Thread: operation cnc

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  1. #31
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  2. #32
    Gentlemen.

    I think hope that I am nearing the end of the design stage. I genuinely need to start ordering in order to finish the design now. Can I trouble you with casting your eyes over what I hope to be my final table and gantry design.
    I have at present omitted the Z axis, or properly finished the Y. Mainly because until I have the bearing houses and rails in my hand, to measure them.(I appreciate the sites give dimensions. But) until I can bite it, Im not confident enough in my drawings.

    Therefore I need some help before I approach linearmotionbearings2008 is it 'Chai?' for a quote on the bits I need.
    Based on what ive previously explained. I wish to have spinning screws, rather than spin the bearings. (for now). This is mainly due to my present ability. I'm going to go for RM1610 screws (under recommendation). I never did understand irvings point within his post on p.21 when he refers to

    "Another option is to upgrade the bearings to be double angular bearings (BK) at both ends. This will increase the critical speed to 880rpm (4.4m/min), better but still not great."

    so, BK is like a bearing (next to the driven end of the screw) and BF is designed just as a support. I assume the BK end needs to be machined to fit the bearing, and the BF is non-machined.

    His point is simply it would be better if I have BF style at both ends. and therefore get each end screw machined to suite?

    So, based on my design. I will need
    (X Axis)
    * 2 x RM1610 (1500mm) screws (machined at both ends, one side will need to be machined to fit through the BF bearing and also so I can fit a driven pulley, and the other needs to be machined simply to fit the BF bearing. Im assuming I just let Chai know that I want to fit a pulley so he leaves enough shaft after the bearing housing. then I just by a piloted pulley and bore it to fit the machined end of the screw?
    * 4 x BF bearing with supported block mouting
    * 1 x ballscrew nut (quite tempted to make my own housing for this)
    * 2 x SBR20 fully supported rail (1600mm) (with 4 bearing blocks) I assume SBR20UU


    Y Axis
    *1 x RM1610 Screw (1000mm) (same question as above)
    * 2 x BF bearing with supported block mouting
    * 1 x ballscrew nut (quite tempted to make my own housing for this)
    * 2 x SBR20 fully supported rail (1000mm) (with 4 bearing blocks)

    Z Axis
    * 1 x RM1610 Screw (300mm)
    * 2 x BF bearing with supported block mouting
    * 1 x ballscrew nut (quite tempted to make my own housing for this)
    * 1 x SBR16 fully supported rail (300mm) (with 4 bearing blocks)

    Right, now I have satisfactorily embarrassed myself with incorrect terminology can somebody tell me if the above sounds about right? Or have I completely misinterpret ted anything?

    while im asking the question.

    assuming Im not bothered about speed initially. Therefore Id prefer to gear everything at a higher resoloution 1 turn of the stepper, means 1/2 a turn of the ballscrew. Therefore the pulleys on the ballscrew need to be twice the diameter of the pulley on the stepper.
    so something like
    10XL037 Flanged Timing Pulley :: BearingBoys.co.uk
    for the steppers
    and
    16XL037 Flanged Timing Pulley :: BearingBoys.co.uk
    for they the screws?

    The steel on the frame is mainly 60x60x3mm which I may get ordered so I can begin building the frame.

    Id appreciate your thoughts.. negative or positive.

  3. #33
    RM1610 is good for X and Y since the higher pitch means you can get a higher feedrate with limited critical speed, however since the Z-axis screw is so short there's no need to do this, so stick with RM1605 on Z to maintain good resolution.

    I advise using bigger rails on X and Z. Particularly Z since the forces on Z are a similar magnitude to Y, so you shouldn't use smaller rails.

    For a 1:2 ratio you don't want 10:16 pulleys for two reasons - for a start 16/10 is 1.6 not 2, and also it's not good to have such small pulleys as you will have less teeth engaged in the belt which can lead to premature wear and possibly reduced accuracy. It's best to use at least 15T, so 15:30 would be good. Also HTD pulleys are better than XL.

