Hi everyone, I'm like a new born baby when it comes to CNC; in particular CNC router machines. But I have watched many many hours on the subject and I am learning a lot. Exciting for sure. Of course I have a million questions but I will only bore you with just one. Note: I am sure there have been many threads on this issue, but this is my first day on your forums. My question is. What are the pros and cons when it comes to the subject drive systems. I am going to build a Kyo Sphinx CNC. I need all the help I can get. Thanks in advance.
A belt is faster and cheaper. Well that's it for all of the positives. A lead/ball screw is far more precise. They can be consistently used in much higher load applications. They retain much much much greater dimensional stability (will not stretch).
I had considered the double belt for mine due to the 1500 mm length. When I added all the belting up, I found that 1/2"-10 five start screws in 6 foot lengths from McMaster Carr were very close in price. The precision sold me on the screws.
An 'advantage' of belts is when a cut job is finished, you can literally push the gantry away from the workpiece by hand, and conversly when positioning the spindle at your chosen start point for the next job, this can also be done by manually moving the gantry into position. Much quicker than by the cnc control machine. I personally have a dual belted 1500 x 1000 ooznest machine that i use for building arcade machines, but will in time be moving over to leadscrews (Possibly over the christmas break)
Indeed and indeed. In fact, despite what I have read about screws being far superior, I am strongly considering going with the belts (at least at the beginning) for THIS very reason. I like this because I am coming from a manually operated Ornamental Mill with X, Y and Z axis doing woodwork. Where I do what you are talking about all the time. And even though My Ornamental Mill does use acme screws, they all are equipped with "half nuts"; that take less than one second to engage or disengage the screw. You can't do this; as far as I know; on the CNC "OX" or "KYO Sphinx". I am opting for the Sphinx system upgraded to a 7050 CNC. Of course I can always shift to screws if I feel the need to upgrade it; because thankfully, the plates are already milled to accept the screws and the anti-backlash nuts. So thanks a million ChillMonster. You have made my day. Note: The X axis (2133.6 MM (84") on my Ornamental Mill has a motor on it; if I wish to use it. But it is NOT a stepper motor, nor is it computer controlled. It uses a Love-Joy connection when you want to use it or disengage it. It does have on and off , direction and speed controls; as well as automatic stops in the X directions, which is great.
I'm planning on building a C-beam with a 1000 X 1000mm or even 1000 X 1000mm cut area if possible. Was checking out McMaster lead screws and they have more than one option to consider. Ultimately I was between these two ( last 2 pictures). My other question will be if I decide to go with one how to tie everything back to 8mm? Or in this case I have to go with whatever size I went with? If that the case is there any manufacturers who offers (Anti backlash nut blocks, nut blocks, flixabile couplers) "i.e" to connect the X/Y/Z rods to the High Torque Nema 23? Sorry if it sounds newbie but I am! lol
Use 8 mm rods and 8 mm anti-backlash nuts sold here on Open Builds. They are already the right diameter and will work for the 1000mms you need and the anti-backlash nuts are inexpensive. If you go with anything else, you will need to hire someone to turn down the ends --or have a friend with a lathe that can do it which is what I did. The only reason I did it was because I needed 1500mm screws in at least 1/2 inch. There were no 1000 mm screws available and they would most likely start whipping at that length. After having them turned down, you will have to find an antibacklash nut that matches the thread. McMaster-Carr sells them and they are more expensive than 8mm OpenBuilds nuts and you have to engineer a mount that will hold them in place properly. The other way is to make your own anti-backlash nuts which involves time and patience as well as a leftover piece of threaded rod and a drill press that is square to the table. Or, a CNC to make the nuts on. Here is how I did mine. Making Taps for 1/2 inch and 3/8 inch Acme precision rods
You could also attempt to bore out the flexible couplers with a drill press. I tried that once...only once. It was painful and I have one less coupler. It probably would have worked on a lathe, but then you would still have to purchase the more expensive ant-backlash nuts.
