My homemade cycle lift table

[chuck hahn]

The plywood also acts as gussets by the way...no twists.

 

[tkent02]

It looks weak against diagonal shifting.

 

[posplayr]

Screwed with 4 inch deck screws, construction wood glue, and 2X4s in the corners where the lock joins in..all screwed and glued. Its not gonna twist, roll, drop, sag, fall or anything else. If I wasn't 100% sure of that, there sure as hell wouldnt be mine or anyone elses bike on it!!!

The weakest link is the 6" or so of the end of each strut (on the jack side). Because the back (away from jack) is cantilevered it is putting the front strut under tension (pivoting about your lock which is in compression) . So if that end grain split the bolts would pull right through and the thing will come right own. That is why I recommended a side plate to prevent that from happening.


Also I don't think anybody has an issue with the strength of the upper or lower boxes; it is the struts and attachments between. Note that your upper and lower boxes are not parallel.

 

[posplayr]

I agree with Pos. I tried this with 4 legs like you did, and found there to be too much sag involved, which, in my case, lead to a certain amount of binding. I knew if I added middle legs, it would help the whole thing maintain geometry, but at that point, I had honed in on another concept. That one involved the table also being the ramp. Front legs became solid, and devised two sets of rear legs: a shorter, solid pair, and a longer, hinged pair, that, when dropped down once lifted, get locked to the shorter, sold-mounted pair. Works like a charm and I no longer have to worry if the whole things gonna come down on liftoff.

Did you ever post pictures?

 

[tkent02]

Also I don't think anybody has an issue with the strength of the upper or lower boxes; it is the struts and attachements between.

Exactly, and once it starts, it will shift diagonally as there is nothing to slow it down. Slap some plywood across each pair of struts, then it can't shift.

 

[ptexotik]

sketchy (dirtbikes, ok)
next

 

[almarconi]

Doing an eye ball statics analysis it looks like the lift has most of the load cantileavered out well beyond the support of that weight( e.g. 500 lbs down at the center stand with only a minimum 50 lbs or so on the front wheel). The struts away from the jack is probably neutral with essentially no load. You could probably just take it out. The primary support is coming from the stop and the jack. The strut closest to the jack would appear to be in elongation. The jack is trying to stretch it. I think thAt strut closest to the jack is most susceptible and could easily bring the whole thing down.

Is the bolts are being pulled by the jack then the strut end grain could split and the bolts would escape letting the whole thing drop. To make this substantially stronger I would make so metal reinforcing plates that capture the bolts and prevent the strut from splitting. A simple 1/8" plate with holes for deck screws to go into the strut would make a big difference.

I have not studied these lifts much but I would assume the lift would want to come closer to where the load is and definitely support from I between the struts. That way both struts have similar loads and be more balanced.


EDIT:
OK I did a little further study and came to the conclusion that while this configuration is not quite as stable as it could be, it does have some excellent potential for making a very stable and cheap motorcycle lift.

After looking at the harbor freight lift it appears that the primary issue is to get sufficient lift (29") out of a hydraulic bottle jack. You do this with reverse leverage so that the short stroke of the bottle jack can be used to get much longer lift. The typical 2 1/2 tone floor jack performs this function pretty well and that is a big plus and opens the door for a nice lift for very little cost while also leaving the floor jack available for other uses.

So in looking back at Chuck's design, it is cantilevered but that is really what makes it weak and with a little effort it could be made quite a bit more solid/stable.

Stepping back and looking at the lift, it is pretty easy to see that the struts are each emulating the same motion that the Jacks are has. The jack uses a lever arm to get the full lift 29" from a short bottle jack. See the inset for a floor jack from HF for less than $100 that has a full 29" lift. With a 13" resting double 2"x6" (with platform)stack height you can get the bike up to 42" if you wish.

One of the issues with Chucks is that it is lifting at one end and sagging at the other so the struts are not maintaining the upper and lower boxes in parallel. By adding a third strut the whole thing cant get nearly as much out of parallel and it even strengthens the lift further. It is going to be more critical to se straight boards and cut all struts to same length and drill the bolt holes in the same place.

Next I would put the adjustable stop at the opposite end to the jack so that when resting on the stop there is not a cantilever but rather a balance of load with the 500 lbs of center stand in the middle.

While your analysis is interesting, I doubt it is relevant here. This is Chuck we are talking about. I doubt he gives a sh#$ about whether you like the design of his motorcycle lift or not. If he is comfortable using it then more power to him.

