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StorminNormann's picture

Any ideas on whether this design will easily tip over?

I drew it out on paper some time back but now that I'm learning designcad, I
sketched it out in that tool (15 min) and realized that tipping over may be a
problem.

This is a router table on lockable wheels. I intend to store my planer on the
bottom shelf when routing and place it on the top for planing. The planer is
approx. 90 lbs.

Now I wished I had saved those college Physics books!

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Thanks in advance,

Steve


Edited 2/8/2005 5:25 pm ET by Steve

__________________________________________________________________________________ It is noble to teach oneself, it is still nobler to teach others -- Samuel Clemens __________________________________________________________________________________ Steve
VomSorb's picture

(post #76362, reply #1 of 32)

LOOKS iffy, but I didn't get my slide rule out.  I wouldn't want to run a wide 12/4 board through the arrangement as drawn.  Looks a shade too tall and the cabinet doesn't look deep enough to me.

bobpowers's picture

(post #76362, reply #2 of 32)

My 75 pound planer is on a cabinet with lockable wheels. It is 26"X22"X33 1/2" high. It is not tippy at all. The height was determined by my assembly table, so it serves as an outfeed table.

BenM's picture

(post #76362, reply #3 of 32)

Assuming you are pushing the wood through the planer in the z direction you only need about 20 pounds of force to tip it over.  I assumed the cart weighs nothing; if it is substantially heavy and if the planer is bolted to the cart then a larger force could be resisted.


If I were you I would find a tried and true set of plans for supporting your planer.  Also, I think most people who own one of these lunch box planers augment them with substantial infeed and outfeed tables.  How are you going to add them to your design?

highfigh's picture

(post #76362, reply #14 of 32)

How is it practical to assume that the cart weighs nothing? The cart's weight(actually, its mass) needs to be considered in order to calculate the force required to tip it and make the whole excercise meaningful. If the planer is fastened to the cart and the cart has a bigger footprint than the planer, the center of mass will be lower and therefore, more stable. Obviously, the heavier the cart is, the more stable it will be.

Steve- make the cart out of whatever you want. If it's wide enough to put the planer inside, it will be stable enough as long as you aren't going to let the boards just hang out in the air after they've gone through. If you have anything to support the boards on the way out, it shouldn't tip. Besides, you shouldn't need to push against it to get the boards to go through.

"I cut this piece four times and it's still too short."
"I cut this piece four times and it's still too short."
StorminNormann's picture

(post #76362, reply #15 of 32)

Good point about not neglecting the weight of the cart itself. I figure that
my design (with 26" depth) will be approx. 42 lbs in 2x4 douglas fir (550
kg/cubic meter or a little over 10 lbs per 8' piece). I plan on adding 3/4" MDF
on both the top and bottom shelves (800 kg/cubic meter) for another 25 lbs a
piece.

The wheels are
Sheperd
Hardware Products model 9287
-- each weighs about 1/2 a lb.  BTW, these
are lockable swivel casters where you press down on the lock with your foot and
the caster is locked from rolling or swiveling. 

Once I add in some additional things -- router, router base plate, rear panel
(basing design on Kevin McLaughlin's article "A Versatile Router Table" FWW #169
Mar/Apr 2004). That should put my cart in the 150 lb range with a center of
gravity not much different from where I have it depicted.

Steve

__________________________________________________________________________________ It is noble to teach oneself, it is still nobler to teach others -- Samuel Clemens __________________________________________________________________________________ Steve
BenM's picture

(post #76362, reply #16 of 32)

Ah, more data.  With a cart weight of 150 lbs, a planer weight of 90 lbs and a wheel base of about 32 inches you could resist a horizontal force of 50-55 lbs.  Also, if you are planing a 2" x 12" board it could be 9 to 10 feet long before its weight would tip over the assembly.  Now you should be okay.


And, not to get into a fight with anyone, but the location of the center of gravity doesn't have much to do with the stability since the location of the applied horizontal force is constant.


Edit - I forgot to convert one of the numbers to feet.  The board will be about 9 to 10 feet long (not 30 feet) before the possibility of tipping occurs.


Edited 2/9/2005 8:32 am ET by BenM

highfigh's picture

(post #76362, reply #17 of 32)

You did move the center of gravity down when you added the weight of the cart and assumed the two pieces are attached, right? It's obviously going to be somewhere between the two, if calculated separately. 50-55 pounds to tip it sounds light to me.Maybe to get it to start tipping. The whole thing will be around 250 pounds, total. 9'-10' sticking out is a fairly long lever arm, though.

"I cut this piece four times and it's still too short."

