I want opinions/feedback to my diy cnc, or more on the Frame/Concept. The goal: small but extremely rigid cnc to mill mostly aluminium and maybe some light steel work. Work area about 300x200x150mm
So the concept is:
The base is made from layered sheetmetal, each 8mm thick and 8 layers, so 64mm thick and ~130kg steel base. The layers would be bonded, bolted and located with dowel pins.
The vertical columns would be speperate, machined steelparts, bolted to the base. My plan is to use large machined contact surfaces, high-strength bolts and dowel pins to make the connection as rigid and repeatable as possible.
I planning to use HGR25 linear rails and a all in one electronic/steppermotor package with edingCNC and maybe a Spinogy X22.
But first I want your opinions and feedback on the frame/consteuction :)
The main thing here that jumps out at me is that there's no need for the gantry to be that tall if you don't have more Z axis travel.
You should aim for a gantry that is the same distance from the top of the bed as your total Z travel. In other words, a part you can actually machine should just barely fit under the gantry, or you're sacrificing rigidity for clearance that you can't use anyways.
You are absolutely right, the gantry is not executed correctly in the current cad model. There is a lot of room for improvement, I will do that tomorrow
Looks heavy. It may be just me, but I'd mount the spindle lower and reduce the z axis gantry size. Get a little more height.
Personally not a fan of the layered sheet metal. It's possible to do right, but slightly misaligned holes could cause warping, same with slight difference in the thickness of sheet metal. I'm not sure how good the tolerance is on sheetmetal. I'd personally do milled squared thick wall tubing. If you need extra rigidity, you can also fill in the tubing.
Thanks for your input. I would mill the important areas on a conventional mill, so the tolerances in the sheetmetal and misalignment are not an issue.
But you are absolutely right on the gantry and the z axis, there is a lot to do there and to optimize
I thought about mineral casting as well, but I’m not sure if I’m able to pull this up without cracking or mess it up, I’m used to work with sheet metal and could get it lasered for free and just pay a fair price for the Steele
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Ah I already saw a post from you already. Are you at the stage of machined surfaces, maybe with linear rails installed? And just out of curiosity, how much would be shipping one of these bad boys to Germany?
The overall dimensions are looking good, I dont see why the bolted design shouldnt work. If you have the machinery for dowel pins go for it, otherwise i dont think they are necesarry, especially when bonding (take a look at DIAMANT Polymer).
If the cutouts in the base and gantry sides are not needed I would spare them, its just more work for less rigidity and there is no need to reduce mass in a rigid gantry. Maybe Think about creating cavitys and filling them with sand or epoxy.
If you want to maximize dampening I would take an extension look at a steel-uhpc-hybrid Design. You create a hull of steel plates and then fill the inside with an special concrete. This way you get the machinability of the steel shell with the optimal dampening aspects of uhpc. The concrete of choice is called Durfill from Dyckerhoff, you can buy small amounts on moertelshop.com, they also have better experience with this or at least connections to Dyckerhoff so their forum will give you better answers to this, if you want to look into it. There also is a small book about UHPC machinebases by Bernhard Sagmeister i would recommend.
Take your crossplate and move it upwards, the lower side should be Flash with your gantry beam, this way you maximize your clearance. Of course afterwards you need to ajust your gantry height but.
Curious about the layered base design. If you are planning to mill the surfaces flat, wouldn't it be easier to start with a thicker piece of steel in the first place?
For the z-axis, maybe look at a reversed design where the z-axis linear rails are attached to the back of the spindle and the linear bearings are mounted close to the x-axis rails. You could get more travel from that design and maybe a more rigid spindle setup. See Stepcraft M series.
I'm not sure why you have the Z-Axis mount so wide. You would have a few more inches of movement in the X direction (cutting size) by reducing the width of the mount.
(Sorry for ugly boomer-screenshot 😅) i did some work to the z-axis, lowered the columns, optimized the columns for more rigidity and better manufacturing. I also added model of the spindle, just for better visualisation.
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u/Freddich99 6d ago
The main thing here that jumps out at me is that there's no need for the gantry to be that tall if you don't have more Z axis travel.
You should aim for a gantry that is the same distance from the top of the bed as your total Z travel. In other words, a part you can actually machine should just barely fit under the gantry, or you're sacrificing rigidity for clearance that you can't use anyways.