starting from scratch- router 1st project

[Neale]

Philippe,

I'm designing a machine which is similar to yours, although slightly larger capacity, and trying to use as many ideas discussed in this forum as possible.

I am working on the Z carriage design and, as you said earlier, trying to keep the moving and fixed plates as close as possible. I cannot see from your CAD drawings how you have managed to fit the ballscrew nut in between the plates. The nut is wider than the profile rail + bearing height - have you put packing under the bearings to increase the space? I can see that you have machined steps into the plates and a recess where the ballscrew nut is fixed.

[idefix]

Hi Neale,
I'm happy to share related information back with you.
I have broken the design so that you can see the area as detailled as possible. Let me know if this is what you are looking for.
As a comment note that for the Z axis my rails are type HGR15 with Hiwin HGW15CA blocks and the screw is a 1605.

Distance from Gantry plate to Z plate (plane supporting the blocks) is 24mm

[Neale]

Many thanks for the details. I had started with 12mm plates but I think that you are using 20mm which allows you to machine recesses for extra clearance, and there are also packing pieces under the rails. Back to the drawing board!

Are you using something like Solidworks for the drawings? The drawings of slides, ballnuts and so on are very detailed and look as if they might have come from the manufacturer!

[idefix]

Yes Neal, using SW for the drawings with some parts already loaded from the web such as rails, blocks and M4 and M6 screws plus the timing belt pulleys. All the rest is own design.

I do confirm that base material thickness for the plates is 20mm (initialy for ridgidity purpose) but helps making the cavities...

[Jonathan]

For a small gain in strength and machining time, you should be able to make the recesses in the Z-axis not cover the whole length, as the ballnut doesn't traverse the whole rail.

[Neale]

That's the kind of thinking that leads to something that looks great in the drawing but is impossible to assemble! In this case, I don't think that that would be a problem but I've painted myself into a corner before now...

[Jonathan]

So think harder! Admittedly I did recently make something that turned out to be impossible to assemble...

Have you checked that the Z-axis belt clears the posts upon which the motor is mounted? If you decide to change the ratio it might not. Also, I wouldn't reduce the thickness of that motor mount beneath the motor, partly because it needs to be strong but also because it adds an extra machining operation which will increase the cost of the part unnecessarily.

[JAZZCNC]

Hi Neale,
I'm happy to share related information back with you.
I have broken the design so that you can see the area as detailled as possible. Let me know if this is what you are looking for.
As a comment note that for the Z axis my rails are type HGR15 with Hiwin HGW15CA blocks and the screw is a 1605.

Distance from Gantry plate to Z plate (plane supporting the blocks) is 24mm

I wouldn't use those spacer plates and just buy thicker Material because your introducing several more operations into the job but more importantly increasing the chance for error.!! . . . . Unless Your getting the work done for free won't be saving any money and will probably be cheaper because of less cycle time involved, also it won't be much lighter.

[idefix]

I wouldn't use those spacer plates and just buy thicker Material because your introducing several more operations into the job but more importantly increasing the chance for error.!! . . . . Unless Your getting the work done for free won't be saving any money and will probably be cheaper because of less cycle time involved, also it won't be much lighter.

I was not enthousiast with those spacers but this is in my opinion the only way to adjust the position of the rails afterward... Because the lower Hiwin blocks are fixed first with positon guaranteed by the machining of straight edges, I still need to be able to adjust the rails... And here is the role of the spacers.

Related to the reduction of the thickness of the motor holder, this is necessary due to the relative short length of the axes. Mechanicl strength will still be plenty because belt tension effort combined to pulley position is only generating low flextural torque.
However, have you some suggestions (little drawing appreciated) about how to design this part in a different way ?

For the Z axis the position of the posts have been checked for sufficient clearance for the belt path. Of course this introduce limitations with the size of the pulley but I don't expect to change from ratio 1:1

Thank you very much for all your valuable comments making this thread alive.

[JAZZCNC]

I was not enthousiast with those spacers but this is in my opinion the only way to adjust the position of the rails afterward... Because the lower Hiwin blocks are fixed first with positon guaranteed by the machining of straight edges, I still need to be able to adjust the rails... And here is the role of the spacers.

Well that's worse than expected then because really you want referenace edges in the Front plate not just the back plate.!!

One way I use to maximise clearence with thin material and low rails etc is to not cut the referance edges into the material and sit the rails and bearings direct on the plate face.!!. . . . To give the reference edges you want for the rail and bearing alignment you then machine and press aluminum dowels into the plates half way on the reference edge you then machine these Dowels half way and flush with material to create the reference edge. This way you save machining and keep the strength of the plate plus have an accurate referance edge to work from. It's also much quicker than milling full length slots.

If you use Ground machine plate then this technique ensures you get the best accuracy from the plate because even the best milling can't match a ground surface to mount the rails on.!

Related to the reduction of the thickness of the motor holder, this is necessary due to the relative short length of the axes. Mechanicl strength will still be plenty because belt tension effort combined to pulley position is only generating low flextural torque.
However, have you some suggestions (little drawing appreciated) about how to design this part in a different way ?

Regards the Motor mounting then just offset the motor and flip.!
See the pic of Cad model for one of the little machines I build and if you want to see the real thing I can take a picture for you.! The bracket is wide and square because I put a cover over the Z axis and it fastens to this plate, to reduce weight pockets are machined in the under side along with a pocket for the Motor.