"I cut this piece four times and it's still too short."
StorminNormann's picture

(post #76362, reply #18 of 32)

Center of gravity -- I may be wrong but it's my understanding that with an
isometric design that the center of gravity for the cart will be equivalent to the physical
center. Before the casters are added the design is fairly isometric. Casters
take the assembly 4 1/2" off the ground on 3" wheels. When locked, I believe the
casters could be considered "feet" that are located, worst case, 2 3/4" inside z
dimension and 1" inside x dimension.   As the planer will be
located over the center of the cart, the total center of gravity will be above
the cart's center of gravity proportional to the differences in the weight of
the cart and the planer.  I estimate it will be about 30" off the floor.

I intend to supplant my in/outfeeds with stands when working with trully
long/heavy boards so I don't see a problem there. My main concern is more about
tipping the cart accidentally like bumping into it while it has the planer on
top.

How are you guys calculating the amount of applied force needed to tip it over?
You sound pretty authoritative :-) Wouldn't the center of gravity have to be
moved just outside the "feet" for tipping to happen? In this case, isn't that
like saying how much force does it take to move a 250 lb weight along the
circumference of the circle bound by the center of gravity and the feet until
the weight is vertically past the feet. This force would be applied at the
cart's edge.

Here's a drawing showing what I mean:

Steve

__________________________________________________________________________________ It is noble to teach oneself, it is still nobler to teach others -- Samuel Clemens __________________________________________________________________________________ Steve
highfigh's picture

(post #76362, reply #19 of 32)

The shape is one consideration, but it's basically in how the weight is distributed. If the shelf at the bottom is heavier than the top, you'll call it "bottom-heavy" and vice-versa. If the base/cart/box or whatever you want to call it has any appreciable weight and the planer is mounted in a way that it won't slide off or become detached, you'll need to push pretty hard to get it to tip over. Another thing that comes into play here is the line of force. The wood is pushed in near the bottom of the planer, below the planer's Cg(assuming it's one of the smaller planers), not at the top.

Cowtown mentioned the position of the casters. If you put them inside the perimiter of the base, you effectively reduce the footprint. Look at mobile bases for table saws- the casters are outside of the perimiterof the base. By mounting the base directly over the casters, you are raising the planer and there's no weight to offset this added height. If you can install a bracket outside the perimiter that allows you to have the planer at the best height for you and just get the legs off of the floor, it'll be stable. Just remember the direction(s) of the force(s) and design it around that. If the force is always along the base, make it longer. If the force is across the base, make it wider.

I'm not calculating this, nor will I since it's been a loooooong time since I had to and I'm not exactly sure where my books are. I do remember and understand the concept though. I remember the force times height part, assuming the planer base is firmly attached to the mobile base and that as the Cg moves outside of the outline of the base, the angle created determines the x(horizontal) and y(vertical, or gravity) force components and as the y component takes over, it's time for the NesTea Plunge. If you get the base to lift by pushing the stock into the planer, the base is either really tall, really light or you're pushing too hard. As long as you use some kind of support for the infeed or outfeed and guide the stock as it goes in or out(depending on where your support is), you won't have any problem with it tipping. Sliding or rolling is another question.

I can also say that as the base gets heavier, the effective height component of the base decreases till it's just like pushing the planer along the ground. Obviously, the base needs to be really heavy for this to happen, but with a 50 pound base, it's not gonna go anywhere unless you push pretty hard along the top edge of the planer. I have a stamped steel machine stand with a laminated top. The top is maybe 18" x 22", about 32" high and the footprint is about 24"x30". My planer lives on top of this and I have never had it try to tip unless I had a long, thick board sticking out of one end with nothing supporting it.

The wheels you showed are semi hard and prone to flat spotting. If you use a wide rubber clad metal wheel, it'll roll smoother after sitting in one place. I looked at similar wheels and may try them, but think I'm going to see if I can find something wider and harder, but not solid, exposed steel.

If you really want to make it impossible to tip, set up some low profile outriggers.

"I cut this piece four times and it's still too short."


Edited 2/9/2005 7:07 pm ET by highfigh

"I cut this piece four times and it's still too short."
Steinmetz's picture

(post #76362, reply #26 of 32)

High,

Splay the four corners or legs outward.
Or, add a wider bottom base to position the casters to a wider and longer 'Footprint' Steinmetz

highfigh's picture

(post #76362, reply #27 of 32)

Exactly, I mentioned outriggers yesterday and they can be mounted so they're retractable.

"I cut this piece four times and it's still too short."

"I cut this piece four times and it's still too short."
StorminNormann's picture

(post #76362, reply #28 of 32)

This has been fun and educational. Thanks for explaining how you determined the tipping force Ben.

