Stell frame cnc 1500X1000. Adjustable table your opinion please

[Boyan Silyavski]

Hi Dean,
First i want to thank you for the help with the machine we talk about that i am building for a friend which wouldn't be possible without your kind help.

I absolutely agree with what you say. I wouldn't want to mislead somebody. I am always speaking in relative terms here, meaning having in mind DIY machines, with best possible price functionality relation, designed to be multifunctional, mainly for wood and for the occasional aluminum job.

That is why i said it will be good if the design is not copied but adjusted to the particular needs. So let me clear some points about the specific design, not to you i mean , cause i kn ow you know it, but to those who read:

-Its meant for wood and plastics. Its meant also for aluminum but only when additional bed is fixed to raise the job
-its meant for deep 3d jobs mainly and Z axis travel -170-200mm
-Its meant for a trunion table to fit for aditional axis for 3d jobs
-its meant if need arises for a removable plasma water bed to be fitted for occasional jobs.

In other words its meant to be all type of machine, so certain sacrifices has to be accepted.

Silyavski think Your fooling your self if you think you won't get any resonance, Even machines built from Cast iron get resonance so you have zero chance of getting None with hollow Steel structure.!! . . . . . Yes it will be less than machines built with thinner material or of lesser construction but I guarantee you'll get resonance which shows at the tool when cutting slightly deep in aluminium and definitely in steel.

That is exactly why the frame is overbuild and a small spindle is used

Also what's the point of going to all the trouble of building machine that doesn't deflect more than 0.01mm only to use a bed material that will deflect more than an elastic band.??? . . . . Waste of time doing all your doing if your going to use MDF in any part of the bed other than has a spoil board.!!
Even then for any kind of acceptable accuracy you'll have to surface it for every Job.!!

I told that to the friend i am building the machine for. In any case, the machine will have 20mm aluminum sheet bed. Over the aluminum 10mm sacrifitial hard phenolic plastic sacrifitial layer. Over it when necessary will be fitted solid 100mm high block of MDF, ply wood or wood, and yes it will be resurfaced each time, i told him so. So basically nothing would flex there. you misunderstood me because of my English, the machine will have 20mm aluminum bed at least,ribbed where necessary, not MDF!

One more point regards adding stiffeners at a later date.?? . . . .WHY . . . when it can be done at the beginning. When ever you weld you have risk of heat distortion so it's not a good idea to be doing this at later date.
Also has most who have built a machine will know and back me up on ounce you have started using the machine you'll never stop to do even simple things let alone major upgrades like welding in stiffeners. . . . . It's known fact if you don't do all the planned things before powering up machine they'll never get done ounce it's working. . .Lol

You couldn't be more right. Thats the truth. My smalll cnc has 2 flimsy bearings and i cant find the time even to dismantle and tighten, as i dont stop it at all.
So I believe it would not be necessary at all. Just said it to remind that if a mistake is made with the design, can be fixed later when testing the machine.



So in conclusion/my conclusion i mean / , if maximum flexibility and at the same time rigidity for heavy duty aluminum jobs is wanted there are only 3 ways to go:
- Make a specific purpose machine from the beginning like Jonathan did for his friend, with removable bed
or if larger machine is desired:
-make a machine similar to how Dean does them, with removable adjustable bed and bottom frame structure
-make a machine the way i propose and use additional bolted beams to raise the bed or lower it, look at the picture below
In these both cases, at the end the material we use is roughly the same. main point in my design being limited space, so the legs can be removed without compromising the integrity of the design and having to redraw it again.



Of course that design can be further developed with cost savings in mind. For example the middle 2 beams from the lower bed can be made dis-mountable, so they can be used for the upper bed and so on... Look picture below.

Thats what i like about the constructive discussion. makes me think and develop. The idea of the removable 2 beams just made me realize what savings that would be on my next 1250x2500 design