Why isn't my bench stable? advice needed

[Tom Scott]

I don't think anyone has said this, but the long stretchers are too low. It is physics in that...the stretcher is resisting the racking motion (not mass). When the stretcher is at the very bottom of the base, then it is the furthest away from the force being applied so it is acting like a flagpole. The higher up you can get it (mid-point or higher) the better.

[Matthew N. Masail]

I said it before, my bench feet only have 4 contact point - there is a curve cut into the bottom of that "flat board". you guys have been and great help and this has been a fairly interesting subject. I didn't think my over hang was too much at 25cm or 1\6 of the bench length, but combined with a high center of gravity from the heavy top is was indeed too much. also the face vise itself weighs 15kg. so the conclusion is that a "light" base cannot handle much of a Cantilever effect, and needs splayed legs on one side in order to mount the face vise on the far side. I didn't want legs flush with my bench top, personal choice, and the stretchers need to be low because I'm adding drawers and shelves, so what I think I'm going to do is move the base to the far right, leaving only 15cm of overhang for the end vise, and I will be adding another leg assembly to the far left, this will give me a nice leg to mount a height adjustable leg vise on the other side of the bench..... might work out quite nicely

[ian maybury]

Hi Matthew. Coming in late, but i'd add to the voices:

Flat feet won't easily rest in a stable manner - even on a seemingly flat floor. Aim for point/relatively small pad support at each corner.

Only a tripod with three contact points is always stable regardless of the flatness of the floor/surface. (almost the first principle taught in jig and fixture design on a mechanical engineering course) A tripod isn't an option on a bench, because it's not laterally stable enough - but the principle still applies. Three legs/points/pads will contact the ground simultaneously. Choose the three that best level the top, glue on packers if needed to achieve this. Then shim/adjust the fourth (short) leg so that all four are simultaneously in contact. (this principle beats trial and error every time when levelling machine tables and the like too - set one jacking screw/support point purposely low, then adjust the other three to level the table. Then ease up the fourth to just close the gap/prevent wobble.)

The legs look quite a bit inboard. Aim to get the points/pads contacting the floor spread as far apart in both directions as is reasonably possible without blocking access to work - by e.g. putting pads under the ends of your existing flat feet.

Deep cross stetchers well tenoned into the legs should stiffen the structure a lot. It may not be too bad lengthwise, but looks likely to be very flexible crosswise.

[Winton Applegate]

Could the items you put in the vice have sufficient weight so as to be beyond the legs and start to tip the workbench?

Yah Will's right I wouldn't clamp any brontosaurus bones in that sucker.

[Winton Applegate]

Steve,

Bench is quite stable.

In the words of Ben in the movie Short Circuit "I'm standing here beside my self".
Stable ?
My guess is you never scrub/jack plane cross grain.

[Derek Cohen]

So I decided to make a new base from my benchtop, this base would allow me to place vises where I want them.

The previous base was rock stable, not a hint of movement, it had legs at the far corners of the bench. the new is base pictured here:
Attachment 306181

the base is only 40" long, and the bottom bars about 23", which is the same as the benchtop. My issue is that the bench is highly unstable, it rattles, and the far right corner bounces when I use the face vise.

-The legs are flat and all for edges are co-planer.

I found that I would need about 30kg of mass on each side on the legs to keep the bench stable, and while that is kinda doable, I use thinking maybe there is a better solution.

also I'd like to know, did I make this with bad mechanics, or is it just not long enough at 40" to counter balance the cantilever effect from the top hanging over the edges?

I'm open to all Ideas besides building a new base.... I have no wood, or time for that anymore.

Hi Matthew

My last bench, which was used over a period of about 18 years, was similar skinny and short base with a longer than stable top (it was not built for handtools when I started out). Yet it was rock steady - because the base was bolted to a wall. You have found that you can steady your bench by adding weighs to the legs. One simple solution is to bolt the bench to the floor (if possible of course). Another - better - alternative is to add a cabinet to the base and fill it will tools. That will add both bracing and mass. It is possibly the only reasonable solution you have other that rebuilding the base, but you will have to wait a while to know that it is successful. I bet it will be. Just leave space above the cabinet for holddowns.

Regards from Perth

Derek

[Tom M King]

I have gotten by for decades with a "portable" 5' bench by putting one corner against a wall-preferably under a North facing window. When I retire, I intend to build a heavy bench, and have been collecting the wood for it for the same decades I've been using the small one at work.

[Matthew N. Masail]

I decided to give myself another week or so to make a base similar to this one
https://dblaney.files.wordpress.com/...l_img_3548.jpg

I think\hope that is a SMART design for stability in a small bench. I'd like to be able to easily move my bench around. I'll have to make it at work since my shop in non operational right now, I'll post the results. Thanks again for all the responses.