Some feedback:

1) can't find better wheels so am going to go with the semi-elastics

2) by deeping the cart from my original 20" to 26", I am going for the same result as adding outriggers.

3) I know that adding outriggers to the cart would probably eliminate any chance of tipping but I have a very small shop (1 bay of my garage) and I would trip over the outriggers (causing me to tip over while the cart doesn't budge)

Well I declare my design is done. Just wish it was built already so I could use it in building it :-)

Steve

__________________________________________________________________________________ It is noble to teach oneself, it is still nobler to teach others -- Samuel Clemens __________________________________________________________________________________ Steve
DougF's picture

(post #76362, reply #20 of 32)

Steve,


"If you really want to make it impossible to tip, set up some low profile outriggers."


This is what I did when I built my portable planer stand.  I extended the footprint 4" fore and aft of the base in the direction of feed.  I ran thousands of bf of material, some as long as 14', and never had  a stability problem.  I did not, however, use locking casters.  When the base is in place, the caster were not in contact with the floor.  To "engaage" the two casters you had to tilt the cabinet back to engage the two casters attached to the outrigger.  The cabinet is easy to tilt and roll.  If you use casters I would recommend wide rubber casters to provide maxium friction. 


Doug

BenM's picture

(post #76362, reply #22 of 32)

I am attaching some of my calculations to explain.  The height of the center of gravity is not relevant until the overturning moment equals the resisting moment.  THEN the height of the center of gravity becomes important.  But when that occurs the planer is already unstable (tipping over) and is not something you want to happen.  The higher the center of gravity the faster it will tip over and the less likely it will be that you can right it.

PreviewAttachmentSize
tipping.jpg
tipping.jpg28.9 KB
highfigh's picture

(post #76362, reply #24 of 32)

So again, 88# is a fair nudge, don't you agree? I can't think of a reason to push that hard on a planer but thanks for doing the calcs and showing your work. lol

Allowing a board to extend that farwith no support isn't a great idea due to instability, as you described and we agree on.

Again, thanks for showing the calcs- this is good info for anyone who would want to make a cart for their machinery.

"I cut this piece four times and it's still too short."
"I cut this piece four times and it's still too short."
Rich14's picture

(post #76362, reply #4 of 32)

Steve,


It probably won't tip in the direction of the wheel movement, unless the wheels are locked. It will become unstable if pushed sideways until the center of gravity of the planer moves about 10" horizontally and is then outside the perimeter of the base. That's about 13 degrees.


If the wheels are locked, it must be tipped about 16 degrees (about 16 inches of horizontal movement of the center of gravity) before it becomes unstable.


Rich


Don't ever learn anything new. Rather than give you satisfaction that you know more than you did, it will only confirm you know less than you thought by opening horizons to things of which you had never dreamt and which you now must explore.

Rich14's picture

(post #76362, reply #5 of 32)

Steve,


I believe that about 23 pounds of force applied in the short dimension of the table, at the height of the center of gravity will push the planer into an unstable tilt.


It would take about 30 pounds to do that in the long direction with the wheels locked.


Rich

StorminNormann's picture

(post #76362, reply #6 of 32)

The planer, a

Dewalt 734
, is 21" long, 18" high, 14" deep. My intension was to orient it
lengthwise along the x axis as depicted but perhaps rotating it 90 degrees on
the XZ plane so that the wood passes through along the x axis makes more sense.  
The planer has in/out feed tables built in.  I intend to use my table saw
and roller stands as needed for additional support for longer pieces. 

 

I chose 36" as the operating height to match the height of my
Ridgid TS3650 table saw
Giving a few inches on either side for clearance means I would need to deepen
the cart by about 6".    That seems a little more stable.  

I'm torn cause I don't want to make the table so deep such that working with
the router will be physically uncomfortable.

Steve

__________________________________________________________________________________ It is noble to teach oneself, it is still nobler to teach others -- Samuel Clemens __________________________________________________________________________________ Steve
Rich14's picture

(post #76362, reply #7 of 32)

Steve,


I don't believe you will have a stability problem, but making the stand a few inches larger in both width and length will make a big improvement in stability and really won't make that much difference in reaching the router.


I think the real issue is lifting that 90 lb mass onto and off the support, to say nothing of putting it on the bottom shelf. I think you'll do that just a few times before you conclude you ain't gonna do that any more! Wait 'till you knock the stand over with the planer as you're muscling it into place. On the other hand, maybe you're 6'4" and weigh 240.


Rich

rrpm1's picture

(post #76362, reply #10 of 32)

Steve,


Mine is rotated 90 degrees from your original design.  I also put flip up infeed/outfeed extensions.  I store the chop saw on the base..they change places when needed..and added a couple of shallow draws under the top for drill bits, etc. adding to the stability.  It's done everything i've asked.    


