[Enk1du]

I'm planning a build using 8020 and a bunch of cncrouterparts.com parts. I want to use the gantry risers that Ahren sells, but I'm not sure what size of extrusion to use for the gantry rail.

The space between the risers is about 44", and I had originally planned to use 3030. According to the "tech toolkit" application from 80/20 the deflection of a 3030 beam from a 100lb point-load at the center of the beam is all of about 0.002" (for a distributed load its 0.001") which seems perfectly acceptable for me given that there is the added stiffness of a 1/4" thick, 4" tall piece of CRS and also I don't think my z axis and everything will weigh anything like 100lbs (current plan is to use the dewalt dwp611 router). However, there is also the issue of torsion applied to the beam due to the cantilevered z axis, and the "tech toolkit" doesn't compute deflections for torsional loads.

I'd prefer to stay with 3030 for the rail given the added expense of the larger extrusion and all the other larger parts it would require, but at the same time I don't want to buy something inadequate only to need to upgrade later.

Does anyone have any thoughts or experiences to share to help me decide? Thanks!

[rabidhamster]

I was in a similar situation recently. Couldnt decide, but in the end, I thought, I'd rather spend the extra now and not worry than spend less and wind up paying for it in the long run.

Im not done with my machine yet, but I got the 1/8" steel rails mounted to the 3 foot 3060 beam and it is massive. 3030 may well have been sufficient afterall. But Im already sorta wishing I had 1/4in rails before Im even done with the machine, if I'd gotten the 3030 gantry that'd be 2 things I wasnt sold on. If you can swing it, you might as well do it now eh.

[rabidhamster]

doublepost:tired:

[louieatienza]

I'm planning a build using 8020 and a bunch of cncrouterparts.com parts. I want to use the gantry risers that Ahren sells, but I'm not sure what size of extrusion to use for the gantry rail.

The space between the risers is about 44", and I had originally planned to use 3030. According to the "tech toolkit" application from 80/20 the deflection of a 3030 beam from a 100lb point-load at the center of the beam is all of about 0.002" (for a distributed load its 0.001") which seems perfectly acceptable for me given that there is the added stiffness of a 1/4" thick, 4" tall piece of CRS and also I don't think my z axis and everything will weigh anything like 100lbs (current plan is to use the dewalt dwp611 router). However, there is also the issue of torsion applied to the beam due to the cantilevered z axis, and the "tech toolkit" doesn't compute deflections for torsional loads.

I'd prefer to stay with 3030 for the rail given the added expense of the larger extrusion and all the other larger parts it would require, but at the same time I don't want to buy something inadequate only to need to upgrade later.

Does anyone have any thoughts or experiences to share to help me decide? Thanks!

Unless you have a big need to keep the weight down, the 3060 might be a better choice. If anything the extra mass and stiffness can only help. I never used the "tech toolkit" but I don't know if those numbers are for static forces. I'm building a machine now, and am using 100200 for the gantry, over a 33" span.

[RicknBeachcrest]

My vote is for the 3060.

I'm building a small machine with a gantry of about 36". I'd rather err on the side of over build then to regret not spending a few extra $.

Here are two 8020 builds that I have gotten lots of good info from:
http://www.cnczone.com/forums/diy-cn...tml#post507104

http://www.cnczone.com/forums/cnc_wo..._rails-11.html

[Enk1du]

Drat, guess the consensus is for the 3060 then. I have to admit its tempting just for the sheer beastliness of it. The price of the ~50" piece that I will order is ~$80 for the ~$160 for the 3060, so with the extra shipping cost due to weight it will be about ~$100 more. Eh, not so bad I guess.