[BriceO]

Hi,

I'm currently building a CNC router of 1.8x1.2 meter to cut wood (and probably test aluminium).
I use profile 8 series and 20mm aluminium plate, 4 NEMA 23 with a gecko G540.

Any comment or suggestion is welcome.

Thanks.

[wizard]

The general form isn't too bad, but do consider the use of gussets, corner braces and tie plates at many of the joints. In some places it might be better to use Steel plates if for no other reason than the material is much cheaper.

[BriceO]

Thanks, it's a good idea. I wanted to use this type of screw as it could reduce cost of having 4040 corner but to screw two profile together some holes have to be made .

[DeanR181]

Hi,

I'm currently building a CNC router of 1.8x1.2 meter to cut wood (and probably test aluminium).
I use profile 8 series and 20mm aluminium plate, 4 NEMA 23 with a gecko G540.

Any comment or suggestion is welcome.

Thanks.

I was going to say exactly the same as Wizard. Put as many corner gussets at all angled connections as you can afford. Just the slightest chatter from an unbraced corner will drive you nuts.


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[BriceO]

Thanks for your comments, I will add as much as I can.

Is there anything else that I should consider? Any criticism is welcome

If everything seems to be ok, I will begin to build it

[wizard]

Thanks, it's a good idea. I wanted to use this type of screw as it could reduce cost of having 4040 corner but to screw two profile together some holes have to be made .

Just to be fair, I'm generally biased against Aluminum extrusions in machine build largely for the cost but also due to some mechanical problems that the offerings have.

The pictured assembly is one of those problem areas in my opinion. That particular screw joint isn't bad for rough assembly of a frame but I have seen them fail after extend usage. Alone the joint will loosen up over time on anything that is loaded to any significant degree. This can happen via the screw stretching, the aluminum webs deforming and simply via the tension in the screw loosening. Depending upon the damage it can be hard to fix properly. One more thing, a extruded section that has more than one hole to bolt into does have some advantages with this sort of connective method in that you have more bolts spread out to control the applied torque.

Now note this is what I have seen in industrial usage of T-Slotted aluminum extrusions. However any part of the machine that can put a twisting moment on the joint is at risk in my opinion. Especially joints that might see high loads during some sort of machine crash.

As you note the cost of system components from the extrusion vendors is pretty high (another strike against extrusions). However you don't need to use those high cost components if you don't want too. One can buy aluminum sheet or steel sheet (much cheaper) and cut to size Gussets and tie plates that can go a very very long ways to making these joints more sound structurally. Actually you don't even need to buy sheet as you can by hot or cold rolled in widths of 6 inches or so. Yes a bit extra work and it does require some tools you might not have at the moment. You would still need to buy corner brackets for a few key areas on you machine or redesign to use cheaper materials. You would also still need to buy T-Nuts and T-Bolts but you can control costs this way.

Oh by the way just because I'm biased against T-Slotted extrusions doesn't mean I completely dismiss their usage. My big concern is the cost, especially once you factor in all the goodies and the structural issues that some often over look. The flip side is that Extrusions are great for people that don't have much of a shop and really don't want to focus on building up a shop.

One final thing I missed from when you first posted:

Putting the gantry linear rails on the top and bottom of the gantry beam might not be the best approach. It really depends upon how parallel the surfaces are and how much flex the saddle allows. While extrusions can be pretty good generally, it is completely possible that the two surfaces will not be parallel enough to prevent binding. In is also a bit more difficult to get the linear rails aligned otherwise and makes the gantry saddle a bit more complex. Finally you also loose a bit of under the beam clearance. On the flip side it is good to keep the linear bearing physically separated to resist torque from the Z axis.

[DeanR181]

Thanks for your comments, I will add as much as I can.

