Let the fun begin !!! ???

[PAULRO]

i have touched base with chai and just need to work out the 16mm ballscrew lengths. i also notice that the bearing shaft diameters for BK and BF are different and am curious to know why this is.



this is my z axis end view, it has 20 mm rails and a travel of 160 mm. i'm thinking of a z axis ballscrew length of 400+ 30 for for a timing pulley. i'm sure this is enough or should i go more?

[Clive S]

I may be wrong but the BK end will have AC type bearings and the BF end will have a radial bearing they use a larger bearing at the BK end. Not sure if they make the ac bearings in the same sizes as the radial.
You will need to order the F measurement on the screw to be at least 30mm I think Chai standard is 15mm. ..Clive

[EddyCurrent]

this is my z axis end view, it has 20 mm rails and a travel of 160 mm. i'm thinking of a z axis ballscrew length of 400+ 30 for for a timing pulley. i'm sure this is enough or should i go more?

If the backplate is 400mm same as the spindle mounting plate you will likely want the outside faces of the bearing blocks to be 400mm apart so they are flush top and bottom, this will allow the maximum travel.
So the BK bearing is 25mm thick (excluding the end cap and locknut) the BF is 20mm thick, so that gives a ball screw length of 355mm between shoulders. Then 12mm turned section on the BF end, 69mm on the BK end (E+F = 39+30). Total length = 436mm. You have to allow for the Z ball nut thickness , this will reduce the overall travel, I drew mine out using Sketchup to make sure I was getting the expected travel.
Also you might as well get the ball screw as long as possible because the price difference for a few mm is going to negligible.
I know it might slow the build but in my case I waited until the ball screws arrived before cutting metal. It was easy to size the metal to the ball screws but impossible the other way round if in error. That's one of the reasons I built the electrical panel first, waiting for the stuff from China.

[PAULRO]

Cheers Eddy, how long was the delay from Chai ? also did you get the ballscrews machined locally or by chai and if so would you recommend it? i might get it done locally because i have access to a lathe but if it's not too costly to get it done by Chai i might go that route but then i have read that some of the screws turn up slightly bent. i have used suppliers from china in a previous life ( job) and remember some of the parts delivered with poor packaging and very little protection ( not all suppliers ). it's very helpful to have the experience of previous builders who have gone down this route, hence all the questions!!!

[EddyCurrent]

I think it took 18 days from payment to delivery. The machining was fine, exact dimensions, good fit to bearings, far cheaper than anywhere else. Holding the ball screws in a lathe is not as simple as a bit of round bar plus they are very hard on the outer skin.
The parts looked okay until I fitted them whereupon I noticed some bending. I decided to straighten them myself and it appears to have worked well enough, it's all in my build log.

[PAULRO]

These are the motors I used, they perform well.
http://www.cnc4you.co.uk/index.php?r...product_id=367

i had a look at these and will go ahead but i'm not up to speed with the rest of the gear required for the electric build . i'm hoping to get into 3d carving at some stage so i would like the m/c to be able to cope with that as well. i don't know if my design needs to be changed to accommodate this requirement. i read a reply to a post recently by jazz stating that a requirement for 3d carving is fast direction changes and high acceleration and it started me thinking that maybe i need to take other requirements into consideration and as my steel will be delivered this week i could make alterations to the frame to allow for this requirement. any input would be greatly appreciated on this.

[EddyCurrent]

Regarding metal work, I think you have it sorted with respect to 3D carving, i.e. adjustable height bed, 4th axis option.
Have you thought about how the 4th axis will physically attach to the frame ? and will material held in the chuck be parallel to the X plane or the Y plane ?
I'm thinking about a 4th axis myself but there's no room in my control panel for the gear, but thinking about it I feel it would be best as a stand alone unit with control wiring back to the main panel via plug & socket.

[PAULRO]

[QUOTE=EddyCurrent;60688
Have you thought about how the 4th axis will physically attach to the frame ? and will material held in the chuck be parallel to the X plane or the Y plane ?
I'm thinking about a 4th axis myself but there's no room in my control panel for the gear, but thinking about it I feel it would be best as a stand alone unit with control wiring back to the main panel via plug & socket.[/QUOTE]

apologies for the delay in getting back to you Eddy, i haven't decided whether to mount a plate to the inside frame to house the chuck or sit it on the blue frame dedicated for the fourth axis. I plan on clocking it true it with a clock attached to the gantry, with regard to the separate panel i hadn't really thought of that option but now that you say it ..... i haven't sourced a panel yet . i'm hoping to pick something up in the region of 800 x 600 x 200 deep if its not too expensive. i have off cuts of 1mm galvanized sheets getting in my way and if the parts that i ordered from Chai are on a slow boat then i might toy with that idea for a panel.
by the way can you recommend any supplier for linear rails ?

[JAZZCNC]

this is my z axis end view, it has 20 mm rails and a travel of 160 mm. i'm thinking of a z axis ballscrew length of 400+ 30 for for a timing pulley. i'm sure this is enough or should i go more?

Why is the rear plate so long.? you only need the rear plate long enough to fit bearings onto and give travel required. If your only wanting 160mm of movement then you would get away with shorter back plate and ballscrew.
Also one thing to take into account if your trying to get every last bit of travel out of screw is to allow for the bolt heads holding ballnut, you can easily loose 10mm depending on how tight you make it.
Regards the Z axis screw bearings then with screw being so short you don't really need one at the bottom if you want to keep cost down and it makes setting up that bit easier.

[PAULRO]

i had intended to use 20 mm rails on the z axis but after reading the various posts of your good self I am now going to use 15mm rails and guides to suit so i think a redesign is in order.
the rear plate should be shorter alright i just left it long enough to house the motor with a body of 100mm long and a plate to hold it.
i suppose the travel of the z axis could be longer but i went with that travel because of all the discussions about the length of the lever created by the extension. i suppose it's another trade off , keeping it to a minimum while having enough scope to machine to a reasonable depth. i'll get cracking at it again tomorrow, my shutters are starting to descend !