I have recently decided to change the path of my build form a small footprint with high rigidity for aluminum cutting, to a large footprint that is able to cut high density foam. The foam will be used to create molds for composite layups, with an average size of around 5’x4’x4’ (ballpark guess).
My question is, are there any issues you all foresee me running into while going to such a large format? My first guess is that the x and y tubing will bend in the middle causing inaccuracies. Will going with a steel/aluminum rod rather than conduit help with bending of the tubes? Does anyone have experience with cutting high density foam?
well my first thought would be look into the LR, anything with more than a 3’ span usually works out better as a LR (that’s why Ryan developed it). next i would say i have never seen a 4’ tall mill (i have seen people use the mpcnc with tall Z axis for 3d printing but not for milling), how do you plan on milling anything that deep? i would think the core would collide with the foam. next to answer your question, yes going with SS or DOM will result in less bed on your X and Y axis, but it will still probably be noticeable. that said if all your doing is cutting foam you probably wont have much of an issue. you will still want mid span supports for your outer rails.
EDIT: also i forgot, with a 4’ tall Z you will be carrying around a lot of extra mass, so you will be required to cut slower (if you figure out how to mill something that deep without the core hitting the material).
5" to 10" is still very deep. i dont know of any end mills that are that long, and when you get into cutting deeper then the endmill you run into issues with a collision between the core/spindle and your work material. have you taken that into consideration?
edit: i think the deepest i have seen is 3" for guitar bodies. not saying it cant be done, just curious as to your plans for what shapes your planning on cutting that deep and if you have considered the issues that could arise from it.
also, like i said do a search for “drop tables” here on the forums, you wont want to have a machine that tall, but you can put your material below the tables surface. resulting you you being able to cut on much thicker objects while having a machine that is only 1’ tall
Yes, you can buy foam end mills that are quite long. With that in mind, I think a drop table with LR instead of a MPCNC would work best for this application although I’m still slightly concerned about sagging due to the large footprint
the lowrider was designed for a 4’x8’ area. so sagging shouldn’t be an issue. if you do have issues there are mods to add extra rigidity to the Y span, and your X span is as rigid as your table.
cool, good to know i would recommend then being very careful with what spindle you buy and your traming of the machine as you build it. a tiny bit of runout in the spindle or the tiniest of angles on your core mounting will result in a big change over 10"
EDIT: and please let us know how it goes! i would love to see a machine making 10" cuts in foam! that would be AWESOME!
There have been some foam machines before. I remember some people making foam wings that were very large. The nice thing is that you can zip along at full depth and as fast as your motors can go. I would get a 24V PSU and a lightweight router (maybe with high rpms?).
Long spans are going to sag a little. I measured mine, which is the full 4’ wide and it was out maybe 4mm at the worst spot. It is a torsion box top with no other fixes for level. You might be able to try mesh leveling if you really needed it, but 4mm over 4’ is not very noticeable and if you keep the operations local, they can be zeroed out each time. Huge carves will be a problem. Through cuts or small carves will be NBD. Pockets and joinery is going to deoend on the application.
Thank you for the input! I’ll need to do some research on proper cutting techniques for high density foam, which will definitely be at play when deciding what router I’ll be going with. It might get a little tricky being able to get a router that can use these longer foam end mills while staying light weight and compact, but I guess that is part of the fun
A 4mm sag is not bad to be honest. That would be within tolerances for the project that I will be using the machine for. This can also be accounted for in CAD and CAM I assume.
The application will be for making two molds for a carbon fiber monocoque chassis which will be used for my university project (Formula SAE). I have been exploring alternative methods for creating the mold as getting these molds manufactured by a machine shop would be about $14k+…
Yes, I believe the problem with that would become dimensional accuracy between each layer. It would not be a problem for large sections of the mold, but when small radii or fillets are introduced into the design there will most likely be issues.
It could be compensated by oversizing the mold by an inch or two but that would require many hours of post processing the foam.
You’re not going to get that kind of depth with a lowrider style cnc. Unless you change the Z to move the table, it’s going to get waaaaaaaaaaay to wobbly with an endmill that long. Even if you build a drop table, you still have to raise and lower the endmill at least as far as it is long.
I think with a drop table it is potentially doable by having the z axis be on the table itself like you said. This would raise cost significantly though…
You could split the difference and have the Z on the gantry move half the full distance and motorize the drop table to move half the distance, halve the microstepping and tie all the motors to move in sync. Then your Z axis has the full range, but the table and the tool only have to move half the distance. Z1 moves the tool up .5 and the table down .5. Or am I just crazy
Might want to make it V1 lowrider style with some wheels under the table as well then. I’m not worried about rigidity, I’m worried about wobble at that height. Even with a drop table, you’re looking at say 32 inches to give the endmill some clearance over a two and a half foot block of foam. Also, the really long foam endmills are in the half inch diameter range, so bigger router is going to be up there.
i would recommend then being very careful with what spindle you buy and your traming of the machine as you build it. a tiny bit of runout in the spindle or the tiniest of angles on your core mounting will result in a big change over 10"
