Leg splay or not to splay?

UKworkshop.co.uk

Help Support UKworkshop.co.uk:

Giles55

Established Member
Joined
9 Jun 2021
Messages
51
Reaction score
8
Location
London
I am making an assembly table/ lay out table/ finishing table. I am using a four by two piece of mdf for the top and I will use cls studs for the frame beneath. I envisage right angle legs bridle jointed to each end of two rails, or I could move the joints inwards away from the ends of the rails and mortise and tenon slightly splayed legs. My question is, is the table more stable with a splayed leg or with the right angled leg, if the footprint of the feet is exactly the same and sit directly under the corners of the table top? I am hoping to use my assembly bench to hand plane some of the boards for a work bench build, so the loads placed upon the bench will be from end to end. Once I am using the bench as an assembly bench the issue of stability is more or less moot. I am interested in hearing mathematically verifiable answers. I am not particularly interested in people’s intuitive thoughts as I already have my own opinion of that. So if there is a definitive answer I would like to hear it, perhaps a question for someone with formal engineering training.
 
Last edited:

Yojevol

Clocking on
Joined
29 Jan 2017
Messages
935
Reaction score
394
Location
Cheltenham
Splayed legs do not add to the overall stability. As long as the centre of gravity of the load is inside the footprint of the legs it will be stable no matter what the leg structure is like (assuming the leg structure is well made, ie, good joints and well braced).
However that can't always be said of the table top as an individual component. If the legs are splayed then it will be possible to load the top outside the leg attachment points, thus putting the top under stress. Taking the splayed leg concept to extremes, if the splay angle is so great that the attachment points are near the tabletop centre, you're going to have an extremely stable undercarriage and a very unstable top.
Personally I wouldn't dream of splaying legs of a workshop bench or table, but I would have the top overhanging the rails by a couple of inches to allow clamping.
What is tour opinion?
Brian BSC M,eng
 

Jacob

Pint of bass, porkpie, and packet of crisps please
Joined
7 Jul 2010
Messages
22,502
Reaction score
2,523
Location
Derbyshire
Hmm, can't entirely agree!
In theory splaying will increase stability as it is a move towards triangulating the structure, which makes racking impossible.
But it depends on how it is done and the details.
For your purposes it would be easier to triangulate by adding brackets or diagonal braces, or if you don't want them, to have a deep apron with M&Ts into the legs to resist racking.
Works most brilliantly and noticeably with the common splayed leg saw stool, which is inherently stable and effectively self tightening if there is any slack in the joint. Also benefits if the top is shorter than the splay so that even if you stand on the very tip it can't tip over.
See Robin Clevett's example in this vid. It's a bit of a cheat as the angles are only approximate, but it will work really well.



Wouldn't translate easily into a big table, unless you made a pair with a table top laid across them, which is a very ancient idea still in use - IKEA do a two trestle table.
Single trestle would work for a narrow table for heavy loads - I've got my lathe on one.
 
Last edited:

Terry - Somerset

Established Member
Joined
22 Dec 2012
Messages
1,223
Reaction score
643
Location
Taunton
They real issue is the stress on the joints - it may be a good idea to triangulate the corners so the horizontal forces created by planing don't cause a simple right angled joint to fail.
 

TheTiddles

Established Member
Joined
14 Oct 2007
Messages
2,937
Reaction score
770
Location
Wiltshire
Based on your explanation of splayed legs, no. The centre of mass remains the same, the pivot line remains the same and you increase the bending moment on the joints for no benefit…

That’s not really why you splay legs for stability, you do it to move the pivot line out, which does increase stability.

Sounds like you’re overthinking this, a built workbench is more effective than a theoretical one.
 

Giles55

Established Member
Joined
9 Jun 2021
Messages
51
Reaction score
8
Location
London
Splayed legs do not add to the overall stability. As long as the centre of gravity of the load is inside the footprint of the legs it will be stable no matter what the leg structure is like (assuming the leg structure is well made, ie, good joints and well braced).
However that can't always be said of the table top as an individual component. If the legs are splayed then it will be possible to load the top outside the leg attachment points, thus putting the top under stress. Taking the splayed leg concept to extremes, if the splay angle is so great that the attachment points are near the tabletop centre, you're going to have an extremely stable undercarriage and a very unstable top.
Personally I wouldn't dream of splaying legs of a workshop bench or table, but I would have the top overhanging the rails by a couple of inches to allow clamping.
What is tour opinion?
Brian BSC M,eng
Ok, thanks, I may as well stick to right angled joinery which is easier to set out and cut since the splay option isn’t going to improve stability.
 

