CNC for Foam Machining

Discussion in 'Lost foam casting' started by Ted Brown, Sep 23, 2022.

  1. Ted Brown

    Ted Brown Copper

    I have been looking at using a CNC for machining the foam so I will have exact dimensions and not have to worry so much about sanding and cleanup. ie: When using the 3D printer, I took into account the aluminum shrinkage, but not the lost wax and the silicone during mold forming. I added 103.5 percent to the printed (Throttle body) and it was perfect after the 2nd try.

    Now that I am fully committed to lost foam, I was looking at a CNC machine. I saw Kelly got one and called the company that made his. The owner of the company did not feel me with confidence about buying one for lost foam. My part is 2" high and has a barrel (Throat) and it appears that most cheap CNC cant raise high enough to clear the barrel to do the inside and outside. The we went down the rabbit hole of a 5 axis, bla bla bla, so I am building a pin router for now.

    Thoughts?

    Ted
     

    Attached Files:

  2. ddmckee54

    ddmckee54 Silver

    Wanna go down ANOTHER rabbit hole? Build you own CNC. I'm in the process of building a CNC router with a 24" x 48" x 6" working volume to remedy that lack of usable Z axis height.

    Don
     
    John likes this.
  3. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Hi Ted, first I would say, there is nothing magic about the MillRight CNCs. Like many things CNC routers are all about feature set and price point. The good thing about machining lost foam patterns is just about anything will do because tool loads are extremely low. In fact, many of the downsides to light weight hobby CNC machines aren't a problem for machining polystyrene foam, and having a light weight gantry can allow for higher speed machining whereas with hard materials, the machine couldn't handle it. I chose the MR machine primarily because of the large work envelop and the rack/pinion drive. The z-axis is more generous than most, it isn't enough for me. I always planned to increase the z travel to about 8". On the MR, it's not hard to do and again, this could pose a real problem for such a machine if you were machining hard materials.

    Ordinary woodworking cutting bits work fine on foam and spiral flutes the best. You'll always have a little sanding for best finish but it is very easily done and fast.

    I'd say the MR after sale service and the activity/support on their user forum is below average. There are FaceBook MR groups but I generally find FB to be a very poor vehicle for technical exchange......more a place to show off pictures of your work.

    There's also the matter of the machine controller, firmware, and post processors. The MR machines are GRBL based, and although open sourced, I'd go a different route knowing what I know now though not a big deal. As far as hardware, I'd probably buy and Avid machine or build my own.

    I always planned to extend the z axis, but the next thing you will encounter is the (un)availability of thick Extruded PolyStyrene Foam (XPS) board. Large billets of Expanded PolyStyrene (EPS) or the white beaded stuff are readily available. It doesn't machine and finish as well but if you get the right density (1.2-1.5 lb/ft3), it can be a close second. However, you may find the shipping costs excessive and finding a seller that will actually send you what you specify difficult.

    If you try to laminate stock to thickness you will find machining through glue joints problematic. So, with the relatively poor availability of thick machine stock I've had little motivation to increase the z-travel of my CNC machine and instead just section my parts so they can be cut within 2" stock height and glue the sections together after machining.

    Best,
    Kelly
     
  4. BattyZ

    BattyZ Silver Banner Member


    Yep and Yep. Second all of this.
     
    Tops likes this.
  5. garyhlucas

    garyhlucas Silver

    F761004E-78AE-4791-AADF-177DA9CCA674.jpeg
    I am building this 24” x 48” x 6” CNC Router with my FIRST Robotics team. Fully enclosed yet fits thru a 35” classroom door. Full coolant pan and pump, and a shop vac. Can slide a 4’x8’ sheet of material thru and cut anywhere on the sheet. Y axis carriage and Z axis are LF castings, as well as the spindle housing, a motor mount and 4 caster plates. Acorn controller and will have a permanently mounted 4th axis/ lathe spindle. We are currently wiring it before installing the Y and Z axis.
     
    Ted Brown and Tops like this.
  6. BattyZ

    BattyZ Silver Banner Member

    Oh how cool!! I did FIRST robotics in high school, (#171 The Cheese Curd Herd '07-'10). "Back in my day, it was all manual machining.." Actually kind of jealous of your project. Getting everything through a door brings back some memories/trauma. lol I wish you guys the best of luck, well, unless you run into my old team...

    EDIT: Can we get a build thread on this?
     
