View Full Version : Advice needed for Z Design

09-09-2012, 09:23 PM
I have an area to mount rails for my Z axis of 240 vertically within 200 accross the plate.

I'd basically just like personal opinions on which you think would be best to use in my situation.

I'm thinking of using 2 rails for the Z equally spaced about centre line of the plate, with the centre free for the ball nut. If it helps at all I am also planning to mount a gear o'end the ballscrew, which will be connected to a pulley belt, which will be connected to the stepped motor mounted upside down inline with the centre of the gantry and inline centre of the z plate.

I'm unsure on whether to use fully supported rail or the profile hiwin rail for this.

Please can i have some help, ideas, suggestions?






http://img.photobucket.com/albums/v248/ROBOTIX/3-Axis%20CNC%20Mill%20Project/th_closeups.jpg (http://smg.photobucket.com/albums/v248/ROBOTIX/3-Axis%20CNC%20Mill%20Project/?action=view&current=closeups.mp4)

09-09-2012, 10:10 PM
Oh Shit sorry Goblin forgot to reply to your email, been busy trying to get some sense and order back into my life.:redface:

Anyway I'll comment here so others see.

Not sure why you have the top and bottom brackets jutting out like that.? But think you'll find the get in the way and won't be needed.
Building a decent Z axis isn't difficult but there are a few things which are best done in a certain way. If you can afford profiled rails then I suggest you do because they are so much better and neater thou supported rails can work very well.
Basicly have the rails mounted on the front plate and the bearings on the rear, this helps support the front plate and gives a variable stiffness according to extension.
Don't scrimp on plate thickness, 19mm is min I'd use.
Use the belt setup like you describe it helps with resonance.
Use 5mm pitch screw not 10mm.

There are many examples on the forum but here's one shown many times. 68136814

09-09-2012, 10:45 PM
Priceless information!

I had planned to have those brackets like that for holding the ball screw suport block bearings but i suppose they could be tapered towards the middle, but i think ill be going away and having another go at all this tomororw now.

I am unsure as well on the size of the hiwin to use, type of profile and bearing block.

Planning to use 20 plate here, and bracings similar to that on the x axis gantry base.

5 mm pitch check, but what about the diameter 16 or 20?


John S
09-09-2012, 10:50 PM
Sorry to hi-jack the thread but any ideas on supplier for hi-win rails and blocks

09-09-2012, 11:03 PM
16mm dia screw will be fine.

The rails I'd use 20mm.? Not that 15mm won't handle the loads they easily will BUT the bearing sizes are tiny and the small size creates issues with clearances for the ball-screw. With 15mm you end up having to put stand-off blocks between the plate and rails/bearings to create the clearance for the ball-screw and Ball-nut.
Even with larger and taller 20mm you still have to create some clearance for the nut, usually by machining a shallow channel in F & R plates but it's much nicer and neater way IMO. The longer 20mm bearings also provide a bit more support has well.

09-09-2012, 11:04 PM
Sorry to hi-jack the thread but any ideas on supplier for hi-win rails and blocks

Sending you an email John check in 10mins.

09-09-2012, 11:11 PM
Sending you an email John check in 10mins.

Could i get a link to that too Jazz?


I'll be back after tommorrow with a redesign hopefully ill get heading somewhre in the right direction with it.

09-09-2012, 11:38 PM
Sorry wasn't sending him a link about hi-win rails. Something else.!

10-09-2012, 09:18 PM
Right, Jazz, Your photos have thrown a real spanner in the works and given me a headache. I know im on the right path now with regards to the rails, but as for the design of the Z im lost. I can see your design as being a good way forward, but i just cant get a perseption in my head on how i can transpose this into my design.

I think my real problem is working out the vertical spacing of the pillow blocks on the rear plate & the length of the front plate and rails to get the spindle down to the table and to have roughly 100mm between the gantry at its lowest point in Z when the tool is raised, and the table. With the chinese spindle mount i know its adjustable to some degree but I just have no idea at this time writing this which is why I Think ill take some real time to come up with something.