Is there anything else that I should consider? Any criticism is welcome

If everything seems to be ok, I will begin to build it

I don’t like to criticise as everyone has good and bad ideas. It’s just good to learn from others mistakes and research. It took me along time to fix on a design which is similar to yours but I chose to have short sides where the linear rails run as I didn’t want any sideways movement. I see with your design that you have high sides and you mention you want to cut aluminium. If I were you, I would reconsider the high sides and see if you can lower them to reduce any chance of movement. The stiffer the frame, the happier you will be. I have attached a photo of my machine so you can see the difference. Hope this helps. Attachment 387038


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[BriceO]

I don’t like to criticise as everyone has good and bad ideas. It’s just good to learn from others mistakes and research. It took me along time to fix on a design which is similar to yours but I chose to have short sides where the linear rails run as I didn’t want any sideways movement. I see with your design that you have high sides and you mention you want to cut aluminium. If I were you, I would reconsider the high sides and see if you can lower them to reduce any chance of movement. The stiffer the frame, the happier you will be. I have attached a photo of my machine so you can see the difference. Hope this helps. Attachment 387038


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Thanks for your comment, very nice machine! What do you cut ?

Maybe I'm wrong but I've read somewhere that it is stiffer to have high slide and short side plate. This is the reason why i choose to do it like that. The sideways movement aren't more important if you have longer side plate? I could have misunderstood something.

[BriceO]

Just to be fair, I'm generally biased against Aluminum extrusions in machine build largely for the cost but also due to some mechanical problems that the offerings have.

The pictured assembly is one of those problem areas in my opinion. That particular screw joint isn't bad for rough assembly of a frame but I have seen them fail after extend usage. Alone the joint will loosen up over time on anything that is loaded to any significant degree. This can happen via the screw stretching, the aluminum webs deforming and simply via the tension in the screw loosening. Depending upon the damage it can be hard to fix properly. One more thing, a extruded section that has more than one hole to bolt into does have some advantages with this sort of connective method in that you have more bolts spread out to control the applied torque.

Now note this is what I have seen in industrial usage of T-Slotted aluminum extrusions. However any part of the machine that can put a twisting moment on the joint is at risk in my opinion. Especially joints that might see high loads during some sort of machine crash.

As you note the cost of system components from the extrusion vendors is pretty high (another strike against extrusions). However you don't need to use those high cost components if you don't want too. One can buy aluminum sheet or steel sheet (much cheaper) and cut to size Gussets and tie plates that can go a very very long ways to making these joints more sound structurally. Actually you don't even need to buy sheet as you can by hot or cold rolled in widths of 6 inches or so. Yes a bit extra work and it does require some tools you might not have at the moment. You would still need to buy corner brackets for a few key areas on you machine or redesign to use cheaper materials. You would also still need to buy T-Nuts and T-Bolts but you can control costs this way.

Oh by the way just because I'm biased against T-Slotted extrusions doesn't mean I completely dismiss their usage. My big concern is the cost, especially once you factor in all the goodies and the structural issues that some often over look. The flip side is that Extrusions are great for people that don't have much of a shop and really don't want to focus on building up a shop.

One final thing I missed from when you first posted:

Putting the gantry linear rails on the top and bottom of the gantry beam might not be the best approach. It really depends upon how parallel the surfaces are and how much flex the saddle allows. While extrusions can be pretty good generally, it is completely possible that the two surfaces will not be parallel enough to prevent binding. In is also a bit more difficult to get the linear rails aligned otherwise and makes the gantry saddle a bit more complex. Finally you also loose a bit of under the beam clearance. On the flip side it is good to keep the linear bearing physically separated to resist torque from the Z axis.

To solve these mechanical problems, do you thing is it enough to add angle steel, gussets,... ?
Do you think there is a better design to solve this problem?

I choose the extrusion way, because I don't have tools to build a steel CNC and I don't really want to buy tools to cut, weld steel,... as I will probably not work with steel later.(And I'll probably move )

I putt the gantry linear rails on the top and bottom because I have less leverage on the z axis (under beam clearance is take into account). You're right it will certainly be more difficult to align them. But I think it's better to do this way than have more leverage. Maybe I'm wrong!

Thanks a lot for your advice!

