building a wooden workbench, how much margin of error is acceptable

[MassiveJim]

I am building my own woodworking bench out of 4x2 and 3x2 timber supplied by local building supplier.
As with all timber you have to deal with twist and bends etc.
the bench will be 2100mm long when finished.
I am making it with 8 legs in total, I am up to the stage where I have the top frame built and attached to the 4 corner legs.
All the legs were cut at the same time so that I could get them all to the same length, and if I offer one of the middle legs up to the legs that are on the bench now they are the same height, however when i put the middle leg in its actual position it sits proud of the top of the bench by about a 1mm
I have put a long spirit level on to check and it looks straight (no visible light coming through under the level) but I am able to press down slightly on the middle of the sprit level.
which I can only assume means the length of timber running down the side of my bench has a very slight bow in it, both sides are the same.

I can obviously shave the leg down by 1mm to get the top level but not sure if this is deemed acceptable, what else can I do though as no timber that is bought is perfect I checked every piece of timber I had delivered and selected what I saw by eye as the 2 straightest pieces for the longest part of the bench

 

[Quartz]

8 legs seems 2 too many for a table that small.

 

[MassiveJim]

8 legs seems 2 too many for a table that small.

fitting a sliding mitre saw in the middle of it

 

[b0rn2sk8]

Entirely normal. You’ll never get two straight bits of construction timber. Wood bows and the amount of bow can change with the moisture content. I’ve picked up a straight length in a store, put it in the garage and a week later it was as bent as a banana.

The best you can do is the straightest bits for the top, it doesn’t really matter if the legs are bowed if it’s level.

 

[lookitsjonno]

I had much of the same problem studding out my garage. As I've gone on i've realised I get better accuracy if I avoid using a tape measure, and instead offer up the wood (using a level if needed) and mark it the length it needs to be

As for your problem right now - i'd trim the 1mm off - at the end of the day "if it looks right it is right"

 

[bainbridge]

Another thing to bear in mind is where the bench will eventually be situated. I made my workbench last year, and had to take a couple of mm off a leg to get it level, but that was on leave ground in the middle of the concrete slab which forms my garage floor. When I moved it into position against the inside wall of the garage, it wasn't level due to a very slight slope where the concrete meets the wall. With hindsight, I should have built the bench and done the final adjustments in situ.

 

[b0rn2sk8]

Adjustable feet are very helpful for this sort of thing.

Getting the top flat is very important if you are embedding a mitre saw. Getting it bang on level is helpful but not the end of the world if it’s a little out. Mines on casters so I chock the wheels I’m doing something which needs to be bang on level.

 

[PlacidCasual]

I think more information about the design of the table would help in answering the question. In addition the intended use. Because my initial toughs on an answer was very different until I read about the mitre saw station.

 

[Martynt74]

I don't get the impression it's being embedded in the surface, but more just that it'll sit on top of the workbench as most are. I'm happy to be proved wrong though.

Not sure if it's too late, but make sure you make the bench deep enough. I had to build out a protruding shelf where my mitre saw sits because originally i didn't have the depth for the sliding function.

 

[Mercenary Keyboard Warrior]

Turn the the bench upside down so the top is against the ground, see if it looks like its got a slight bow, if so dampen it slightly, cover it and weight the whole thing down with plenty of weight should be able to warp it back to straight

 

[ttaskmaster]

Why so many legs? I made a Nicholson bench 8 foot by 3 foot out of 3x2 and 4x2 PAR and that still only needed four legs...
As above, get the bench in situ and then make any adjustments. The only things you must get right for a woodworking bench is the top planed properly flat, and the top square to the face of your vice.

 

[MassiveJim]

I can take a picture of it tonight when I home but it won't show much, a bow of 1mm in the middle of a 2m long timber isn't really going to be noticeable, I can barely see it with a straight edge on it.

I will be embedding the sliding mitre saw into the top but I am hoping to also have a piece of wood that can fit into the space to cover the gap if i ever need it.
I also want to add a table saw to one end when I find one for a reasonable price, having done a little bit of research most places I look are suggesting the DeWalt DW745 as a "starter" table saw but its £500 new, I'm not willing to pay that much for one at present.
and possibly a router station at the other end if I get round to that.

Width of the bench was originally 1200 but I looked at it last night in the garage and it was just a bit too big for the space so I have cut 300mm off the width now.

Floor is another issue, I think crazy eyes laid this floor, its not level anywhere, so that is another hurdle I will have to overcome as I am planning on having this bench on wheels and shoving it in a corner then wheeling it out when its needed. I currently have the bench sat on 3x2s that are top of the 18mm ply sheet I am using for the top so that I can rule the floor out as causing this issue

8 legs only because I am cutting the top out for the mitre saw. so the middle is going to need support.
the 4 legs currently fitted are made from 2 4x2s glued together, the middle legs will just be single 4x2
the bottom shelf is made from 3x2
The top will be a sheet of 18mm ply

I think given what has been said, I'll shave the 1mm off the middle legs.
Its probably not ever going to sit right on the garage floor anyway with it being so unlevel.

 

[b0rn2sk8]

To be fair mine has 8 ‘legs’ because I have a miter saw embedded into it. The 4 main legs in the corners and then 4 legs which support the shelf with the saw on it (which also folds down hiding the saw under the bench) and the top of the bench has the main supporting beam has a section removed for the saw.

It sounds like a similar bench to what the OP is making but far less over engineered. Mine just went together with screws and I can take it apart again if needed.