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mobile base #2: issues, asking for advice

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Blog entry by Holbs posted 576 days ago 2082 reads 0 times favorited 11 comments Add to Favorites Watch
« Part 1: compound lever for mobile base Part 2 of mobile base series Part 3: 85% tuned up »

I found out using solely a compound lever assembly to lower & raise casters on the bottom will not work. The entire carcass will pivot on the lower lever at 1 pivot point. Meaning, the carcass will tip forward or backward, especially if running over a power cord or floor obstruction.

I didnt want to give up on my compound lever all together. As my criteria for a mobile base is:
1.) all lower and raising operation to be done as i face the machine within arms length.
2.) not wanting to hunch over, or get on knees, kick something or “thrust” carcass forward or backward to set casters.
3.) casters raise up allowing base of carcass to settle.
4.) i do not want to pull a muscle to set casters down from too much torque, hence compound lever assembly.
5.) i do not want to trip over casters that jut out at the 4 corners.
6.) i simply wants an assembly i can lightly apply pressure and move a lever 6”-12” and be happy.

this will work. i just have to figure out the details :)

my second prototype retractable casters, up 1”. mind you, this is a total rough draft run to see how it works, so no funny talk about things not being level, or placement of hinges, etc :)

and now settled on carcass base with casters retracted:

with this configuration, the compound lever is only the actuary to push the caster plate downward into place, as the casters will be attached to a 2×4 going horizontal. i foresee a good many mortises and tenons to practice on, with haunches.
The problem i am encountering, is the vertical 2×4 piece that engages the caster plate. the caster plate is roughly at a 20degree angle as the carcass sits on the ground. the vertical 2×4 engages and then wants to bow out 1/8” – 1/4” as the caster plate becomes horizontal. This “seemed” acceptable, but i still do not like it. But cant figure out how to have the 2×4 vertical piece “slide” or “rock” across the caster plate.

i put my body weight on the carcass and with just small screws holding things together, it lifted the carcass and myself up 1”. i’ll be using nuts and bolts in a final assembly.
i can not extend out the casters, as i want them as close as possible to the leg framing structure. but i think they are at a ok distance from each other when i move the carcass around. these are 3” casters. if i went 5 or 6”, they would have to come closer and that would be too close, i think.



11 comments so far

View Milo's profile

Milo

851 posts in 1954 days


#1 posted 576 days ago

Holbs,

I hate to say it, but I think you are trying too hard. TOO many moving parts maybe?

I had a similar discussion in the forum last summer. Here is the link, and there are some pictures also.

http://lumberjocks.com/topics/40090

Hope it helps!

-- Beer, Beer, Thank God for Beer. It's my way of keeping my mind fresh and clear...

View Holbs's profile

Holbs

515 posts in 664 days


#2 posted 576 days ago

i think i searched every youtube video regarding mobile bases, Milo. The issue you raised in your progress report is one i do not want to encounter. The one about pressing down really hard just to raise the carcass stand. or the torque and pressure involved that could rip off the catches themselves.

hence.. compound lever :) this may or may not work out. at least, i’ll be learning alot along the way. mortise & tenons which leads to understanding different species of wood with pro’s/con’s, then chisels which leads to diamond stones which leads to sharpening center. these retractable wheels will lead to a planer stand with infeed/outfeed torsion box arms. this should be a good spring, i think :)

View Reddog's profile

Reddog

17 posts in 597 days


#3 posted 576 days ago

There was a pretty neat mobile base solution in Shopnotes January 2006 that used a compound lever action to raise the machine and used a screen door latch to lock the base in a raised position. There’s a thread about it at
http://www.bt3central.com/showthread.php?t=54516

I’ve never built it but thought it was kind of slick because it could be operated without bending over.

View Holbs's profile

Holbs

515 posts in 664 days


#4 posted 576 days ago

reddog: if i can fine tune this compound lever design, you will just have a left & right arm to push down on 8”-12” to raise the carcass with 1 finger. plus, no bending over or getting on knees :)
bt3 central. cant see the pic the OP posted about. guess i’ll sign up to see it, as i’m very curious.

View Mark Kornell's profile

Mark Kornell

482 posts in 1165 days


#5 posted 576 days ago

Holbs,

As you’ve constructed this, the caster plate moves in an arc that is perpendicular to the direction of the applied force. Therefore, your mechanism needs to allow for this lateral movement. You could insert two hinges in the vertical 2×4 in question – one below the upper pivot point, and one above the lower pivot point. The hinges would need to be able to deal with the stresses involved without too much play.

The other option would be to orient your compound lever so that the lever force is in line with the arc movement of the caster plate. In other words, rotate the lever mechanism 90 degrees.

-- Mark Kornell, Kornell Wood Design

View Holbs's profile

Holbs

515 posts in 664 days


#6 posted 575 days ago

Iguana.. i was thinking to put a dowl pin at the bottom of that vertical 2×4, and a hole in the caster plate. this would force the 2×4 to “arc” with the caster plate as it is pushed downward, instead of engaging the caster plate 1/8” at top of arc. this would allow the lateral movement to a small degree, which is what is needed and i believe should be ok as long as no 1000lb machinery sitting on carcass (i may make individual tables for my rigid planer, mitre saw, etc).

i do not understand what you mean by rotating the lever mechanism 90degrees. the entire mechanism including up and lower pivot arms? or just the vertical 2×4?

View Reddog's profile

Reddog

17 posts in 597 days


#7 posted 575 days ago

Found a better link showing that base right here on LJ

http://lumberjocks.com/Hersh/blog/22788

View Milo's profile

Milo

851 posts in 1954 days


#8 posted 575 days ago

Reddog,

That’s a pretty cook find. Nice job!

-- Beer, Beer, Thank God for Beer. It's my way of keeping my mind fresh and clear...

View Holbs's profile

Holbs

515 posts in 664 days


#9 posted 575 days ago

to a point, i’m creating something similiar. as in, using compound lever assembly to lower/raise casters. my crazy medieval way out of bounds sinister idea has more to do with making an assembly that is more convenient to me. as in, 2 levers located at front of machine at or above waist level, low push down torque to engage casters, leaves underneath cabinetry open (for storage, or clipping bin, etc), and the idea of putting heavier objects on a movable work platform without worrying how much force will be needed to engage casters or construction weight limits.

something about gears & levers… using mechanical advantage, makes me smile.

View Mark Kornell's profile

Mark Kornell

482 posts in 1165 days


#10 posted 575 days ago

Holbs,

You are right in that the lateral movement is fairly small, so all you need is to allow for a bit of play in the pivot points of the the lower vertical 2×4. A dowel pin in the bottom of the 2×4 going into a slightly oversize hole will probably work just fine. Since you’ll have a wood-on-wood engagement of the 2×4 on the caster plate (rather than the force being transmitted through a pivoting pin), you may want to consider the choice of wood so that you don’t excessive wear or crushing. A 2×4 rubbing on plywood will probably result in the plywood being damaged in fairly short order.

If you put a small block of 2×4 on the caster plate, end grain up (i.e. oriented in the same way as the vertical 2×4), and the hole for the pin in that block, you’d have end grain 2×4 rubbing on end grain 2×4, and that would wear better.

And yes, I meant rotating the entire lever system by 90 degrees. The way the levers pivot, the lower vertical 2×4 would naturally follow the arc made by the caster plate. That orientation may not be a convenient to store/use, though.

-- Mark Kornell, Kornell Wood Design

View Holbs's profile

Holbs

515 posts in 664 days


#11 posted 552 days ago

mark…see #4 blog. i ditched the worry about lateral movement by removing the vertical piece of 1×4 all together.

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