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Assuming there are no clearance issues with the table/nut, are there any disadvantages to mounting the motor under the table, parallel to the leadscrew?
Another of my soon-to-be-infamous-for-low-quality example images:
Attachment 4426
(not sure if the picture worked, ISP is being a pain today)
I'm hoping that a pulley system of some form would be suitable to belt-drive the leadscrew from that location.
IMO I dont see any problems with mounting as drawn as long as the spindle protudes enough for a pully, and I think it keeps things tidy.
Jim
here! here!Quote:
Originally Posted by GTJim
and if you think your drawings are basic i do all mine in paint!!! so you will never win that competition.....
You could mill a pocket in the shaft side of the aluminium to accommodate the pulley if there is not enough space.Quote:
Originally Posted by GTJim
Pulleys are definitely good plan as they will let you change the ratio allowing the stepper motor to be put in the right region of the speed/torque curve. You can also swap them round to get more resolution if required.
This is similar to what i did with my first machine.
http://www.mycncuk.com/forums/attach...2&d=1269125465
Plenty of pics on my build
http://www.mycncuk.com/forums/showth...tempt-Of-A-CNC
Sorry for the delay in replying. Had ISP issues for a few days and my posts seem to intermittently require moderator approval (though I think it's when the post includes links).
Jonathan: I think I'll be looking at some kind of pocket, but I still haven't started to research the pulley systems yet so I don't know what I will need in terms of size and clearance.
AdCNC: Awesome build. This axis isn't fixed to the main structure though, it will be the X axis unit mounted on the Y axis.
I used XL pulleys , but HTD 5mm pitch is better. I've found 1/2" wide best to be fine. It's best to use reasonably big pulleys to reduce belt wear. In general minimum 5 teeth engaged with belt.Quote:
Originally Posted by Rogue
ADCNC: like the setup with the coolant etc...
Just to prove how slowly my brain works... by 1/2 wide do you mean I need to accomodate a diameter of 1/2", or it will protrude 1/2"(+bit sticking out for setscrew) from the mount?
I meant the width of the timing belt should be at least 1/2". You can calculate it ... but that works fine for me so etc.
I would want the shaft to stick out as far as you can get it to as it depends on the pulley, where the setscrews are and the position of the other pulley.
Fair enough, so until I settle on a firm number I'll pencil in 1 1/2" clearance from the surface of the mounting block for the pulleys. I suppose judiciously placed idlers would also help with increasing the engagement with the belt.
Is belt something that can be shortened easily, or will I be confined to designing around what is available?
Idlers shouldn't be necessary. I made the mount with the holes for the stepper motor slotted to allow tensioning the belt and different size belts and pulleys.
You can't change the lengths of timing belts - the only way is to buy a different length. You can work out the length with something like this:
http://www.sdp-si.com/cd/default.htm
Also:
http://bearingstation.co.uk/products/Belts
Hi Rogue,Quote:
Originally Posted by Rogue
I often use timing belts on machines and in the configuration you plan on using.
I've built several machines which use's them on all axis inc Z Axis and they work great without any issue's. They have all the bennafits Jonathan states plus they have one other little known plus. They help reduce resonance, which if bad can affect motor performance.
I've found 20 tooth 15mm wide HTD to be the best for 1/1 connection. They wear the best and easy available at any bearing company. They also have the best size boss on the pulley for using a decent sized grub screws or small bolts for gripping the shaft.
If you want to up the ratios's say 2/1 or 3/1 then 15 tooth is about the smallest I would use on the driven side using steppers, thou be aware the boss size is too small for decent grub screws so you have to then drill between the teeth and make sure the head of the screws is below the surface.
Also be aware that a lot of company's supply the pulleys with a small pilot bore which you then bore to the size required. Drilling with a decent drill press is possible but very easy to get wrong and create runout and if done this way then I'd recommend drilling smaller and reaming to exact size. . . Job best done on a lathe.
Yes they do a good job at reducing resonance.
Get them delivered to me and I'll bore (or ream) them to the right size on my lathe for you. Just pay me the postage...it's only a 5 minute job, if that.Quote:
Originally Posted by JAZZCNC
The stepper & ratio issue is something I've yet to address. I need to work out the benefits of the various ratios first. I'm pencilling in 1:1 until I've had a good think over a hot cuppa.Quote:
Originally Posted by JAZZCNC
I may well avail myself of your services, though it might be some time away. Thanks!Quote:
Originally Posted by Jonathan
Smaller pulley on stepper = better resolution, which is generally not that big a benefit.Quote:
Originally Posted by Rogue
Larger pulley on stepper = higher speed, up to a point which I've not yet managed to reach.
