Small rigid router - Design advise needed

[mitchejc]

Hi, this is my first stab at the design after having a good look at some of the great builds here. Any advice or comments would be greatly appreciated! Requirements for the machine as following
Exclusively for machining aluminium
Cutting area: 600mm x 450mm x 150mm.
Speed is not a great issue
I got hiwin HGR15 rails and blocks and Chinese 1605 ballskrews and ballnuts so I'll use those.
Since aluminium is not cheap here I'm going for a welded steel design and then alu on Z because there's a bit of machining required there.


Some basic dimensions for reference.
Distance between gantry side rails: 800mm
Distance between top and bottom rails on gantry: 300mm
Z plate with 250mm
Box section used is 160x80x3mm and 120x80x3mm
10mm 10mm sheet for flat parts to be laser cut
Y carrage and Z assembly is 25mm alu with a 10mm plate at the back


A few questions:
Will the long belts (+-650mm on Z and 550mm on Y) cause any issues? HTD 5mm pitch x 15mm width with 20tooth pulleys
The gantry is very rigid and HEAVY but I'm worried about ressonance. Can one fill it with something that's not going to add a lot more weight that will help with resonance.
Does the 3 rails on the gantry make sense? I've got 1 on top and two at the bottom.


Please comment if you spot anything that's not going to work or things I can improve without adding major cost

[Clive S]

You could shorten the z belt by moving the motor and turning it the other way up so that the pulley if facing down. ..Clive

[mitchejc]

Thanks Clive, I'll give that a go then I can also move my Y stepper up a little bit to shorten that belt.

[Blackrat]

ja ja wat se jy :P

why even go with belts ? are you going to have a step down ratio ?

i wouldnt bother with the 3rd rail, i think it will just make it harder to clock up ...

what or how are the two bottom rectangle tubes fastened ?

looking good :D

[EddyCurrent]

Looks pretty good but to make life easier later I would draw in your energy chain, drag chain, whatever you call it because it could affect some aspects of the design such as , mounting brackets, length of travel in X direction. Also consider limit switches and homing switches locations.

[mitchejc]

Thanks for the advice EddyCurrent. I will start adding those as I can see it might be an issue with the design as it is now, especially the drag chain running on or behind the gantry.

Looks pretty good but to make life easier later I would draw in your energy chain, drag chain, whatever you call it because it could affect some aspects of the design such as , mounting brackets, length of travel in X direction. Also consider limit switches and homing switches locations.

[mitchejc]

:-)

No, its just 1:1 ratio. My understanding is that belt drive will make the machine a little smoother. X and Y would be possible to do direct drive but Z will be difficult as I'm trying to keep it as flat as possible.

Not sure but I'm thinking of welding on tabs or a piece of flat bar on both sides that will allow me to bolt it to the table.

ja ja wat se jy :P

why even go with belts ? are you going to have a step down ratio ?

i wouldnt bother with the 3rd rail, i think it will just make it harder to clock up ...

what or how are the two bottom rectangle tubes fastened ?

looking good :D

[Tom J]

hi
Are you going to use servos or motors with encoders, if not, than you should change design for one motor on X but with two screw on each side. Loosing steps issue - big problem when you mill harder stuff like alloy.
I had the same problem - its complicate design, but for long term your gantry always run smoothly, without jamming on one side

[mitchejc]

Tom, thanks for the advise. Yep, I have EasyServos which are basically steppers with encoders but if I have any issues with racking I'll certainly go the single motor route.

[mitchejc]

Thanks for the advice so far. Muchappreciated! Plan is still to build a base with aflat top and then bolt my machine on top of that. I'm basically done building the base and I'll post a few pics soon so its now time to start focusing on the actual machine.


I really had a hard time deciding onthe gantry design. I know the box section designs are proven and works verygreat but if possible I would like to try something a little different with a welded structure made from round tubes, angle section and flat cross supports. Tubes will be sand filled. I'm hoping to get away without epoxy leveling so the idea is to have the X and Y rails sit on 10mm thick ally plates bolted on top of the steel that I can hopefully machine flat and parallel. If that fails I'll go the epoxy route.


Below is what I have in mind. Pleaselet me know if you spot any fundamental issues or things I canimprove. Steel parts are blue and alu parts are grey



The core of the gantry looks like this consisting of 76mmx5mm round section, 50mmx5mm angle section , 100mmx10mm flat bar and several 10mm and 6mm thick braces