  7. garyhlucas

    garyhlucas Silver

    Our team is Mercury 1089. Made it to worlds last season. I’ve machined all the parts for the robots on my homebuilt CNC mill. I was lucky to get 4 THK high speed high precision linear slides with 18” travel. One is a spare. I a router for one spindle and a minimill R8 spindle for hard materials. Lots of R8 tooling available. 14388D3A-4568-4E3B-9F68-FCB7FC300188.jpeg
     
  8. Ted Brown

    Ted Brown Copper

    OK. After hesitating for various reasons, I pulled the trigger on a small CNC router. Most CNC machines I looked at had a limited "Z" height, but I thought, why not route a 2" high with two (2) 1" high pieces? since my pieces were small (5"x 5"), figured it would work and so far I am really impressed with the quality of the pieces. I a still figuring out the details of the software, but I already have the pieces made in my 3D printer which made it much easier. It has a learning curve, but not too bad so far. The biggest thing so far is the software is set up for carving wood and not foam, so the feed rates are really slow. I know there are ways to increase the feed rate, but I was happy just to get a piece of foam that looked like what I wanted.
     

    Attached Files:

  9. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Those look good. Glue them together and just a few minutes of finishing with with some worn 220 sand paper will greatly improve the pattern and resulting casting finish.

    What's the carving software? Do you know the post processor used?

    Best,
    Kelly
     
  10. Ted Brown

    Ted Brown Copper

    I had the parts already drawn in TinkerCad for 3D printing and exported using .stl format. I imported it into Easel (30 days free for the pro version) and just used Candle (which comes with the printer) and done. Importing from .stl did change the size, but an easy fix. I am now redrawing the part in Tinkercad so it's only 2 parts. I am using a shop vac positioned close to the spindle, but I will change that out with time. I will keep you posted on my progress.
     
  11. Ted Brown

    Ted Brown Copper

    OK, I redesigned the making of the part for speed and ease of gluing, etc. The bottom part is made up to 1" and the second part is the remainder of the 1", glued together and sanded to make the 2 parts look like one. The Injector boss is added last and hides a "holding tab" used during CNC. I am highly impressed by the detail and texture of the parts and my only gripe is the sanding of the parts where they were connected to the 1" foam. If I was able to dial it in where it cuts completely through, there would be no sanding of the bottom plate. I have noticed that 1" foam varies in thickness (.010-.040) and I those connections will have to be sanded down. There are some light tool marks on the injector boss, but I actually think I might leave them and sand others. I'm going to make a few more before I cast so I can make sure I have some type of consistency. It takes about an hour per part to cut out, but I start the cut and watch TV, sand, or whatever while the CNC runs. I will let you know how the finished part comes out, but right now the CNC project is a GO!!!
     

    Attached Files:

    Last edited: Oct 25, 2022
  12. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Looks good. I use 1.3% (.013"/in) for shrink. After you get molten metal and mold managment figured out, lost foam is all about the pattern.

    Best,
    Kelly
     
  13. Ted Brown

    Ted Brown Copper

    OK, Guys, I'm SOLD on LF. This was my first-time pour with Lost Foam and I am highly impressed with the quality and detail of these throttle body tops. 2 of the 5 we poured are what I would call seconds, and they are really good. In the last 2 we poured the mold collapsed because the sand was so hot, it melted the foam (didn't see that coming). Using the CNC machine makes really nice patterns that are reproducible over and over. I plan to make about 100 throttle body tops over the next year which are a part of the Corvair EFI kits (replacing the steel ones). Thanks for everyones input.
    1stQuality.JPG
    TJIM9481.JPG IMG_1183.JPG IMG_1247.JPG IMG_1242.JPG
     

    Attached Files:

    CNC-Dude, Tobho Mott, rocco and 3 others like this.
  14. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    Looks good....congrats on success.

    What were the flaws? How/where you gate, position in mold, pouring cup, pack the mold, coat the pattern, are the nuansce things that help yield consistent results.

    Yah, can't do that. You need cool mold media.

    At first, that seems like a pretty sporty number for LF that might make you lean toward conventional sand casting, but if you do them in batches of say 20-25 at a time, you could nest/cut 4 patterns at a time on the CNC and potentially hang the four patterns on a tree/sprue and cast them four at a time as well. You'll also find that dip coating the pattern is a huge time saver.