Giles55

Established Member
Joined
9 Jun 2021
Messages
51
Reaction score
8
Location
London
Hmm, can't entirely agree!
In theory splaying will increase stability as it is a move towards triangulating the structure, which makes racking impossible.
But it depends on how it is done and the details.
For your purposes it would be easier to triangulate by adding brackets or diagonal braces, or if you don't want them, to have a deep apron with M&Ts into the legs to resist racking.
Works most brilliantly and noticeably with the common splayed leg saw stool, which is inherently stable and effectively self tightening if there is any slack in the joint. Also benefits if the top is shorter than the splay so that even if you stand on the very tip it can't tip over.
See Robin Clevett's example in this vid. It's a bit of a cheat as the angles are only approximate, but it will work really well.



Wouldn't translate easily into a big table, unless you made a pair with a table top laid across them, which is a very ancient idea still in use - IKEA do a two trestle table.
Single trestle would work for a narrow table for heavy loads - I've got my lathe on one.

Thanks, I am going to stick with right angled joinery, legs directly under the corners, I will add some appropriate bracing to stop any racking.
 

Giles55

Established Member
Joined
9 Jun 2021
Messages
51
Reaction score
8
Location
London
They real issue is the stress on the joints - it may be a good idea to triangulate the corners so the horizontal forces created by planing don't cause a simple right angled joint to fail.
Thanks, I am going to stick with right angled joinery and add some bracing. A friend of mine recently made a shelf unit, he added two horizontal rails inside the top and bottom shelves, just at the back and it completely cured the racking. I think I will do something similar, adding a second rail beneath the top rail, between the legs on the side which sits against the wall. I am also running a rail down the middle, between the two leg assemblies, at foot height. I think I have just proved that a picture is worth a thousand words.....ha ha ha
 

Giles55

Established Member
Joined
9 Jun 2021
Messages
51
Reaction score
8
Location
London
Based on your explanation of splayed legs, no. The centre of mass remains the same, the pivot line remains the same and you increase the bending moment on the joints for no benefit…

That’s not really why you splay legs for stability, you do it to move the pivot line out, which does increase stability.

Sounds like you’re overthinking this, a built workbench is more effective than a theoretical one.
Thanks, I am going to stick with the right angled joinery option and keep it nice and simple.
 

niall Y

Established Member
Joined
1 Nov 2018
Messages
120
Reaction score
111
Location
CARDIGAN
I have a small work bench with splayed legs. It was built to hold a large metal working vice. It is very solid,with 4 inch sectioned legs and comes up to waist height. It is very stable and allows me to give things a lot of 'welly', when they are in the vice.Probably more akin to a sculptors bench.
Something with a small top and tall legs. such as a chair or stool certainly benefits from a small amount of splay, but for a table it's not really needed. However, I do remember my parents having a G-Plan dining table with splayed legs, but this was more for the aesthetic than the structure
Also, anything with a splay to it I invariably end up tripping over in the workshop.😦
 

Jameshow

Established Member
Joined
4 Oct 2020
Messages
2,863
Reaction score
1,602
Location
Bradford
Add a decent apron say 9" deep minimum and this will counter the main loads of racking from planning..
 
Last edited:

Giles55

Established Member
Joined
9 Jun 2021
Messages
51
Reaction score
8
Location
London
I have a small work bench with splayed legs. It was built to hold a large metal working vice. It is very solid,with 4 inch sectioned legs and comes up to waist height. It is very stable and allows me to give things a lot of 'welly', when they are in the vice.Probably more akin to a sculptors bench.
Something with a small top and tall legs. such as a chair or stool certainly benefits from a small amount of splay, but for a table it's not really needed. However, I do remember my parents having a G-Plan dining table with splayed legs, but this was more for the aesthetic than the structure
Also, anything with a splay to it I invariably end up tripping over in the workshop.😦
I have decided to keep it simple and go with right angled joinery as I believe splay wouldn’t add anything extra to this project, if the footprint of the feet is under the corners of the top( whether splayed or right angled), it’s not going to make a difference to stability with or without splay. It will be interesting to see how it turns out in practice.
 

D_W

Established Member
Joined
24 Aug 2015
Messages
9,519
Reaction score
1,915
Location
PA, US
I can't think of a good reason to have splayed legs sticking out on an assembly table. It may not be often, but there could be a chance that you want to have something run down the side of the table for alignment and splayed legs will get in the way. If strength is an issue, just build the base a little bit more heavily.

I'd bet a lot of people copy Chris Schwarz and others and then end up cutting the legs of their sawhorses and wishing for a wider horse that is straight up and down.
 
Top