So I machined a couple of foam patterns for the pump housing I’d like to cast. First one took 11 minutes to machine both sides. The second I increased the feedrate to 106 ipm and it took 7 minutes. Add about 5 minutes for two toolchanges for each part and about 2 minutes in flipping it over. So call it 45 minutes for two including clean up of chips. Cam programming time was about 1/2 hour working from the 3D model. This part may be cheaper cut from a solid block of aluminum on a larger high speed CNC machine especially since there really isn’t a need to cut away the back of the body which I did for casting. I actually have the block of aluminum and I think I will cut one that way on my little for comparison. I can essentially run the same program by just changing the cutting parameters for aluminum. The cam program will recreate all the tool paths in just seconds. I could also machine a solid pattern for sand casting too. I have the flasks to do that. Again I would use the same program but have it create draft on all the profiles inside and out. This part only needs compensation for shrink on one surface so it all should be real simple.
Looks good Gary. Looks like there are two thicknesses of foam plank in the first machining picture. Is the bottom board just a waste board? What features were used to locate the pattern when the opposite side was machined? Just the perimeter of the plank? I presume the backside was machined first...correct? You said this was a peristaltic pump...correct? Does the motor/rotor mount directly? Need bigger pictures....800x600...so old eyes can see. Now to cast and machine. Gotta close the deal! Best, Kelly
Kelly, I didn't have any 2" foam, two 1" pieces glued together. 1/4" hardboard to protect the table under the part. Two of my clamps bolted to the table and aligned with the axis. Top of foam block used to align the X axis. Center of the large hole is X0,Y0. After flipping I had to pick up the center of Y axis. Jog to one side and just touch, press 0. Jog to other side, press 1/2 and you have center. Machined the front side with the big opening first, that took 2 min for round opening. Cut U channels using ball mill plunging, that took 4 minutes. Flipped and cut back side, finishing with outside profile using holding tabs feature so part didn't move. In the old days programming manually I would simply reach in with a wooden stick after the mill was most of the way around and simply press the part down as it finished. Did this on lots of aluminum parts. Yes a peristaltic pump. They are very simple but surprisingly expensive. This housing bolts to an aluminum Cface worm gear box directly, using its bearings and shaft for support. A simple rotor with two rollers, a clamp block for the hoses and a clear cover and its done. I need 4 for a job where it runs just 5 minutes once a month. So no need for fancy, just reliable. We will program the motor to move the rollers back and forth each day to keep the tube from getting a set in one spot. I will post a drawing of the system it goes on. It's pretty neat.
What did you use for glue to laminate? Things that burn out well tend to gum up the cutter. Hot melt, contact cement, two sided tape are terrible in this regard. Things that don't gum up the cutter tend not to burn out well. Thinned shellac is great and works like contact cement......but doesn't burn out as clean. Best compromise I have found for laminating is thinned white glue. But it can be a bugger to get it to dry in bigger panels. -(modest) Heat helps. Look forward to it. Always like seeing castings being used in the end application. Best, Kelly
I use Elmer's spray craft glue. Just a very light spray seems to hold very well and it burns out well in Aluminum.
Have you machined or sanded a joint glued with it? There are lot's of choices that bond foam well but if you are machining or sanding a joint.....not so much. Best, Kelly
I used the 3M spray contact glue and you can see it didn't cut cleanly. These first parts are just to get me something to cast to learn the process. I'll get a piece of 2" material going forward to eliminate the gluing. I'll try the white glue too. Shellac is alcohol based? If so maybe there is some other alcohol based adhesive.
Yah, that group of adhesives I mentioned immediately loads cutters, usually the worst on the back side, but also front and bottom. Then there is no relief to the cutting edge and it then gouges as it continues to cut. If you touch one of these glue joints to a sanding belt or drum, it will instantly load the abrasive with glue and become a foam burner instead of foam sander. There are contact adhesives specifically for extruded polystyrene. 3M 78 for example. They aren't any better for our purpose. Yes, and alcohol doesn't attack Polystyrene and has high vapor pressure so it dries fast. If you coat a surface, allow it to dry (heat gun or hair drier take 10-15 seconds), then apply a second coat, it will reactivate the first coat, and as it begins to flash, you can stick panels together almost like contact cement and even have a little working time. The big advantage of shellac is it's a very thin glue joint. Clamping or compressing the joints helps maintain thin full contact joints. If you machine through them at steep angles, they do well but shallow feathered joints are more problematic. It's sandable but the foam will usually abrade more rapidly on either side of the joint leaving a high pot. It doesn't burn out as well but there is very little of it. Search shellac. Might surprise you where it comes from. Make sure your joints are true and flat, thin the glue just a little, if laminating press the panels with weight or vacuum bag, or if not laminating use packing tape to keep the joints in compression while drying. Still loads the cutter, just not as bad. No glue at all is definitely the best route. I understand you can buy the commercial extruded PS in 6" sheets special order.......one day I might just do that if I have a job that calls for it. If I had my druthers, I'd prefer nothing in the pattern except PS Foam......no glue, no wax......those additions are only practical compromises. Glues are essential from a practical standpoint but can be the bane of the lost foam pattern makers existence. Best, Kelly
It works best for me if I use a very light spray. I doesn't take much. Yes, I've sanded it and machined it.
