Tiddy CNC.

[TonyD]

Different question. Into the much loved world of mechanical and forces. :)

I'm planning on using a Y axis gantry thats made out of a 4 pieces of 15mm Ali plate, the front part has a slot as per previous discussions to allow the moving Z Axis to connect to the Y Axis screw.

Key question on my mind right now is the length of the block which will support the gantry onto the rails relative to the center point of the spindle.
As shown below, it feels right to me that the gantry support block should at least extend to the spindle center point, no maths to back this up but without this dimension it feels to me like the gantry would be out of balance relative to the forces acting on the spindle. Any comments? Only concern is that the block is 260mm in length right now and thats a fair amount of X Axis travel I'm eating up. Naturally the klunky design of my Z Axis, which was made with a press drill only is not very compact and thus adds to the problem. I'm comfortable with the design as is as job #1 when Im competent with the machine will be to make a new better Z Axis but thats for the future. Comments welcome. Tony.
PS. I know there's going to be a side plate etc, I'm just looking at this one component now, happy to take feedback an anything else though.

[Jonathan]

Only concern is that the block is 260mm in length right now and thats a fair amount of X Axis travel I'm eating up.

The deflection due to the bearings on each axis is inversely proportional to the linear bearing spacing squared (which is obvious from the formulas in the Hiwin linear guide datasheet), so increasing the spacing by a relatively small amount can make a big difference. That's why it's important to space the bearings out as much as you can afford to, assuming the part they are mounted on is strong - which currently isn't the case as it's just a plate which would benefit a lot from a triangular/trapezoidal piece on the side. 260mm is not bad...probably not much point going above 300mm as other parts of the design will have a greater effect on the overall stiffness.

[TonyD]

Folks. I've been wondering about some more design concepts and I thought I'd ask for some advice. I should start out by saying that my goal is to orient the machine at a relatively steep angle but as I've played around with frame concepts I have no idea how to approach that yet. I've found that one step at a time suits this pursuit in my mind…So I'm hoping for some vertical but may go for regular horizontal. The basic parameters are a 1500mm X, 1100mm Y and currently a Z with a conservative 150mm, plenty scope for changing the Z once I can make some parts.

So. I have considered three basic options and presented them from a front view and my basic question is how to place the rails and screw so that the Y Axis gantry is best supported with minimal adverse forces being introduced?

Option A is the most conventional I think? Option B has the virtue that the screws are under the machine, need to take more care over a frame that allows this. Option C seems to put a lot of force on one side of the linear bearing block. Any suggestions, comments welcome. Sorry it’s not in CAD but I'll flesh out the winner into a more detailed model later. Thanks. Tony.

[TonyD]

Next Steps.

Hello all. I've made some progress lately. The control system is nearly finished (bar some limit & home switch mounting), and tested on The Z Axis which is just about there. The Y is nearly there, just need to mount the stepper which leads me to the frame. I have looked at many frame's and tried to come up with my own. There were three features I was looking for

i) I wanted the frame to be robust enough to support cutting aluminium
ii) I wanted to be extend the rails over one end for over sized jobs (thanks jazz)
iii) Thinking of the over size issue, I wanted the frame to be tall enough that I could mill out the lock on a door.

The machine will be inside so I'm looking for welded frame sides with bolted cross members. I also decided I didnt want the hassle of a moveable bed, frankly I want to get the thing built (this year), so left 110mm of Z travel from the tip of the spindle, I think thats enough for general use? I also decided at this stage to have two rails (in orange) welded to the sides as support for the drop-in welded bed frame (purple). With the exception of the top rails, everything else is 50x50x3. I havent costed it yet, will probabily have to revise on that basis alone but wondered if there was any feedback on the design so far. Thanks.

[Boyan Silyavski]

Next Steps.

