[millhead]

Hi,

I have an idea for X and Y backlash reduction with the stock leadscrews, and would like your comments.
The idea is so simple, there must be a problem with it!
Simply, use a 20 lb gas spring to exert pressure (pre load) in one direction on each axis. The gibs need to be well lapped so the saddle moves freely, to reduce friction.
This has the added advantage that it is self compensating for nut wear.

The only price you pay would be a slight reduction in rapid speeds.

[stephenrc]

As long as the cutting tools puts a force less than 20 lbs on the table against the gas spring. Which means you would be making very small cuts, if any.

[M250cnc]

Millhead

Thinking about your idea i see two problems.

One: is excessive wear on the nuts.

Two: when climb cutting, if the cutting force was great enough it could overcome the gas spring with the inevitable consequences.

Phil

[TXFred]

My gibs are very well machined and are so tight that I cannot disconnect the leadscrew and push the table by hand. And I can exert a lot more force than 20 pounds.

But a .030" depth cut with a .25" is still able to overcome this and cause the backlash to become evident. That tells me that the cutting forces are much greater than 20 pounds.

This is an original idea, but I don't think that it will work. A strong enough air spring to overcome the cutting force would place a massive load on the stepper motor, requiring a motor upgrade.

Fred

[HellPhish]

Millhead

Thinking about your idea i see two problems.

One: is excessive wear on the nuts.

Two: when climb cutting, if the cutting force was great enough it could overcome the gas spring with the inevitable consequences.

Phil

what about old cylinder valve springs? take the damper out and put it over the screw between 2 washers. a stock sbc spring pressure isnt that high but would do very nicely.

[hoss2006]

Spring pressure between 2 ballnuts in a typical double nut setup is 100-200 lbs to counteract backlash.
The ball bearings can handle that force, don't think a stock screw and nut would last long.
Hoss

[Dano523]

Lap the gibs and polish out the tracks.

On the Y block, bearing it instead of the current metal on metal method.

Slit the screw blocks, and add set screws so you can tension the nut against the screw. The current screw blocks are Brass, but if you go with a Delrin split blocks instead, you can get a better tighter fit of the treads.

Done correctly, your in the .001 range of lash, and that is tighter than even some larger manual machines.

And yes, when I get the chance may even try to come up with some Delrin spring pressured blocks that should last longer than the split designed, which will not required readjustment as the block threads begin to wear.

[TroyO]

I keep looking at the Belleville Springs that Hoss shows on his site...

http://www.hossmachine.info/Shop_Info.html#belleville

The thought being... what about tossing one or more of those in the kerf on a split nut design? Especially a delrin type. I'm not sure of the pressures developed by those washers though.

Anyway... if it develops enough to open the kerf up you would have to compress the nut to install it on the leadscrew, but once you have it assembled it should compensate until it ran out of spring.

[millhead]

Lap the gibs and polish out the tracks.

On the Y block, bearing it instead of the current metal on metal method.

Slit the screw blocks, and add set screws so you can tension the nut against the screw. The current screw blocks are Brass, but if you go with a Delrin split blocks instead, you can get a better tighter fit of the treads.

Done correctly, your in the .001 range of lash, and that is tighter than even some larger manual machines.

And yes, when I get the chance may even try to come up with some Delrin spring pressured blocks that should last longer than the split designed, which will not required readjustment as the block threads begin to wear.

Yes, I have already replaced the Y bearing block with a Ball bearing block, lapped the gibs etc.
The purpose of my question was specifically to get feedback on the idea of preloading the table and saddle , rather than replacing the nuts with a different design.

The consensus seems to be "It ain't gonna work".

I like the idea of split Delrin nuts. Have you actually done this, and how long has it lasted? How did you tap the Delrin nut for the non standard screw?
I would love some details on this.
Thanks.