    The BK and BF mounts both hold bearings, the difference is the type and quantity. BK has two angular contact bearings inside, which means it can resist both radial and axial loads, whereas BF just has one 'standard' bearing in it, so only supports the ballscrew radially. If I were you, since you have the lathe, I'd make my own bearing mounts from aluminium. It's not that complicated and you'll be able to do a much better (and cheaper) job of it than the ones from China. They are often too tight a fit, or the seal rubs on the nut or other annoying thins to correct. I've never bought the BK/BF blocks myself, but I know people who have and they've all needed tweaking.

    Also making your own ballnut mounts is a good plan simply because it's so much cheaper. Here's one I made earlier:
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    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  4. #34
    Jonathon, Jonathon... How on gods green do I even start thinking about making something of that caliber? they really are amazing. But I am a realist as much as I could probably make one, if I set my mind to it. The other 7 just wouldnt be the 'same'. :-D Just looking at them, their accuracy makes me feel sick. Its one of these situations where I need to see them before I know what Im doing... For example you have mentioned seals, Ive heard circlips mentioned. All of this is assumed knowlege that you guys have gathered from building a mk1 machine first. And I think ultimately this is what I am going to have to do.

    An example, if I need 1500mm of drivable screw. (inside the supports) then how do I calculate how much 'extra' I need at either end to go through the housing (your suggesting I do not buy from the same supplier), and also through the support on the other side and through a pulley that I also havent bought!. This is why (I guess) for me it may be easier to just buy the supported bearing housings from the china supplier and if necessary re-make them based on the design on the ones that come with the screw? (can you see my thought pattern?) On previous threads on here I noticed your original build thread for your first machine. This machine was significantly different to your present one, and I guess you learnt from your mistakes on that build to gain the knowlege you have today?


    You say i should upgrade my X axis rails, they are already SBR20... what is an upgrade to them?

    So, taking on board your comments, a modification to the shopping list would be

    (X Axis)
    * 2 x RM1610 (1500mm) screws (machined at both ends, one side will need to be machined to fit through the BF bearing and also so I can fit a driven pulley, and the other needs to be machined simply to fit the BF bearing. Im assuming I just let Chai know that I want to fit a pulley so he leaves enough shaft after the bearing housing. then I just by a piloted pulley and bore it to fit the machined end of the screw?
    * 4 x BF bearing with supported block mouting
    * 1 x ballscrew nut (as above re housing)
    * 2 x SBR20 fully supported rail (1600mm) (with 4 bearing blocks) I assume SBR20UU


    Y Axis
    *1 x RM1610 Screw (1000mm) (same question as above)
    * 2 x BF bearing with supported block mouting
    * 1 x ballscrew nut (as above re housing)
    * 2 x SBR20 fully supported rail (1000mm) (with 4 bearing blocks)

    Z Axis
    * 1 x RM1605 Screw (300mm)
    * 2 x BF bearing with supported block mouting
    * 1 x ballscrew nut (as above re housing)
    * 1 x SBR20 fully supported rail (300mm) (with 4 bearing blocks)

    Although your comments re-pulleys is useful. Its another answer that fills my head with more questions... I think il put off buying pulleys until I have stuff on the workshop floor I can bite.

    I genuinely really appreciate your thoughts, Im absorbing as much as I can. Your clearly an immensly clever lad but Im just a normal bloke!. The entire point of me building a machine is to be able to get to a point where I can make 'things' more accurate, Its a chicken and egg situation. If I had a rig, this rig build would be as easy as you make it sound!

  5. #35
    Quote Originally Posted by kingcreaky View Post
    But I am a realist as much as I could probably make one, if I set my mind to it. The other 7 just wouldnt be the 'same'
    I very nearly captioned that photo with 'can you spot the mistake'!

