View Full Version : Attach the cross bearers first or attach support board first?

Tue 14 September 2010, 18:48
The plans prescribe cross bearers welded to the longitudinal beams and then attachment of the support board.

My question is whether I can attach the cross bearers to the support board and then attach the massive construct to the longitudinal beams.

In my mind it will be easier for me to keep everything square(r).

Also I was thinking of tacking the cross bearers to the beams and then drilling for the bolt-together construction. Any input?

Tue 14 September 2010, 22:05
Red, that is mentioned as a preferred method of attaching the cross bearers in the plans so it should be fine.

Wed 15 September 2010, 07:31
Hi Red

My suggestion is to not mix the welding and bolting of the cross bearers.
If you are concerned about squareness then drill your holes slightly oversize as this will provide some retrospective adjustment.
As little as .5mm oversize will give a surprising amount of adjustment. It will not slop around once tightened as the combined clamping force of all the bolts is massive (use M8.8 grade HT bolts)

It is much easier to predrill the holes in a drill press with all the mechanical advantage this machine brings to the party. Should you choose to tack then drill in place you will need to substitute muscle power for this mechanical advantage I speak off.

I had one hole in my X beams to Y cross bearers that was a tricky fit up, this was the only one I hand drilled as an experiment !!
Use 20 x 6 mm drilling templates to ensure your drilling patterns are perfectly symmetrical. Use a center punch to stop the drill bit wandering when marking the templates and also straighten the templates along one edge of the x and y beams to ensure your offsets remain consistent.

Square the table and tighten the bolts, then put a square support board on that to get confirmation your table is square. This provides a nice check step.
Also remember that ultimately the thing you also want square is the top of the X beams where the rails bolt to, so don't forget to check that as well as the base.
Refer to my build thread for further photos of how I made a bolt together design. My last comment is to remind you that blazing away with the welder and forgetting the bolts all together is way quicker. Gerald knows his stuff and that is what the original design calls for.


Thu 16 September 2010, 22:27
Jim and Ross,
Thanks for your responses.
My idea was to mark (using a grid of chalk lines), drill and countersink the support board, then lay the beams under the board and mark (centre punch) where the holes need to go.

Then take eack beam out and drill it in the press on the centre press marks.

Then bolt beams to the board and lay the beams plus board on the upside-down longitudinal beams and then tack it in place and drill the holes with the drill press by moving the drill press, not the beams. Then bolt together the supports and beams.
I can cut the tacks and unbolt when I have to move the table interstate in the future.

I may defer attaching the leg sub-assembly until after I've drilled the beams, so the legs don't get in the way.

Then I anticipate flipping (hah! 600kgs worth) the table by throwing a "turning the tables" BBQ and bribing 10 strong blokes with free food and beer to perform the flip.

I take your points on play in the bolt holes and squaring the table across the beams, rather than the support board.
Also, I would not contemplate hand drilling - for me it's a sure way of getting wobbly holes!
I imagine that I can get the rails parallel (and at 90 degrees to the y-carriage) even if the table is out of square by a few mm, but please tell me if there's hidden problems with this concept (or the above procedure).

Thu 16 September 2010, 23:12
Gerald has made a table by attaching the support board to the cross bearers, he has said so on the MM forum previously.


Fri 17 September 2010, 01:53
I made my life easier adhering to Big G's advises & build procedure.
I built the table down side up, aligned the two side frames as parellel as I could, then measured the beam locations. Clamp the cross beam on the main beam before tag welding. Then full weld one side that is facing the sky & weld the otherside after flipping the table over.
The most practical way I know for aligning the main beam parallel is by checking the diagonals with a measuring tape to within 1mm.http://www.mechmate.com/forums/showthread.php?p=36616&postcount=124 (see my built)
Squareness of the cross bean isn't critical. As the board, the cross beams & main beams stocks are not perfect (&never will be). IMHO, just get them square enough to my eye to avoid embarassment when visitor come by is square enough.
PS, my cross bearer lenght are not that well controlled.. they fall within +/-10mm...
As for drilling the board mount holes on the MDF spoilboard after welding was completed, , I marked them up using measuring tape, taking the table centerline as datumn.
Oversized the hole by 3mm & use large washer.

Fri 17 September 2010, 03:48

My suggestion would be to put heaps of thought into which way is going to work for you.
There are many factors that can come into play, like limited height to turn the table over, enough floor space to do so and so on and so forth.

We built and welded our tables very differently to the procedures explained in the forums and to be honest I really do not think it matters which way you do it, it really comes down to doing whats best for you. Providing you put the thought into it, as well as the time to get it right and for you to keep checking what you are doing along the way. I'm sure you will succeed.:)

Something else to think about is being able to weld upside down depending on which way you decide to go!! :eek:


Sat 18 September 2010, 01:26
Thanks all.

Tony - it's exactly the up-side down welding that I'm trying to avoid. Hell, even sideways welding is challenging for me!

Many years ago I rebuilt a snapped toyota corrolla (rusted through chasis). We bought a sheet of 3mm steel and cut out to templates and then welded up boxes that fitted over the existing box frames. Was able to take it back bush bashing again to get to those remote surf spots. Anyway, it was a unique project that exemplifies what you suggest. In our case it was lots of cups of tea in the garage staring at the car, parts and progress, contemplating the next step and its implications

Tue 21 September 2010, 03:11
An update:
Wiser, more experienced views have prevailed.
Went out and got some plate to use for jigs for the cross support holes.
Did the calculations a few times, drilled holes in the wrong place in the jig, covered them with tape and redid calcs. At least the jig steel was cheap!
Plan now is to mark and drill the cross supports, align to beams, mark and drill again.

This way I get to pick up one 10kg support at a time and can get the table ends the "right" way up before attaching the cross supports, rather than flipping the built table.

Wise men, thanks for your help.