many of them it is a bit underpowered when I may have too much of a weight towards the front of the trailer. I was thinking of adding a small single stage hydraulic cylinder in the front working off the same line the big cylinder is being fed to assist in lifting. Does anyone see any problems with that? The small cylinder would only go up about 12", then be free of the dump.

I'm glad you brought this"helper"cyl up Pete. I believe as you do that the first few inches are far more taxing on the cyl in sissors configuration. I also have pictured the added cyl pushing until extended then loosing contact with bed until bed is lowered. I have wondered about the necessary modifications to use existing pump to power the add on cyl. If this sound's interesting to OP,I'd like everyone to help explore this farther. In building a new trailer,the attraction is saving cost of large cyl by incorporating 2 less expensive cylinders. Here's my most perplexing issue. Must added cyl be rated at or above pump capability? Will added cyl suffer from continued pressure after reaching max extension while sissors cyl continue's doing it's job?

 

[texasranger556]

I'm glad you brought this"helper"cyl up Pete. I believe as you do that the first few inches are far more taxing on the cyl in sissors configuration. I also have pictured the added cyl pushing until extended then loosing contact with bed until bed is lowered. I have wondered about the necessary modifications to use existing pump to power the add on cyl. If this sound's interesting to OP,I'd like everyone to help explore this farther. In building a new trailer,the attraction is saving cost of large cyl by incorporating 2 less expensive cylinders. Here's my most perplexing issue. Must added cyl be rated at or above pump capability? Will added cyl suffer from continued pressure after reaching max extension while sissors cyl continue's doing it's job?

If you tee the second cylinder with the primary cylinder the oil will flow the path of least resistance which would be the vertical "assist" cylinder until it tops out. Then the oil would all go to the scissor lift. You'd have to make sure the reservoir on your pump holds enough oil to fill both cylinders.

One possibility to consider...if you were dumping down hill and the load sticks to the point of taking the bed's center of gravity aft of it's hinge point, it could suck the oil out of the assist cylinder and slam the bed all the way "up" and possibly bend something.

A situation something like this:
AFV Dump truck tips - YouTube

 

[jaxs]

If you tee the second cylinder with the primary cylinder the oil will flow the path of least resistance which would be the vertical "assist" cylinder until it tops out. Then the oil would all go to the scissor lift.Perfect,just what I want You'd have to make sure the reservoir on your pump holds enough oil to fill both cylinders.Should be simple to accomplish.

One possibility to consider...if you were dumping down hill and the load sticks to the point of taking the bed's center of gravity aft of it's hinge point, it could suck the oil out of the assist cylinder I don't understand and slam the bed all the way "up" and possibly bend something.

A situation something like this:
AFV Dump truck tips - YouTube

I'm not understanding why the assist cylinder would/could worsen the risk of doing this.

 

[petegoud]

If you tee the second cylinder with the primary cylinder the oil will flow the path of least resistance which would be the vertical "assist" cylinder until it tops out. Then the oil would all go to the scissor lift. You'd have to make sure the reservoir on your pump holds enough oil to fill both cylinders.

One possibility to consider...if you were dumping down hill and the load sticks to the point of taking the bed's center of gravity aft of it's hinge point, it could suck the oil out of the assist cylinder and slam the bed all the way "up" and possibly bend something.

A situation something like this:
AFV Dump truck tips - YouTube

This will be a winter project. I did mount a little 4 ton hydraulic jack to one side to lift the front about 8". That was enough to let the main cylinder take over and do the job it was supposed to do. I had to be careful not to twist the bed using the small jack on the one side. This seems to be a common problem with these dump trailers, especially if the load is situated to far forward. Trying to load the trailer more towards the rear to make the dumping easier also sometimes makes the towing very unbalanced. If I get this done I'll post the results. If anyone else tries this, I hope you'll do the same.

 

[jaxs]

This will be a winter project. I did mount a little 4 ton hydraulic jack to one side to lift the front about 8". That was enough to let the main cylinder take over and do the job it was supposed to do. I had to be careful not to twist the bed using the small jack on the one side. This seems to be a common problem with these dump trailers, especially if the load is situated to far forward. Trying to load the trailer more towards the rear to make the dumping easier also sometimes makes the towing very unbalanced. If I get this done I'll post the results. If anyone else tries this, I hope you'll do the same.

Make's towing dangerous to say the least.

 

[4570Man]

This will be a winter project. I did mount a little 4 ton hydraulic jack to one side to lift the front about 8". That was enough to let the main cylinder take over and do the job it was supposed to do. I had to be careful not to twist the bed using the small jack on the one side. This seems to be a common problem with these dump trailers, especially if the load is situated to far forward. Trying to load the trailer more towards the rear to make the dumping easier also sometimes makes the towing very unbalanced. If I get this done I'll post the results. If anyone else tries this, I hope you'll do the same.

It looks to me like he forgot to unlatch the tailgate. I'm not sure what the dumping mechanism has to do with it.

 

[texasranger556]

The video was just an extreme example of an instance where the center of gravity of the dump bed shifted so far back that it flipped the truck. If you had a 12" "lift assist" cylinder tee'd into the main cylinder, it would allow the dump bed to "free wheel" up and bang against whatever stop you have at the end of the scissor lift travel rather than gently top out under pump pressure.

Maybe a sequence valve would prevent that behavior, I've never messed with one though.

 

[pmsmechanic]

If you tee the second cylinder with the primary cylinder the oil will flow the path of least resistance which would be the vertical "assist" cylinder until it tops out. Then the oil would all go to the scissor lift. You'd have to make sure the reservoir on your pump holds enough oil to fill both cylinders.

One possibility to consider...if you were dumping down hill and the load sticks to the point of taking the bed's center of gravity aft of it's hinge point, it could suck the oil out of the assist cylinder and slam the bed all the way "up" and possibly bend something.

A situation something like this:
AFV Dump truck tips - YouTube

I've thought about this for a while. I don't think you are making a valid point. (Though it's definatly worth thinking about) A scissors type hoist has a dual acting cylinder. It has pressure on both side of the piston. If you T the lift assist onto the lift side of the main cylinder and just use the lift assist as a single acting cylinder it'll work. The load will never take off as the main cylinder still has oil on the down side of the cylinder. If you T the lift assist into both sides of the main cylinder then there is a possibility that it can take off but only as far as the volume of oil inside the lift assist cylinder will let it.

Just to try and clarify what I'm describing here. The main scissor lift cylinder is a double acting cylinder and the lift assist is working as a single acting cylinder.

After thinking about this overnight I'm going to say that you are partially right. The load will take off if it over centers. You can control the load by releasing the hydraulic lever on the tractor. The effect of the volume of oil in the lift cylinder would be lessened with a restrictor installed in the hydraulic oil line going to the single acting cylinder

 

[currierej]

I'm also interested in this post, I'm commenting so I can follow.

 

[texasranger556]

You're right that a double acting cylinder would be less prone. The only scissor lifts I have worked on were in dump bed inserts we used to install in pickup trucks. They had an electric pump and a single acting cylinder which is what I had in mind.