The main thing is as you increase the speed of a stepper motor the torque to start with is fairly level, then drops. You want to size the pulley such that the motor is operating mainly in the region before the torque drops off.
Also I expect a smaller pulley on the stepper motor will get better acceleration.
Just for example with a 13T pulley on my Y-axis stepper, and 12T pulley (bit too small really) on the 10mm pitch screw I get 36,000mm/min (1417 ipm). Changing the 13T to 30T gets about 55m/min (2165 ipm), and changing to 42T gets 60m/min (ipm = lots). Clearly the 42T pulley isn't worth the extra <10% speed given the significant reduction in resolution. Microstepping the stepper motors to artificially gain resolution is really only cheating yourself after about 1/4, maybe 1/8 of a step. The accuracy of micro-stepping depends on the motor and what it's connected to. In general apparently it is not that accurate, but still use it for general smoothness.
You can do some pretty impressive things with 10mm effective pitch as I'm sure JazzCNC will soon demonstrate...
If you haven't bought the screws yet then I'd go with 1/1 and get the correct pitch screws best suited to your needs. Mainly for simplicity.Quote:
Originally Posted by Rogue
2/1 will double the torque but half the speed and so on. 1/2 will double the speed but half the torque and so on.
One of my machines use's 1/2 with a 20mm x 5mm pitch screw which effectivly gives me a 10mm pitch screw but with reduced torque, the plus side being it's a simple belt & pulley change and I have full torque and high resolution but at half the speed, It works good.
2/1 is usefull if you have small Nm steppers which tend me able to spin faster than larger steppers but with lower torque couple these with a high lead screw and smaller steppers can be made quite strong.
How would you like me to do that Jonathan.? With my little Aztec friend. . LolQuote:
Originally Posted by Jonathan
Yep, that's just what I was thinking. I'd like to try one of those on my machine.Quote:
Originally Posted by JAZZCNC
"The correct pitch screws" should really read "what I manage to find when I have the cash in my hand".Quote:
Originally Posted by JAZZCNC
Realistically, C7 1605 screw is what I'm looking at: £20 each for X/Y axis, not sure how much it would cost to get the ends turned down though. No idea about ball nut yet, whether to wait for longer and save for proper ballnuts, or look for a cheap alternative and later replace.
My build is influenced by the fact that I've just completed a course and I'm trying to get back into the workforce, hence not putting down lots of hard cash in one go. I'm hoping to be working again by the time the design phase is finished and the purchasing begins :whistling:
Personally I'd go with 1610 it's a better all round pitch. Not sure what you mean by only buying the screws and sorting the nut later because it's normal to buy the ballscrew and ballnut together.
RE: Turning. Even thou I have a good lathe and capable of turning my own screws I dont bother and buy them pre-machined from china, It's just not worth me doing it my self for what they charge.
I'd save and buy the ballscrews before buy cheap and replace later as it's often more than just quick swap over job due to the differant way the connect or work, Plus cheap acme lead screw is rubbish and good quality acme lead is more expensive than ballscrews from china.!!
Ok just for jonathan Here's what 10mm pitch gets you.!!Quote:
Originally Posted by Jonathan
Johnathan if you want the code your welcome to it, or any body else for that matter. It's a 17mb file thou and over a million lines of code, If I remember correct it took about hour n half.
I did another after that but with the Welsh dragon on the back side but didn't take any pics. . . . Looked good thou.!!
Enjoy and the pics don't show all the detail or do it justice. . . 150mm diameter 10mm Ali plate cut with a 6mm 90deg carbide chamfer/spot drill.
Was amazed when I first saw that - I still am.Quote:
Originally Posted by JAZZCNC
Yes please! I've got some aluminium that size so why not...I believe you did it with a 6mm spot drill, 90°? As better excuse than most to finally buy some spot drills I guess.Quote:
Originally Posted by JAZZCNC
I agree that 10mm pitch is definitely the way to go if you want good feed-rates.
Ye me too I must have looked at it for days and every time I saw a bit more detail I'd missed.Quote:
Originally Posted by Jonathan
It's also mesmorizing to watch the toolpath do it's stuff the bloody thing bounce's all over the place, so much so when first started cutting I very nearly stopped it because I thought it had FUBARD.
