My new 6040 improvement plan.

[Desertboy]

So you went with 2x15mm hiwin on your x axis?

I was looking at my machine last night and weighing up the options. I think I can potentially leave my ballscrew and 20mm shafts on and ADD a 15mm hiwin, possibly 2 hiwin. Sounds crazy, but actually looks easier.

My main worry with the 15mm rails- spec says the attaching holes on the trucks are M3 threads. Is that right? Seems a lot of force for 4x M3 screws to handle.

They're M4's at least my original Hiwin's and the clone rail I linked to are M4, the carriages are also M4.

My spindle mount actually bolts through the mounting plate and directly into the Hiwin's.

My X is 1.2m original Hiwin's, Y is the 1.5m clone rail I linked to (I only paid £99 but they are still a bargain at £120) & Z is 45cm Hiwin all 15mm

There's 90 T nuts holding the 1.2m and 1.5m to the extrusion with M4's you have no issues the extrusion will fail before the bolts lol.

Stainless steel bolts are not strong, high tensile are much much stronger next time I will use high tensile and they are cheaper to boot.

I've destroyed so many M4 A2 stainless bolts the caps round off so easy.

[PaisleyPCdoctor]

I was going to ask how you drilled the holes to ensure proper allignment- I would struggle.the tbolt to extrusion will probably figure in my plans. Much simpler.
Thanks.

[m_c]

The biggest problem is that you'd be bolting the rails to aluminium, not the bolts themselves.

There are various calculators online for bolt strength, and the first one I've just found puts an 8.8 grade M3 bolt at proof load of 2920N, and minimum ultimate load at 4020N. To put that in context, that means you could hang over 400Kg onto the bolt vertically, and it should not snap.
However I very much doubt an aluminium thread would support that 400kg.

I'd be looking at either helicoils, or bigger threaded inserts which I've currently forgotten the name off, to help spread the load on the aluminium.

[PaisleyPCdoctor]

The thought did occur to me about load on threads, albeit not as precisely as you.

The way it's looking the rails will probably be mounted with trucks facing up and down (above and below the existing rods, so load will be perpendicular to the bolts, rather than trying to pull them out, if that makes sense.

If I end up leaving the 20mm rods in, it shouldnt be an issue. The load will be shared in some fashion between 4 bearings (or six if there's space to double up on the square rail trucks).

I've ordered a single 15mm hiwin clone from uk with 2 carriages. It'll be 100x easier to visualise a working plan with them in front of me.

Also- might have mentioned- to avoid the definite coking up of manually drilling all those mounting holes- I'm gonna use a bit of 2020 extrusion between rail and aluminium backplate. That seems less rigid but at least I can do it.

[PaisleyPCdoctor]

I've destroyed so many M4 A2 stainless bolts the caps round off so easy.

Typical, I always have a bag of m4 a2 Allen key bolts in van. Use them to replace missing ones on machine access panels I work on. Thought I was being clever buying stainless, but I've decapitated 2 so far. I feel your pain. Lol

[PaisleyPCdoctor]

I recieved my 500mm long, 15mm hiwin clone guide rail and carriages today. Sure singly quick.

Looks good, except these have M3 holed on the carriages (2x20mm spacing).
Suppose it will be all right as I'll end up with 2 of these rails in addition to my 2x20mm round rails. I'm sure the M3 threads will take the punishment.

[PaisleyPCdoctor]

I was thinking for ages last night about ways to increase the rigidity of the bed frame. Came up with all sorts of ways that would probably work, but I had a simple idea this morning.

I've got some 900x600x60mm concrete paving slabs laying around. I'm going to place the cnc on one of them and bracket the frame to that. It surely won't be able to twist and it will add a fair amount of mass to help prevent it bouncing around on fast movements.

Best of all, it's free.

[PaisleyPCdoctor]

I've figured out how to add the 15mm square rails.

New backplate, 20-25mm thick aluminium, 100mm high. 2020 extrusion bolted to top and bottom edge. Square guides bolted to extrusions. Mounting plate coming out from under existing x axis bearing assembly for bottom rail.

Square block on top of top carriage to mount into handy t-slot in the spacer above existing bearings.

2 carriages top and 2 carriages bottom.

[Desertboy]

Don't take the carriages off the rail EVER! Bearings can and do come out those carriages so the best thing you can do is put a bolt in either end for now so they're captive.

I think you have low profile rail which is why it's M3 not M4, it's still plenty strong and a superior solution to the round rail by a million times lol.

That's crazy quick delivery, how much did you pay? if it's not too rude a question.

[PaisleyPCdoctor]

15mm x500mm square rails with 2x carriages was £37 off eBay. They were posted from uk but still surprisingly quick for Christmas time.

I ordered a second today, it'll arrive before I have time to build anything anyway.

I'm quite worried about getting the mounting holes correct. I think I'll mock it up in acrylic or something first. Once it's correct, I might pay someone to machine it in aluminium. Might be able to do it myself- we'll see. Lol.

I plan to buy two 20mm rails , 750mm long to replace the y axis bearings. Looks like a pretty easy job. That's gonna cost me £124 (china). After that, there's not much left and I'll just have to get on with actually milling stuff.