Reply with QuoteThe reason your not finding any above 5 inches or so is because once you get above that its hard to keep it rigid. The only way I could see getting 12+ inches of x travel would be to move your cutting bed and not the spindle.
12"+ z-axis?
I've been searching through this forum for info and design ideas...maybe my search skills aren't up to snuff...but I haven't been able to find many builds with a 12"+ z-axis. Can anybody point me to their builds or builds you know of that have a 12" z-axis? I'm leaning towards just buying a FLA-300 but I need more z depth than 5", preferably between 10"-12".
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The reason your not finding any above 5 inches or so is because once you get above that its hard to keep it rigid. The only way I could see getting 12+ inches of x travel would be to move your cutting bed and not the spindle.
I think it's important to know what you plan on cutting.
mostly foam and possibly some lite wood cutting
Foam wouldn't be much problem since the forces places on the cutter or hot knife would be very low. Wood however is entirely different. It's possible but budget and tolerances will be the ruling factor. Cutting wood with the z axis extended down to 12" will require a beefy y and z axis. Maybe a steel build.
Usually the DIY builds here with long Z axis are portal-style routers, with raised and supported sides. Check out the 5-axis builds of Bartuss and others; while you may not go 5-axis, they all have long Z travels so you can get an idea of how to support the axis.
Not to mention if you're moving that far, the spinal/router becomes an issue as it can contact the work.
If you're just worried about being able to carve 2" into the top of a 12" block, then make the table removable/adjustable.
Hi you might like to have a look at this link:
http://www.cnczone.com/forums/diy-cn...is_design.html
I would like to be able to do some 4th axis machining on my mill once its finished. So my z-axis will be adjustable. Rather than the maximum z depth touching the top of the table, I can adjust the height of the z-axis so its new maximum depth is to the centre of the 4th axis. The overall stroke of the z-axis will be approximately 220mm/8.5''.
Hope this helps.
I got around 10" on mine. I like the use of profile rails like this. They tend to work really well, and make for a stiff axis. All the plates are 3/4" thick.
I have 17" of Z travel on my router. Gantry shake is a constant problem. Unfortunately I built it with a 6" travel and then my needs changed drastically so I have been forced to reinforce things and live with other things. If your doing a small machine I would do steel fixed gantry and move the table. If you have to move the gantry then over build it from the start.
Derek
You can also get away with more travel by making your gantry taller and using profile rails. This allows you to use a thicker material for your Z plate and spread your guides out father.
I am going to make up a rule on the spot here, but you can probably get away with extending your Z plate 2-3 inches longer for every inch you widen your gantry. Does this make sense? I wanted extra travel on my machine, so this is what I did. Even though I don't use that much travel I still enjoy the 10+ inches, and it's nice to know its there if I did need it. Good luck with this! It's a really good question that I have not seen covered in too much depth here.
Although it can be more complicated to implement, for longer Z travel, it may be better to fix the bearing blocks, and attach the rails to the carriage assembly. Many commercial gantry or portal style CNC with long Z travels do it this way.
When I added a 4th axis to my machine, this required a complete redesign (and rebuild) of the entire machine in order to accommodate the additional Z axis travel. The original build only had 3.125" of Z travel, which was riding on a 4" wide Y axis rail (using eccentric bearing blocks similar to CNCRouter parts design- except 3/8" rails instead of their 1/4" thick rail design).
I changed the Z axis travel from 3.125" to 13" of travel, which made the 4" wide Y axis rail too narrow. So, I replaced the Y axis rail with 8" wide rail to stabilize the Z axis carriage. I spaced the bearing trucks of the Z axis rail 6" apart, to help with stability (the actual addition to the Z axis was 18" lead screw).
The router mounting plate was constructed with 3/4" thick aluminum plate, and 1" thick blocks were machined as the "Router Clamps". As one might imagine, when fully extended this resulted in excessive flex of the Router mount assembly. So, I added 2"x1/4" thick angles to mid-travel of both sides of the assembly, and 1"x3/16" thick angles at about 60 degrees to reinforce the Router Clamps to the plate (to preserve perpendicularity of the Router Clamp blocks to the plate).
