8 x 4 build

hi before i update on any other parts i just want some advice regarding bed frame for stability and rigid. frame is made up of mild steel and is 100mm x 150mm.

cheers

ash

http://www.mycncuk.com/attachment.ph...id=15891&stc=1

looks fine to me, but I would perhaps suggest making butt plates, and bolting, to allow for adjustment. I was so grateful for them when I was assembling mine

http://www.mycncuk.com/attachment.ph...id=15896&stc=1

Add some vertical diagonals too. Diagonals make things rigid.
If you don't have 100x150 steel tubes already bought then I would advise smaller profile with more thickness. Also you have strange overlapping 100x150 vertical posts in lower part of the frame...

thanks guys, i will be using butt plates and as for the strange overlapping its because there was beams going across the bottom too but trying to keep cost down while keeping a strong frame, i have changed the frame now using 90x90 profiles 5mm thick. here is the frame.

cheers

ash

http://www.mycncuk.com/attachment.ph...id=15897&stc=1

does anyone know a company that can pre drill holes for the linear rails ect?

cheers
ash

That frame revision looks sweet now Ash.

.Me

thanks lee

just throwing in my gantry design, the z axis is inside the x axis frame which is supported by 2 200x100mm 10mm thick mild steel box, the z axis has a maximum height of 250mm (would like to go higher but 250mm seems to be the recommended height for rigid and stability.)

what do you think?

cheers

ash

http://www.mycncuk.com/attachment.ph...id=15898&stc=1http://www.mycncuk.com/attachment.ph...id=15899&stc=1http://www.mycncuk.com/attachment.ph...id=15900&stc=1

Are you going to use screws at that length ? driven with a motor on the end.

do you mean ball screws? if so then yes both sides :) using nema 34 motors and servo drivers.

cheers

ash

Have you a read through this build log? Lots of renderings at the start and photos of the frame later on that might help.

http://www.mycncuk.com/threads/6619-...2060#post52060

Quote:

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Originally Posted by reefy86

do you mean ball screws? if so then yes both sides :) using nema 34 motors and servo drivers.

cheers

ash

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Ok then have factored in the whip of the screws at that length etc.

hi clive, what do you mean have factored in the whip?

cheers

Quote:

---

Originally Posted by reefy86

hi clive, what do you mean have factored in the whip?

cheers

---

Ball screws have a critical speed that you can reach before they start to whip I am not an expert on this but I would have thought that if you are using screws that long you might need rotating ball nuts. Do a search on here there has been plenty of talk about it.

i used rotating nuts, on my 8x4 build because of the whip effect Clive mentions.


skip to about 1:15
https://www.youtube.com/watch?v=IY2Vx-FKjzM

http://www.mycncuk.com/threads/8242-...t=wall+mounted

thanks guys i will take a look :)

i want to hide my z axis stepper motor rather then having it stuck in the air so it requires a belt and pulley, is there a requirement to which i should aim for? more teeth the better or the opposite?

cheers

ash

i recommend to brace the legs with the diagonals , not the way it is now, there is no force pushing on the braces on that orientation

:)

think this maybe my final design on the frame, what do you think?

cheers

ash

http://www.mycncuk.com/attachment.ph...id=15930&stc=1http://www.mycncuk.com/attachment.ph...id=15928&stc=1http://www.mycncuk.com/attachment.ph...id=15929&stc=1

I would suggest you don't need the flat bar as it's not likely to add anything, where you've got the angled sections on the "feet/legs" of the frame, move those up into the rectangular spaces or add some there, they will serve you much better.

.Me

The flat bar will not add much stiffness and will in all likelyness resonate...what are you doing to stop the chips from collecting on your rails as they're right in the path of the flying chips. Would like another look at your Z axis as I seem to remember thinking that your beating carriages were too high up which means alot of length hanging down unsupported?

I don't really know what I think because I can't see what you are trying to achieve.

update on design thanks to the help from Dean :) the frame is made out of 90mmx90mmx5mm mild steel and 200mmx100mmx10mm on both y and x axis. all plates are 25mm thick apart from the end plates that connects to the ballscrews as they will be tentioning the screws so they are 30mm, ball screws are r2020's on x and y and z axis is r1610. the y axis will have a rotating ballnut and ball screws fixed both ends and then tentioned. on both y and x axis i will be using 25mm profile rails and 15mm on the z axis. im not starting with electronics yet but i do know ill be using nema 23's 3nm but still learning here.

thoughts anyone?

Ash

Attachment 17694Attachment 17695Attachment 17696Attachment 17697