Got my Y and Bed beams ground, and rail lands machined on the Gantry Beam. The steel bed beams are just 2"x 4"x 1/4" & Y Rails 2"x 8"x 1/4". My bud's shop has all kinds of surface grinding equipment. These are by far the straightest things in my shop and could easily become my primary standard straight edges. I have ground 1/2" MIC 6 aluminum plate for the bed surface. I also have 2x4 stock for the legs and plenty of steel for a sturdy base. Guess I'll have to get on with ordering steppers, controller, and building it out. I have a zillion mounting holes to drill and tap for the linear rails. I'm not setting any speed records but am managing to keep moving it along here and there. Best, Kelly
I am guessing your bud also has a large ganite surface plate. Have you tried checking them against the plate (and each other) either grossly with a feeler gage or checking for hinging? Putting a bit of Hi-Spot Blue on them would be ideal. If they are truly flat they should hinge 1/3 of the way from each end for starters. What is your target flatness tolerance? Grinding long thin pieces flat can be a test of patience no matter how good the equipment. Denis
Know that feeling all to well. Been planning on putting this on my big mill for an embarrassing long time...
Kelly, A couple of things to think about. I just got done building a 7 axis automated tube lathe on a 6"x10" x 96" steel tube frame. All rectangular steel tube is rolled from round tube. It is really common for them not to be rectangular and instead a trapezoid or parallelogram. So it can be really difficult to assemble them square to the ground surfaces unless you also machined some pads on the sides. If you didn't I'd highly recommend you clamp the ground sides to accurate straight edges and then very carefully shim everything. Next thought for you. If you are using steppers it is important to oversize them. People compare cheap steppers to expensive servos and tout how much better the servos are. My homebuilt machine has Nema 34 800 in/oz steppers and in 10 years has never missed steps, even when breaking the damn tool right off! I highly recommend Leadshine drives. The tough part was getting real ones not copies, almost all on Ebay are copies. Automation Direct now carries them so you cn be sure they are the real thing. Get 80 volt drives and drive the motors with at lease 68vdc. This will give you the fastest speeds and best acceleration. On my machine with 5mm pitch ball screws directly driven my rapids are 300 ipm. I highly recommend the Centroid Acorn controller. All one package from the same company, no dicking around to get it to work. Got one for the CNC router for the school and it is very nice.
Kelly, I'd be happy to loan you an autoreverse tapping head if you want it. I have two, one does up to 1/4", the other goes to 1/2"
It's a pretty sophisticated business that has been doing grinding for 60+ years. He’s forgotten more about grinding flat surfaces than I’ll ever know. I told him what they were for and he proceeded accordingly. Since measuring them would have been as much or more work than grinding them, I didn’t put him through it, but he said as they were mounted in the machine he'd expect <.001" over the length. He said the mag table wouldn’t have moved them nor did he take enough stock for movement from residual stress to be much of a concern. Well, let’s see. I got the steel beams for free. The 2x8s from the remnant pile at my son’s place of business, and the 2x4 from my former business. My bud ground them for me for a bag of vine ripened tomatoes he uses to make ghost pepper sauce which I also got a jar of so I’d say a tolerance of plus or minus one tomato. At present, my CNC router relies on Delrin V wheels riding on extruded aluminum beams, so along with the steel beams 25mm linear rails and bearings on the new machine, I’m expecting some improvement in both accuracy and rigidity. I didn’t check the bed beams. When I had them sitting on my saw I did place the 2x8 beam surfaces back to back and could not see light nor get a feeler gauge of any thickness to insert at any point. At this point, I don’t think it makes much sense to try to more accurately measure or improve the beams. I have to drill and tap a lot of holes in those nice ground surfaces which will undoubtedly disturb that surface and need to be stoned/touch up. I do have a plan of attack for assembly aids and order and although there are some things I can do to help, practically speaking no matter what I do, there will always be iterative fitting and shimming required as I eventually level and tram the machine. The 2x8s actually weren’t too bad in this regard at least to what I was expecting. They varied .015”-.020” across the 2” dimension but most of this was the walls being somewhat narrower near the center on the 8" faces. They were pretty consistent (+.005) out near the corners. I didn’t pay any attention to the 2x4 bed beams in this regard because the only thing that really matters is that the ends are square as possible and they are the same length, but on the latter, even precise control of length won’t matter because the faces of 2x8s beams aren’t straight enough to realize the benefit so they’ll need to be shimmed where they bolt to the 2x8 faces anyway. Was planning on N34 closed loop steppers…..two of them on the Y and one on the X. Don’t need it on the Z. An extended stack N23 will do there. Those high torque N34s weigh 5kg! The price difference to buy the highest torque versions (12N-m/1700oz-in) is minimal. I figure there’s a small price to be paid in additional mass and inertial mass of the rotor for buying more torque than needed and some concern about more severe hardware damage in the event of crash. I was looking at the packages at Steppers Online. They’re the higher voltage but won’t be Leadshine drives. My ball screws are 10mm so ½ the steps/sec for a given speed and happier area of the stepper torque curve. I’ve been looking over the drive manuals for these packages. May invite your input on them vs LS. I’ll have to have some further discussion with you on this. I take it you are using that with CamBam. Are you using the CB supplied PP or other? That’s a generous offer. They’re all M5 & M6. Can the collets grip them? Best, Kelly
Kelly, Yes the collets are tapered rubber type, no problem with metric. They are both Tormach units, with TTS shanks. However I made an adapter to Morse #2 so I can use them in the drill press too. We built a couple machines with StepperOnline drives, seemed to work ok but they were not very technically competent. Gave us stupid answers to questions we posed, and we knew better. Closed loop really isn't. What they do is tell you they missed steps, but can actually correct for that. Now if you feed the encoders to inputs on the Acorn that would be able to close the loop because it can actually move the motor to where it ought to be, I believe that is possible but you'd have to ask Centroid. Clearpath has a simple feedback method called ASG when you command say 500 steps the motor moves 500 steps and if the move completes the SG signal turns on so your controller knows the motor got there. So internally it corrects the location. This works quite well on the 7 axis machine as it puts very little processing load on the motion controllers.