This improved performance drastically, but still results in a small amount of flex. The additional weight added to the gantry, also required a larger motor (from 300 oz in to 900 oz in NEMA 34's). All for the sake of adding a 4th axis. Which I have tested, and tuned, but rarely ever use.
So, there is a trade-off for extended Z axis travel. The shorter the travel, the more rigidity that is preserved. The longer the travel, the more of the assembly that will be "Cantilevered" (I.E. hanging out unsupported into thin air!). Since tooling lengths are the actual limit of travel needed, a table with adjustable height would be a better option, than increasing the Z axis travel.
20/20 Hind sight is better applied, when listened to as the voice of experience- and applied as "Foresight" in designing a build! Yes, the additional Z travel is a convenience in moving the axis completely out of the way to access the table for clamping work pieces down, or removing them. But it is not something that is really needed, as the machine could just as quickly be jogged into a position (along the Y axis) to be completely out of the way, during work piece mounting or removal.
Here is another link that I found quite useful when I was thinking about the z-axis:
Building a CNC Router Step 4: The Z-axis assembly
If you want more z-axis travel, you have to pull your gantry bearings further apart to stabilise the z-axis. The link above shows how this can be done, but unfortunate you will lose some travel along your gantry.
The above link gives a good guide to making a rigid z-axis however I highly recommend louieatienza comment.
The link listed provides some good advice. I am not an engineer by trade, but the anaylisis provided are the actual "trial and error" results one can expect when actually putting a build into use. I actually did consider fixed bearing blocks, with the rails mounted on the Z plate. However, this too, is a trade-off. As it adds more weight to be driven by the Z axis motor.Originally Posted by WB-1
Although it is some times an expensive option to do, building, trying, and then redesigning, and rebuilding will yield improved results. Asking the question: "What will it do, IF designed this way?" can only be answered by trying it out. Then altering the design, and try it out again, to compare the results. You may just find that the way forward, ends up being the way back! (In terms of improved design).
I have been thinking of adding a counter-weight to the Z axis, by adding a second set of rails along the opposite side of the Z axis assembly (along which the counter-weight would ride), with a cable with one end attached to the Router clamp block of the Z axis, and looped over a pulley, and the other end attached to the counter-weight on the opposite side of the Y axis rail.
Since observing the small amount of flex during cutting, is reduced, by simply applying a slight pressure on the Router clamp block during cutting. (Really, just resting my hand on the Router clamp- no real pressure being applied, just damping). Again, won't know until I try it out!
My thoughts on this are two fold: damping of the Z axis, and less work on the Z axis motor during upward movements of the Z. Since lost steps have NEVER occurred during a plunging action, only during a lifting action of the Z. Since plunging is assisted by gravity, it is the lifting which seems to require the most force.
If your router by itself shows flex that can be improved by simple hand contact I suppose the router mount is WAY too flimsy and should get some gussets, ribs or other stiffening. For that matter, if anything on the machine moves visibly by hand or can by influenced by hand, the rigidity of the machine is kind of marginal.
Similarly for the z-plate. Instead of messing with counterweight band-aids it would be better to select a suitable drive. For that matter, the z-drive of my machine is surely not optimal with a 15mm pitch lead screw and huge 1600in-oz stepper (my fault) but it never loses a step zipping around 50 pounds of moving z-stuff. So I guess a more reasonable 380 in-oz stepper and a 5mm pitch lead screw should do at least the same job or better. If lifting a few pounds of static mass on the Z screw up your machine I would be concerned that machining forces and acceleration can do the same.
Here's a nice one, used for foam molds. The video of him machining his own S57 replica was taken down however...
Homemade cnc router - YouTube
You can easily get the 10-12" of travel you are looking for on an FLA type of machine by reversing the motion of the Z-axis. That is, have the motor,screw,router and ways travel up and down on the bearings which are fixed on the Z axis carriage. You need to add an adapter plate which I believe CNC router parts sells.
I did this on my machine which has about 10 inches of Z travel. Because the 8020 extrusion and the ways are going up and down it is very rigid. It is also extremely easy to build, no custom machining involved.
