Thread: My baby 15" x 15" machine
in re-designing i cant keep the shape of everything i want if i fully get away from the 60x40 box section across the top and bottom of the y axis bearings as i need the spacing of the 60x40 so that the y axis carriage doesnt bind against the y axis rails
a picture might help
if i change the top and bottom yellow pieces to 50x25 i cant see any way it will work without wasting a whole load of 50x25 and i'll be honest since dropping the 60x40 i'm cutting corners to try and get all the cuts i need out of 2 lengths of 50x25 @ 7.6mtrs
Can you sub in some angle iron for some of the bits of box?
Angle Iron is £10-£20 for 6m and I think there are parts where you could get away with, for example the green bits on your pic?
Equal Angle Steel Bars - F H Brundle
while i wont rule that out my mission is to make the whole machine bar a few bits of steel plate i might need from just the 2 lengths of 50x25.
i acctually had an idea last night, i've been struggling since realising that the bearings are only 45mm to only use 50x25 as this way there is no spacing between the y axis rails and y axis bearing mounts, basicly the machine would rub against itself, where as when i used the 60mm across the y axis bearing mountings it spaced enough away from the rails.
now my choice was to stick the the 60x40 just for this bit, but even ordering to pieces cut to length is a big jump in cost that i dont really want/need.
so my idea is i'm bound to have some scrap pieces of 50x25, and thinking about it i could quite easily cut one side off a section and leave myself with some 3mm shims that i could use to space out my problem
tell ya what the stuff you linked upped my order by £15 but.. looking around i found some 25mmx5mm x 3M which is perfect i dont really need 10mm thick, my only concern with doing it this way is if the box section is uneven, then adding an uneven piece of flat bar to the top will make it worse possibly?
I've done it!!!
that is designed the whole machine using only 50x25x3mm box section..... oh and a little bit of 25x5mm flat bar as very helpfully recommended above... i had to give in somewhere as i needed 60mm spacing in a few places which using 50mmx25mm box section wouldn't allow... the fact is the flat bar adds on £4 to my total order so i cant grumble about that.
so the picture below is obviously missing a bed, but i have basically spent the last week or maybe longer re-designing this whole machine within the limits of the screws and rails I've already received. the reason for this was due to me using the drawings from another site for the rails and bearings making basically all measurements out.. but it actually worked in my favour as it reduced the need to have 60x40mm box section in my build.
the colouring is purely to make it easier to count the lengths and for me to picture which bits move together, so purple is the x axis and the bed when its done, blue is the gantry, yellow is the y axis carriage and green is the z axis carriage. i am also yet to design a spindle mount as i am planning to do this in another program so that i can export it to dxf and have some lucky member from here cut them pieces for me, the plan is to mount it to the 2 pieces of box section that the rails are mounted to.
the biggest changes to this from my earlier designs are the x axis screw is now located a hell of a lot closer to the bearings which if i understand right should reduce any racking, my only concern here is do i need to add a length of box section on the outside of the screw bearing mounts to reduce flex here? in my mind they don't go under any stress when the screw turns but if someone tells me i'm wrong it'll be the next change.
I've also reduced the height of the machine which is one of the reasons there is no bed at present as the current z axis would smash straight through the previous design, the height now from x axis bearing center to y axis bearing center is 265mm.
all the bearing spacing's are as follows
z axis center of bearings on rails 120mm
z axis rail spacing 175mm ( should be 180mm actually)
y axis rail spacing 180mm
y axis center of bearings on rails 198mm
x axis rail spacing 804mm
x axis center of bearings on rails 255mm
this gives a total cutting area of x = 400mm, y = 529mm, z = 100mm which considering i originally said 15"x15" and its now more like 16"x20.5" i'm very happy.
the total length of steel up to here is around 8mtr's of 50x25x3mm and 1mtr of 25x5mm flat bar so i have around 7mtr's left to make the bed with which i know will take most of that 7mtrs. that brings the total cost of steel to £76.31 and the only other things i need to fabricate are the spindle mounts and stepper mounts which i have a feeling both will come from alu but i'm not sure yet.
so provided i dont need any more steel the total to date is £629.18 and thats for spindle, rails, bearings, screws, ball nuts, screw bearings plus all the steel to fabricate the frame
This wouldn't correct a seriously bent or twisted piece but it would level most stuff enough for mounting rails on:
homemade surface grinding machine - YouTube
As long as you are starting out with a fairly straight piece this should sort out hot rolled steel, assuming you already have a variable speed drill press all you need is grinding head and a jig.
But if your steel looks like this abandon all hope now! :)
PS - Have you thought about how you are connecting all this together? (welding/bolts/brackets/epoxy etc) It might be worth putting in all of your bolts and brackets or you will have a nasty surprise when you can't tighten the bolts you have bought because another bolt is in the way.
Last edited by D.C.; 28-12-2012 at 08:13 AM.
most of it is going to be welded, i will be bolting certain bits to leave room for adjustment
i am nearly there now, my main concerns are do i really need the turquoise bit?? would i get away with using a bit of flat bar instead? i have enough room in my steel for that piece but only just so i would rather use something else and keep that length spare incase i mess anything up.
also anything wrong with the bed? i dont know what i am going to cover it in yet, i would like to say alu but more than likely it will start out as mdf
re-designed again.. this time i've included a second ballscrew on the x axis, now due to my mis understanding of earlier comments i've kinda messed up a little bit in that i designed the machine to work around a single screw on one side. i've now been shown the errors of my ways and intend to fit a second screw. but i will go ahead and build the machine get it all wired and working to an extent before i order the second screw.
so here is what i hope to be my final design.
i may change it a little as far as mounting the bearings for the x axis screws as it's come to my realisation that the spindle will hit the cross beam at the front before it gets to full extension thus cutting about 40mm off my workable area. i've also realised that had i not rushed in to buying the bits from chai i could have either reduced the size of the axis screws for the length of rails i have or better still ordered bigger rails as there is about 75mm of wasted travel along the x axis, but i'll have to live with that as long as i get my 15" mininmum cutting area i'm happy.
this kind of stuff hurts far less when you have not yet started building!. Your far better at sketchup than I!!!.. Im no expert but do you think the gantry beams (purple) may be a little thin? not that it matters I suppose because you can always add extra support if it does flex. As the two beams are on their side I should think they will be ok on the X plane, however applied pressure on Z while Y is in the middle may perhaps cause flex? Mind you it is only around 15" wide so it might be ok... what do you think?
when do you hope to start building?
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