Hello all. I've made some progress lately. The control system is nearly finished (bar some limit & home switch mounting), and tested on The Z Axis which is just about there. The Y is nearly there, just need to mount the stepper which leads me to the frame. I have looked at many frame's and tried to come up with my own. There were three features I was looking for

i) I wanted the frame to be robust enough to support cutting aluminium
ii) I wanted to be extend the rails over one end for over sized jobs (thanks jazz)
iii) Thinking of the over size issue, I wanted the frame to be tall enough that I could mill out the lock on a door.

The machine will be inside so I'm looking for welded frame sides with bolted cross members. I also decided I didnt want the hassle of a moveable bed, frankly I want to get the thing built (this year), so left 110mm of Z travel from the tip of the spindle, I think thats enough for general use? I also decided at this stage to have two rails (in orange) welded to the sides as support for the drop-in welded bed frame (purple). With the exception of the top rails, everything else is 50x50x3. I havent costed it yet, will probabily have to revise on that basis alone but wondered if there was any feedback on the design so far. Thanks.

Hi Tony,

I am currently doing my first real build so take my word with a grain of salt but i spend a lot of time considering, redesigning, calculating and so on...

So looking at your idea i could not help but share my thoughts, even if they are quite influenced of my current design. I hope it helps though. Sorry, i dont mean to hijack your thread

What i don't like at your idea is that the diagonals actually don't reinforce the profile where the rails are.

I went on my design from 60x60x4 to 100x100x3 as i was faced by the same problem as you, great lengths and a lot of cutting and soldering.

So here i just twisted a bit my design to accommodate it to your measures and needs. Much less rails, much stronger, much simpler to execute and cheaper, as much less weight. I would like to hear what others say but i am quite sure is strong enough for routing aluminum, not scratching.

All in all there are 17.8 meters of 100x100x3 x 9kg per meter = 162 kg






My thoughts about bead and gantry:

I made my gantry design to be from 2 pieces of 100x100x3 soldered together, just to have in mind when considering the following.

For me to build a machine and later to upgrade it is not OK, i mean what you say for your Z depth. Please take a look below for my solution to this.
My Z plate is 500mm long. My useful Z travel is 200mm, but i will limit it to 180mm. However the idea is the bead to be deep but over it to have a cheap wooden structure 100mm high to serve as a removable table. So now the working area is raised and there the aluminum or normal jobs will be cut. The table can be made from a couple of MDF sheets glued together or whatever scrap. Even from ribbed inside wooden structure to weight less and easy removal.

So with everything soldered i would have quite versatile machine/ in fact its not for me the machine/ .


Of course you can add 2 x 1600mm rails and make the bed removable, but i don't see a reason for it as you can remove the wood bed instead and keep everything much stronger. I believe on my design there is no need to add anything or change anything, as even it looks simple is thought to withstand forces from all directions. The only thing that comes to my mind that can be bettered is to place everything at asymmetrical distances to avoid frame vibrations further



If you use Sketchup i will be happy to send you the file with the table i draw with your dimensions so you can play with it.

I hope that will give you some ideas .

PS. One key part of that design that i forgot to mention is that there are plates that fix the rails supporting beams. I will lasercut them, but they can easyly be fashioned from something else. They play the role of not permitting to the beams to vibrate left right, looked from front and also seal the profile end.

[TonyD]

Silyavaski. Thanks for taking the time to modify your model with the dimensions I am looking for. I have to say your frame design does look so much more solid than the one I designed. The one one constraint I have is that I need to move the machine in the house so I cant have it all welded. I can see though that if I made the cross members you have proposed as bolted rather than welded, this might work. I'll have another look at the Z height and see what that means for the rail height. Thanks again. Tony.

[CraftyGeek]

Tony - it may be worth seeing if you have another local steel yard near you. My local supplier charge £4.1 +VAT per meter for 50x50x3 (£147.60 for 30m) as a base price & charge less than that if you order a reasonable quantity. I also get them to cut some of it to size for me - depending on quantities, they charge 50p per cut or less...this means I can fit it in my car & pick it up myself removing the delivery charge as well as saving me time cutting stock to size.