Workbench top - how flat?

Re: Workbench top - how flat?

Todd O. Cronkhite Maine Native, Presently Away

>Well Derek, I'll tell ya'. I'm not machinist and couldn't measure down into thousandths if i wanted too. I flattened my bench top until I was satisfied by sighting around the top, and by running my hand over it. When I didn't feel like there was valleys, and it passed the look test I called it good.

I laid a straight edge on it at various angles, and yes, I see a bit of light here and there, but that's fine by me.

I see no need to get it flat as a precision ground instument, after all you're working wood, and not trying to put Man on the moon.

Todd O.

Re: Workbench top - how flat?

Kevin French

>The real problem will come IF you try to plane thin stock on the bench.

Re: Workbench top - how flat?

Derek

>Todd,

Thanks for the opinion. I am using a straight edge and feeler gauges to get an idea of the flatness - I don't pretend to think that my measurements are super accurate but the gaps are somewhat measurable.

One example of when it makes a difference was when I made some chairs. a small difference in the plane of the legs of a chair can make a noticeable difference.

Re: Workbench top - how flat?

Jack Guzman from Maine

>You want to be able to use your bench top as a reference.If you are glueing up a frame and panel door for instance.If your bench is flat you can tell if your frame is also flat.Also when checking stock for warp it will rock on the high spots when laid on a flat surface.It's hard assembling things if your top isn't flat. However I don't think it has to be perfect.

After about 6 years of abuse I think it's almost time to pay a little attention to my bench top.---Jack

Man I hate mils

GolfSteve in Calgary

>To address your first question...my bench is as flat as possible in the small area that I do most of my dimensioning work on (about 2-3 feet long by 2 feet wide). The remainder of the bench is as flat/straight/untwisted as I can get it. Overall I'm probably within 0.5 to 1.0 mm over 8 feet, but in my "precision" area, I only see slivers of light under my straightedge, which puts it into the less than 2-3 thousands of an inch range.

As to why I hate mils, we built a large "mill" in Australia, designed by Canadians and Germans, fabricated by Spaniards, Aussies, Germans, and Malaysians, and partially erected by an American. There was huge confusion when the American misinterpreted a mm or micron tolerance (I forget which now) as mils (thousandths of an inch). Much hilarity and beer drinking ensued when the confuscation was understood.

mils have to be one of the worst unit in the world (I also hate viscosity units). They can be misinterpreted as anything from millimeters to microns, to thousandths of an inch, to angle measurements for artillery (1/1000 of a degree), to millilitres, to 24,000 danish feet (4.6805 miles), to circular mils for wire sizing calculations, and sometimes refers to a million of something, but at other times refers to one-one thousandths of something.

:-) Nevertheless I think I understand you.

Re: Workbench top - how flat?

ThomD

>Actually woodwork and machining are roughly in the same accuracy range. FWW did a good article years ago on how small the tolerances really are in good woodwork, they can easil be the the sub thou range.

Right now my bench is not well set up and it needs some work. I do have a planing beam that is pretty good. I actually thing the problems can be more severe with stiffer pieces of wood they will deflect and accuracy is afected. With really thin wood the usual projecets are not all that accurate anyway, or where they are like a guitar top, it easily lies flat if the surface is smoothly deformed. I suppose there are lots of ins and outs depending on the work one does.

One thing that is very important before wasting time on the top is to start on the base. Ensure it is level and stable, or however you want it, then work your way up. Even at several inches thick the top will deform if the base is not accurate. And then the base needs to be secured to the floor. I have never bolted one but it needs to be marked for it's place and designed not to move.

Re: Man I hate mils

David Charlesworth

>With a good straightedge, it should be possible to have no gap of more that 0.004". (Sheet of good quality paper)

I would hope to get the critical front section where drawer sides and other components are planed even better.

As Kevin says, hand planing thin stuff is the most critical.

David

Thanks for the feedback folks!

Derek

>I think I may continue to tweak on it for a while and try to get it better - especially along the front edge.

Hand planing is a lot of fun but it is time consuming and I do have to do a lot of sharpening when working on a piece this large.

Re: Workbench top - how flat?

George in Lowell Mich.

>When I flattened my bench I used my scrub, my #5 & #8 as the combination plane / straightedge. I worked until I couldn't see light under it.

Work safe

George in snowy & cold Lowell, Mich.

small stuff

Joe Piotrowski - Chicago Burb's

>I guess depending on the sizes of things could you just place some MDF over the top. shim it flat and then plane small stuff?

if a work bench might get moved around a lot would it be wise to go with a torsion box design?

not to hijack the thread but inquiring minds need to know :)

TIA,

Joe P.