    Quote Originally Posted by kingcreaky View Post
    . :-D Just looking at them, their accuracy makes me feel sick. Its one of these situations where I need to see them before I know what Im doing
    They're a copy of a common design on eBay. I started with 2" square aluminium bar, used the lathe to face both sides and bore the hole in the middle. Next I milled two opposite sides to the correct size using a fly-cutter (hence the nice finish). I then spotted and drilled the holes using the milling machine by just moving to the correct co-ordinates for each hole and finished off by milling the other 2 sides and the corners. The milling was done using CNC and g-code written then saved as I went along, but it could just as easily be done manually. I could have started with aluminium bar closer to the final size to save some milling, but since my lathe has a 4-jaw self centering chuck it's more convenient to use that than get a load of rectangles on centre with the 4 independent jaw chuck.

    Quote Originally Posted by kingcreaky View Post
    ... For example you have mentioned seals, I've heard circlips mentioned.
    The BK block has a rubber shaft seal on both sides to help prevent swarf etc getting into the angular contact bearings as that would rapidly destroy them. There is a groove for a circlip on the other end of the ballscrew, which doesn't seem to achieve much.

    Quote Originally Posted by kingcreaky View Post
    An example, if I need 1500mm of drivable screw. (inside the supports) then how do I calculate how much 'extra' I need at either end to go through the housing (your suggesting I do not buy from the same supplier) ... easier to just buy the supported bearing housings from the china supplier and if necessary re-make them based on the design on the ones that come with the screw?
    I'm suggesting you do, but it's not compulsory by any means! Clearly you can get the standard mounts to work, it just may require adding shims between the bearings, machining a spacer so that the nut doesn't rub on the shaft seal and possibly opening the bearing bore out a little so that the bearings are not too tight a fit. Or they might be fine. To me that doesn't seem worth it when I can just make my own and know it's going to be accurate from the start, in addition to gaining flexibility with the design and learning something the process. You will need to have a look in other threads about how to make them - the drawings are readily available.

    Quote Originally Posted by kingcreaky View Post
    On previous threads on here I noticed your original build thread for your first machine. This machine was significantly different to your present one, and I guess you learnt from your mistakes on that build
    Short answer is yes. My initial machine was constrained significantly by the cost of getting the proper components, hence I tried to make as much as I could to save money. Everything between the X-rails (so Y and Z-axis essentially) hasn't changed since the first build. I just removed the silly tall gantry sides and made a better frame. I'm glad I did it this way since it forced me to try new things, such as using a bearing riding on a threaded rod to make a cheap drive with negligible backlash.

    Quote Originally Posted by kingcreaky View Post
    You say i should upgrade my X axis rails, they are already SBR20... what is an upgrade to them?
    SBR25, or minimum 15mm profile rails (linear guides). Latter is a bit too expensive though.

    Get the Y and Z ballscrews with the standard end-machining since they are quite short, so critical speed is not a problem, but do ask Chai to increase the length of the cylindrical portion on the fixed end of the screw (dimension F on his drawing) from 15mm to 25mm to accommodate the pulley.

    Since the X-axis ballscrew is quite long, to get the best feedrates you can put a pair of angular contact bearings on both ends, so you could get the ballscrew machined the same on both ends.

    Here are the standard end-machining drawings from Chai:

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    You can see from those how much 'extra' length you need for each ballscrew. If you ask Chai for RM1610-1000mm for instance, he will machine it such that the total length is 1000mm and the actual ballscrew is 924mm with F increased to 25mm.

    Quote Originally Posted by kingcreaky View Post
    The entire point of me building a machine is to be able to get to a point where I can make 'things' more accurate, Its a chicken and egg situation. If I had a rig, this rig build would be as easy as you make it sound!
    The thing is you have got the machine to make this machine. When I decided to make my CNC router I had a milling machine and mini lathe, so I used those to make all the parts, such as bearing blocks and ballnut mounts and thus have never had to pay anyone to make bits for me. I did mill the Z-axis plate square on the school Bridgeport milling machine, but that was mainly just for aesthetics.
    Old router build log here. New router build log here. Lathe build log here.
    Electric motorbike project here.

