Another quest for flatness

[AndyG]

Hi All,

It feels like I've been away from the forum forever, there have been all sorts of things going on. One of which has been moving house, which has in turn meant setting up a new workshop!

One of the first big jobs was to get a proper tool bench put in. The plan is to create a router/mitre saw/pillar drill bench along the longest wall. I really wanted the router part of the bench to be flat. Unfortunately the top parts of the frame were a bit off, so I had to improvise, and here is the solution.

I attached a bunch of M10 fully threaded coach bolts to the top parts of the frame. These are held with nylon lock nuts. You can see the housing that will enclose the router.

Another set of nuts and washers then support the first layer of the top, 18mm MDF. The idea is that the top can be held straight be adjusting the supporting nuts.

A top view of the first layer

Once the first layer has been coaxed into being flat (something that took a bit of tweaking, but wasn't too bad) the second layer is placed on top. This layer has clearance holes that fit around the nuts and washers.

The two layers are held together with some M6 bolts and pronged nuts.

The final stage is to put the third layer on. This is currently gluing to the second. The end result is that if everything needs re-flattening, the 2nd and 3rd layers can be removed in one piece and the 1st layer adjusted.

This is probably a massively over engineered solution. But it is solid, I guess it should be with 3 sheets of 18mm MDF. Hopefully though that mass will help keep any vibrations down. The next job is to create a hole for my shiny new router lift!

Andy

 

[sawdust maker]

WOW!

Over engineered, it could be. But I admire the work and determination to get a flat surface. It must have been a nightmare getting all those nuts level.

well done.
Paul

 

[Shultzy]

I don't think its over engineered for what you are trying to do. One thing puzzling me is how do you get to the nuts holding the first board down if the top two boards are glued together?

Don't confuse "flat" with "level" as you can have one without necessarily needing the other :wink:

 

[johnnyb]

norms design seems to rely on laminating 18mm and 10 mm mdf with a laminate adhered with contact cement. would that be flat (enough). surely it would be better to laminate the reverse as well. the book care and repair of shop machines(superb) suggests screwing angle iron to the reverse to keep it flat. this seems to make sense. your method is very clever and allows small hollows to be eradicated. but is fiendishly complex...... i also think contact adhesive would allow small bumps to develop as it is very tricky to spread perfectly evenly.(norm uses a roller)

 

[spadge]

I don't think its over engineered for what you are trying to do. One thing puzzling me is how do you get to the nuts holding the first board down if the top two boards are glued together?:wink:

Thats just what I was think :?

 

[AndyG]

Thanks for the comments.
I had similar reservations about how easy it would be to adjust the top flat. But in the end it really wasn't that bad. I started by tightening the centre-most bolt and slackening off all the others. The next thing was to set just one row of bolts, getting the top flat in that dimension. These were tightened and that line was now fixed flat. I then set a set of bolts perpendicular to the last. At this point. I had a cross of bolts tightened holding the top flat in two dimensions. The last point was to bring the nuts up for the remaining supports.
There was a slight problem with the board moving when tightening the nuts, but it was very slight.

As for readjustments... The top two layers (glued together) are attached to the bottom layer via the M6 bolts. Undo those and top layers can be removed. The base layer can then be adjusted, before replacing the top. That base layer is held in place very solidly, so the flatness of the reattached top layers reflects that of the bottom one.

Andy

 

[Anonymous]

Why not just use 50mm mdf ?

 

[AndyG]

Why not just use 50mm mdf ?

Fair point. I suppose mainly because it was easier to get hold of 18mm MDF

 

[Gary H]

Great job Andy! If only I had the time and patience...

I just hope you get the hole for the Router lift right first time. I'd hate for you to have to start over :shock:

 

[AndyG]

I just hope you get the hole for the Router lift right first time. I'd hate for you to have to start over

Me too. I'm planning on making a jig and testing it A LOT first...

Andy