[bensaad]

hello guys
i wanna your opinions and suggestions for this cnc frame base in the picture attached bellow

[jaguar36]

What are you going to use it for? How are you attaching it? How do you plan on assembling it? Each red tube is going to weigh more than you can lift.

Without knowing much it looks like you have an awful lot of steel in the red parts that are essentially just acting as a stand to hold up the grey parts. Assuming that amount of steel is within your budget, I would make the grey pieces, particularly the long rails as thick and as big as possible (A couple of gussets would help tremendously as well). Then make the red parts way, way thinner, probably more traditional legs with diagonal braces.

[bensaad]

Hi jaguare,thanks you for your reply
-the cnc i am going to build it would be used primarly as a router for wood ,plastic and aluminium or maybe as a plasma cutter,didnt decided yet ,i wanna make it to be valiable for any purpose ,and it would be weldmelt assembled

-I don't have any steel on hand and haven't checked the cost yet, but I changed my plan in hopes of cutting the cost down a bit
by replacing the red tube with 250 x 150 x 5 mm and the gray tube with 150 x 100 x 3 mm because this is the thickest wall I found available at the moment from the supplier.

-I also changed the design by reducing the number of gray tubes as shown in the attached photo.

the total weight of the frame would be around 530kg

[peteeng]

Hi Ben - Its sort of overcooked for what you describe you want to do. You have to consider how you will move this and assemble it. The legs are usually bolted onto the machine bed ie you set up the legs then land the bed on top. The bed is levelled by adjusters or by the legs feet. In terms of assembly your hurdles will be keeping the bearers flat and level. Welding this sort of structure and keep it flat is a bit tricky. Then there is the issue of stress relief of the structure so when you machine the rail and rack lands they remain flat and straight. The ends of the large tubes need to be sealed as tubes like that vibrate and create lots of annoying noises. A machine that size I would consider to be made in modules that can be managed and bolted together vs a monolithic weldment.

Large RHS sides are rarely flat. They will be cupped or crowned. So the tops will need to be machine flat. How will you do this? and do you know about stress relief? Peter

[joeavaerage]

Hi,
overall I like it.

I know that 300 x200 x9 is a industry standard size but can you get any? That section is listed by steel suppliers in New Zealand for instance, but all of them supply on indent,
ie its got to come from overseas. That is likely slow and there could easily be a minimum order value which would put it out of reach.

I can get 100 x 100 x 9 no trouble, whether I buy direct from a steel supplier in 8m lengths or in smaller lengths from architectural steel manufacturers whom commonly use and stock
this size.

The last question is about thermal stress relief. One of the main reasons that puts hobbyists off welded steel frames for CNC is that the residual stress from welding will cause the structure
to move for many years after construction, especially if you machine a surface say to make it flat, and it can distort quite alarmingly. The gold standard for stopping this is thermal stress relief TSR.
The parts are placed in an oven, taken up to 650 ⁰C, held for a while and then a long slow cool down period. The problem will be to find a heat treater who has a big enough oven to put it in.
The second issue is cost. The last time I had some done (COVID era, say 2 years ago) was $6NZD/kg (approx $4USD/kg).

There is another alternative called Vibratory Stress Relief, and is much cheaper and not size restricted, but its less effective than TSR especially in thin sections such as RHS/SHS steel.
I had my cast iron axis beds Vibratory Stress Relieved, it saved me nearly $1800NZD!

If you look at Jaguar's build thread you'll see that he is bolting every thing together and thereby avoiding any welding which would require TSR.

I presume that your intention is to machine the rail beds that they are flat? Your machine is large and so I would suggest that you check to find a shop that can machine such a sizeable
frame and the cost of it. I suspect the cost of machining will make you weep. No matter how long I do this (CNC) getting stuff precision machined (when I cant do it myself) always makes me weep
with the cost!