No better excuse IMO. . lol . . . . . I'll dig it out and send your way.Quote:
Originally Posted by Jonathan
Ah, I don't think my post was as clear as it should have been, my apologies.Quote:
Originally Posted by JAZZCNC
I'm planning to go for ballscrew+ballnut, but I noted that, depending on where you look, there seems to be a big jump in price from the ballnuts without preload/zero backlash to the ones that do have it (which I would think are preferable). Going cheaper would get me running sooner, and having a working (albeit lower precision) machine to play with while building up more funds is preferable to me. There also seemed to be suggestions for ways to increase the effectiveness of the lower end ballnuts, though now that I think about it, they may have been talking about the acme setups. Hmm.
As for turning the ballscrews, I suppose that's a matter of perspective. If you have the skills and equipment but your time is money then yes, turning the ends down to fit the bearings probably is better left to the supplier. Would I do it that way? Ask me in 5 years :smile:
1610 rather than 1605, you say? I shall run that though the collection of calculations I'm building up.
The following picture is a rough mockup of what it's running - working area was originally planned at 200mmx200mm for the table, will have to be bigger simply to fit the stepper in the location parallel to the screw. The gantry will be close to the table but large so the X can run up quite high and still be supported, for reasons discussed elsewhere. "Scale" is a dirty word as far as this picture is concerned, don't read too much into it. The XY will not be completely seperate from the gantry, it was just easier to draw that way!
Attachment 4466
That is several steps beyond awesome, and something to aspire to in the future. Is there a drool icon? If not, why not?Quote:
Originally Posted by JAZZCNC
Not really I have the time, equipment and the skills but ballscrews are hardened and the indexable tips required cost me nearly as much as what I get charged.Quote:
Originally Posted by Rogue
So to me it's not worth the hassle and all thou unprobable still possible risk of error.
RE: 1610 or 1605. I should clarify this depends on the intended use of the machine. If your going to use it to cutt intricate jewelry or want very fine detail then the small pitch is better but for a general allround machine then 10mm pitch works best in my experience.
All round, I'd guess. If I understood the earlier posts correctly, if I had a system for changing pulleys I could get the higher precision if needed, at the expense of speed? If so, this is one of the things that interest me about pulley systems.
That's precisely what I thought. I would machine a ballscrew if someone asked, but it's just not worth is with linearmotionbearings2008 prices on eBay.Quote:
Originally Posted by JAZZCNC
That is correct. Lets say, for example, you have a standard stepper motor so 200 steps per revolution. The travel per step on a 10mm pitch screw will be 0.05mm with direct drive or 0.1mm or 0.025mm depending on if 2:1 or 1:2. Using microstepping will get finer resolution up to a point.Quote:
Originally Posted by Rogue
Though I would normally advise 10mm pitch screws (I probably did earlier!) since this is such a small machine it may not make a lot of difference...having said that the main thing is getting high acceleration, otherwise you'll run out of travel before it hits top speed and has to decelerate. To do that a 2:1 (bigger on stepper) with a 10mm pitch screw would be ideal since the motor has to input only a quarter of the kinetic energy into the screw when accelerating compared to a 5mm pitch screw.
Your 'system' for changing pulleys is just an allen key plus a bit of space.
Agree with what jonathan says just one thing to point out 2:1 10mm pitch is effectivley 20mm pitch. If you can live with this loss of resolution then it's a good way to go.
What's your main intended use.?
Edit: Jonathans comment about accelleration is even more important if you plan to do lots of 3D and intricate V carving. 3D and intricate carving is very time consuming, esp vcarving, with lots of very small moves required with the Z axis dancing around all over the place. The problem with low accel is the commanded feed rate actually never get's meet and therefore the cutting time increase's. On very large 3D jobs this can run it several extra hours or even days.!!
5mm, 10mm .. . it all depends on what motor is driving the screw. If it's a 3nm motor then clearly a different ratio will be optimal when compared to using a 1nm motor.Quote:
Originally Posted by JAZZCNC
If you're using it for PCBs then you'll want good resolution, so probably best to use swappable 1:2 pulleys. Can't really thing of anything else that would require it. Maybe engraving, but generally for engraving it's relative position that matters more than absolute which means microstepping is more valuable.
Right, the "intended use" question.
1: PCB milling (from one extreme...)
2: Panel making for instrumentation - aluminium and as-yet-undetermined plastic, <5mm layers, mostly cutting external borders, internal holes for switches. Engraving text. Nothing intricate.
3: Small components as needed for above, odd little brackets etc. Aluminium mostly.
