Quote Originally Posted by JRR View Post
Thanks for the detailed help. I believe you are suggesting that it would be more effective to find a machine with a larger capacity than my little 2/3, keeping it for the smaller jobs. I do love tinkering though and 'fixing' the machine so it does a bit more could be a fun activity.
Trying to squeeze two dozen clowns into a Smart ForTwo might be fun, and it might be possible, but the car will not get far. Even if you can get it to drive, the first bump you hit will collapse the suspension. Similarly, you might be able to increase the capacity of your Rabit to 4x its design rating, but it was not designed for greater forces, so it won't last long.

Is the maximum surface area one square inch or one cubic inch? Slight difference...
Think about the "units" of pressure the machine is rated for... pounds per square inch. The injection pressure with a 10mm plunger is roughly 20,000 psi. On a part that has one square inch, that is 10 tons. The force keeping the mold closed is 5 tons. Not going to happen. A larger plunger has less force, so the 15mm plunger only puts out 8520 psi, which is about 4.3 tons... enough for 1 square inch, if everything is absolutely perfect. A larger plunger will have even less force.

And when I say 1 square inch, that is "projected area," or the area at your parting line. That is the amount of area where the plastic tries to press your mold halves apart. Holes in the part are subtracted from the total area, since there are no forces pushing the mold apart where there is no plastic. On the part, walls that are perpendicular to the parting line do not try to push the mold open, they try to push the side of the mold out, so they don't really count when sizing the clamping force.


As an example, one part I am looking at making is roughly 2" X 3/8" and is hollowed out, and has a small post. Weight is around 4gm (my postage meter doesn't handle small weights well). Made of Nylon. Are you suggesting that this can be done using two shots? How would one do that?
If you replace the controller, you can set it up so the plunger goes in to its max and immediately withdraws and plunges again. It must be fast, or the first shot will freeze off before the second gets there. It will not be an easy setup. You will need to use the Mold Closed sensor to detect when the plunger is withdrawn, and immediately turn around. It won't work with materials that freeze quickly. With soft sticky rubber pellets I had to use an air cylinder to pack the barrel (they were making a bridge, and would not fall)...you might have to do this so you are not waiting on gravity to fill it between shots.

Just remember, this trick will not increase your clamping force. It will only fill up a deep cavity that has an acceptably sized area at the parting line.

I did try tapping the 10mm bolt once loosened but no joy. Perhaps it needs to be heated up to 200C first - that suggestion was in the manual too.

Where is the FTP archive here? I'd be interested in seeing what I may have that may be missing.
After much googling to find the pesky link, I realized I downloaded it from your link!