Craig

[joeavaerage]

Hi,

by replacing the red tube with 250 x 150 x 5 mm and the gray tube with 150 x 100 x 3

To be honest I think reducing the wall thickness is a mistake, I would go with the thickest wall you can get.
As I posted earlier 100 x 100 x 9 is easy to get, so I would use that as your standard throughout. The next size up is 200 x 200 x 9, but I cant find any here (NZ). The steel suppliers
list 200 x 200 x 9, 200 x 200x 12 and 200 x 200 x 16, all on indent. If I was going to the trouble and expense of ordering steel on indent I would insist on 200 x 200 x 16!!!! No messing
around.

Craig

[routalot]

I would have concerns about that second version's spoilboard being the bottom of a trough.It will be more difficult to position sheets and will hold dust and shavings very well.Are you planning to add adjustable feet to level the machine or will you use shims beneath the frame?

[joeavaerage]

Hi,
does it matter that the machine bed be level? What matter if it slopes uphill or downhill a bit. The machine bed should be that rigid
that it stays flat whether it be level or not.

If you are concerned about chips and swarf not having a means of escape then leave a gap, say a couple of inches at either side to allow a place for the swarf
to drop out.

My recommendation would be to have the spoil board sitting atop the multiple cross members and that they all be 100 x 100 x 9, and the upstand sections at each side be of the same material (100 x 100 x 9).
Rather than weld the cross member to the upstand sections I would bolt them. That would mean that you don't require TSR for the entire frame. It would also mean that you could machine
both top and bottom surfaces of ALL the sections BEFORE you bolt them together. That would save bigtime on the machining costs.

Craig

[bensaad]

My recommendation would be to have the spoil board sitting atop the multiple cross members and that they all be 100 x 100 x 9, and the upstand sections at each side be of the same material (100 x 100 x 9).
Rather than weld the cross member to the upstand sections I would bolt them.

hi craig
but how do i bolt the crossmember part toth side sections ?

[peteeng]

Hi Ben - You say the machine needs to be useful for any purpose. This could be an error. A machine that is designed as a general machine will mean its overdone in many areas. Overdone in engineering and overdone in cost. For instance look at plasma machines and they are very lightweight and very dirty. This contradicts the purpose of cutting timber for instance in which it needs to be clean and sturdy (but not massive). So you need to be clear what the machine is for (eg why is this thing so big?) and you also need to move onto the gantry and other bits as they are all connected....Lots for you to do yet, more rabbit holes to fill... Peter

[bensaad]

HI
After reading all the comments above and taking into consideration the suggestions provided
I came up with this design in the pictures attached below
it aslo reduce the qty of steel used and the cost too
2 pieces of 250X150 tube and one piece 150X100 ,6 meter lenght
about the machine purpose peter suppose it would be used as a router

thanks for you all
bensaad

[peteeng]

Hi Ben - A "router" does not define what your going to use it for. Is it for flat sheet work, furniture? duct work, cabinet making? etc etc. Each of these require a slightly different operational design... also I don't think you want chips falling on the floor. Build a good dust extractor system and close the sides. Sweeping up floor dust gets tiresome after a while... and a machine like this should make lots and lots of dust!!

I'm assuming this is for 8x4' sheet work? If so this means its a front loader with the long side going into the machine. Usually, it's an advantage to load the short side into the long side. ie it would be a column machine with low mounted rails. Have you considered this in your design? If you are loading thick 8x4 sheets they are really heavy and you will need a feed in table. Then to get the parts out you will have to lean over the high tube... Also if doing sheet work are you going to use vacuum to hold it down? This has to be thought thru as well.... Peter

[bensaad]

If so this means its a front loader with the long side going into the machine. Usually, it's an advantage to load the short side into the long side. ie it would be a column machine with low mounted rails. Have you considered this in your design?

hi peter
did not undestand you

[peteeng]

Hi Ben - If you pick up a piece of ply or mdf by yourself on the short edge and try to load it into this machine you will find it difficult. Sheet loading is easier if you load on the long side. You will need a feed in table. So you place the sheet on the table which is the same height as the machine bed, the feed in table will be on castors. Then slide the sheet into the machine. Is this a 8x4" XY size? Attached is an image of a conventional 8x4 router. It has "low" rails and a gantry on columns. This allows side loading and end loading. Side loading is preferred as it uses less loading space and is easier to load and unload pieces.