[DeanR181]

Thanks for your comment, very nice machine! What do you cut ?

Maybe I'm wrong but I've read somewhere that it is stiffer to have high slide and short side plate. This is the reason why i choose to do it like that. The sideways movement aren't more important if you have longer side plate? I could have misunderstood something.

There are so many ways to build a frame, and all I am trying to emphasise is to make the machine as stiff as possible. Having high sides of the gantry needs thick side plates but having high frame sides where the rails seat needs to be braced a lot. The longer the span, the more vibration will be noticed. Short and thick does the trick.


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[DeanR181]

There are so many ways to build a frame, and all I am trying to emphasise is to make the machine as stiff as possible. Having high sides of the gantry needs thick side plates but having high frame sides where the rails seat needs to be braced a lot. The longer the span, the more vibration will be noticed. Short and thick does the trick.


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Forgot to mention that I cut hardwoods, acrylic, aluminium and a lot of marine plywood.


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[CNC_Josh]

Hi BriceO,

your project looks very interesting. Is there any progress ? I am thinking about building a similar CNC with a smaller cutting area of roughly 1000 mm x 600 mm.

Best regards, Josh

[millhouse_]

Hi. I like the design. It keeps the gantry lighter (smaller sideplates), stronger and with the rails on the frontplate of the z-axis gives great depth. I'm currently building a similar one. But not that large. 1000mm x 800mm:

[fretman_2]

Millhouse_...where are you purchasing your extrusions?

Hi. I like the design. It keeps the gantry lighter (smaller sideplates), stronger and with the rails on the frontplate of the z-axis gives great depth. I'm currently building a similar one. But not that large. 1000mm x 800mm:

[millhouse_]

@fretman_2

I don't remember where I bought the profiles. It was a german online shop. The profiles are 80x80 Nut-8 schwer and 80x40 Nut-8 schwer. I "think" the shop was http://www.alcom-international.de but i can't promise for sure.

[millhouse_]

Today I found this one on ebay and love the design:


What a monster!

[fretman_2]

Can you provide a link to the eBay post?

[fretman_2]

Thanks!!

@fretman_2

I don't remember where I bought the profiles. It was a german online shop. The profiles are 80x80 Nut-8 schwer and 80x40 Nut-8 schwer. I "think" the shop was http://www.alcom-international.de but i can't promise for sure.

[wizard]

To solve these mechanical problems, do you thing is it enough to add angle steel, gussets,... ?
Do you think there is a better design to solve this problem?

Generally it doesn't take much to improve these joints mechanically. What is best to use at anyone joint depends upon the joint and machine of course. If the extrusion only has one or two screw bores in the extrusions you almost always need to use something to reinforce the joint. Flat plates can be good enough in some instance and in others you may want a right angle corner bracket.

Note too that in some cases your joint reinforcements can also be leveraged for other purposes. For example in a bench top machine you can have joining plates at the four outside corners to keep the frame ffom racking. At the same time these plates can act as levelling screw plates.

I choose the extrusion way, because I don't have tools to build a steel CNC and I don't really want to buy tools to cut, weld steel,... as I will probably not work with steel later.(And I'll probably move )

That is the one huge advantage of aluminium extrusions, often you can get the stuff cut to size with very good precision.
The machine can then be put together with hand tools. This can be accomplished with steel if you live in an area with decent fab/machine shops but your costs are likely to be a bit higher. With steel you would also have to work a bit more on specifying exactly what you want fabricated.

I putt the gantry linear rails on the top and bottom because I have less leverage on the z axis (under beam clearance is take into account). You're right it will certainly be more difficult to align them. But I think it's better to do this way than have more leverage. Maybe I'm wrong!

Thanks a lot for your advice!

As for the gantry there are a million ways to skin this cat. I tend to prefer designs that are ""easy"".

Dave

[millhouse_]

@fretman_2 It's sold, but heres the link: https://www.ebay.de/itm/CNC-Fraese-P....m43663.l10137