Re: Re: backlash reduction

PTENGIN@... wrote:

> From: PTENGIN@...
>
> In a message dated 01/25/2000 7:50:06 PM Hawaiian Standard Time,
> jmelson@... writes:
>
> << I have about .001 - .002" backlash on all axes, and I really can't tell
> where
> it is coming from on any of the axes. The X and Y are used precision
> ballscrews, though, so it could easily be wear. But, the Z screw is new.
> Everything on a knee mill is cantilevered. I'm amazed we get the accuracy
> we do. If I have a test dial chucked in the spindle and touching the bed and
> then push down on the front of the knee, I can see .001 or more. This is with
> all axis locked. I guess this is why jig borers are never set up as a knee
> mill. More of a gantry or bedmill setup.

Interesting. The knee is the only really solid thing on my machine. One trick
I learned a LONG time ago was to always lower the knee below where you
want to go, then bring it back up to the desired height (when lowering).
The arrangement of the dovetail and elevating screw causes the knee to tip
the front down when lowering, but presses it against the main parallel surface
when raising. I get about .001" Y-axis shift when reversing the Z axis.

> I have to adjust my Y axis on my series 1 Bridgeport at least once a
> year. I can see the ways loosen up with the DRO. The table crabs and makes
> the DRO reading stall or go back a thou when changing directions.

Yup, my Y slide is a horrible mess. It really looks like somebody used the
flat part of the Y slide as an anvil! UGH! I guess it was just from dropping
tools and parts on there for 40 years. I have way covers, now, and that
pretty much keeps stuff off there. But, it really needs a scraping, bad.

> I suppose
> the quill could cock just a smidgeon to show the same .001 backlash reading.
> I would indicate the head casting to quill clearance and have the CNC move
> the quill up and down slowly. You may see more side to side movement than
> you'd like. And/or back to front.

Well, even on my badly worn Bridgeport J head, the quill is ROCK SOLID!
Amazingly so! Of course, that is a pretty hefty quill. The quill and spindle
weigh somewhere around 100 Lbs. I can show no quill deflection at all.
I can deflect the entire head itself about .001"/100 Lbs side thrust, but the
quill deflection is about 1/10 that! The spindle can be measured moving about
.001", but that is the oil gap in the bearings, which will not occur when the
spindle is running.
I will do this test, but I already know the answer. Zero. I don't have an
instrument fine enough to measure this. All I will see is the scratches and
mars on the quill surface.

> Lightly used manual mills will die faster than a heavily used CNC if
> there is no one shot or auto lube. I strongly believe in the Bijur oilers
> ability to resist rapid wear and thus looseness in machine tools.

I have already installed the tubing, and a selector valve that sends the
lube to one pair of lube fittings at a time. I'm still feeding this with
a grease gun until I get around to making a motor-driven lube pump.

Thanks,

Jon