Your design is stiff but if your loading manually all day it will become a chore. Just something to think about. If your only going to do the occasional 8x4 sheet then make the machine a half sheet machine. Considerably less cost, less space required etc etc. You can still do a full sheet just need to step it through.

Thats why the machines purpose is important in the design phase. No good having an 8x4 machine if your only going to make bread boards or guitars... Everyone wants a "big" machine but one day you will wish it was smaller. Especially the first time you have to move it. Peter

re machine design / assembly logic.

This is a big machine and will have dead weight issues when being assembled. It will be difficult to assemble unless you have an overhead crane or forklift. You do need to design the machine, so it is assembled like a pyramid. Lay out the legs then the frame then the base etc etc. Each bit is laid on top of the other bit. I see some of the cross members are bolted underneath the long members - rethink this so each step is on top of the last step. Life will be much easier that way for assembly and for adjustment/alignment of the parts.

Re- legs - You have three "legs" on your machine. Only use two, placed inboard from the ends. If you have FEA or simulation you can figure out where these are placed so the table remains flat. Usually about 25-30% inboard.. Saves weight, and $$$.

[bensaad]

Thank you, Peter. As a beginner, I have learned a lot from you. You always give us your valuable information
following your sugestion :
- Each part is laid on top of the other part beginning by the legs

i modified the design a bit as the images attached
- instead of placing cross members tube in the bottom of the big tube section i moved them on top and bolt them that would make also sheet loading easier as you said
- added a 50X20mm flat bar to install linear rail and the rack,
i choose 20mm thick to side install the rack(i saw someone did it in youtube) ,it will be flat machined ,the problem is how i would attach it to the tube by welding or bolting

- about 3 legs vs two ,the supplier sell the steel tube by pieces (6 meter lenght) ,the machine leg lenght is about 2 meter then no cost saving Either way I have to buy two piece
- also i read in one of your post , using Braze welding does not need stress relief rectify ,if this is better then bolting? i have a braze welding equipment .
- about the machine assembly ?i have a forklift too.
what your thought in this design and thank you in advance

[peteeng]

Hi Ben - Looking good.
1) braze welding - MIG or torch? either is fine if your good at it.
2) The flat for the rail to be machined, you would braze that on. Since you can braze, braze everything that you need to
3) I would consider making the 250x150x5 RHS smaller. The frame is massive for what you have intended and although you have a forklift, weight does matter in terms of $$$. Consider that many aluminium extrusion machines work really well at this size, yours still will be stiffer and heavier than those using less steel
4) Your models do not include the corner radius of the sections. Find out what that is because its quite big and you will need to model that for bolt clearances and placing things at the edge (which you can't due to the radius)
5) also you need to find someone who can machine the rail and rack lands. The way you have it it can be faced and side cut in one setup. Very good.

Peter

[peteeng]

Hi - We all need one of these!

https://youtu.be/M22SIZ1OIhI

[peteeng]

Hi Ben- You will mainly set up jobs in the middle of the machine so I suggest a middle longitudinal as well. So down a size on the outer longs and one more up the middle. Plunging loads are high and big jobs will deflect the middle down a bit. A central support will help as well. Peter

[bensaad]

hi petter and thanks

-I down the size of the red tube to 200 x 150 mm. In my humble opinion , the machine should be kept high off the floor as well.
Going less than this size makes the machine closer and more susceptible to dust i think.

-i added a middle longitudinal support(200x150mm) as you suggested but i am confused about the size and the way i added it

-the corner raduis of 200x100x5mm is 10mm,and for the 100x100x4mm is 8mm
i got the information from this website
https://www.smartbuild.uk.com/post/r...ius-dimensions

- added a 200x100x5mm for the x axis gantry

-for the assembly of the machine, I see using the bolt in all part except the flat bar i will brase weld it

the new design shown in images attached bellow

what your thought petter

thanks in advance

[bensaad]

Hi
I made a mistake
The big red tube is 200x150 mm not 200x100
As I mentioned in the images,sorry