CNC Router - Bed Size 1300x2700 - Design Review

[Royster1992]

Hello All,

I Have nearly finalised my design for my CNC and would like the thoughts of people who have built machines in the past.

This is my first build and quite a big one at that.

Running with a 2.2KW Router at this point.

Some other specs as follows:

- Mach4 as my Motion Control Software.

- Inventor HSM for my design and CAM software.

- Breakout board is from PoLabs - PoKey57cnc

very nice board please check it out at https://www.poscope.com/product/pokeys57cnc/

- Neva 23 3.5A Motors biggest of the 23's

- Aluminium as my base structure(i work at an aluminuim workshop and can get it very cheap.

- Rack and Pinion for My X & Y, 8mm ACME for my Z.

- Some C-Beam and running gear from opens builds.

Please View my model at https://autode.sk/2Mak9j6 this will only be available for 30 days.

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[awerby]

It looks pretty good so far. I'd question the use of dual round rails top and bottom for your X axis. You really only need one per side, especially considering that the engagement with the rack below will stabilize the gantry sides. If you've got the money for all those rails, it would be better spent on a single pair of profile rails, which are considerably better than the round kind.

The gantry sides are unconventional, built as they are from sections of tube. They'd be stronger if tied together with plates on both sides.

When you say those motors are the "biggest" - are you talking about holding torque? People often focus on that number to the exclusion of all else, but the inductance is at least equally important. If the inductance is too high, you lose top-end speed, which is important if you're cutting wood. You don't say which drivers you plan to use, but they determine how much power you can feed it, and in turn, how much inductance is too much.

[wizard]

Hello All,

I Have nearly finalised my design for my CNC and would like the thoughts of people who have built machines in the past.

This is my first build and quite a big one at that.

Running with a 2.2KW Router at this point.

Some other specs as follows:

- Mach4 as my Motion Control Software.

- Inventor HSM for my design and CAM software.

- Breakout board is from PoLabs - PoKey57cnc

very nice board please check it out at https://www.poscope.com/product/pokeys57cnc/

- Neva 23 3.5A Motors biggest of the 23's

- Aluminium as my base structure(i work at an aluminuim workshop and can get it very cheap.

cheap is nice! Just make sure the materials are suitable for the job at hand. It is one thing to produce a compromised machine for low cost but if you have some flexibility choose the best materials for the job at hand.

- Rack and Pinion for My X & Y, 8mm ACME for my Z.

I believe (based on a quick look at your model) that you have the rack and the linear bearings/rails mounted on different beams. This adds to assembly complexity and as such I would try to avoid it. Also as Andrew pointed out the dual rail solution may be more expensive than going with a larger profile rail. A profile rail might be stiffer, it is all about implementation.

In any event Instead of having two sets of rails to get parallel and in plane with each other you now have four plus you have the racks that need to be properly aligned also. It might not be a problem if you have experience and access to a well equipped machine shop. However for most DIY builds it is additional complexity.

- Some C-Beam and running gear from opens builds.

Be careful with C-Beams and open builds, they do not have the most robust of extrusions and as such I'm a bit concerned about the span of the gantry beam. You are spanning a little over 4.25 feet and the gantry beam just looks thin to me. There is a sticky that covers gantry beam design and ultimately a big tube is the way to go. The gantry by design is only supported at each end thus it needs to be stiff because there is not opportunity for bracing.

Please View my model at https://autode.sk/2Mak9j6 this will only be available for 30 days.

For the most part though the machine looks very nicely thought out. I'd nail down the mechanical design a bit better before worrying too much about the electronics.

The other thing here is what you intend to use the machine for and the materials to be worked on. Also your expectations with respect to finish are a factor.

[ger21]

I would extend those side channels so that all 3 are full height.

And as Wizard said, only have one side beam. The small lower beam will flex a LOT.

The weakest point will be the V wheels, imo.

[Royster1992]

Hey Guys,

Thanks for your opinion.

I have access to a Extrusion CNC so any holes etc that I need to line up wont be a problem.

as to the linear rail I have done what Awerby has said although my ESP is telling me that I need one top and bottom.

back to the drawing board will post a new link once updated.

thanks very much for your input

[Royster1992]

Ok Please see link https://autode.sk/2MeRHg3
I have updated the drawing to include 20mm Profile Rail
Strengthened the gantry use two 150x50x5mm RHS Beam 6160 T6 Aluminium
the design isn't 100% Complete as yet but its the overall design I would like your opinion on.
The bottom rail is 60x35x5m RHS 6160 T6 Aluminium - this would require a lot of force to flex it.

[ger21]

You only want one rail on each side.
1) The only thing the bottom rail is doing is keeping the sides perpendicular to the table.
Making stronger gantry sides will do the same thing, for a LOT less money.
2) If the two rails are not parallel to within about .002", the bearings may bind enough that they won't move.

There's a reason that ZERO commercial machines, even those costing $150,000, use two rails per side. One is more than strong enough.


And the rack should be mounted just below the top rail, rather than on that separate rail.

[wizard]

You only want one rail on each side.
1) The only thing the bottom rail is doing is keeping the sides perpendicular to the table.
Making stronger gantry sides will do the same thing, for a LOT less money.
2) If the two rails are not parallel to within about .002", the bearings may bind enough that they won't move.

This is key, trying to run any type of linear rail in opposition like that creates all sots of problems. You need build precision that can't be achieved on a machine made out of extrusions. For the little bit of extra money it costs one can make the gantry supports wider and thus stiffen that part of the machine with a single rail solution. It should be noted that there are threads in this forum where guys have had significant problems trying to get closely spaced rails to run properly when on the same plane. So yeah I have to reiterate that those rails will do nothing but cause him grief during assembly.

There's a reason that ZERO commercial machines, even those costing $150,000, use two rails per side. One is more than strong enough.


And the rack should be mounted just below the top rail, rather than on that separate rail.

[Sevenmead]

C beam is super weak. I upgraded mine twice. Here is the overview of my second and final upgrade.