4: If possible, larger aluminium pieces. The "low gantry, tall Z" design is because there might be the occasional taller but narrower piece. (...to the other)
Ideally making new bits to improve the mill or make a bigger, better, shinier one!
I don't expect it to handle steel but you can flippin' well bet I'll give it a try to see what happens :naughty:
I'm hoping that I'll be able to make it stronger/more sturdy by leaving the gantry to handle Z. It also means I can consider adding a counterweight system later if I get adventurous or drunk. I have no idea if it needs one, I just always thought they looked cool. Not... ehh... a proper "technical" answer, I know :redface:
Engraving would be flat text for a control panel, nothing fancy. I might need to do something fancy every now and then to try and justify it to my wife, but thankfully she has low standards. Well, when it comes to husbands, anyway :whistling:Quote:
Originally Posted by JAZZCNC
Ermm. . . Not a good idea IMO realying on micro stepping. Really it's horse's for course's when you get into the finer engraving area and resolution rules. So it's finer pitched screws all the way but at the sacrifice of speed. . . . If I intended main use as engraving then fine pitch's would be used for the resolution not M-Steps.Quote:
Originally Posted by Jonathan
Micro stepping is good but mainly for smoothing motors.
Scrap the last post then. .:rofl:Quote:
Originally Posted by Rogue
This is one of the things which I need to get my head around as well. From what I read, microstepping is good... but it's bad. People report motor problems disappearing when they start to use it, but from what you say it seems to be an inferior way to achieve good resolution. I'm assuming that there is a middle ground somewhere that I need to find (not too fine a pitch, not too many divisions for microstepping).Quote:
Originally Posted by JAZZCNC
Depends on a few factors really and the drives being used also play a big part to how micro stepping is implimented.Quote:
Originally Posted by Rogue
10x micro stepping is about the max usable and beyond this is just pointless unless you have a very high pulse width which is beyond the capabiltys of the std parallel port. . . It's gets complicated so wont go there.!
Generally micro stepping should be used but mainly for motor smoothing at lower speeds IE: small tiny moves and lower rpm's but after a point micro stepping becomes an inderence more than a help and this where the drive comes into play.
A good drive will use a technique called morphing where it changes from micro stepping to full stepping along the power curve. This also brings resonance into play and why belts can help.
Poor drives without morphing and usually mid band resonance compensation can suffer from resonance issue's caused by the vibration frequency's that interfear with signal performance and affect the motors making them run really badly and sound dreadfull. . . . Belts act as a natural damperner.
Good drives like Gecko's etc use morphing and Mid band resonance damping and this really does make differance.
If you work on the principle that micro stepping works but mainly to help with motor smoothing at lower rpm's but with the side affect of slightly improving resolution ( too a point) then you wont go wrong. Just don't relay on it soley to give you the resolution you need.
Like I say the good drives do make a big difference.
Go to the Gecko site and read the FAQ section it has some good info on how morphing and micro steeping works.
I... ahh... won't go into my original driver plans which involved a PIC and some fairly shaky ASM :whistling:
I was actually looking at the linistepper kit originally, again on the grounds that I could probably put a set together for the cost of a single Gecko in the short term. I know "short term" is a dirty word on this board, and knowing my luck unipolar motors will have a whole extra set of problems attached to them :rolleyes:
In my experience with helping folks who have try'd to make your own drives and use oddball steppers etc becomes false economy with the end result being wasted time and money.
Good for the experience but with the same result. . Inferior performance and poor reliabilty . . ending in scrapping and buying "Proper drives an motors".! . . .BUT. . .By no means let me saying this put you off thou because it's all a good learning experience. . . Keeps you out of mischief as well. . Lol
Another reason I'm glad my wife has low standards.Quote:
Originally Posted by JAZZCNC
I've got some odd steppers lying around to play with for PIC projects, though I had grand dreams of extending functionality in ways that isn't actually needed or, indeed, useful.
Steppers are far enough down the line that I'll hopefully be better placed to source better components. I plan to make up some linistepper drivers anyway, whether or not for the CNC, as there's always mischief to be gotten into!
I'm not saying rely on it, just it might help. Clearly the result will be slightly distorted.Quote:
Originally Posted by JAZZCNC
I already mentioned about microstepping accuracy (or rather lack of) in post #15...
One thing I'm going to try and do with my stepper driver design is make it effectively run using microstepping, for smoothness, yet only require the number of pulses for whatever microstep division you choose. Effectively it will move through each of the microsteps for every step pulse.