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  1. #41
    Quote Originally Posted by Christian Knuell View Post
    Seeing it from this perspective you'd be right - but my personal opinion is that limit switches are not only unnecessary but even give a deceiving sense of security they cannot provide:
    I agree upto a point but here are some cases they are required. Servo's for instance will just take off at full speed if there positioning system fails or gets interupted. So in this case they are very much required.

    Also with small fast router machines it's very easy to jog from one side to the other which can result in banging into end stops etc often. Esp when first learning. Again I agree a machine that breaks with just a small limit crash is Crap but enough of this banging and eventually damage will occur so best avoided and for just a few sheckels more is it really worth not having.??



    Quote Originally Posted by Christian Knuell View Post
    What sometimes makes sense is reference switches to automatically home the machine. But even though they can make life a bit easier in some situations they are rarely necessary:

    [LIST][*]Usually you clamp your workpiece just anywhere on your machine and need to touch it off anyways because your machine has no eyes.
    • In this case knowing machine zero is absolutely pointless - it is just a set of numbers without any meaning for the actual machining process.
    • Only in case of step losses it can safe you a little time to get back to the correct workpiece zero - if your workpiece isn't destroyed anyways which will most likely be the case... And a machine losing steps regularly enough to make you want homing switches is again just crap or badly set up ;-)
    • But even in this case you can usually just touch off again (if the reference edges are still available)...

    [*]Reference switches are only necessary if you have things like tool changers, tool length sensors or fixed clamping devices on your machine. [*]And: if the switch isn't precise (or a chip gets in between) machine home will also be imprecise accordingly. Many cheap homing switches are much worse than touching off the workpiece.
    This I mostly Disagree with.!!

    Homing switches are THE most useful thing you can put on your machine. I'll give examples to why.

    Only yesterday I was cutting parts in large expensive sheet of aluminium when the cutter broke. The part wasn't damaged but it was my last cutter so the Job was stopped. The corner of the material where I choose Work Zero had been cut away. So how without Home switches do I get back into absolute position when my reference point is gone.?
    Yes I could go back into Cam and choose some hole to re-reference from etc but this all costs time and effort. Home switches provided resonable quality remove all this hassle.

    Example #2 Same large piece of material and Large Job with multiple parts nested into material. So large I don't have time to do in one sitting. Again Zero ref has been cutaway. Home switches allow me to pause the Job or break the Job into smaller jobs and still quickly get back into position.

    There are other examples like power cuts or PC crashes etc that back the need for Home swithces but again for the small cost it's silly not having them.
    The only thing is that if you need high accurecy homing then you need Good Home Switches. I find even your Cheap Chinese Proximity switches are more than good enough for 99% of Routers or DIY'ers using Milling machines.

    So for the Small cost and the fact Limits and Homes can share the same switch it's Stupid not to have them.!!
    Last edited by JAZZCNC; 21-09-2015 at 03:44 PM.

  2. #42
    Quote Originally Posted by JAZZCNC View Post
    Every thing neil says is correct .
    Was me not Neil but agree with you on use of the term 'absolute'.

    I ran without homes and limits for several months, then added some switches (but never got round to wiring them up) and one day jogged into one and smashed it to pieces and banged into the end stop. Makes you realise how powerful these machines are and to keep your hands out of the way.

    Just got round to adding limits and homes so should be OK now.
    Building a CNC machine to make a better one since 2010 . . .
    MK1 (1st photo), MK2, MK3, MK4

  3. #43
    Quote Originally Posted by routercnc View Post
    Was me not Neil but agree with you on use of the term 'absolute'.
    Doh I blame coolant fumes.!!

    Quote Originally Posted by routercnc View Post
    I ran without homes and limits for several months, then added some switches (but never got round to wiring them up) and one day jogged into one and smashed it to pieces and banged into the end stop. Makes you realise how powerful these machines are and to keep your hands out of the way.
    Ye try snapping a 12mm Carbide cutter by hand.!! . . . Even a small machine will snap one like a carrot.!!

  4. #44
    Thanks - lots of really useful info. I know a lot more about limit/home switches now.
    So 3 switches it is. Based on the above, I cannot really see why you would want to use separate home switches - unless you want some very special home position?
    And let us switch tune. I have updated my model with a single Nema 34 motor for the Y-axis and an adjustable mounting flange, as suggested by Silyavski. Is 20T pulleys/idler pulleys ok for this, or should you choose larger ones?
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  5. #45
    Quote Originally Posted by ngundtoft View Post
    Is 20T pulleys/idler pulleys ok for this, or should you choose larger ones?
    Yes they will be fine arranged like this with nearly half the teeth engage. Don't want to go too large other wise the extra interia starts to affect things.

  6. #46
    I have been thinking about how to design a holder so that you can route dove tails at the end of boards.
    This is not a function I will be using every day, so it should be simple and it should not compromise the machine in other ways.
    I read the thread by EddyCurrent and how he has done it. It looks good and stable and I am sure it works very well.
    However, I don’t want this function to interfere with the precision of the bed, so I am not too happy with the removable plate. Also, for handling, I find it somewhat impractical to have this opening in the middle of the machine. All that is needed is a jig that will hold the work piece in an accurate and repeatable position. So I was thinking of placing it at the end of the machine, as shown in the model. You simply fasten the work piece with one or two clamps. I may have to extend the cantilevers/ rails to get sufficient overhang for the spindle or alternatively reduce the length of the frame, since this machine is already getting fairly large.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  7. #47
    I remember Jazz showing (it had a red frame I think) a design that did just this, it could take panels etc on the front to rout the ends. This is one thing that I'd on my list for mk2.......
    Last edited by njhussey; 24-09-2015 at 09:04 PM.
    Neil...

    Build log...here

  8. #48
    Something like this works well for holding boards on end.

    Slots with Pockets on backside.

    Click image for larger version. 

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  9. #49
    Thanks JAZZ. This is actually a brilliant design. It is simple to make, it can be removed from the machine when you are not using it and the width it can accomodate is adjustable.

    The only thing that may not be optimum is the thickness of the material you can clamp. I remember using this type of clamps (although much smaller) and the reach is not so big. I tried to find the reach for similar types. I only found this specification for a single one and it was 3". I am not sure if that means it will go from 0 to 3" or if it is just the maximum. Maybe you can use this type of lever clamp instead (although they are quite expensive):
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  10. #50
    There are many ways to do this and many types of clamps to help but the simple and easy way's are often the most affective. In this case it would be a simple spreader bar which is bowed so when clamping wide boards pressure is applied in the centre.

    I was only really offering simple example of how to do it but not really being specific regards clamping etc.
    Last edited by JAZZCNC; 25-09-2015 at 01:12 PM.

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