 

[rustybronco]

The plans I've seen for home made motorcycle lifts had the floor jack slid further under the table.

http://motorcycleliftplans.weebly.com/index.html
http://www.afabonline.com/table_lift_plans.htm
http://www.millerwelds.com/resource...attachment.php?attachmentid=1225&d=1174412234

 

[tkent02]

While your analysis is interesting, I doubt it is relevant here. This is Chuck we are talking about.

If it starts to fail he can just stick his hard head under there. That will save it.

 

[chuck hahn]

True Dale but I mismeasured how far the jack had to go under and had already glued and screwed the first front cross member in...so it has to be what it is.

The original scenario was gonna be 2= 2X6s married together about 12 inches in from the front plate..thus allowing the jack to lift further back and also have the force displaced along some of the decking. Much the same principle as weight is spread across the decking and joists in house building...so much joist spacing + the thickness of the deck will support X amount of weight per square foot..blah blah.

But overall we have max of 500LBS spread across a 8X2 deck made of 2X6s with 3/4 plywood. 3 cross members in the table top also, so I feel I am way over the spread as far as how much actual weight it will support. Do you think so Dale?

 

[tkent02]

The deck is stout as Hell, Chuck. No worries there.

 

[chuck hahn]

The base is just as solidly thought out and constructed too I think. I am gonna get a steel jacking plate at some point rather than the plywood one. I have access to some old real estate signs made of about .100 thick plate steel and then the decals laminated to them. Thing is I doubt they wouldn't also flex as the jack is trying to spread the 2 halves apart?? Maybe laminate a sheet of it over the plywood plate??? Drill holes and use lots of 3 inch deck screws and fasten it over the plywood jacking plate??

 

[rustybronco]

The only thing I would be concerned about is the table wobbling from side to side. You might want to consider using oak in place of the four pine uprights.

 

[tkent02]

The only thing I would be concerned about is the table wobbling from side to side. You might want to consider using oak in place of the four pine uprights.

This is what I was talking about. Put the struts inside the frame instead of outside, put a sheet of plywood over each pair of struts, then it can't shift or wobble at all.

 

[rustybronco]

This is what I was talking about. Put the struts inside the frame instead of outside, put a sheet of plywood over each pair of struts, then it can't shift or wobble at all.

That would require a complete revamp of his table, but an excellent suggestion for a 'MARK II' version of it.

 

[posplayr]

While your analysis is interesting, I doubt it is relevant here. This is Chuck we are talking about. I doubt he gives a sh#$ about whether you like the design of his motorcycle lift or not. If he is comfortable using it then more power to him.

To tell the truth, I'm not sure what the relevance of your comments are.

As self indulgent as my post might be, at least to some extent it is an attempt to be constructive and add food for though for anyone looking to build one of these contraptions out of wood (my self included).

 

[posplayr]

The only thing I would be concerned about is the table wobbling from side to side. You might want to consider using oak in place of the four pine uprights.

After looking at those other designs especially the wooden one, I'm realizing that the stability of Chucks design has little to do with the strength/stiffness of the struts. All the weight is sitting on basically 3 points, the jack (1 point) and the stop which is really like the two legs of a table.

I still don't see any benefit to the cantilever, as it is stressing the front strut in tension and providing a weakest link mechanism for the whole lift to collapse.

 

[chuck hahn]

But to put the struts inside the frame I would have had to notch a recess inside each crossmeber to allow the struts to fold all the way down so the top would rest on the base.

I purposely drilled and sleeved the struts and the frames with 1/2 galvanized pipe so as to take up some of that twist induced at the pivot points. I tightened the bolts and had a shim between the frames and the stru so to leave just some movement of the struts but not wobble around..follow me here? I use 1/2 inch bolts ( same diameter of the pipe ID so no slop there either. Its tightly done up..trust me when I say this.

Red Loctite on everything so nothing will come loose or move.

 

[rustybronco]

Jim, the wood fibers in pine are much softer than oak, plus oak makes a nice bearing surface for the bolts and has less crush to it than pine does.

It might be splitting hairs, but I personally think using oak as a bearing surface for the bolts, will add rigidity to the side struts as long as they are close to the wood they are being placed against and will twist less than pine as well. If the side struts are tightened against the long horizontal members and the wood has little ability to flex, the two legs of the table will only have to support the vertical load.

My non engineering degreed $.02

 

[ptexotik]

Your construction is great.
But a Cooley up there utilising the kick stand platform ? Does Joe Whelan know about this!?? HA
(send me some of that OKL crack, bro ... gotta be da kind! )