Lifting cart - Metal tolerances and lubrication

[ripatip]

Hello,
nice to join the forum.

I have (2) two questions about an upcoming project. one is about tolerances, and the other is about lubrication and wear.

I'm building a lifting cart to help me pick up some heavy loads in the shop. Think of it as a mini forklift. my design is based off of this YouTube video https://www.youtube.com/watch?v=kMpnh2C8mc0 I have made a few modifications, including having the winch at working height. see my drawing below. most of the time the load will be under 50 pounds but sometimes up to 200 and rarely over that but I want the capability of 400 or 800. I did not show the extension assemblyIn the drawing ( forks and separately a platform)

the one piece I have not purchased yet is the 2"x2"x60" main beam (pink colour in drawing) and the sliding orange sleeve around it .The thickness of the metal will be 3/16" thick if constructed of steel or 1/4" if aluminum ( not 100% decided). the only reason I'm considering aluminum is that I'm trying to keep the weight down. moving heavy pieces harder than it used to be which is the main reason why I'm building this. of course tapping a bolt into aluminum for the extension assembly is not as strong.

--1--
the dimensions of the orange steel available for purchase at my local metal supermarket( square welded tube) piece that will ride up the beam will be either
1) 2.5"x2.5" x 0.238" leaving 0.012" gap around on all sides For the metal to slide on a 2 x 2 beam
2) 2.5x2.5" x 0.215" leaving 0.035" gap around on all sides For the metal to slide on a 2 x 2 beam

I would like to choose option one, but I don't have a lot of experience with tolerances, especially for welded square tube. of course I'm giving myself more room for option 2, but the sliding action will not be as good. I would like to get option 1 if I can get away with it

--2--
if two pieces of metal are going to be sliding up and down, I'm going to need some lubrication. I have been trying to decide if
1)oil or
2) grease will be better.

The concern is that the oil will make its way to the bottom of the cart due to gravity. is this wrong? I am not certain that this will happen. if I use grease, It will stay in place, but I am not sure if the sleeve metal would easily slide with the grease taking up some volume with tight tolerances. maybe just a small amount of grease?

and finally the concern about using aluminum beam is that the leading edge of the sleeve which will be steel( which will need to be intentionally rounded over) will wear away into the beam under heavy loads causing long gouges. but if the wear is minimal, but I suppose that's okay.

I would love to hear your thoughts
Thanks

[rmac]

ripatip,

Welcome to the forum, and thanks explaining your question so clearly.

I'm not an expert, but my gut feel is that the gap is way too small with option one. Another gut level opinion is that if you need lubrication at all (which you may not), grease would work better than oil because (as you noted) oil would eventually just run out onto the floor.

A few more things to consider that you may not have thought of:

1. If the inside corners of the outside tube have a radius on them, they might interfere with the outside corners of the inside tube unless they also are rounded over. Unless you can get detailed specs for the tubing, your best bet might be to visit the metal supplier and actually play with the material to see if it's going to fit together as you expect.
2. With welded steel tubing, the wall may be thicker than specified along the weld, and this could also prevent the tubes from sliding freely. There's a longish YouTube video here that discusses this problem and offers a few different ideas for solving it.
3. I think you're walking a pretty fine line with the bolt holes tapped into the thin material of the slider sleeve. If the bolts go in all the way, they'll lock up the sleeve. But if they don't, you'll only catch a thread or two which may be on the weak side (especially in aluminum). Maybe think about other ways to attach the extension assembly to the slider sleeve.

With any luck, others will chime in with more informed opinions about the questions you've asked.

-- Russell Mac

[ripatip]

ripatip,

Welcome to the forum, and thanks explaining your question so clearly.

I'm not an expert, but my gut feel is that the gap is way too small with option one. Another gut level opinion is that if you need lubrication at all (which you may not), grease would work better than oil because (as you noted) oil would eventually just run out onto the floor.

A few more things to consider that you may not have thought of:

1. If the inside corners of the outside tube have a radius on them, they might interfere with the outside corners of the inside tube unless they also are rounded over. Unless you can get detailed specs for the tubing, your best bet might be to visit the metal supplier and actually play with the material to see if it's going to fit together as you expect.
2. With welded steel tubing, the wall may be thicker than specified along the weld, and this could also prevent the tubes from sliding freely. There's a longish YouTube video here that discusses this problem and offers a few different ideas for solving it.
3. I think you're walking a pretty fine line with the bolt holes tapped into the thin material of the slider sleeve. If the bolts go in all the way, they'll lock up the sleeve. But if they don't, you'll only catch a thread or two which may be on the weak side (especially in aluminum). Maybe think about other ways to attach the extension assembly to the slider sleeve.

With any luck, others will chime in with more informed opinions about the questions you've asked.

-- Russell Mac

Thank you for the insightful thoughts. that interior beam square tube does have a radius on the outside corners. That tool presented in the video seems like a good idea, but I have difficulty purchasing something like that for a one-off job.

It's interesting that you say it may not actually need lubrication. it never occurred to me that it may not be necessary.

the "purchase" or hold was my concern with aluminum, however this is the exact reason why the orange sleeve is to be steel tubing rather than aluminum, and furthermore if it was steel, this leave would be rubbing against a softer material if the beam is made of aluminum.

[LIALLEGHENY]

What the video doesn't show is how easily he can raise items once he adds some weight onto the "forks". Without some kind of bearing surface (slippery plastic) or bearings riding against the tube you're going to find that lifting something with weight is going to be a problem..Think of how a forklift mast is constructed with bearings on the carriage. I would stick with steel for the tube, not aluminum, it's too soft, unless you had a wide bearing to run against it.

Nyle

[ripatip]

What the video doesn't show is how easily he can raise items once he adds some weight onto the "forks". Without some kind of bearing surface (slippery plastic) or bearings riding against the tube you're going to find that lifting something with weight is going to be a problem..Think of how a forklift mast is constructed with bearings on the carriage. I would stick with steel for the tube, not aluminum, it's too soft, unless you had a wide bearing to run against it.

Nyle

I have shaft fitted into two pillow blocks with bearings that will be welded to a small piece of steel fastened at the top of the beam. The roller is the type used for hand trucks I think over 2000 pound rating. the roller has two bearings on its own for a total of four bearings. the winch I have is the Dutton laison and worm gear winch (40:1) mechanical advantage that will be attached to a drill motor. my plan was the drill motor seemed to be too difficult over time, to replace it with a dedicated motor.

interesting point about a bearing rubbing against steel beam