[svarzaru]

This might be totally stupid, but my Z (Taig) doesn't have any backlash, presumably because of the weight on the spindle & motor. Wouldn't this work on X and Y as well? Use a few pulleys and hang some weights of the beds?

I have servos is that makes a difference.

Thank you.

[SCzEngrgGroup]

This might be totally stupid, but my Z (Taig) doesn't have any backlash, presumably because of the weight on the spindle & motor. Wouldn't this work on X and Y as well? Use a few pulleys and hang some weights of the beds?

I have servos is that makes a difference.

Thank you.

It would work only as long as the weight exceeded the maximum machining force the axis would ever see. And the extra weight would roughly double the load on your drives when moving in one direction, while reducing it in the other, so your rapid speeds would go down in one direction, and up in the other. You'd increase friction and wear on the ways and screws as well.

Regards,
Ray L.

[project5k]

yea, in theory i can see where you would come up with that.. and its not a terrible idea, i once saw a guy that used springs.. but just like Ray said, its gonna have other effects that might not be so disireable..

not to mention that when you remove power from the drives, that the weight might pull the table all the way to one corner of its travel..

also you've gotta think about the vectored forces.. lets say that you pull on x in the + direction, at the center of the y travel, then when you get to y++ max or y-- max, the weight will be pulling, at a vector angle in the y- direction when your at y++max, and in the y+ direction when your at y--max, thus adding even more load to things, and this vectored force will vary all along the travel of the axis...

then theres all the cable and pullies and complicated-ness of it, and it quickly becomes more trouble to upkeep than just fixing things the right way.

again, i dont want to belittle your idea, keep thinking, but on this one, i think the added complexity and potential other drawbacks might out weigh the gains....

[rowbare]

Check this out:

http://www.cnczone.com/forums/showpo...44&postcount=2

[project5k]

well now thats interesting, how does it work out with the strings pulling at an angle?

do you have the one weight and that pulls on both the x and y?

[SCzEngrgGroup]

Check this out:

http://www.cnczone.com/forums/showpo...44&postcount=2

The way that guy did it is clever, in that he has a single cable and weight providing the force simultaneously for all three axes - A very clever and elegant solution. It's certainly more feasible to do that on a small machine like a Taig, where cutting forces are pretty low enough that you're not talking a lot of weight required. You wouldn't want to even try that on a large machine. But it will wear the screws, nuts, and ways at roughly double the normal rate. A hobby machine will likely see little enough use to make that a perfectly valid trade-off.

Regards,
Ray L.

[project5k]

yea, thats true, and assuming that the drive system is strong enough to accelerate the weight in addition to the table, and not hurt the speeds too much, then its a possible solution...

i still wonder about the vector loads tho... seems to me that it could show up around the middle of the table

[SCzEngrgGroup]

yea, thats true, and assuming that the drive system is strong enough to accelerate the weight in addition to the table, and not hurt the speeds too much, then its a possible solution...

i still wonder about the vector loads tho... seems to me that it could show up around the middle of the table

No, if you look carefully at the photos, you'll see there are two pulleys attached to the left side of the saddle, so the balance of forces on the saddle does not change with position. The one outboard pulley is roughly centered between the cable anchor on the front of the saddle, and the pulley on the rear of saddle, so the fore-aft forces are roughly balanced at all times. Similarly, the X axis sees a constant, almost purely longitudinal load regardless of position. This is the very clever part of the way he did it.

Regards,
Ray L.

[project5k]

good point, i missed that before... so i guess it really would work ok then... hmm interesting.

[BobWarfield]

Sounds clever, but...

If you ever stick an indicator on a machine and then lean on the machine even just a little bit, it is surprising how much the machine deflects. I've done this on MUCH larger machines than a Taig, and you can still measure deflection. I have read maintenance procedures for full on VMC's that talk about this issue too.

Not sure I want a backlash cure that will deflect the machine. I'd rather work it out on the leadscrew. Maybe everything pulls in just the right direction to cause no ill effects, or maybe that machine is never even close to being in proper tram. Hard to say.

Cheers,

BW

[SCzEngrgGroup]

Sounds clever, but...

If you ever stick an indicator on a machine and then lean on the machine even just a little bit, it is surprising how much the machine deflects. I've done this on MUCH larger machines than a Taig, and you can still measure deflection. I have read maintenance procedures for full on VMC's that talk about this issue too.

Not sure I want a backlash cure that will deflect the machine. I'd rather work it out on the leadscrew. Maybe everything pulls in just the right direction to cause no ill effects, or maybe that machine is never even close to being in proper tram. Hard to say.

Cheers,

BW

You would for sure need to tram it with all the weights in place. And at least the way the pulleys are arranged, nothing is pulling very hard laterally on the column, which is probably the flexiest part of the whole thing.

Regards,
Ray L.

[svarzaru]

What that guy did is what I had in mind, except he made it self contained, so he had to attach things to the column. I was just going to direct the weights to hang of to the back side of my bench.

Since the screws on the taig are the same for X,Y,Z and the Z is supporting a much bigger load then the 7lbs he is using, I will have to assume that the screws are beefy enough for this.

I'll give it a shot to see how it works.

Thank you everyone.