I am new to the community. I have just received my MPCNC bundle. I would like your advice and opinion on building a MPCNC with a 4x4 ft working area. I plan on using the machine to build signs out of wood, sign foam, HDU and cut vinyl. The minimum Z height is fine with me.
I’ve been researching and reading multiple topics regarding rigidity and strength of different materials. The Stainless Steel quick and dirty test had quite a bit of info.
I am thinking of using 3/4 EMT for the frame with mid-span support and 1" stainless steel tube 0.065 for the gantry rails. This would make a little more cost efficient since I can get the EMT locally and order the stainless tube online from speedymetals.
Do you guys think it would be good enough in terms of rigidity and accuracy? I am willing to go even thicker tube if needed. Or, I could scale it down to a 3x4 ft working area if it would be a big improvement over the 4x4.
Welcome Alex. Unfortunately because of the part design, you won’t be able to mix conduit and 1” tubing. If the plastics that you ordered are labeled with a “J”, you must use 1” tubing (25.4mm o.d.)
If they are labeled with a “C”, you must use 3/4” conduit (23.5mm o.d.)
I built one with 48x48 tubes- screwed down to half a sheet of MDF - which gives me a 36x36 cutting area. I’m pretty happy with the X and Y precision, and Z is OK for small jobs when I mount my job in a corner, but it’s really hard to get the bed flat and level over the larger area - it needs some auto bed compensation software like a 3D printer, and a probe technology - there’s a project for a long winter evening. On top of that, there’s substantial flex in the tubes so Z is not very reliable over large spans.
Having said all that, I have done some nice signs and some large cutout panels - they came out great. I’d build the big one that you want - you can always cut it down later if you are doing a small project where you need more precision - or make two sets of cross bar conduit and three extra legs - shorten the travel when you need to.
One word of advice - for my setup the wiring harness was only just long enough and the belt provided was too short by a couple of feet. You will need to buy more on Amazon to get the build complete and you will need to make a wiring extension for one of either X or Y.
If the signs are mostly through cuts, then it will be ok at that size. You may want to think if ways to build signs up from multiple layers of cut out parts, instead of trying to make things in one big piece. You’ll want to start with pretty conservative settings.
Aluminum is going to be hard (nearly impossible) at that size.
V carving, or engraving with a V bit is going to be tricky too, because the Z may not have the precision you want at that size. If you are 1mm too deep, then the width of the line will be wider than you want. A sharper bit will have less width error with the same Z error.
I know you just bought a kit. But at this size, even for just through cuts, the Low Rider excels. If you are thinking of doing some engraving or carvings, then you should consider building this MPCNC smaller, make some smaller signs, then sell them to buy the LR and have two machines, with a good compliment of features.aybe not the advice you were hoping for. But I think that would be the fastest way to a working business.
As a bonus, having one CNC is great, but you need to be there to watch it anyway. So having two means you can watch two jobs at once.
@blainesgarage
I forgot to mention that I only ordered the bundle without the 3D printed parts. That’s why I was asking if I could combine the EMT with the 1 in tubing. So I was thinking I could mix the two types of printed parts and adjust as necessary. Also, do you recommend PLA or ABS?
@jeffeb3 Do you think the accuracy would be good enough with steel tubing? Eventually, I will try to do aluminum, but for now I will keep it to wood and sign material.
Regarding the Lowrider, the more I was reading I realized it would work great for what I need. Let’s say I splurge and buy a kit for the lowrider, is that going to make aluminum cuts possible? Because that sounds really tempting.
One last question - what spindle to you recommend for the MPCNC given the work that I want to get done? I was going to start with the Dewalt, but if you think something else will be better on the long run, I am willing to invest into it.
As it happens, for my double decker build I wanted to use 3/4" EMT for the side rails and 1" for the gantry and Z rails. So I made a side roller specifically for “C” rails and “J” gantry tubes. It’s part of a larger random collection of pieces for the double-decker here: https://www.thingiverse.com/thing:3709811
Specifically the part you need is: C_Roller_With_J_Gantry: allows “mix-and-match” rails where legs and side rails are 3/4" EMT conduit while gantry and Z-axis is made from 25.4 mm tube.
I’m not quite sure if the corner pieces need to be adjusted. The Z gap between the side rails at the corners determines the Z gap and must be consistent with the gantry rails, but with differing diameters it’s less obvious what the gap should be.
I don’t think the steel makes that much difference. Aluminum has a smaller window of settings that work. A lot smaller. The machines that do well with aluminum are smaller MPCNCs. It is possible to cut aluminum on the LR, even at large sizes, but you need to be on your game. It will be slow enough that doing large cuts would be painful. But feel free to prove me wrong. I have been surprised many times before. A small MPCNC for al, and a big LR for mdf and sheet goods is a good combo.
The dewalt routers (660 for mpcnc and 611 for LR) are both very powerful and accurate. They will be more than you need. They are also a great value, if you’re in north america.
I will add, my rough estimation is that the steel tubing might add 20% to the rigidity, and making it 48" vs. 24" would make it 4x floppier. There are a lot of things that isn’t capturing. But those orders of magnitude are close.
I decided to build a MPCNC with a 24x24 working surface. Outside diameter about 34.5 according to the calculator.
I am going with DOM tubing. Thinking of using .065 for the frame and z axys and .083 for the X and Y for gantry support. Is it worth upgrading the moving X and Y rails for accuracy?
Also, how much is the working height affecting the accuracy? I would like to be able to fit a piece of 4x4 stud. Does that mean my working height has to be a minimum of 4 inches?
It would have to be taller, need space for the endmill. Best way to accomplish that is to have the table be moveable, so your legs are still short. See Dui’s mpcnc built in china thread.
Mine are short almost touching corners rdd s to feet . Can cut about 2.5 inches I believe will measure it in the morning most of my cutting is 3/4 inch to 1 inch
The length of the legs doesn’t really effect accuracy directly, the legs are one of the strongest parts. What matters is the distance from the gantry pipes to the bottom of the bit - as this is the lever arm that twists the centre assembly.
Thus you could build the machine with 5 or 6" legs, if you block up smaller pieces of work so you can work without extending the Z axis too far.
The converse is true, too. If your Z motor is way up in the air, that’s a long lever arm if anything is attached to it (which is why Ryan harps on NOT ATTACHING ANYTHING TO THE Z AXIS, like your vacuum hose).