DIY Build of Aluminium CNC Wood Router without Workshop & Tools

[JAZZCNC]

Last query on the limits of thread in 5mm thick aluminium... When attaching the supported round rails on top of the beam on the X-axis is it then necessary and best to run a length of thicker flat bar through the box section to take the bolts?

To be sure then Personally yes I would.! . .BUT. . If you use M5 bolts then with smaller pitch and keeping the centres closer together with the higher quantity of bolts you could get away with it.?
I've done this with steel 4mm box section and it's worked ok.! . . It's just with softer Ali @ 5mm could be marginal.?

At the worst you can just add the thicker bar through at a later date if it doesn't feel right or causes problems.?

The Angle gantry sides should be ok because of the squat nature and the fact it's driven from both sides.! The thing to watch out for is that the Angle both internal and external are close to 90deg.? The round rail bearings will handle some discrepancy but you don't want too much.!! . . . Bracing will help absorb any resonance and can only help.

I've noticed from the pics you have 2 plates on the bearings and cutaways in the gantry sides for what looks like access to the bearing bolts.?
If you use 2 plates then you don't need access to the bearing bolts and can bolt the top plate direct to the bearing plate so no need for access slots. The beauty and point of 2 plates means it makes gantry squaring easier without having to worry about bearing bolt access.

[WandrinAndy]

I've noticed from the pics you have 2 plates on the bearings and cutaways in the gantry sides for what looks like access to the bearing bolts.?
If you use 2 plates then you don't need access to the bearing bolts and can bolt the top plate direct to the bearing plate so no need for access slots. The beauty and point of 2 plates means it makes gantry squaring easier without having to worry about bearing bolt access.

Splendid... I wasn't looking forward to "hacking" out those cutaways, but thought I had read somewhere that one should allow access to the bearing bolts... and now know that's to allow for gantry squaring.

It will be so much easier doing it the way you suggest. I had already included four bolts (M8?) holding the plate and angle together, so will maybe tweak these to be a tad closer to the bearings and add two in the middle for good measure and just drill holes in the angle to accomodate the bearing bolt heads.

[Jonathan]

I guarantee that an M5 or M6 hole will not strip in 5mm of aluminium for the loads that are imposed upon it on your gantry.
When calculating the length of thread engagement required the standard method is to calculate the required thread for it to require a higher force to strip the thread than for the bolt to snap when placed under tension.

For M5 the calculation (reference here) results in minimum 4.0mm engagement and 5.0mm engagement for M6. However this assumes the thread is steel, so you have to compensate by multiplying by the ratio of the material's tensile strength. This clearly results in slightly greater values.
This is still not a problem since the force on each bolt is small in your application, particularly if there are a lot of them. You are not going to get anywhere near the force required to snap a bolt. The concern is more ensuring they do not work loose, so I would thread-lock them to be safe. Since you are using SBR rails I reccomend thread-locking the bolts that fix the rail to the aluminium mount since they can also work loose.

[JAZZCNC]

I guarantee that an M5 or M6 hole will not strip in 5mm of aluminium for the loads that are imposed upon it on your gantry.

Argh but I bet you won't guarantee he won't strip one while tightening and that's the danger with so few threads.!! . . . . Carefully does it.!!!

[WandrinAndy]

Argh but I bet you won't guarantee he won't strip one while tightening and that's the danger with so few threads.!! . . . . Carefully does it.!!!

How did you know that Jazz? I have been known to strip thread in thick steel on more than the odd occasion. lol

[Jonathan]

Argh but I bet you won't guarantee he won't strip one while tightening and that's the danger with so few threads.!! . . . . Carefully does it.!!!

Yeah if we're taking this seriously then use a torque wrench, but I prefer to calibrate my hand and shout 'click'

[JAZZCNC]

Yeah if we're taking this seriously then use a torque wrench, but I prefer to calibrate my hand and shout 'click'

Yeh I,ve always said bet you have a good wrist action. .