[the_tool_man]

Hi all:

I'm getting together materials for my first build. One of the nice things about where I work is that I can buy metals through our raw material department, and take advantage of really good pricing that the company gets without having to buy big pieces. The only problem I am having is that we don't use the 1.5 x 3 x .125 rectangular aluminum tubing, used in the gantry, at work. I have two options. I can get a solid bar (4.2x the mass) at work for about $32, which is about what I would pay for the tubing shipped from Metals Depot. Or I already have a piece of 8020 extrusion 1530 profile (2x the mass) for free. Would these heavier pieces have any ill side effects, or would the mass be helpful to dampen things a bit? These would be somewhat stiffer, which wouldn't hurt, either. Your thoughts?

The above ignores the difficulties in machining the alternates to attach bearings and the Y rail. For the moment, I'm just concerned with the effect of increasing the mass of the gantry.

And if anyone knows of a less expensive source for the tubing, I'm all ears.

Thanks in advance,
John.

[awerby]

I wouldn't use solid bar for this, and it seems that you'd need two of those extrusions in order to have a place to run the screw. They look fairly stiff, but mounting the rails on them might be difficult, depending on what exactly you're using for rails. In general, stiffness is good in a gantry, but mass is not. Your stepper motors have to be able to move it around freely, and a massive gantry will have a lot of inertia, which will tend to make the motors lose steps when it changes direction.

What other shapes does your company regularly order? If you provide a list of them, we'd be better able to advise you on which to use where. Are you trying to make a router from a certain set of plans? If so, which one?

Andrew Werby
www.computersculpture.com

[the_tool_man]

Are you trying to make a router from a certain set of plans? If so, which one?

I'm using the Momus plans (Version 2.0).

[the_tool_man]

I didn't realize how infrequently this forum is read. No hope of a quick reply, lol. I ended up ordering the 1.5 x 3 tube from OnlineMetals.com. Cost $26.48 with shipping.