So my LR4 is ready to move to the 1st of three high school shops that it will occupy over the next few months. This year’s builds will have me cutting/carving XPS foam more than any other materials. I’ve hand carved xps for years using palm routers with 1/4" shank profile bits, edge bits, hot-wire knives, dremmels, and various sanders. This year i want to turn that task over to the LR4.
My Builds will be:
Shrek Jr (Shrek’s Outhouse, Farquad’s caslte entrance, Dragon Wings, and railings and balusters.)
Beauty and the Beast (knives, forks, spoons)
Cinderella (castle walls and then the carriage which will be 3/4 ply)
My intensions for the XPS was to use various thicknesses from 1"-2", dependent on the piece. some will get a 1/4" luan/ply backer. My plan is to use Illustrator to create my dxf files and then use EstlCam to adjust the carving depths (like Christian demonstrates in his “Tick Tack Toe” video)
So any advice on bits, feeds and speeds, should I bond the 1/4"backers (where needed) upfront and cut all at once or will the Titebond II dull bits too quickly? For thicker, more detailed pieces, am I better off planning layers of individual cuts on smaller thicknesses( like castle wall with grouting lines and a window cutout, then a second cutout for the brick window moldings and top castle-block molding)that would get glued together , or just use a thicker piece and carve all the elements form a single piece?
any advice/insights would help me a ton! I’m 3 weeks behind on getting the LR4 to the school so it’s a bit of “Trial by Fire”
Not an expert by any stretch of the imagination, but I’ve done some foam cosplay props and foam Halloween props and have some thoughts.
First, if you have a stock LR4, I don’t think you will be able to full contour cuts in 2" foam. The LR4 has a Z working distance of 100mm. In that space must fit the stock, the bit, and any clearance, and you are just a bit short on working space to be able to do cuts completely through the foam. It will work fine to texture the top of the foam, and you could do a partial contour cut to show the cut lines and finish the cut by hand.
I’m a proponent of assembling afterwards. If something fails, you lose less material, and you can often use material more efficiently if you do things piecemeal. If you do glue first, I doubt the Titebond will dull the bit.
I couldn’t find the referenced Christian Tick Tack Toe video either on this forum nor on YouTube. I’d be interested in seeing the process you reference.
If you are going to be doing 3D objects like statues, you might take a look at Fusion 360 Slicer. This is a depreciated project (no ongoing work), but you can still download the appliction, and it works just fine offline. It takes a 3D model and slices it up creating DXF files containing paths that, when cut out and stacked, will give an approximation of the 3D object. After gluing the pieces together, you will have some sanding to do. I’ve been playing with this app for some laser projects. You will find a tutorial and links to the app here.
Also, here’s a video showing my work on a middle school production of the Little Mermaid…if you’re interested and have 25 to rabbit hole. https://youtu.be/5v1TWaqN5pM
Someone with an LR4 will need to give an answer to your idea. I have a Primo that I specifically designed to have an adjustable Z axis just so I could do 2" foam. Looking at the parts list, the LR4 uses 150mm linear rails, so it is possible your idea has merit. If he can find an appropriate router bit that leaves just a bit over 2" exposed and can figure out a hold-down strategy without exposed clamps, he doesn’t need to buy much space.
The bit would need to be at least 50 mm long. 50 mm material thickness and 50 mm bit length and 2-3 mm clearance for moves would use up all of the 105 mm available travel. It appears that he would need to raise the Y rail/rolling surface, or lower the spoil board.
I would vote against doing laminated 1/4 backer with the xps on the cnc. For foam I cut full depth as fast as possible on the lowest Makita or cobalt rotation speed. For plywood, you can’t cut that fast and the bit will get hot if you do and then when the xps melts, you get to try and get it off the bit.
But you could cut the 1/4" plywood and then get a following bit and cut everything out of 1" or 1.5" xps because those are easy enough to find. Xps is pretty linearly priced for thickness. So you could laminate plywood plus xps plus xps to get the desired thickness.
I cut this out of 1/2" foam, but 1" or 1.5" or 2" foam cut similarly if your bit cut edge is long enough.
********** I think the cnc max speed is set less than the 2750, but for my system, it runs as fast as it can. If it hangs out too long, the fuzzies will melt and then you have problems… just get it through it. If the cut edge is rough, then slow down the feed. There is a satisfying hum when cutting foam. There shouldn’t be any chatter.
I think I got the 2 flute up cut from aliexpress, but I can’t see the order - so it may have been from amazon. I got a 1" 2 flute updcut from the local big box for about $15 and it worked well until I started cutting 1.5" and 2 passes was a deal breaker for me with foam. However I also got this straight edge one and it worked fine on that last cut (easy to cut fingers with this one):
6 mm diameter with 52 mm cut length 2 edge. Collet was a little loose, but it held and I had to slide the router up as high as it would go in the mount and raise the z all the way up. A 38 or ~40 mm cut length will work for 1.5" xps foam.
The last time I did bigger foam pieces was the year before Covid. My (adult) daughter has lately been sending me ideas for a new costume, so maybe there will be some foam cutting this year. If I remember correctly, I ran my parallel passes at 2000mm/min to 3000mm/min. At these speeds I lost steps on the first contour cut, so I backed off to around 1000mm/min and reduced the DOC to something like 8mm for contour cutting going forward. Note that if you are running your system at 24V, you may have more torque when running at 3000mm/min than I do with my 12V system.
I did all my foam cutting with a ball-nosed, 1/4" two flute bit. It was the first bit I tried, it worked well, and I never tried any other bit to compare.
With my early pieces, I used a small stepover (parallel passes), when meant very little sanding. But later, I increased my stepover since sanding the foam was so easy compared to wood. It wasn’t worth the extra machine time just to knock off a bit of easy sanding.
I use Fusion 360 for my CNC work. One thing I’ve done a few times (in wood) is to take a 3D model and slice it into layers (3/4" in my case). Each layer was carved, and then the layers were assembled. As long as you don’t have major overhangs (one-sided milling), the assembled pieces will resemble the 3D model. This is different than the Fusion 360 Slicer above in that the input to the CNC machine is STL files, not DXF files. EstlCAM will do 3D carving using STL files, but since I don’t use it, I cannot give you further information.
Also, here’s a video showing my work on a middle school production of the Little Mermaid
A lot of fun technical problems your group solved. I bet the school is happy to have parents like you.
