543
« on: November 24, 2009, 02:18:23 PM »
Great looking machine Barry. I like it. I do have a question for you, though.
Put an indicator at the bottom of the Z axis, so as to read the distance between the axis and the table.
Push the top of the Z axis.
Pull at the bottom of the Z axis.
How much did it flex?
Keep in mind you will have the section with the trucks added on, along with the spindle, and any other mounts. All adding more weight to the equation.
I too, have a gantry made with 80/20. The rails are mounted the same as yours-directly to the 80/20. The posts, however are made from steel. The length of the gantry is roughly the same. I think yours is a 2 or 3 inches taller than mine. I am less than pleased with my gantry. Actually, it is one of the "live and learn" lessons on my build. I found that the rigidity of the 80/20 is comparable to a wet noodle. Well, o.k. maybe not that bad literally, but in terms where you need a halfway decent finish on a part, it's a pretty fair comparison. I find that the Z-axis bounces around so much (because of the flex in the X-axis) that I have to make more finishing passes than I should have to, and the speed at which I make the finishing passes is far slower (to minimize the bounce) than what it should be. This in turn can create other problems, especially if you need the speed, to get a proper cutter finish. Cuts in the X directions are fairly good, but when you exert any force or motion in Y or Z directions, the demon shows its teeth. 3D paths and\or many short changes in movement are an absolutely horrid affair. That sums up 90% of the machining I do, coincidentally.
In my case, you don't even need an indicator to see the flex, and my Z axis has only 6 or so inches of travel. I'm in no way trying to shoot your design or build down. I like it, and hope that you can throw it off the top of a building, run over it with a tank and explode some C-4 on it, and it never skip a beat and run like a champ. I'm simply stating a concern where a potential flaw is present, and thereby saving you allot of grief at a later stage. It would be much easier and convenient to fix it now rather than later, (if your has the same problem as mine) as you are somewhat still in the design and build phase.
I see that you have dual ball-screws for the Y movement. I had a short ball-screw on mine for testing purposes. I didn't have 2 long ball-screws, so I decided to drive mine with 2 belts. Big mistake, wish I would have bit the bullet and purchased 2 ball-screws like yours.
Guest
Show Posts
Ain't that the darn truth. My scrap yard is much more populated than my 'show and tell' yard by far. Nice to know I'm not alone.