Today I got tasked with making new gripper jaws for an assembly cell. I saw the email before I made it into work while drinking coffee eating breakfast.
I'm using some 3" square 95A Shore urethane to make some vee shaped grippers that hold a round part we clamp onto and then torque 6 fasteners to about 36 foot pounds.
I knew it was coming since I figured out what durometer material was being used. Quality had a shore hardness tester.
Anyway, I took my high priced 3x3x36" chunk of urethane and made a test cut in the band saw. Sliced off a 1/8" piece nice and square. Cool. Make a mark at 7.5" and take another cut. I get a crooked cut, thankfully the crooked made my part longer at the bottom so I didn't waste the urethane.
Okay, I'll change the blade, it looked okay but I've seen the saw cut crooked when someone else ruined the blade. Medium horizontal saw, 12'6"x 1 variable pitch.
Take another test cut on end of remaining stock. Nice and square.
Cut another chunk for the other jaw, just as crooked and I even slowed the cut down to nothing and even lifted out of the cut a few times. I was even running coolant.
I do not know what is going on there. I can cut a chunk of steel just fine and square.
To save time milling this crap (trust me, this stuff stinks to machine), I used the vertical metal bandsaw to wack off 3/8 inch down a side. Other than the drift angle being about 25 degrees to cut a straight line that went well.
Now clamping it in the vise hard enough that it would not pull out, raises the material
0.10" or so. I learned to clamp it, face it, measure it, reclamp it putting the vice handle at the same angle. Putting the counterbores in the right place might take some thought or bigger holes ;)I would have liked to try a dry ice and alcohol bath to make this stuff hard but no one knew where I could get dry ice. I did put the two chunks in a freezer in the lunch room to cool them. I'm not sure that made them more machinable but I figured it can't hurt.
Due to the milling I have to do, I fabricated a plate that I can screw the part to since there is no other way to machine it.
Tomorrow I'll fight with it again. I had to order a counter bore. At least it will be sharp, you need sharp with this crap.
I *really* want to get my wood shop set back up so I can make a mold for using castable urethane to avoid much of this.
Wes