Steel frame for 8' * 4' cnc bed ?

[flanagaj]

Hi,

I am in the process of designing the bed for my CNC machine and would appreciate any guidance regarding frame dimensions and material choice.

My plan is to weld a steel frame together with 10mm * 50mm plate welded to the sides of the upper rails, which will then be milled by a local machine company in readiness to accept the linear guide rails. They have quoted £800 to mill the side rails and drill all of the holes.

Their machine is super accurate and will ensure that the rails are 100% parallel and level to each other, resulting in super accuracy. Whilst £800 is expensive it will save me the headache of getting the rails aligned

My plan is to base it on the axyz 4000 series machine as shown below.

[JAZZCNC]

First can I ask the main intended use.?

[flanagaj]

First can I ask the main intended use.?

The main use will be for machining timber panels for furniture and timber for boat making. I would, however, like to have the flexibility to be able to machine alloys as well, so having an accurate machine would be ideal.

I don't want to use aluminium profile section as I think those machines have poor resale if you ever decide to build another one.

Do you have any suggestions that might be of help ?

Thanks

[Jonathan]

The main use will be for machining timber panels for furniture and timber for boat making. I would, however, like to have the flexibility to be able to machine alloys as well, so having an accurate machine would be ideal.

If it's mainly for wood then that sort of accuracy is not going to make an appreciable difference. £800 sounds a lot ... invest it in profile rails etc. How can you be sure that after the frame has been machined when you fix it to the floor it does not distort.

Getting the rails parallel is not a problem - once you have the gantry mounted and put a couple of bolts in one rail the other will self align. Either that or you can use a DTI to align them by affixing it to one carrage with the needle against the other rail.

Another way to get them parallel in the vertical plane is to mount them on (the right type of) epoxy. Pour the epoxy on the rail mounting surfaces with a channel (or several channels) in between and gravity will level it 'automatically' with very high accuracy.

[flanagaj]

How can you be sure that after the frame has been machined when you fix it to the floor it does not distort.

I too did think about this and came to the conclusion that as the machine is to be made from pretty substantial material it will not be able to distort. Do the large professional cnc machines get aligned up on site when they are delivered ?

Another way to get them parallel in the vertical plane is to mount them on (the right type of) epoxy. Pour the epoxy on the rail mounting surfaces with a channel (or several channels) in between and gravity will level it 'automatically' with very high accuracy.

I have read about this, but never did find out where the "right type of epoxy" can be sourced.

I don't want the machine bolted to the floor, I just want it to sit on the levelled feet.

Do you think that once a frame is constructed from 80mm * 80mm * 6mm box section and then machined it will still be able to distort ?

[JAZZCNC]

Hi Ian,

Completely agree it's not neccesory to spend £800 to get the machine you want.

Regards your question of do they setup professional machines on site then yes they do and to a very high degree taking a great deal of time using very costly precision levels etc, also they are bolted to the floor more often than not on shock dampening feet.

Obviously good build quality is required but Setting up the machine while in situ is the key to an accurate machine, time taken here will make or break the machine.
The heavist machines built from quality cast iron still bend and twist requiring carefull leveling and setup so don't think for one second 80x80 is substantial and won't move or require setup.!. . . In real machine terms it's banna material.!!

Also regards Epoxy, Yes it will self level to a high degree but it still requires the machine to be fixed and levelled to high degree before application and will only be accurately level to that one spot.

Basicly what I'm saying is if you want good accurecy then Yes 80x80 will do what you want it to do and with good build quality and attention to detail will give the accurecy you require but the machine needs to be fixed down with adjustment built into the design.

If good strong design with carefull welding and attention to detail is used, mixed with very carefull setup then you will easily surpass the accurecy you desire without having to spend £800 on surfacing.

£800 would be far better spent on using quality components.!!

[Web Goblin]

80 x 80 x 6 box section can still distort. The size of the machine you are building will be rather heavy, 80 x 80 x 6 box section aint light. Unless you level it very well it will still move. If you decide to bolt it down then make sure it is perfectly level on its feet or you will pull it out of alignment with the bolts.

Ian

[Karl]

We would certainly be interested in hearing the personal experiences of anyone who's used epoxy et al to level the top rails of a larger frame. Our Mark-3 machine will be for 8' x 4' sheets. (That said, we're still assembling the bits for MK-2).

Karl

[flanagaj]

80 x 80 x 6 box section can still distort. The size of the machine you are building will be rather heavy, 80 x 80 x 6 box section aint light. Unless you level it very well it will still move. If you decide to bolt it down then make sure it is perfectly level on its feet or you will pull it out of alignment with the bolts.

Ian

Do you think that is over sized ?

[Web Goblin]

Do you think that is over sized ?

No I dont think the material is oversized.
If you want a really sturdy machine then you cant really oversize the frame material, within reason I might add. Box section steel itself isnt really that strong unless you start going into heavy wall thickness stuff and as Jazzcnc has said getting your construction right to start with will make all the difference and would save you £800 on machining.

Ian