Backlash compensation problems

jbastos wrote:

How can i do it easy on the mechanic?

On real Bridgeports, the nuts can be slit in half to make two complete nuts that
fit back in the same place in the yoke. Then, the screw that clamps the nut
in the yoke will squeeze the two halfs together. You have to do a bit of
adjusting and testing to get the right setting so that the leadscrews don't
bind at the ends of travel, where there is less wear.

You'd be amazed at how much this can reduce the backlash. You can also
check while you are in there that the yoke is not loose inside the saddle.

I can't say for sure this will work on your specific machine, but if it is
a clone of the Bridgeport, they may have made it in a similar manner.

Jon

Do you have leadscrews? correct? Ballscrews improve the mechanics a lot.
Do you have belts? Direct drive also improves over belts.
Angular contact bearings on the end of the leadscrews? Probably not, they also improve the mechanics...

I have leadscrews, and i rectified them a month ago they are even from start to finish, exchanging for ballscrews is a bit out of my wallet because the machine is a little big and has high load. No belts, X and Y are direct attack and Z has a gearbox. On the start and end of leadscrews they have a bronze nut and 2 top roller bearings for each end.

No, this is the whole fallacy of backlash compensation. It ONLY works for drilling holes,
where there is no smooth X-Y motion. That can be done. Otherwise, it really DOES NOT
WORK! The fact that the table is not constrained by the leadscrew, and has a range
of free motion that the motor cannot control, is the basic problem.

I'm putting aside the idea of using backlash compensation.

On real Bridgeports, the nuts can be slit in half to make two complete nuts that
fit back in the same place in the yoke. Then, the screw that clamps the nut
in the yoke will squeeze the two halfs together. You have to do a bit of
adjusting and testing to get the right setting so that the leadscrews don't
bind at the ends of travel, where there is less wear.

The nuts on my machine have the same system. It's a game of better backlash, worse load and back. They don't squeeze at the ends since i have rectified the leadscrews.

I was thinking, if i add position feedback with an encoder or digital ruler would that compensate the backlash?

Another ideia and the cheapest, with backlash compensation if i slow down the maximum feedrate on the machine and increase the stepgen maximum acceleration to the maximum i can would that reduce the backlash error? On the linuxcnc it says that the stepgen maximum acceleration should be between 1.5 to 2.0 times the maximum acceleration, can i reduce the maximum acceleration and speed and set the stepgen maximum acceleration around 5 times the maximum acceleration?

jbastos wrote:

Do you have leadscrews? correct? Ballscrews improve the mechanics a lot.
Do you have belts? Direct drive also improves over belts.
Angular contact bearings on the end of the leadscrews? Probably not, they also improve the mechanics...

I have leadscrews, and i rectified them a month ago they are even from start to finish, exchanging for ballscrews is a bit out of my wallet because the machine is a little big and has high load. No belts, X and Y are direct attack and Z has a gearbox. On the start and end of leadscrews they have a bronze nut and 2 top roller bearings for each end.

Rectified how? On a lathe or on a cylindrical grinder? Most probably on a lathe... so the result is...
How long is your table? Maybe I can get you some not expensive ballscrews.

Rectified how? On a lathe or on a cylindrical grinder? Most probably on a lathe... so the result is...
How long is your table? Maybe I can get you some not expensive ballscrews.

I rectified them on a lathe. X axis as 1500mm full length and 1000mm threaded, Y axis as 600mm full length and 450mm threaded aproximately.
What is the typical backlash on a ballscrew axis low quality and high quality?

jbastos wrote:

I rectified them on a lathe. X axis as 1500mm full length and 1000mm threaded, Y axis as 600mm full length and 450mm threaded aproximately.
What is the typical backlash on a ballscrew axis low quality and high quality?

Low quality machine tool ballscrews typically will have backlash of about .001-.002"
or .02 - .05mm. High quality ballscrews have zero backlash.

There are also power transmission ballscrews that can have quite a bit of backlash
with single-row ballnuts. But, these are usually not used on machine tools.
You can spot them, they often have a black nitride finish.

Jon

I think i'm going to continue to use leadscrews but i'm going for double nut to adjust the backlash, ballscrew are expensive for my wallet and i think i can do good work with a backlash like 0.1 ~ 0.05mm.

On my machine leadscrew diameter is 32mm, if the nut costs around £120 and the ballscrew C5 £7.5/100mm i got a total for the 2 axis around £390 + the work adapting and other pieces i may need. Thank you for the link, didn't know that site. For the 2 nut with the adaptation i will spend around £40 and i can still have all the manual functions connected by all those gears to the leadscrews. I think i can get backlash around 0.05mm, but i will post the results after the change.

What is the length you need?
You can also consider less diameter ballscrews. They do not need to match the leadscrews diameter.