    One other thing you'll find, is you become more open to customization since the patterns are hand made anyway.

    Best,
    Kelly
     
  15. Ted Brown

    Ted Brown Copper


    Thanks so much. I was about to give up on casting until I saw your pin router/LF on youtube.


    The 2 that I said were seconds were due to small porosity holes on the bottom of the throttle body. I really should have not said seconds, as they are not perfect like the other 3. I gated in a variety of ways, Upside down with "L" Sprue, TB upside down with the gate and none really seemed to make a difference. I did have a couple of blowouts on the ones I dipped once and brushed. I was able to peel the blowouts off and the part was perfect. I think I need to dip 2 times and not worry so much about it being too thick as those done much better. I started using a saws-all pressed up against the metal to vibrate the can so the sand was very hard. I also built a pyrometer and would start the pour at 850c and this seems to be the sweet spot. I am not that worried about the porosity as the holes were surface and very small.


    Lesson learned. Going to get a couple of extra buckets of sand ready. Wintertime is coming to the south!!! at least what we call winter.


    I will need a larger setup to do more than 1 at a time, but this has got me thinking about investing in a bigger setup. If I don't count the mold failures (which was common sense that I didn't have), I had a 100% success rate. I look on the Facebook marketplace for casting stuff, but it appears few southerners cast since the 1860s, but I keep looking. I have tried conventional sand casting, lost wax, and lost PLA... I am firmly a foamer!!!


    Making them with the CNC router is the Bomb.com and I don't have the patience to do them manually. I put a 6" x 6" x 1" block on the router, send the instructions, and about an hour later, it was done. I know I could make the faster with a pin router, but that is a lot of work setup and still requires another skill that I have not mastered. Other than gluing the parts together, it's ready for dipping.

    Thanks for this forum and for Kelly leading me out of the casting wilderness.

    Ted
     
  16. Ted Brown

    Ted Brown Copper

    I've been out of pocket for a while with the addition of a new baby (13 months old) and I am still a partner in an ISP company (day job). Now with all that said, I have still been putting in the time on the CNC and casting, just not able to do it very often. Before I was gluing two 1" finished parts before as my part is 2" high. My results had me spending time gluing, sanding to removing the parting line to get it usable and presentable.

    I bought a new CNC machine that had a 4" Zed which allows me to make 1 piece parts The Chinese CNC I bought had taken a really sturdy and larger CNC and had put a controller/driver board from a cheap 3018 CNC. This worked fine if the CNC was run super slow, but would skip when the board got hot, and at that point the part becomes trash. I emailed the company and explained why the CNC was not working properly and that it needed a larger board and stepper motor drivers. They emailed me back and said to fix it and that they would pay for the parts (which I had already ordered). The parts arrived and I can run this CNC as fast as I want without error the company refunded me the invoices I sent from amazon!!! I am now using Foamular 150 2" board and cut into 8 x 6 blocks which comes to about $1 per part. I could cut 2 at a time but we're talking pennies now.

    NOTE: I don't change bits between roughing and finishing. The reason I don't use a roughing bit and then change to a finishing bit is that I want to put the part in the CNC and walk away. I can work on other items in the shop, watch TV, or even better...spend time with my new baby girl.

    I ordered a long 1/4" bit (4") which was not cheap but figured since I am cutting foam it will last forever. The 1/4" bit made more mess than my vacuum system would pick up and the detail was not to the level I wanted...but very usable and happy with the results. The removed material sticks to everything, so I had a lot of mess in my carriage and screws which I was constantly cleaning. Each part takes around 1 hour with a 1/4" bit, but the mess made me look further.

    I ordered a 1/8" x 3" bit (more expensive than the 1/4") and it works perfectly. I get the nice detail and smooth finish and the vacuum keeps up with the routing material. It is 2 times slower but well worth it as I don't have the mess (except emptying the vac). So now when I go into a shop, I screw a blank into the CNC board, tap the computer, and walk away. The part requires very little sanding except for the bore which I may fix later by altering the G-Code. The castings are almost perfect every time and usually, any defects are from my less-than-professional sanding.

    I am now dipping my parts and have an established orientation and sprue length, so a little like a production line. My next step will be a bigger furnace and then probably electric, but kind of leaving a lot of this to my brother. We started trying to cast together and this project is a great brother project and in our old age has brought us even closer. Our latest results were 8 of 8 and would not have been possible without the forum's help. It now takes 1hr, 4omin per part for high quality, with no user intervention except to reload blanks and remove finished parts.

