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  1. #71
    Not much point using bigger than M8, so most people use that.

    To aid alignment when assembling you could machine reference edges on the relevant plates, if you've got a milling machine?

  2. #72
    I have got a mill but its not big enough for the cross pieces at 1100mm long to do that. I could maybe do reference edges on the side plates.

    Thanks for the info on M8 :)

  3. #73
    I use M8 for bolting together the Gantry your copying. M5 for fastening profiled Linear rails.
    In general you'll need an assortment of M5,M6, M8.

    Depending on how your fastening Steppers then you may want M4 But I tend to use M5 and tap the stepper. If your bolting thru stepper then some times depending on stepper frame M5 socket head will touch motor side, not always but does happen. I just whiz head against bench grinder rather than use M4. I try to keep different bolt sizes to minimum, fewer tools needed and less variety of bolts required.
    If tapping the stepper you can use M6 without any problems but M6 is no good for bolting thru stepper has head is much too large.
    Last edited by JAZZCNC; 18-10-2013 at 03:47 PM.

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  5. #74
    Thanks JAZZ that's all really useful to know.

    The nema 23 inside the gantry is bolted face on to a plate that uses a screw to adjust the tension and another to lock it off so I would imagine bolting straight through with m6 tapped frame in the motor will work well there.

    As for the z that will probably be the m5 (with head modified if needs) as the design calls for it to be bolted to the mount rather than the other way round.

    Hopefully I can get the gantry built over November if work allows and then have December to get the frame cut and welded up for the base.

    I have not put any feet on the frame design and was thinking about sitting it on a concrete pad in the garage that I will run some levelling screws over. Does this sound like an ok base for a machine like this? I will be bolted down ideally which is why I'd rather it was as level as poss to avoid distortion to the frame

    Or should I bolt it down as I weld it up?

  6. #75
    Quote Originally Posted by fvfdrums View Post
    I have not put any feet on the frame design and was thinking about sitting it on a concrete pad in the garage that I will run some levelling screws over. Does this sound like an ok base for a machine like this? I will be bolted down ideally which is why I'd rather it was as level as poss to avoid distortion to the frame

    Or should I bolt it down as I weld it up?
    Best if bolted down but it will be heavy anyway so won't exactly float away. Thing you need to avoid is not putting machine in twist.
    Don't know how you plan to get X axis rails on same plane but which ever way then do it after the machine has been situated where it's going to live and fastened down.

    Don't bolt it down has your building it. When building try to find level and flat surface that is not in twist to work from, don't just work from floor unless you absolutely know it's perfectly flat and not in twist. If you don't have decent surface then It's worth taking the time to build one. If the work surface is in twist then the frame will be in twist when welded up.

  7. #76
    My original idea was to pour a temporary surface to do all the welding on and then remove this once done.

    Alternatively I suppose I could make a torsion box to assemble from.

  8. #77
    Got a text at 7am this morning to say the Motors and drivers should be here today, thats crazy they were collected in HK at 10pm on friday night and are here this morning now thats service!!

    So hopefully I should be able to add a few more pics to the component pile.

    I had "yet" another question, whats the smallest or should I say recommended diameter for a 5mm pitch HTD timing belt pulley running 1:1 - is there a minimum number of teeth people would recommend (other than as many as possible) being in contact with the pulley at any one time?

    The reason I ask is not for the z or the y as they are simple straight connections with the pulleys in front of each other.

    Its the X where I am driving the two screws with the single belt, I can get half the way round the pulley on the left hand side however on the side with the motor I am going to have to put in some idlers to make the belt contact more with the pulley so I can nearly get about 120-130 degrees around one side of the pulley would this be enough?

    I thought about doing one belt connecting the two axis and then stacking another pulley on top of the right one and driving this but my concern was "if" the belt were to snap (the long one between two axis) then one side would still be driven by the drive pulley and could cause some bending if it carried on and the other stayed still. Where as if the one belt were to go they would both stop.

    Suggestions?

  9. #78
    Wouldn't go lower than 20T.

    Regards the one belt connecting 2 screws then that's how my machine runs and I've not snapped a belt in 6 years use so wouldn't worry about it.!
    If you want to be extra careful then use spring loaded NO limit switch with bearing on end tensioned against the belt and wire in series with E-stop so if belt breaks tension releases and causes an E-stop.

  10. #79
    I think I have them as 24 teeth at the moment so i guess that should work.

    Motors and Drivers have just arrived. Well packaged and look good so one more package to come from Chai and I can start on the Gantry. I would just rather have the parts with me to measure from before I start drilling and cutting.

    How long does Chai generally take to get things machined etc once the order has been placed? I know it takes 1-2 weeks to ship.

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  11. #80
    Quote Originally Posted by fvfdrums View Post
    How long does Chai generally take to get things machined etc once the order has been placed? I know it takes 1-2 weeks to ship.
    Can't tell you that but Usually arrive between 9-12 days from placing order. Often any delays comes from UK end.!!

    24T will work fine.

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