If you bud got them so that you can not slip a feeler gage between them when back-to-back, he did do very well as all cold-rolled products (as opposed to cast by comparison) have a great deal of internal stress due to the cold rolling process. So, he must have been flipping them as he ground one face and then the other until things were in relatively good equilibrium. Otherwise you would have some pretty bananas. It will be interesting to see what happens when you start drilling the ground faces. If the holes are small relative to the face width like maybe a .25” hole on a 2” face and are relatively sparse, I would guess all will be well. If the holes are large and all on one face as opposed to both front and back, I’d be concerned that you may see some distortion. I doubt your design allows for those holes to be in the unground surfaces where distortion in the plane perpendicular to the ground face might not matter so much. Back 50 yrs ago when I was summer help at Link-Belt in Cedar Rapids (40 miles from you) we had huge drive-in heat treat ovens in which weldments were stress relieved prior to finish machining. The heat treat reduced embrittlement from welding the various rolled alloy steels and improved dimensional stability. Denis
Only one side of each beam was ground. Maybe just luck but it would have to be some mighty residual stress to pull across the two 8" tall 1/4" walls. The thickness of the ground sides were all very close to .225" and the unground sides all very close to .234", so I figure he only removed ~.010" which is pretty darn good when you look how uniform the width of the ground surface is along the 43" beam length. You can see in the previous pictures the 2x8 beams cleaned up 100% but there were a few small spots on the end of a couple of the bed beams, which are inconsequential. I just stacked the 2x8s back to back, turned off the lights and backlit the beams. Using the feeler gage was a bit nebulous because the beam radii feathered into the ground surface and a feeler of about any thickness would start to grab where they knifed together, but certainly not insert into the ground region. The thinnest gauge I had was .002, but when I could not see light when they were stacked back-back, I lost interest in fiddling with feeler gauges. They get holes for M6 cap screws on 60mm centers the length of the beam. If grinding didn't move them, I doubt the holes will have any affect except erupting the metal surface in the vicinity of the drilled and tapped holes, which is easily delt with. Still a long way to go before it's a machine. Best, Kelly
Seeing the beams on the saw with that perspective I see that rather than being maybe 6 or 8 feet long they are maybe 4 feet or so. And, I agree, that make a big difference when then the aspect ratio is much smaller than I imagined, the resistance to bending is much greater. M6 caps on 60 cm centers should be nothing. Grinding technique and skill makes a big difference. I learned a few years ago that plenty of flood coolant and rapid traverse reduced thermal distortion effects on long springy parts. Believe me, it was necessary to flip those parts and be very careful about magnetic chuck effects to get them straight due to internal stresses. I am sure you have milled cold rolled parts that rolled up as one side was milled. Hot rolled is not nearly so bad and my cast iron castings, even without formal stress relief, hardly move at all. After stress relief, they just stay flat within a tenth on 18 inches and that is as close as I can confidantly measure. Denis
Those beams sure look pretty! Really cool to see the big pieces come together to start to visualize the absolute beast this thing will be. Something to keep in mind with a controller selection: the ability of software to correct for hardware issues. AKA skew correction. I believe most cnc router controllers have it nowadays. It has been VERY helpful with all my machine builds. Granted, I bet this build won't need near the .140 over 24 inches one of my machines did!! However, I was able to compensate for the lack of square in the software (LinuxCNC at the time) and machine wooden inserts that fit into some cabinets my buddy was making. Some software will even allow for ballscrew mapping as well. Just something to keep in mind when your machine is .001 off...lol Looking forward to more pictures!
