Fully supported linear bearings - Radial squareness

[Slixxor]

Hi Guys, Just a very quick question. I am building a new machine and have done my research here and on other forums to build a good sturdy design for milling timber, ali and steel.

I am using SBR20 fully supported rails and they definitely have a very tight fit (zero play) in all directions except for the radial axis with the rod.

I have built the frame and everything is pretty much completely square as I tack welded the whole frame and adjusted accordingly. The only part that is not completely level is the top box steel that the linear rails will be mounted to. Both sides are completely planar but both sides also lean inwards slightly across the top where the rails will mount.

My question is: The bearing are extremely tight except for the radial side and they offer enough play for me to level the bearing mounts flat to the gantry. Is this acceptable as it is considering all other sides are completely square or would I need to level it using epoxy?

I recognize that in a perfect world It should be perfect but I cant see why it wouldn't work the way it is considering the mounts will allow me to twist around the linear bearing.

Photo:

[mekanik]

slixxor
Welcome to the forum.
As i see it your frame still requires some more welding, the base looks sound enough although we prefer some diagonal bracing, but the top rails are just hanging out there only supported @ either end, you really need a couple of stiffners to tie the top rail to the main structure.
I would personally go with epoxy leveling as you will get some more movement when you incorporate the bracing.
Regards
Mike

[Slixxor]

Thanks for the feedback. Yes I do need to support it more. I will add some gussets and some 45° angle beams to support the top rails and some on the lower section as well. Steel used is 65x65x3mm box.

[Ger21]

I am building a new machine and have done my research here and on other forums to build a good sturdy design for milling timber, ali and steel.

I am using SBR20 fully supported rails

I wouldn't consider SBR20's to be anywhere near rigid enough for milling steel.

[Slixxor]

One step at a time. :)

This is my first machine so I will take my time with it. I'm happy for a job to take 5 hours to complete if it has to. The only time I will be milling steel is for small components. I will build it first, try my usual maple ply and then some 5060/6065 ali. If it goes well I will chance mild steel with some carbide bits. but it isn't critical.

I am not a machinist by trade, my profession is custom software and electronic design. I have worked on some GRBL controllers in the past. I decided to do this project to have a worthwhile machine in the lab and learn something on the way. I am writing my software front end (similar to Mach 3 but much nicer) that will work specifically with my machine bed size with a heavily modified version of Arduino GRBL that is running at 200kh on an STM32 ARM cortex board.

From looking around the forum I see a lot of skill gaps. Most users seem extremely proficient on machine design and structrual engineering but lack the electronics skills. I am quite the contrary. Finding myself reading google e-books on structural integrity and CNC/crane gantry designs.

I am more than happy to invest my skills in helping people out and love getting some good advice in return. I will weld up these gussets and some supports tonight.

[mekanik]

Hi Slixxor
If you have your design in some kind of software post it, and the guys with more experience than myself will offer advice, really need to see the gantry arrangement.
Regards
Mike

[Paul3112]

Hi Slixxor,

I am in Melb Aus. If I can assist you in any way.

You might not of seen this thread http://www.mycncuk.com/threads/4356-...upported-rails
The square tube will rhomboid with side load ( assuming gantry uprights are the top of the frame )
Three trucks are better than two trucks ( better load spread )
Regarding tool load what spindle are you using ..kW RPM etc ,, have you seen "CNC Cookbook"

Finally, Hey Ger, Very nice to see you here.

Paul

[Slixxor]

Hi Paul. Yes I have seen the page. I am planning on using a 2.2kw water cooled spindle. Z axis range of 300mm. My rails for Z are 450mm long. I am adding 45° gusset/supports to both sides of each corner of the frame. I will be running dual ball screws on the X axis to minimize racking each with their own nema34 34HS59-5004S. Still havent decided if I'll be using the same size stepper on Z just yet or slightly smaller.

I haven't done a cad example of my design for reference. May do shortly pending work commitments.

[Neale]

Sure that those Nema 34s are a good fit for this size machine? Nema 23 would be more usual and this is a situation where over-building is definitely a bad thing. I was talking to someone last night who bought someone else's project router and with Nema 34 ("bigger must be better") he was getting no more than 1m/min when with the correct motors he should have been seeing 5m/min or more. Big motors come with much more inertia and high inductance which are both speed killers. Might be worth a bit of investigation?

[Slixxor]

The bed size is 1300x1000. I am happy to run whatever I need in order to be able to mill aluminium comfortably. I opted for the 34's due their torque at low rpm. Can anyone suggest a nema23 suitable for the application, they certainly are cheaper :)