[bensaad]

hello
i am a newbie to cnc design and wanna know your opinion about the cnc router design in the pictures attached bellow
iam using hrg20 linear rail and 1.25 module rack ,nema 23 425oz stepper motors in all axis
the frame build from 80mmx3mm square tube
and thanks in advance

[peteeng]

Hi Ben - Sorry - no pictures attached try again via the go advanced at the bottom of the panel. Peter

[burs]

Hi Ben - Sorry - no pictures attached try again via the go advanced at the bottom of the panel. Peter

The images are now visible.

[peteeng]

Hi Ben- In principle the concept is good. 3mm is a bit thin at the bearings and track so a doubler or different tube is the go there. Are the tubes aluminium or steel? Peter

[bensaad]

hi peteeng and thanks for your reply
the tube is steel 80mm*3mm

[bensaad]

or maybe this design is better?
need your advise

[peteeng]

Hi Ben - I would not use the construction extrusion. Too costly and not very stiff. Your original design is simpler and just needs local tuning. The less parts and simpler the design the better. KISS Peter

[bensaad]

Hi Ben - I would not use the construction extrusion. Too costly and not very stiff. Your original design is simpler and just needs local tuning. The less parts and simpler the design the better. KISS Peter

whats you mean by local tuning?

[peteeng]

Hi Ben - 3mm is a bit thin at connections so use a 3mm plate as a doubler to make it thicker. Since the original design was steel use 3mm steel to get 6mm total at areas needed. Peter

[joeavaerage]

Hi,
for the marginal extra cost of thick walled rectangular tubing I would go for the thickest wall you can find, probably 6mm, but not impossibly 9mm or 12mm.

There is no substitute for machine stiffness, so I would not consider 9mm or 12mm excessive.

Craig

[joeavaerage]

Hi,
the commonly stocked SHS (thickest wall) here is NZ is 75mm x 75mm x 6, the next size up is 98mm x 89mm x 6mm and thereafter its 100mm x 100mm x 9.
All the SHS in 10mm, 12.5mm and 16mm wall is available on indent order only. Given that NZ is so far away from anywhere, indent order is somewhat of a barrier.

Craig

[peteeng]

Hi Ben - 80x80 is a bit narrow to place two rails on and have room for a drive. That is if you place the drive on the same face as the rails. 80mm is narrow for say two 20mm rails anyway. 100mm or 120mm would be better. My medium size router uses a nominal 110x90mm fabricated section with the rails on the 110mm face. My latest designs use a 200mm top and 120mm deep section. The rails are on the top not the front. This makes organisation of the cars easier (in my view that is) Once you start putting in cars and a saddle etc other issues will arise to solve. Peter

edit - You have modelled the sections with sharp corners. Steel sections have a big radius in the corners that you will need to model so you don't put things like rails or racks on the edges like in your model. These radii take up a lot of space....

[bensaad]

hello peter and thanks for your advice
for x axis i plan to use 100x50mm squre tube because 80x80 is a bit narrow to place two rails as you say
and for the y axis what if i add 2080 vslot profile to simplifying linear rail and rack installation using t nut,Will this have an effect on the rigidity of the machine?
for the corner radius of 80mm square tube i think its 3mm,i can send them to local turner for rectification and making it flat

[bensaad]

hello
the max wall thikness i found is 4 mm

[bensaad]

Hi,
the commonly stocked SHS (thickest wall) here is NZ is 75mm x 75mm x 6, the next size up is 98mm x 89mm x 6mm and thereafter its 100mm x 100mm x 9.
All the SHS in 10mm, 12.5mm and 16mm wall is available on indent order only. Given that NZ is so far away from anywhere, indent order is somewhat of a barrier.

Craig

the max wall thikness i found is 4 mm

[joeavaerage]

Hi,
where abouts are you?

All the standard steel sections list 75x75x6 and 89x89x6 and 100x100x9. Keep looking. 100x100x9 is a favourite of engineers/architects for columns in houses.
Try companies that specialize in architectral steel fabrication, you will find thick walled SHS and RHS.