By using the 8mm rods and anti backlash I can build a 1000 X 1000mm overall dimension (800 X 770mm travel area) with no issues, right? But I can't use the regular 8mm rods and anti backlash to build a 1200 X 1230mm (1000 X 1000mm actual travel area) unless I went with a screws that at least 1/2 inch, right?
Yes, you are correct. 1000 mm rods would not be long enough. I did not catch the 1000 x 1000 mm cut area. I would go with the 1/2" - 10 five start. I like mine, they are very accurate. I bought these McMaster-Carr and they were only off by 0.3 mm in 1000 mm of travel. Here is how I did mine. Lead Screw Driven Ox Derivative (850x1500) Another way to mount the larger threaded rod: The Frog: CNC Router It is a good build to read. I used his experience to make mine.
There are also these anti backlash nuts and couplers. dumpsterCNC - acme components No need to turn down the rods. I did not see these when I built mine. Cool!
Cool! So I can use the 1/2" 10 five start. With the Anti-backlash Leadnuts, threaded couplers to connect the screw to the Nema. Thread Clamps/Super Thread Clamps to be screw onto the lead screw and up against the bearings. That way I don't need to a lathe to turn down the lead screw shaft, right?
Yes. You could use those. Watch the video here The Frog: CNC Router if you want ideas how to do it. You should be able to get all the matching 1/2 inch parts. I like flange mount bearings with set screws. It eliminates the need for thread clamps and you need bearings anyways. Take your pick McMaster-Carr. You mount them outside of the plates the threaded rod runs through (like I did in my build and he does in the Frog build) so there is tension on the threaded rod. I have no issues with screw whip even at 8000 mm/min which is the fastest I have attempted.
What I did on all bearing collars was carefully take the bit used for my m3 tap (Drillpro T Handle Ratchet Tap Wrench with M3-M6 Taps and Drills) and drilled into the rod through the hole the set screw would go into. Then I would tap the hole in the rod. I screwed a longer m3 screw through the threads in the collars and into the threads in the rod. None have ever come loose or slipped. I did something similar where the shaft couplers attach on both the threaded rod and the stepper shaft. Word of caution, it is very difficult to drill these holes with the possibility of breaking the bit. Use cutting oil.
This thread was created to find the pros and cons of belt pinions and lead screws. Please keep that the subject of your posts. Thanks so much pat
Sorry pat. I didn't mean to get away from your subject. It's on me. Giarc was just answering my questions.
Very good question Kevon Ritter. My required dimensions for the Sphinx I am going to build is: X=2,133.6MM (7 feet long), Y is 480MM and Z is about 10MM. Obviously on Z there is no problem. X and Y have a problem in that my system requires the ability to move the Gantry in those axis often rapidly by hand (explanation would be too long for this thread); but for X I have an additonal major problem. IE: I have been UN successful in finding an 8 mm lead screw any where near my X dimensions. So I contacted the experts at OpenBuilds and they suggested I use belt and pinion. Thus the reason for the thread. Thanks for asking the question Kevon. 'Preciate it!. pat
What do you plan to machine That X span with a single c beam is just not going to work for anything harder that foam and soft woods. But then again, I like to make 5mm passes in aluminum. My point is, you pretty much need to build a different machine. Even I designed a much bulkier version for a mere 1000mm span. I'd either use 3/8" or 1/2" for that.
hi, i am going to build 1500X1000 mm workbee cnc but need screw driven, can you please advise where did you found this 1/2" screw 6 feet long? really appreciate for your suggestion.
A follow-up question, I am building a X=1000mm Y= 750mm Z= 500mm, I will be milling 1/2" aluminum plates, I have the opposite problem, I want to use screw drive, however I cannot find a 790 or 800mm, 8mm, 4 start unless I purchase a 1000mm and cut it which I would hate to do, however the GT2-3 belt and pinion appears if can take the strain. I would appreciate your thoughts.
