Gantry rails

[alexis221]

Hi. I have a pair of 10"THK RSR9W(Wide) That I plan on using for my gantry z axis. Are these long enough and strong enough for all purpose cnc router? Thanks. I am using a porter cable 2 1/4 horse router.

[ger21]

There probably a little on the short side. I don't know how long the blocks are, but you can probably get 2"-3" (maybe 4"??) of travel out of them. Depends on how you design the Z-axis. They should be plenty strong, provided that what you mount them to is very strong, preferably a think plate that can't flex. By themselves the rails may seem a little flimsy.

[alexis221]

Thanks. I think they are on the short side. What length should I look for in this style rail?

[ger21]

That would depend on your design and intent. How much travel are you looking for?

[alexis221]

Well I'm looking to do some of everything.....some carving, and 2d work. The bed is going to be 3' x 4', and i am trying to design my gantry but affraid my slides are too small......What would be considered a normal travel distance. Thanks.

[Zumba]

Don't be tempted to make your Z-axis too long. I think you may be fine with the 10" rails you already have.

Long Z-axis travel = long lever arm = very high moment forces on your bearings and frame.

[alexis221]

I was thinking maybe going to 15 inches to squeaze out a few more inches in travel....hhhmmmm alot to think about.

[Zumba]

Draw your machine out in a CAD program before buying another piece of hardware.

[ger21]

You want to be able to reach the table with the shortest bit you'll use, and clear the part with the longest bit you'll use. Anything more just gets you more flex in the machine, as Zumba said. Being able to move the router up and down in it's mount will let you get away with less z-travel. If you try to get the most travel possible for maybe 5% of the work you'll be doing, you may be sacrificing cut quality for the other 95%. Bigger is not always better.