First I am not a newbie to cnc. I am also not new to making guitars.My home shop includes a mini mill cnc converted to ballscrews, a midsize mill and 10" lathe. I have a fairly well endowed wood shop and I will spare you the long list. At one point I ran an automation store on ebay where I was able to collect supplies for this project as the company had lots of scrap available.. I have looked and looked for a stiff cheap prebuilt router system but have found nothing suitable under 3k. I need accuracy as some of the work will include very fine inlay work. So what do I have. extrusion 8020 1.5" x 3" (yes inch size) enough for the mill and more 3/8 and 1/2" aluminum sheet/ I will need to check the 3/8 for flatness. enough for parts and two risers Brackets and screws for the extrusion (lots) THK LM ballscew / linear rail in a steel channel which includes a motor mount. I cannot remember the model number. I got this for the z axis. Ballscrew for the X axis Singe start. Over 36" I can make most of the parts necessary to build the router. I dont want to build a really big machine so I really need a working table size of 24 x 40 inches. 1. How high should the z access actually be. I think I can get 6" out of the THK part as I believe it has 12" of travel. 2. How come I do not see any machines using SBR (round) linear rails on this forum 3. Has anyone mixed ballscrews and acme I have had a hard time finding any router builds fitting my description that can put and indicator on the spindle and not see lots of runout. Any help you can provide.
I haven't posted my machine build here, or anywhere else for that matter, but on my CNC I'm using SBR16 rails except for the Z axis where I use SBR10. I don't use ballscrews since I bought all the parts as a bundle on AliExpress and the bundle included Acme screws. I didn't use aluminum extrusions. I used only 3/4" plywood. I haven't put a dial indicator on the spindle but if I understand you correctly that is not needed since I flattened the sacrifice board with the spindle.
Sounds like a somewhat similar setup to mine- if a little further along. I don't have space to put/run the wood tooling I have now. Feel free to look through my "heavy router" build and discussion here, since it seems like more along the lines of what you're looking for: M4: 1510SS Heavy Mk.I - lots of pretty renders in the build (not much else so far, still collecting parts), lots of simulations and design iterations in the thread. The simulations will likely be more useful to you, of course, since I specifically looked at spindle deflection based on machine geometry. The entire point of that build is to replicate the quality and capability of a $10-15,000 router for less than $3000. Now with the 4th axis it's pushing that some, but of course others can modify as necessary. I'm doing right around 12" of actual Z travel, but I also intend to machine blocks of tooling foam and provide 4th axis swing room, harder materials like aluminum would generally be 2" or less. 6" would be plenty for most sheet- and thinner block, like guitar bodies- material. The longer it is, the more deflection you'll see. If you can get it down to maybe two inches of travel with a minimum spindle-to-table distance of around two inches as well, you should be set for most materials with reasonable tooling stickout whilst bringing your deflection down into negligible ranges. There are some, but given that profile rail is so cheap these days and provides better stiffness figures in more degrees of freedom at tighter tolerances, there's not much reason to go with SBR any more. That was a much better bet in say, 2015. I haven't, and I wouldn't. Well, I wouldn't use leadscrew in automation anyway, unless the tolerances were quite large (20 thou or so) or it was a single direction of force (eg. a passive weight against gravity). I did Tr8*8 with a half-bearing rotating nut for my laser head, because gravity holds it in place, with belts on X-Y. Which is why I did mine the way I did- if I were in a larger shop, I'd do a steel weldment, but since I have to be able to carry everything out of a basement in the end, it's extrusion with some steel reinforcement for now. Typical extrusion hobby machines lack rigidity and aren't intended to really have any anyway- they're for learning and very basic production, 99% of the time.
Sounds good. Yes if you put an indicator on the spindle or any tooling you will most likely be able to push the spindle forward and backward or side to side. Under deep cut loads for me that would be a problem. I also would not want to worry about change in humidity affecting the machine. Besides its actually easy to bolt together extrusion. I have looked at BOB's cnc machines and that is not where I am going. You should post your machines.