Craig

[peteeng]

Hi Ben - Construction extrusions are convenient (anything convenient has a downside) but they are expensive and very poor structural elements when compared to std extrusions or std SHS/RHS steel. See attached. You need to stay in the one universe I think. So stay in steel or aluminium world... Std Aluminium extrusions have square edges if that's what you want. There's lots of ways to solve various issues, you need to develop the design a bit more... eg if you use 3mm for the structural elements this is too thin for threads. So use a 6mm doubler (or backing plate as some say) that is threaded to match the bolt pattern. In this way you get local stiffness at hard points plus the thin bits are good for the global parts as this keeps the weight down. eg if you used a 100x100x3mm al square extrusion for the gantry then use a 20x6mm thick strip (AL or steel) and thread it to match the rail holes. Slide it thru the section and get a couple of bolts in and off you go. Al has the advantage that its easy to make things from, a cheap drill press, a jig saw some files and your good to go and it does not rust (my pet hate)

One thing to think about is what are you going to use the machine for? If it's for flat product, plastic and timber then the machine can be very light. If it's for aluminium then it needs to be very rigid...Peter

edit - regarding mounting rails on construction extrusion. Put bluntly it's not very stiff. Look at those thin edges your bolting too. I know its done but if you do the math you'll see that they flex quite a bit. Do it with a backing plate or thick tube and its much much stiffer and betterer....

[bensaad]

Hi Ben - Construction extrusions are convenient (anything convenient has a downside) but they are expensive and very poor structural elements when compared to std extrusions or std SHS/RHS steel. See attached. You need to stay in the one universe I think. So stay in steel or aluminium world... Std Aluminium extrusions have square edges if that's what you want. There's lots of ways to solve various issues, you need to develop the design a bit more... eg if you use 3mm for the structural elements this is too thin for threads. So use a 6mm doubler (or backing plate as some say) that is threaded to match the bolt pattern. In this way you get local stiffness at hard points plus the thin bits are good for the global parts as this keeps the weight down. eg if you used a 100x100x3mm al square extrusion for the gantry then use a 20x6mm thick strip (AL or steel) and thread it to match the rail holes. Slide it thru the section and get a couple of bolts in and off you go. Al has the advantage that its easy to make things from, a cheap drill press, a jig saw some files and your good to go and it does not rust (my pet hate)

One thing to think about is what are you going to use the machine for? If it's for flat product, plastic and timber then the machine can be very light. If it's for aluminium then it needs to be very rigid...Peter

edit - regarding mounting rails on construction extrusion. Put bluntly it's not very stiff. Look at those thin edges your bolting too. I know its done but if you do the math you'll see that they flex quite a bit. Do it with a backing plate or thick tube and its much much stiffer and betterer....

ok thanks
now if i go for the steel tube 100X6MM should i use the same profile 100X6 for all machine part table frame ,legs...or 6mm for the machine axis and thinerprofile say 3mm for the other machine parts

[joeavaerage]

Hi,
it depends on what sort of stiffness you want. If you want to cut aluminum then you want as stiff as you can get.....and that means 100 x 100 x 9, not 100 x 100 x 6.

By all means use lighter material for things like legs and stuff like that, but anything you want to bear cutting forces should be a stiff as you can possibly make it.

There is one certainty about CNC machines, there is no such thing as too stiff. Were you to go overboard someone might comment 'you could still do a good job
but with a lighter machine', but no CNC'er ever tires of an overbuilt machine, but tire immediately of an underbuilt machine.

Craig

[bensaad]

Hi,
it depends on what sort of stiffness you want. If you want to cut aluminum then you want as stiff as you can get.....and that means 100 x 100 x 9, not 100 x 100 x 6.

By all means use lighter material for things like legs and stuff like that, but anything you want to bear cutting forces should be a stiff as you can possibly make it.

There is one certainty about CNC machines, there is no such thing as too stiff. Were you to go overboard someone might comment 'you could still do a good job
but with a lighter machine', but no CNC'er ever tires of an overbuilt machine, but tire immediately of an underbuilt machine.

Craig

hi peter
why i planed for lighter machine because i have already the electronics part with nema 23 425oz stepper motor,But now I am confused if i can use these motors with such a rigid machine as you described or should i upgrade for nema 34 too

i pursached these motor because first i planed to build printnc cnc from threedesign but i found ballscrew not suited for large cnc 8X4 and high quality ballscrew are very expensive
but now i found this plasma cutter in alibaba and i liked its simple design and inspired me to build a cnc router like that