[Redeeman]

Hello.

I have a bf20 type machine, identical to the pm25mv, but i have some issues.

the first issue, of which i have zero clue about, is, that when i lock the X axis down with the two screws in the front, the y axis becomes very very hard to run.

I dont understand it, but I have determined that when i lock down the X axis, the Y gib is somehow tightened quite a bit more. I have determined this by taking out the front Y gibscrew, and with X axis unlocked this slides out quite easily, but if i lock down X, it does not.

any ideas at all?


my secondary issue is that at both ends of the X axis, its binding/getting hard to run, i have the suspicion that this is because the X axus leadscrew nut is not fully aligned, causing the leadscrew to bend, which is harder at the ends closer to the bearings holding it. I think that this is the reason because I cant think of anything else, plus, the backlash (which is around 0.3mm, perhaps a bit more) on the X axis has some friction in it, whereas the backlash on the Y and Z axis has near zero. Does this sound plausible? is there something i should check first?

Thanks

[photomankc]

The binding at the ends of travel is not uncommon unfortunately. For a number of reasons the ends of the table can close up the clearance between the gib and the dovetail and make the table much tighter at the extents of travel. Leverage also comes into play as the weight of the table levers against the dovetail with more force as the overhang increases. Weight on the table increases this effect. Break-in time at the ends of travel can help. It may help to center up the bearing blocks too as that can contribute. Loosen the bolts that hold the far end bearing block on the table just enough that it can move around a little. Run the table all the way in at that side so that bearing is now close to the side of the X/Y saddle. Now tighten the bolts down on the bearing block. Repeat on the other side. That should line the screw and bearings up on those far ends and make it a little less difficult to turn.

If it's still very hard to turn when at the end with the loose bolts then you know that really isn't the issue.

[Redeeman]

yeah that is my suspicion aswell, im more in doubt as to what causes the Y axis to be harder when the X axis is locked

[photomankc]

Yeah, that's a stumper. I can't picture the interplay that would cause that to happen. I'd pull out the ol' dial indicator and start looking for movement between the base/saddle when you lock the X gib and try to isolate where is it coming from.

[Redeeman]

i cannot determine where it moves, i can however determine that if i pull the Y gib 2-3 centimeters out, tighten down X, i can push the Y gib around 1 centimeter less in than with X unlocked.

im somewhat at a loss on how to proceed here.

[Redeeman]

An additional detail I have found is, if i run the X table all the way to either of sides, Y also locks up and becomes hard, regardless of whether the X axis is locked in position or not.

It really seems to me that SOMEHOW the Y axis "sled" is being bent out of shape, which seems ridiculous at it is about 20mm thick. I have no idea what more to try. I have tried taking the table off to examine the Y sled, theres nothing "bad" to see at all, everything looks fine.