New Large Slab Levelling/Milling Table

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MF1000

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After getting my slabs cut into useable large ‘planks’ my current milling setup is not big enough to cope with a 2.1m x 1 m project.

My current table was a very simple low cost build from ‘scrap‘ timber with a 4ftx4ft ply bed and 4” high sides from mdf. The router sled was made up from 18mm mdf I had spare.

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I really need an 8x4ft table but that presents storage issues and is a beast to handle too. After a few doodles and problem solving (helped by a few single malts 😀) I hit on the idea of making a modular table.

My Bora centipede 1.2x1.2m would be ideal as a stand and a 2ft overhang at each end could be braced and supported with a workmate or two to give a solid base. To make the whole thing more easy to store I wanted to split the bed in half ….but then how to mount the 2000mm linear rails.

After looking at various clamp ideas I hit on using some 4x2 cos timber to mount the linear slides and fasten them to the bed using 5 x C clamps recessed and screwed into the base of each rail. This will joint the two halves of the bed together and stiffen the edges of the bed whilst supporting the linear rails. If I also only needed to use a smaller table I could reposition the rails on one half only.

Today I made the two bases and completed most of the bracing …pics to follow when I try to move the build on tomorrow.
 
Build a large milling table that I can easily store in my garage. Once built it will be used to mill two slabs of 2.1x 0.6 x 50mm beech that will be jointed to make a table for my eldest.
 
Dodging the showery weather today and I’ve managed to mock up the table setup using just 1 cross rail to allow me to determine the dimensions for the router carriage.

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I now need to find a local metal fabricator to make two drop plates with flanges to bolt into the linear slides of the cross rail and provide a mounting flange for the router mounting plate.

A change to the method to secure the 100mm cls to the Base plate is needed so I think I’ll use bolts through the stiffening ribs into inserts fixed in the cls timber.
 
Get a cheap stick welder. Mine is ROHR brand, was cheap and has been great. Tricky at first but a great skill to have. I’ve made no end of stuff with it, saved me a fortune.

By the way, dare I mention, a #5 hand plane would do the entire job. No I won’t mention that.
 
I’ve around 15mm to remove from the two slabs to level them ….im sure it’s possible with a plane but the blisters and sore muscles/aching back etc I’d give a miss. Although the use of a router and milling cutter isn’t quite purist, it has its own level of satisfaction and skill to do it. I introduced a newbie to milling yesterday on some oak cookies he had - the look on his face of what he could achieve etc was more than worth it and I gave him my old mdf router sled to help in on his journey.
 
That is going to create a hell of a mess!
Will that centipede hold the weight of the slab? I hope you're using something else.
Will support 3500lbs according to Bora 😁😁….so I think I’ll be ok at around 350 lbs

I’ll be fitting a custom sled for the router with a 32mm vac take off to route to my Axminster twin motor vac
 
My concerns would be:
1. ensuring the two main runners are flat, easy enough with a long plane over the CLS
2. ensuring the runners are not in twist, not so easy. I used a pair of cross strings from corner to corner.
3. ensuring the rig does not move as the router weight swings from one side to the other

Fitz.
 
The cls is just to support/locate the 20mm rails mounted on a triangulated alu base - incredibly stiff…..I won’t be screwing it down too tight 😀

The cross rails are of the same 20mm bar/alu support so i doubt the router will deflect it at all across the 1200mm span

i have a depth gauge that I can use to check the router height to base plate at any point on the bed an if needed shim up the cls
 
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i have a depth gauge that I can use to check the router height to base plate at any point on the bed an if needed shim up the cls
If the whole setup is in twist then I think the router height to base plate will still be constant. As an example imagine after setting it up perfectly flat you lift one corner of the set-up, there will be enough flex that I expect you could lift it by at least 1cm without the other corners moving at all. The base plate will flex with the rails so the router height to plate will remain constant, however the finished piece will have one high corner, it will be twisted.
 
To be honest, I really wouldn't believe what Bora say. I'd want to climb onto the cls and jump up and down on it before trusting a fast spinney-thing going awol as the centipede collapses! Just my opinion of course, glad I'm not trying it!
 
I have little doubt that the Bora will easily support the weight of this setup and remain stable, but will the flatness/twist of the top not simply be a mirror image of the ground or floor it sits on? If the floor is perfectly flat so will the top be, but if not, the top will reflect any twist of the floor.
 
I have little doubt that the Bora will easily support the weight of this setup and remain stable, but will the flatness/twist of the top not simply be a mirror image of the ground or floor it sits on? If the floor is perfectly flat so will the top be, but if not, the top will reflect any twist of the floor.
The osb bed of the table has been braced with 3x2 CLS to prevent any effects from an uneven floor.
 
Ok last attempt :) as @TomGW and myself have commented the flatness of the bed will be crucial, which you know. However, the cls bracing and rails will not be sufficient to ensure flatness and there will need to be an element of adjustment during set up.

The reason I say this is because the structure as designed is large and you have significant leverage at the corners, which means it will be ‘relatively’ flexible. Even when you set up a machine like a lathe, which is structurally much more rigid than your bed, it will take adjusting to get flat as the lathe bed will mimic the floor it sits on.

It’s not a weakness of your design it’s just physics, materials are only so stiff. Setting up with a pair of cross strings will easily allow you to check there is no twist. You can then shim corners to get it flat.

Fitz
 
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