Long axis router on mill

[MechanoMan]

I have been playing with my Taig for awhile, but now I have a need to machine some wood that will be like 32" long 7.5" wide 1.5" deep.

Not within the Taig's X-travel, not by a long shot. Thought about running one 12" section, remounting the work 12" further down, running the next 12" section. People said go start over with a gantry router, which is certainly a good idea.

But I did have another idea. What if I JUST build a long X axis here, and mount it onto the Taig table, move the stepper there, and disable the Taig's native X-axis? This kinda makes sense I think. I mean we're not building an entire machine which saves a LOT of $ and work and problems to deal with. There's plenty enough Z-clearance over this kind of stock to accommodate the height of the extra hardware. There was never a need for more Y. I think if I bolted the Taig down so it doesn't just fall over, it shouldn't be bothered by the off-center weight. It's only wood and super-accuracy is not a top issue. Nor will the table need to deal with coolant dripping on it so MDF isn't out of the question.

But, I could see using this quite a bit. Something that wears out easily could become a problem.

Make sense? Where am I gonna get a 32"+ travel leadscrew and slides... cheap?

I see a few "lathe" leadscrews on eBay that long. Is there any reason they can't be a CNC milling machine axis? I see ones with a "slot" cut down the entire length, through all the threads. What's that even for?? I saw mention of "not for power feed" on some. Is that because the threads won't support fast travel or what? If the seller doesn't say, how can I identify one which is appropriate for CNC use vs one which is not?

I did note that if the auxiliary X-axis could in theory be used in conjunction with the existing X-axis, and it would only need like 20" of travel because the X-axis can already move 12". But it'd create absurd, perhaps insurmountable complexity on the CAM software and in Mach3, as well as an extra driver and wiring. I don't see how I could justify this to save 12" of leadscrew and slide length on parts I'm gonna have to go out and get anyways.

[Horsedorf]

what about making someting that you can sit the taig into, that has linear slides and bearings that then go over it.. king of like.. a table with a cut out that you slide the taig into. You can get the round stock with pillow block bearings for relatively cheap, and if accuracy TRULY is not *THAT* critical, what about using allthread rod and a pair of nuts seperated by a spring to control backlash? If it's woodworking and only has to be within a few hundreths of an inch, or 5 hundreths, that might work? and it'd be relatively cheap, and relatively durable. Then to use it, just unplug the current long axis stepper and plug it into this thing, as for the short axis, possibly secure the taig to the wooden table by it's x/y table and let the short axis move the taig around? though note, the direction would be reversed on yah.

Donuts for thought.
Horsedorf

[metalworkz]

If you really want to avoid the extra costs, why don't you do a test with a smaller simple part the needs to be repositioned on the table to work all the toolpaths. That way you use what you already have and simply implement a good repositioning technique. I have done several parts larger than my SX3 mills X table travel and even one project where I repositioned and rotated the blank and everything worked out great. The parts were not as long as your stated planned part, but the technique is basically the same. You will just need to reposition as needed to finish the part. I have plans on making a sliding plate table that will locate on pins to my work table and allow me to reposition to exact dimensions, and something like this will enable precise positioning of the part on the machine. I think this is a cheaper, simpler method than building a bigger axis etc. Just another alternative. Good luck!
Regard,

[MechanoMan]

I certainly CAN, but I imagine doing 100 or more of these, in various designs. Hundreds, if things work out great.

Repositioning like 3x per side is a huge liability. For one, I would not be surprised if minor discontinuities showed up. Two, it may require larger stock to accommodate the additional mounting/alignment holes. Three, and most significant, if I can leave it for an hour and a half to shape and detail a side, great. I'm goin shopping and this was no big deal. If I have to come back every 30 min then I can't do anything else major and it IS a big deal.

That's my reasoning. An axis big enough to one-pass this work would be more than worth it IF I know what I'm doing. What I want to avoid is the old "buy something on ebay that looks good, have no idea how to mount it onto a motor and slide, buy a bearing and leadnut and find they won't fit, pay a bunch to have someone custom-make a leadnut then find I asked for the wrong thing, then have someone reveal that the leadscrew will never work the way I want due to some clear-cut problem..." Hey, I know how this sort of thing goes by experience too.

[metalworkz]

I didn't realize you had plans of doing many of these parts, and that certainly makes a big difference. In that case the idea of the longer axis is a better solution, and the cost for the parts to make it will be made up with the quantities you plan on doing. Just keep in mind that the linear rails and leadscrew/ballscrews will need to be a bit longer than the overall travel you need. The overall length of the rails minus the distance across the carriages will be the actual travel, and similar with the leadscrew/ballscrews. I am building a CNC router/mill and have acquired my linear motion rails and screw from eBay.
It will only be approx. 24" x 24" travels. If you watch ebay you can find some good deals, but it may take a while to find exactly what sizes you need.
Regards,

[rfwyzard]

The "slot" in the leadscrew is called a "keyway" and it's for mounting a gear which powers the crosslide feed. Buy a couple of linear bearings and 2 shafts for your slide. Use threaded rod to move it. If you use the 4th axis, you can combine the x axis with the 4th to get more movement without going real big on the 4th.

[MechanoMan]

Originally Posted by rfwyzard The "slot" in the leadscrew is called a "keyway" and it's for mounting a gear which powers the crosslide feed. Buy a couple of linear bearings and 2 shafts for your slide. Use threaded rod to move it. If you use the 4th axis, you can combine the x axis with the 4th to get more movement without going real big on the 4th.

Threaded rod, like just allthread from Home Depot?
I had that down as a possibility, but it seemed like it'd be considerably less durable and probably have backlash issues.

http://cgi.ebay.com/TR12x3D-Trapezoi...3286.m63.l1177
Hmm, leadscrew by the inch. It certainly seems like a good deal, except I don't know how to get/mount a motor, end bearings, or leadnut for it.

Are there issues with the screw whipping around in long lengths when the leadnut is off to one side? A steel rod can sag given enough length, and then spun quickly might do a little "jumproping". And compression as the leadnut is pressed away from the large open span would increase the effect. I guess that is only with very small leadscrew diameters though. This rod is 12mm so I don't think it'll be a problem.

[MechanoMan]

Now something like this:
http://cgi.ebay.com/ws/eBayISAPI.dll...m=330278432093

Can that be an axis all by itself, or does it need the support of linear guides?
I'm having trouble finding any cheap parts capable of 36"+ travel, so I'm kinda starting to think again about leaving the existing X-axis plugged in and mounting this on top and using them together. I could run a script to translate all X-moves into X+4thAxis moves so it slides both of them, thus 24" of X travel on the auxiliary slide + 12" on the Taig's original X axis = 36". Yeah well in theory.

But looking at that, does it actually have tight tolerances to prevent slack movement in the Y or Z directions? I'm not sure. It looks like a guide where only the length down the screw is tightly controlled and was intended to be used with linear guides and slides.