All, I am in the middle of building a Primo and I tripped over something and would like some input. I am using Stainless tubing, PLA using the recommended settings from Ryan. The build area is 24" x 24" x 4". This should be close to the recommended dimensions. I completed the torsion box table, and started to mount the feet. During the process I noticed that the join between the top of the foot and the actual XY horizontal tube holder flexed. No matter how I tightened the central screw, there is flex in the joint. I have not completed my testing yet, however the stainless tubing does not flex when I use something solid for either end. When I put it back on the feet, that joint that I describe does. I do not know how much, I have pulled out the dial indicator and need to measure. I understand the need to print these parts separately, to make them printable (At least I think that is the case). However has anyone noticed this and if so, what about using something like gloop or epoxy to essentially join these together to eliminate the flex? Let me know I am curious.
My first thought is to finish putting it together first and look for flex again. The top of the leg also gets locked in a corner, and THAT corner gets locked on tubes in a way that means several pieces have to flex in order to get any movement.
As long as you check again before belts, it’s really easy and quick to disassemble back to where you are right now.
I went and looked at it again, and you maybe right. Thank you for the feedback. I may still go back and fuse the two pieces together. More to come on this. I always wondered why the leg was not a solid piece. The burly had all sort of leg replacements that not only stiffend the leg but also added the belt tensioners. Obviously the belt tensioner issue has been taken care of.
If anyone else has seen this please speak up.
The one thing that I did do was place a piece of thin sheet metal between the bottom foot and the MDF to keep the tube from pushing down into the MDF.
It seems to me (and I’m often wrong) that most of the “stiffening” leg mods were devised by folks trying to run a taller mpcnc. You are pretty close to short. I’m still not convinced that once it’s all together the legs present a significant amount of flex. After building my primo, even with the most excellent core, a lot of other things are going to flex BEFORE the legs, no matter how much you can get them to move by leaning on them.
Your machine will (hopefully) not get flexed by anything other than resistance at the endmill, so by the time the legs are a consideration, you’ll probably have a lot of other things to take care of.
I actually cut holes in my mdf to let the legs drop through. Did a pair of runners for the short sides, with 2 holes each. Made squaring REALLY easy. Fix one side down, measure the right length to one leg from the other side, pivot the final leg until the diagonals match, pin it with the nailer and screw everything together.
My teeny tiny mpcnc was even easier because I could put all four holes in the base. That was the easiest build ever.
It is funny that you talk about installing the legs. I did not recess the leg, however that is a good idea. I did however install one leg and then the others squaring as I went. When I was done, I was off a 1/16" and it drove me crazy until I was able to move it around to get it square. 2+ hours to redo the holes and whatnot. Screw movement during the drilling process caused the misalignment. The one change that I would make to the legs is to make the holes on the bottom mount larger so that the foot could be moved around. In the torsion box, I placed plywood below the MDF for something that the screws would bite into. Worked great.
I remember using my slicer to print just the first 5mm or so of my first MPCNC foot, and I used that as a drill guide for my actual feet on my table. I probably still have that guide in my CNC drawer in the garage. Those feet are long gone by now though.
Ryan does a great job and this is in no way a dig; I do think that the foot could be designed a bit differently to provide more room for drilling and screwing down to the support boards. It is just a bit to tight and does not provide very much room for moving around while installing. In my case the drill holes moved a bit, even with punching and caused all sorts of issues with alignment. Jeff, I really like the idea of the shorter piece for clearance for drilling etc.
It is all good. More to come on the potential deflection issue after I get the top sides mounted.
