Well I think I found out why my parts are not cutting right.

[knight_toolworks]

good idea on the dial indicator. I find about .005 play in the y axis with pressure from 2 fingers. after that it gets far harder to push. at most 001. trying to move the y in the x direction.

[daski]

Bit deflection is your problem. We have the same thing here and we just input a different size for each bit. a 250 bit is usually input as .258-.267. We do a test cut and adjust accordingly. All that matters is what the final cut is so testing and measuring when it's not cutting may help, but won't solve the problems. You need to find out what it is doing under load then compensate for THAT.

[Gary Campbell]

Dave...
To properly diagnose this problem, you must be aware that if the bit is deflecting, the cut edges of the part will be at an angle. It is impossible for the bit to deflect and not be at an angle to the part. These angles may not be easy to measure, but are noticable.

IF the part edges are square, the problem is not with the bit, it is somewhere in the moving parts of the machine.

Even tho the workarounds may be the same for both problems, (bit diamter trickery or reduced speeds) to properly diagnose and fix the problem there are, of course, two different courses of action. I prefer a fix to a workaround, but its not the easiest path.
Gary

[ron brown]

You are chasing a moving target. As Gary stated there are a LOT of things that can and will change with time. I am not sure metal softens from use, but bearings and gears do wear and it may be useful to try test cuts in a different part of the table.

IF your parts require real tight tolerances, you may be using the wrong tool or just pushing the tool too hard. Many problems solve themselves with slower feed and proper chip load.

Some bit deflection problems can be cured by simply using a larger diameter bit.

Ron





Ron

[Gary Campbell]

Ron...
Nicely stated... chasing a moving target. My machine has 29 roller wheels and 5 rack and pinion pairs. a couple thousandths wear on each and cut accuracy and quality goes out the window. Thats why maintenence is so important.

You are right, IF the bit is deflecting, installing a larger bit should cure most, if not all of it. In our case a larger bit actually increases the error at the same speed. That make me lean to either slack in motion parts or deflection of structural parts, something that I am hard pressed to believe is happening on our PRSalpha. Time to start replacing parts.
Gary

[knight_toolworks]

I can't find where the slop is except the .005 in the y. everything else seems pretty solid.

[wmcghee]

I know you said you changed your pinions, but it you may need to check the set screws in them again. I tightened mine about a month ago, and the last few days my machine would not hold a tolerence. I pushed on my x and y and the farthest x side did have play in it. I checked the pinion screws and they were loose. And the y pinion was also loose, but not enough to move when I pushed on it. But it still affected the cut. Just something you may want to check again.

[knight_toolworks]

I will but I tightened them pretty well and the problem was still there right after the new install. when I removed the old ones they were still tight too.

[Gary Campbell]

Steve...
How are you testing for the "slop"? I use a 1/2" drill rod in the spindle, and then, using a small fishing scale hooked to the rod, pull 25-30# in the X and Y direction and see what is moving using a dial indicator.
Gary

[knight_toolworks]

your method was better I used a dial Gage and magnetic base and pushed with a couple of fingers. I was wanting a scale but did not have one.