[Kent A Bathurst]

Hi Matthew. Coming in late, but i'd add to the voices:

Flat feet won't easily rest in a stable manner - even on a seemingly flat floor. Aim for point/relatively small pad support at each corner.

Only a tripod with three contact points is always stable regardless of the flatness of the floor/surface. (almost the first principle taught in jig and fixture design on a mechanical engineering course) A tripod isn't an option on a bench, because it's not laterally stable enough - but the principle still applies. Three legs/points/pads will contact the ground simultaneously. Choose the three that best level the top, glue on packers if needed to achieve this. Then shim/adjust the fourth (short) leg so that all four are simultaneously in contact.

Or - the method I used - I got 4 industrial swivel leveling mounts. They inset into holes drilled in the leg bottoms, through heavy-duty tee-nut type plates. Just use wrenches to adjust and lock all 4 until the top is level in all directions.

There is enough swivel in the assemblies to account for unevenness in the floor.

ALso - I have drawers on top of the stretchers - as you plan. I am willing to bet that if I weighed the contents and the drawer cabinet itself, it is greater than the weight of the bench itself. The drawers are full of screws, drill bits, hand tools, etc.


http://www.mcmaster.com/#standard-le...mounts/=vto5p4

[ian maybury]

I didn't like to mention engineered adjustable feet in the current (neanderthal) company Kent, but probably a very good idea on an uneven floor. Carefully selected to be really strong and firmly mounted as there could otherwise be problems if sliding the bench sideways.

On the sloping legs Matthew. I'm sure you're well aware, but it's the distance apart of the support pads that will determine the basic stability of the platform in any given direction - not the angle. The angle becomes relevant if it makes it possible to achieve a given (e.g. wide) foot placement without obstructing hardware, your feet or your access - but otherwise won't necessarily add anything much except a fair amount of complication...

[Winton Applegate]

On the sloping legs Matthew. I'm sure you're well aware, but it's the distance apart of the support pads that will determine the basic stability of the paltform in any given direction - not the angle. The angle becomes relevant if it makes it possible to achieve a given (e.g. wide) wide foot placement without obstructing hardware, your feet or your access - but otherwise won't necessarily add anything much except a fair amount of complication...

I hope I wasn't misleading when I mentioned "angle bracing".
I was thinking along the lines of this but hopefully more elegant.

[Kent A Bathurst]

I didn't like to mention engineered adjustable feet in the current (neanderthal) company Kent, but probably a very good idea on an uneven floor. Carefully selected to be really strong and firmly mounted as there could otherwise be problems if sliding the bench sideways.

Even Neanders buy hardware, hinges, etc. Except The Most Reverent George Wilson, who who I think casts his own metal, and goes from there. The Gandalf of the Neander Forum, methinks.

I mentioned "industrial" in my post - the link I provided aren't even the ones I got - there is another group that is seriously industrial - I had access via my work, and got that style at a stupid price because we built machinery.............but for normal use, that price is likely not required.

You can mount the ones I showed, and drag the bench as needed. But - once you do, you are now on a piece of real estate that is unlevel in different planes that the spot you left. The swivel feet will accommodate that change in planes, but the bench top may no longer be dead-nuts level.

[Matthew N. Masail]

I didn't like to mention engineered adjustable feet in the current (neanderthal) company Kent, but probably a very good idea on an uneven floor. Carefully selected to be really strong and firmly mounted as there could otherwise be problems if sliding the bench sideways.

On the sloping legs Matthew. I'm sure you're well aware, but it's the distance apart of the support pads that will determine the basic stability of the platform in any given direction - not the angle. The angle becomes relevant if it makes it possible to achieve a given (e.g. wide) foot placement without obstructing hardware, your feet or your access - but otherwise won't necessarily add anything much except a fair amount of complication...

Thanks Ian. of course I know it has to do with the footprint. I knew building this base that it would have a cantilever effect I just didn't think it would matter so much.

[steven c newman]

Rarely need to
Scrub plane.jpg
But sometimes I do..

[Pat Barry]

I decided to give myself another week or so to make a base similar to this one
https://dblaney.files.wordpress.com/...l_img_3548.jpg

I think\hope that is a SMART design for stability in a small bench. I'd like to be able to easily move my bench around. I'll have to make it at work since my shop in non operational right now, I'll post the results. Thanks again for all the responses.

I don't know. Sure that new design might be nice but first is your bench racking or rocking. Rocking all you need is to shim it. Racking all you need is to crossbrace it. The way I understood it you just built the new legs. If it were me I'd fix the racking or rocking and be done with it.