Squaring the table, part 2...

[geneb]

Ok, I've got everything all put together and I've used the CR command to cut down an oversized sheet of 3/4" MDF down to 96x48 to use as test victim/spoilboard.

Knowing I had issues before I started cutting, I figured if this was messed up I could just keep cutting it down until it was square.


As measured diagonally I get 107-1/8" one way and 107-3/8" the other. This makes me think I may have a trapezoid on my hands, right?

I measured the length of the panel in multiple places and get 96" every time. I measured the short width in multiple places and I get 48" every time.

From what I've read from the many discussions here, this should definately NOT be the case. If nothing else I should have a detectable trapezoid on my hands and I don't.

Have I made some silly mistake in measuring or am I just looking a gift horse in the mouth? I've measured the diagonals four times, twice from either end of the table. Came out the same each time. I'm totally confused.

Oh great learned ShopBotters, help!


tnx!

g.

[fleinbach]

Gene,

I'm not sure what you are saying

"If nothing else I should have a detectable trapezoid on my hands and I don't."

You do not have a trapazoid but a Parallelogram. This means your machine is not square to the table but very close.

You need only make a minor adjustment to correct this.

Read this post on squaring the X car http://www.talkshopbot.com/forum/show.cgi?tpc=7&post=43809#POST43809

[geneb]

I'm sorry Frank, my mistake. Right idea, wrong word.


What bothers me is that I should see some evidence of the parallelogram in my measurements. However, at every point I measured around the table, I got the 96" or 48" that I was expecting. Is a run of the mill tape measure not capable of showing me the error in the table?

I'll try the stop block trick you mentioned and re-run the spoilboard outline program and see what I get.

tnx!

g.

[rob_bell]

I'm sure if you think about it you'll realize that a parallelogram, even a very eccentric one will give perfect 96" x 48" measurements all around. It's the angles that are off, not the linear dimensions.

[richards]

Gene,
The gantry on my machine is not totally perpendicular to the X-axis (and, without enlarging the bolt holes, I can't 'tweak' the machine into perfect alignment), hence the reason that I used two combination squares that were set with a difference of 3/32-inch. Currently, I'm using Frank's method to pull the gantry up against the stop-blocks before powering up the machine. His method is faster and just as accurate. When I've finished working for the day, I jog the gantry to a position just short of the stop blocks, so that I only have to manually move the gantry 1/2-inch or so in the morning (with the power off).