Hey guys, ok a bit over a year ago I started a small business manufacturing some small wood and plastic objects, I build bottom feeder squonk vape devises. when I first started I knew almost nothing about CNC but I did a lot of research and came to the conclusion that a small cnc router should fit the bill nicely and I winded up buying a Romaxx 2X3 router table. I really wanted to buy a cam master stinger at the time because from all of my research this looked like the best machine in the range I was searching but it was just not in the budget, but seeing as this Romaxx was ~ a $5K machine and it looked pretty beefy compared to most of the other wimpy machines I looked at I figured it should at least be decent, right? yeah, ok :P
since then I have learned quite a bit more about cnc and about routers and machines in general and I quickly learned that the machine I bought was really not as great as I originally thought. it uses V wheels that ride on steel tracks and even though it at first appeared to be a robust machine with welded steel frame, all ball screw and not some cheap Chinese extruded aluminum type deal, it still is just very flimsy where it really counts. I can actually grab the router when the Z is extended down and literally move the cutter tip back and forth over .25" with just flex alone, and this much flex has just made it impossible to really hold any kind of tight tolerances because no matter how well I try to dial it in, cutting forces can just cause so much deflection. I now learned the hard way that V wheels just suck :P
being stuck with this machine I did the best I can to make due and I have been getting by with it until now but I am now at the point where I just really want something better. from the beginning I have always looked at both routers and milling machines and of course if I had the money I might have just went for my at the time dream machine which would have been a tormach 1100 at the time, but that was just no where near my budget and still isn't, and I also was really Leary about restricting myself to such a small work envelope compared to even a small router. in the end I came to the conclusion that the only way I'm going to really get the right machine for myself is to just build it myself. I have fabrication and welding experience and I would want to build an extremely rigid and beefy fixed gantry welded steel machine was the conclusion I came to.
I went out and ordered up some steel and started to design my ultimate machine, I have been slowly collecting linear rails and I just recently bought a 2.2Kw ATC spindle, I planned to weld up a beefy frame and gantry and have it heat treated after and then either have the linear surfaces milled flat or pour an epoxy bed for the rails, I also planned to design the gantry in such a way to be adjustable to fine tune the geometry and get a perfectly square machine that was really 90* on all axis. I do still believe this would be a great plan and know I can build something that would be ideal, but I also now realize that a build like I have in mind is going to take a lot of time and I will def not have this machine done any time soon. lately my Romaxx has been getting worse and worse and I'm at the point now where to continue to use it for a few more months even, I will need to at the very least at least replace all the V wheels just to buy myself some more time so I started AGAIN to look at alternatives...
I am new to CNC but not to machining, and I actually have a small manual floor model knee mill in my garage. it is a decent machine, made in Taiwan cast iron from the 80's but it the equivalent of the grizzly G0730 or G0678 machines, just from a different importer and a different name tag slapped on it. I have in the past considered converting this machine to CNC but the spindle is very slow, like 2k rpm slow and the bearing growl whenever I even get close to that kind of RPM, I just run it very slow, not at all ideal for the mainly plastics now that I work with. well in my deliberations and options searching and trying to think of a solution to my situation a light bulb finally went off over my head, what if I used the base and the frame and XY table all from the knee mill, but replace the head with my new 2.2Kw ATC spindle and mount that on a pair of linear rails for the Z axis...
the more I think about this idea the more I am liking it, I think this machine can really give me a great end result, the X and Y are very solid and are nice and co-planar to each other already and very rigid compared to anything in the router world really, and now with the 15-30K rpm ATC spindle, it would be awesome for the work I do. I can build the Z axis with only ~6-8" travel and make it extremely rigid not having to worry so much about weight since it is fixed to a relatively heavy cast iron mill column, and having a knee that can manually be raised and lowered means I can use whatever vises or fixtures or even 4th axis I could ever want even with only 6-8" of Z stroke because I would have another 17"+ that I could raise or lower the table too, something no router table could ever do. this might actually be the best of both worlds for me
this is the machine I have more or less without all the variable speed head electronics:
one pretty cool thing is the head is a turret style and can actually spin around 360*, so my plan is to actually spin the whole head around and replace the rear motor mount with the new Z mount and ATC spindle, this will actually allow me to keep both the low speed head for steel, and then rotate it 180* and switch to the high speed spindle when I need to. since the stock spindle is belt driven I can easily just mount the existing spindle drive motor above the existing spindle like a bridgeport style head, giving me 2 completely different heads 180* from each other, on a turret that only needs to loosen 3 bolts to spin it around. I can even build in positive stops to quickly relocate it to the same co-ordanats with each head swap so no re-dialing in and re-tramming making swapping from the slow spindle to high speed as painless as practical
now I know this is not the end all/ be all when it comes to CNC knee mills and it is not a bridgeport or other really heavy duty CNC mill, but remember I am comparing it to a router table here and my main use is CNC'ing plastics mainly, although with this turret head I can actually wind up still being able to do even steel when I eventually remount the motor and add a servo to drive the quill on the stock head side of the turret. the 8" X 18" work envelope is a bit smaller than I would have ideally liked but the items I build are only 2" X 3.5" in size so I can def manage with eve this smaller work envelope given the trade off of much more rigidity than I would get with most router table designs.
so, thoughts? I am going to have a few questions about the actual conversion and I would have liked to start a build thread once I get this underway but this is such an odd ball hybrid that there really is no ideal place for me to put this thread, sure as heck couldn't put it in the router build forum, so here made the most sense to me I think.