  6. #36
    ok, bits ordered (warning: communication with chai is a bit difficult, generally a one day delay with every message due to time zone) then, when you do get a reply its questionable if he has undertood your meaning).

    X Axis
    * 2 x RM1610 screws(1603mm Total length) I need (1500mm) of screw, so 1500mm PLUS one end machined to type A (except dimension F to be 25mm instead of 15, and the other end machined again to type A, but without any F
    * 4 x BK12 fully supported bearing with supported block mouting
    * 2 x ballscrew nut
    *2 x SBR25 1600mm fully supported rail with 4 bearing blocks

    Y Axis
    *1 x RM1610 Screw (This one, id like the TOTAL length to be 1000mm, but one end machined to type A (except dimension F to be 25mm instead of 15, and the other end machined again to type A, but without any F
    * 2 x BK bearing with supported block mouting
    * 1 x ballscrew nut
    * 2 x SBR20 fully supported rail (1000mm) (with 4 bearing blocks)

    Z Axis
    *1 x RM1605 Screw (This one, id like the TOTAL length to be 300mm, but one end machined to type A (except dimension F to be
    25mm instead of 15, and the other end machined again to type A, but without any F
    * 2 x BK bearing with supported block mouting
    * 1 x ballscrew nut
    * 2 x SBR20 fully supported rail (1600mm) (with 4 bearing blocks)


    So, I now have some momentum. Im a few hundred quid lighter. But most importantly the ball is rolling. So now not just out of my depth :D BALLS DEEP and out of my depth.

    Just have to wait for my contact to return from South Africa, to make an order for the box section to commence making the table. (hopefully will have this by the end of next week (mon 19th)

    I have soo many questions, Ive tried my hardest to research them before asking, but straight answers from the experienced is so much easier! as often you go off and read something, then come back here and read contradictions and end up banging your head against the wall and opening another beer.

    So some questions gents. First one; what am I searching for in order to get videos, detail etc on the process of software behind creating a work-peace once the machine is made. Is there such thing as a machine simulator? I understand Mach3 simply takes an input file.. a dxf? So I can draw the workpeace in autocad {if i had a licence} -- what about sketchup?. What is and why do people use solidworks?

    Second One;
    Anybody want to face inevitable persecution and real off a list of recommended electronics? or maybe even just the electronics your using so I can copy!. I have previously mentioned what steppers I have,

    Nema23 Stepper Motor 3.1Nm x 3

    I understand the trick is more voltage to the stepper the better.

    I read good things about these Leadshine AM882's for controllers.... anygood? thoughts?

    can anybody suggest anything better? Realistically, im not going to build my own power supply to then plug it into the hundreds of pounds worth of controllers ive just bought.... il just spend a little bit more a buy a power supply aswell. Reccomendations?


    then, the other big question is breakout board... /controller board. I like the idea of one of these Cat5 units (as my computer is firmly mounted in workshop and usb and parrelel has a finite distance)


    Finally, if I use 3mm steel box section. Im going to need to drill and tap it to accept bolts that will affix the linear rails etc. Therefore is 3mm thick enough?


    look forward to your replies.

    Once my machine is done, and I have used it a few times. The next thing Is I plan to hold an open evening. All will be invited to my workshop for coffee and cakes. The idea being anybody who (like me) is just coming into this, feels ridiculously out of their depth, and wants to see a machine work, see the process from start to finish and ask limitless stupid questions and get straight answers can attend! You all Watch this space :-D

  7. #37
    Just a heads up......I ordered 4x 1200mm SBR25 but received them measuring 1210mm. They must have better value tape measures in China!

  8. #38
    For all that are interested. Finished design.
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  9. Looking good, how are you connecting the steppers to the frame?

  10. #40
    hey, thanks for the reply!

    I see "you lot" mill out these sexy pocketed aluminum peaces of art. take a photo stand back and say 'that'll do'. I dunno glue? bluetac? nails?

    Il probably make some steel brackets initially until I become a certified wizard.

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