On Tuesday 25 September 2018 04:02:01 andy pugh wrote: > I can't help thinking that the way to determine the amount of > correction needed is to actually machine a test bar and measure it.
This is also true. But that test bar costs money too. ATM, I am considering a tapered gib setup on the front of the carriage because the compression of the bellows when working almost directly under the spindle nose seems to be lifting the left side of the carriage off the v-way. There is now a nearly full width gib in place of the original two tabs, both of which were so worn that someone in the past had moved the anti-spin dowel to the other side of the bolt to use it reversed. The one on the left was badly worn, the one on the right also served as the carriage lock but had been worn and over tightened so much that bolt was bent. So I put a full width brass bar there while I had the carriage turned over machining enough space for a pair of thin roller bearing thrust washers to support the X screw, installed into the ends of the original hand crank boss you can unscrew from the front. The brass bar's left end is also the home switch activator, tripping it about 6" out from the spindle. But this brass bar normally clears the bottom of the bed lip by around 20 thou. The tapered gibs works great on TLM because its carriage is so narrow its nigh impossible to use a qctp on it and keep the point of the tool within the carriages footprint on the bed. But I have a vivid memory of the difficulty in getting the brass, tapered gib dead straight with a file that wasn't straight so there wasn't a spring effect in setting it. The first month I used it, the final wear-in used up much of the adjustment range but its now quite solid and hasn't been readjusted since. The difference in how TLM handles a 15 thou deep cut in steel 2" in diameter is amazing, no more tipping the whole carriage in the direction of the spindle allowing the tool to dig into the workpiece by 70 thou, bringing the spindle to a stop in 1 degree of rotation and breaking or stripping the teeth off the belt and timing pulleys between the 1 hp motor and the spindle. And usually breaking the carbide chip in the tool too. But since the carriage on the Sheldon weighs 25 lbs, I didn't think it needed the holddown precision of a tapered gib. But the compression of the bellows on the left side of the nut seems sufficient to disturb it, cutting around 3 thou smaller moving right than when moving left for about the last inch to the spindle face. Thats something I didn't foresee when I covered the screw with a pair of bellows that will prevent swarf from getting into the nut. Relocation of the ball nut to the right on the back of the apron would be the only fix, leading to the same problem on the right, but which end of the bed are you usually working on? Losing 6" of travel at the right end due to fully compressing the bellows may have been the better choice, but that would also need the nut reversed on the screw if access to the greasing zerk was to be maintained. It can't be put in the middle of the apron because of the window and slider plate for the x motor mount. A new apron could be made I suppose, relocating the x motor left or right far enough to help, but removing the bellows covering the screw is not an option as its totally prevented any screw contamination. That of coarse would foul up the symmetry of the aprons front panel since the jog dials and such are on it. Sigh. I'll see how far to the right I can move it as the grease fitting is so close the grease gun can't get to it now, but 4 bolts release it so a gun fitting can access it. A half an inch would help, a lot. Needs more round tuits for sure... ;-) Theres that old saw about hindsight always being 20-20 or better. :-) Thanks Andy. -- Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