    Ted
     

    Attached Files:

  17. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    It all sounds quite familiar!

    I use 2-flute 1/4" spriral end mills and ball nose for 90% of my cutting, and agree, I'll use the same bit for roughing and finishing because for foam it just doesn't matter and isn't worth the tool change. Whether or not you need an 1/8"D as opposed to 1/4"D depends on the part features. If the radii are not too tight, you can do just as well with the larger bit and fine stepover for finish passes. That speeds things up a lot on the 2.5D MOPS and and 3D roughing with coarse step over using the larger bit. One thing that is often overlooked, you really don't need a bit with a cutting height the full depth of your part. Even though I have 2" CH on many bits my depth of cut is rarely more than .5", so other than clearing chips, you really just need the reach and overall length to cut 2" deep.

    I buy from ToolsToday and Yonico. TT has great selection and quality, but you pay for it. I buy Yonico from:

    https://www.precisionbits.com/up-cut-bits/?features_hash=15-9536_16-9749_19-9580_33-11467
    https://www.precisionbits.com/ball-nose-spiral-bits/

    They're not Amana quality but not far from it and you'll never notice the difference for cutting foam and soft materials. Another trick to get more reach out of shorter bits is to buy a collet extension. It won't work for all fetures but if you have some relief from the diameter on part features, it can allow the use of much less expensive bits.

    Amana shank extensions

    https://www.toolstoday.com/v-12218-te-130.html
    https://www.toolstoday.com/v-12484-47648.html

    I use them on straight bits but more often for chamfers, round overs, point engraving profiles etc. They are available for 1/4" bits too.

    On dust collection, yes, the foam becomes charged and sticks to everything and can defeat some of your dust collection. It can get tricky on deep cuts. It's really a subject all to itself for another thread but I use a small diameter shoe with a soft brush, and high vacuum (shop vac) instead of shop dust collector, and ground the piss out of everything. I chased my tail for weeks. The static discharge from dust collection was crashing my controller/programs. After grounding, not a single crash. Also use a dust deputy cyclonic seperator to prevent your shop vac filter from rapidly plugging extending time between cleaning from minutes to days.

    How do you like MACH?

    Best,
    Kelly
     
  18. Ted Brown

    Ted Brown Copper

    How do you like MACH?

    Loaded question. At first as a Candle user...NO. I was confused and frustrated until I figured out the GRBL board was overheating causing 90 percent of my troubles. A quick fan fixed it, but I had to run it slowly to keep the stepper motor current down. The small CNC worked pretty much out of the box and was cutting patterns within a few hours of assembly, not so with the MACH3, but again Controller board issues were causing most of my issues.

    I could not find any GRBL-type controller that would handle 2 amp steppers, I had to go with MACH3. It is NOT simple like Candle, but after I got it figured out, I can see a lot of value in this now. It has a lot of inputs/outputs for many other devices, so my answer is now: Yes. I have the spindle speed control on manual until I get more comfortable.

    I used a NOVASUM controller ($70) and three (3) individual stepper drivers to control this machine and I can run it as fast as I want. I also lowered the stepover percentage for higher quality now that I can run faster.

    Ted
     
  19. Al2O3

    Al2O3 Administrator Staff Member Banner Member

    I dont use MACH. I downloaded the trial at about the same time I did for CamBam. I still have the trial version loaded but it's probably been 9 months since I opened it.

    90% of my start up problems were caused by static discharge disrupting the controller and also an issue with the grbl post processor. A fella on the CamBam forum made one change to my PP (I think wrt to how it interpreted curves) and ever since, it has been rock solid, throws no errors, and spits gcode that just runs without issue.

    As far as CAM, I think within a couple hours I was using CamBam's 2D CAD and cutting foam with CB genrated CAM programs.

    Best,
    Kelly
     
  20. Tops

    Tops Silver Banner Member

    I am running a LinuxCNC system with a Gecko stepper motor driver and external power supply. Works well for most things I do and is well supported with post processors across many CAM platforms. I have not updated in years. I am impressed by the GRBL on my 2D laser and whatever runs my 3D printer. The biggest gains for me has been trying more advanced tooling strategies in CAM. A bit more learning curve but faster run times on the CNC are worth it.
     

Share This Page