[rabidhamster]

Hello all.

Is there a generally accepted "Foolish to go past" limit on the length of your Z axis?
I'd originally planned to build my 8020 machine with 6-7 inches of Z travel, now I'm starting to worry that may be too much to stay rigid. Perhaps its more reasonable to just go 3-5 inches instead. I'd like to be able to cut out a storm trooper helmet in one piece, but I'll mainly be cutting much thinner wood, aluminum, and hopefully brass...so perhaps the shorter travel will be wisest. The Gantry is 36" 6030 w 1/8" CRS bolted on back, the risers will be either 1 or 2 pieces of 3030 stacked, laying down and bracketed with more aluminum. I'll be using a 2.2kw Chinese spindle on THK rails.

Any experiences, tips, hints or conjecture will be fully appreciated.

[adprinter]

Hello all.

Is there a generally accepted "Foolish to go past" limit on the length of your Z axis?
I'd originally planned to build my 8020 machine with 6-7 inches of Z travel, now I'm starting to worry that may be too much to stay rigid. Perhaps its more reasonable to just go 3-5 inches instead. I'd like to be able to cut out a storm trooper helmet in one piece, but I'll mainly be cutting much thinner wood, aluminum, and hopefully brass...so perhaps the shorter travel will be wisest. The Gantry is 36" 6030 w 1/8" CRS bolted on back, the risers will be either 1 or 2 pieces of 3030 stacked, laying down and bracketed with more aluminum. I'll be using a 2.2kw Chinese spindle on THK rails.

Any experiences, tips, hints or conjecture will be fully appreciated.

When I added a 4th axis to my machine, I increased the Z travel from 3.5" to 13" which required the installation of an 18" lead screw, and rail system. This added lots of extra weight to the gantry, since to ahieve the most stability on the Z required changing the Y axis rail from a 4" wide (tall) cross-bar to an 8" wide (tall) cross-bar. However, the reality is the actual (usable) length of travel is limited to the tooling's length. Since most tooling only comes in 1.5" to 3" lengths, the extra travel of the Z only serves to introduce unneccessary flex. All for the sake of a permanently mounted 4th axis along one side of the table (which I rarely ever use!). Don't get me wrong, it's nice to be able to jog the Z up out of the way when clamping things down, or removing them from the table. And it accommodates mounting things like milling vices on the table, without clearance issues. But most items I cut, are only about 1.5" thick (3D carvings, and profile cuts). So for the most part, the extended Z travel isn't needed. I am currently in the middle of extending the X axis of my machine, and am considering spacing the bearing trucks of the Z axis further apart (to increase stability, which will decrease total length of travel).

[louieatienza]

I originally built my second machine with 5.5" of z travel (though it can reach 8" of the table allowed.) I cut guitar bodies that are 1-3/4" thick, though, which requires a spoilboard. So 1/2" spoilboard, 1-3/4" blank, 2" flute length with bit sticking out about 2-1/4", rapids plane of 1/2" (to clear screws and such) and that leave me only 1/2"... Believe me, that's cutting it tight, there's not much room for error.

You can defintely machine a part even if the bit is not long, as long as the collet, router frame, and carriage clear (a large bowl for example.) You can also start off with stub tooling, and finish with extended reach tooling if need be. You can also make a riser platform to cut thinner stock.