the local electronic genius has work for 3 months ahead. And i am not into electronics repair really. Sometimes simpler is better.
Today after whole day drawing, considering, redrawing, considering... designed the ball screw assembly on Y/ the long axis that moves the gantry/.
I wanted it sturdy, compact, at the right place and most of all easy to rectify and assemble. Following step by step. Still have not figured the belt length, so a minor correction maybe tomorrow. Other challenge was how to keep the working distance at maximum and at the same time ball screw length minimal.
Designed the hard stops with threaded holes for proximity sensors. A bit overbuild but for sure there will be crashes as the guy is a new to CNC.
Some pictures. Have to finish the design this weekend in order to buy the rails, ball screws and order the laser cut pieces.
I don't really understand why the spindle motor is sitting so far below the gantry?
The maximum depth of cut is usually the longest tool that you can fit.
If this to engrave the top of a large object, to clear hold down fixings or what?
Isn't it more a case of the gantry being positioned high, rather than the spindle being low?
If the bottom of the gantry was level with the top of the x-axis it wouldn't be anywhere near as bad?
as i mentioned before but maybe you missed it, this machine exclusively will be used for 3D jobs most of them in the 140mm-170mm height region. Not for lettering, woodworking or similar.
The guy is doing model yacht building. So shapes would be very strange
So the Z that enters the zone below the gantry should be thin, as not to touch the other parts of the model while the bit is routing deep below hollowing something.
Check my picture and will see for yourself what i mean. Its a specific 3D job machine. I don't believe that reinforced 20mm steel plate for the spindle with 10mm ribs is flimsy as you suggest.
If you have any other ideas i am open to suggestions. Point me to a better solution and i will change the design.
Last edited by Boyan Silyavski; 24-08-2013 at 12:39 PM.
in my opinion with so wide Z axis plates you just wasting a lot of material and travel in Y axis direction.,
with 20mm profiled rails you can do Z axis on 160mm wide plate, and extend travel in Y direction, or just save matirial in all you built.
you are quite right. However let me explain please. 10cm more of rail on both sides+10cm more of screw+10cm more of steel profile=no more than 60 euro, which is irrelevant in this build. If we look into KG , they are 5-6 kg more on the gantry
However an ATC is very expensive. And is quite necessary for 3D jobs. Should the need arise to upgrade, for the mere cost of 2 more short supported rails and bearings+another chinese spindle i can mount double Z axis with minor modifications and most importantly without compromising the work dimensions. One spindle will rough the other will detail and finish.
I mean, there also some other points of the design that are done with some things in mind. Its not a general hobby machine.
After some tinkering i woke up that i am not making the CNC for myself and that i am overbuilding it too much. And overthinking it about the eventual future. Went to the local metal shop and checked the profiles. There was 140x80 profile that seemed quite good, so instead of searching for the 180x80, i sat down and redesigned everything, it was fast though taking away things. Changed the profile sizes, took away the reinforcing plates on the gantry, though i left place if i later decide there are vibrations. redesigned the Z narrower and so on. The benefit is that the profile enters the magic 6m number, as they sell it by the 6m.
So following your advice i finished with smaller and lighter gantry, like 30kg, shortened it and now everything is exactly as it should be, no over sized stuff in my opinion. 1000x400x170mm working area, as wanted by the guy.
What do you think?
It won't allow any better clearance when cutting has the Tool length mostly dictates this and your spindle support plate will still catch just like the bottom of Z axis would.
Much better option IMO would be to flip the rail and bearing setup so you have a variable length lever when extended giving much better strength and just build a sturdy spindle bracket that allows percentage of the spindle body to extend below Z axis plate.
This extension along with tool length will be give enough clearance for most 3D work. If the guy needs more clearance then better to buy longer tool and cut slower than compromise the machine in all other areas.!!
With the proximity sensors (Or limit switches) because of the small gaps required to work correctly then I wouldn't put them at the ends were they will get run into if crashed. Position them so they get passed by or over this way nothing gets crushed.
I redesigned it following the advice. Now things seem better / to me at least :-) / . What about the result? By the way i have bought already the spindle brackets/2/ . I liked the design because can fix them on a guiding plate so if i have to move them its easy to align them.
So now the rails move and the bearing blocks stay at optimal position. If he wants to cut thin material he can fix a 10cm high MDB surfaced table made from a couple of boards glued together so there will be no need to change spindle position at all. And take it off when he likes to do deep jobs.
Can i cut the motor shaft from the back side? Is it enough place for the cables of the motor? See picture. I need to further redesign it a bit otherwise i have to solder it with the motor in place , he he he. Ok, i wouldnt do it so. Just joking.
Last edited by Boyan Silyavski; 26-08-2013 at 12:35 PM.
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