why does my workbench twist?

There are basically two or three ways you can make a joint rigid

##Joinery

Maybe I'm wrong but it looks like you used butt joins held together with a single screw and some glue. Glue works best on joins where long grain is pressed against long grain. Glue generally doesn't work well on end-grain.

Only having a single screw means the joint is more likely to twist and rack.

The traditional way to join table parts is to use mortice and tenon joints, a quicker/easier alterative is to use two or three dowels per joint. I find lap joints are easy to cut and very strong and rigid when glued - they don't look very spiffy but that doesn't matter for a workbench.

(screws are there only to clamp glue until dry)

Obviously, this doesn't help with your existing structure but you might wantto consider this aspect next time you build a bench or table etc.

##Bracing

Michael Karas covered this in his answer. This can make a huge difference. In your shoes I would add bracing to make the structure more rigid. Adding boards as an apron around the top may help if well secured to the legs.

why does my workbench twist?

There are basically two or three ways you can make a joint rigid

Joinery

Maybe I'm wrong but it looks like you used butt joins held together with a single screw and some glue. Glue works best on joins where long grain is pressed against long grain. Glue generally doesn't work well on end-grain.

Only having a single screw means the joint is more likely to twist and rack.

The traditional way to join table parts is to use mortice and tenon joints, a quicker/easier alterative is to use two or three dowels per joint. I find lap joints are easy to cut and very strong and rigid when glued - they don't look very spiffy but that doesn't matter for a workbench.

(screws are there only to clamp glue until dry)

Obviously, this doesn't help with your existing structure but you might wantto consider this aspect next time you build a bench or table etc.

Bracing

Michael Karas covered this in his answer. This can make a huge difference. In your shoes I would add bracing to make the structure more rigid. Adding boards as an apron around the top may help if well secured to the legs.

why does my workbench twist?

There are basically two or three ways you can make a joint rigid

##Joinery

Maybe I'm wrong but it looks like you used butt joins held together with a single screw and some glue. Glue works best on joins where long grain is pressed against long grain. Glue generally doesn't work well on end-grain.

Only having a single screw means the joint is more likely to twist and rack.

The traditional way to join table parts is to use mortice and tenon joints, a quicker/easier alterative is to use two or three dowels per joint. I find lap joints are easy to cut and very strong and rigid when glued - they don't look very spiffy but that doesn't matter for a workbench.

Obviously, this doesn't help with your existing structure but you might wantto consider this aspect next time you build a bench or table etc.

##Bracing

Michael Karas covered this in his answer. This can make a huge difference. In your shoes I would add bracing to make the structure more rigid. Adding boards as an apron around the top may help if well secured to the legs.

why does my workbench twist?

There are basically two or three ways you can make a joint rigid

##Joinery

Maybe I'm wrong but it looks like you used butt joins held together with a single screw and some glue. Glue works best on joins where long grain is pressed against long grain. Glue generally doesn't work well on end-grain.

Only having a single screw means the joint is more likely to twist and rack.

The traditional way to join table parts is to use mortice and tenon joints, a quicker/easier alterative is to use two or three dowels per joint. I find lap joints are easy to cut and very strong and rigid when glued - they don't look very spiffy but that doesn't matter for a workbench.

(screws are there only to clamp glue until dry)

Obviously, this doesn't help with your existing structure but you might wantto consider this aspect next time you build a bench or table etc.

##Bracing

Michael Karas covered this in his answer. This can make a huge difference. In your shoes I would add bracing to make the structure more rigid. Adding boards as an apron around the top may help if well secured to the legs.