 

 

StorminNormann's picture

(post #76362, reply #11 of 32)

Thanks for your input guys. I appreciate the good advice.

I'm going to add another 6" to the depth and rotate the planer as shown here:

I might have gotten away with it as it was but just don't like the thought of pushing it up against a power cord or some such and having everything topple over.

BTW, really liked how easy it was to modify the design in DesignCAD. Just pulled a few points here and there and got the updated drawing.

Steve

Edited 2/8/2005 5:25 pm ET by Steve

__________________________________________________________________________________ It is noble to teach oneself, it is still nobler to teach others -- Samuel Clemens __________________________________________________________________________________ Steve
cowtown_eric's picture

(post #76362, reply #12 of 32)

hey some marvelous physical analysis there, but none of em mentioned that the castors ain't gonna be at the corners, probably two inches in at least, and if the wheel is pointed inwards, yer losing another inch of stabilitycause the centre of the wheel is offset from the centre of it's mounting plate..... ie, the platform base could become approx 6" smaller in both dimension given worst case (all wheels pointed into centre)

As for running over extension cords, it don't take much more than a thick piece of debris to stop a castor dead while the load above it keeps on a-moving.

My 2040 planer is on a big mobile base, and a welded steel rack supports a perfomax 16-32 just above it. Centre of gravity and mass would make ya think its wonderfully stable, but if it comes off the garage slab onto the slightly sloped driveway, it is obvious that that theory doesn't equate with reality. It becomes quite tippy (on the side to side axis) until back on flat land again.

For them physicists, my pea brain thinks that when the castors rotate suddenly to adjust to the slight slope, the centres of the wheels change their height by a fraction of an inch, and in doing so they introduce a moment of rotation to the assembly, which given the weight involved, incorporating a large amount of momentum, which then produces "tip".

And that's before there's a 12' plank running through either. My stand is however stable on the "long axis" though, even with long boards.

20 or 30 lbs of force don't strike me as being that hard to produce if you have to assist a board to feed smoothly.

So build the base bigger than you think, you can always cut it down. It gets hard to add more base later on!

Eric
in Calgary

Rich14's picture

(post #76362, reply #13 of 32)

cowton,

Man, you are absolutely right about all those issues with the casters. Everyone was focused way above them.

They really hamper the design. There are lots of good design solutions that lift wheels and allow the solid perimeter of a support to contact the floor.

Rich

WillGeorge's picture

(post #76362, reply #8 of 32)

I have a 13 inch planner on a 3/4 inch plywood stand with casters. 18" deep X 26" wide X 32" high. I have never had a problem with it but then again I have never run a 6 inch thick 15 foot log throught it!


Really, I just run about 2 to 3 inch thickness about a Max. of 8 foot and never had a problem with it tipping. However I do run around and hold up the outfeed end of the stick for everything.

Have a great day.. Life is wonderful even if you are having a bad day!

GHR's picture

(post #76362, reply #9 of 32)

rough numbers...

8' board, about 40# = 12bdft = 1.5" x 12" x8'

might tip.

8/4 x 12" x 11' certainly will tip it.

Dave45's picture

(post #76362, reply #21 of 32)

I used to have a similar setup and - although it never tipped over - it never seemed really stable.  I have an "anvil" that is just an 18" piece of railroad rail and storing it in the bottom the stand really helped.

GHR's picture

(post #76362, reply #23 of 32)

Having thought about this a bit ...

Your planer will produce unacceptable snipe on any board large enough to tip it over.

You should not be pushing boards through the planer. The planer has feed rollers for that.

I expect that any worries you have are unfounded.

cherryjohn's picture

(post #76362, reply #25 of 32)

I put mine on a "Workmate"...............solid as can be.  I can clamp it down to the top and with the low splayed legs it wold take a runaway truck to knock it over.


Wicked Decent Woodworks


Rochester NH


" If the women dont find you handsome, they should at least find you handy........yessa!"


Edited 2/10/2005 12:23 pm ET by CHERRYJOHN

Wicked Decent Woodworks

(oldest woodworking shop in NH)

Rochester NH

" If the women dont find you handsome, they should, at least, find you handy........"

jeffno's picture

(post #76362, reply #29 of 32)

you could design in some outriggers that rotate into position when you are using the planer...

StorminNormann's picture

(post #76362, reply #30 of 32)

You're right. I do have some clearance underneath the bottom shelf to mount something that could be swung into action if needed. I'm going to wait and see how stable the cart is first.

Thanks,

Steve

__________________________________________________________________________________ It is noble to teach oneself, it is still nobler to teach others -- Samuel Clemens __________________________________________________________________________________ Steve