Replace gas strut on X3 - New struts or maybe counter weights?

[wwendorf]

I'm finally getting annoyed with the stock strut on the X3 so I think i'm going to do a replacement. I finally have a good system down from zeroing and positioning my mill to my vise, but it's a larger vise so I now need the greater height.

I know a number of people on here have done it, and I was hoping that those of you who have done it would be willing to share where you ordered it from. I'm actually hoping to do a twin strut installation to keep the head as balanced as possible, but i'd be interested to see any pics of counterweight systems as well. I've read about a few of them on here, but haven't seen any pics.

I'm in the US so that is a consideration too as far as buying new struts. I'm also going to be building a tool release mechanism like Hoss did for his X2 Freak. Eventually I want to build a tool rack, but for now i'll settle for hitting a button to release my tools.

Thanks in advance,
Wade

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[neilw20]

Here is what I did.
385 mm travel is best with a 20KG strut either side of the head.
It will work much nicer 2 struts.

http://www.cnczone.com/forums/showpo...54&postcount=3
http://www.cnczone.com/forums/showth...011#post397011

[wwendorf]

Where did you order the struts from?

Wade

[neilw20]

Local supplier of custom struts, made in Korea. Quality good.
http://www.strutsaustralia.com.au/about.htm
They charge them to whatever pressure you require.
I suggest 1 or 2 K875-22-xxxN. Extended length 875mm, stroke 380mm.
Two 20KG each. or 1 40KG load. syil one was 60KG which is WAY TOO HIGH, and causes uneven surface finish. The xxxN is Newtons.(stupid unit IMHO)
I just want to test with bathroom scales.

[Journey_Man]

Hey there wwendorf...I found this Web Site in the US...
http://www.acecontrols.com/

[wwendorf]

Not having luck finding struts. I can get 400mm struts with a max length of 900mm.

Back to looking!

Wade

[Journey_Man]

Will the GS-22-400 work? (15.75 Stroke / 34.02 Extended)
Quoting neilw20
"I suggest 1 or 2 K875-22-xxxN. Extended length 875mm, stroke 380mm."
875mm=34.448 / 380mm=14.960....Close enough???
Bob

[syil]

Local supplier of custom struts, made in Korea. Quality good.
http://www.strutsaustralia.com.au/about.htm
They charge them to whatever pressure you require.
I suggest 1 or 2 K875-22-xxxN. Extended length 875mm, stroke 380mm.
Two 20KG each. or 1 40KG load. syil one was 60KG which is WAY TOO HIGH, and causes uneven surface finish. The xxxN is Newtons.(stupid unit IMHO)
I just want to test with bathroom scales.

if you have any test,maybe can provide some suggetion on this parts.
then we change the best one.

[neilw20]

http://www.cnczone.com/forums/showpo...54&postcount=3
http://www.cnczone.com/forums/showth...011#post397011
http://www.cnczone.com/forums/showpo...73&postcount=2
http://www.cnczone.com/forums/showpo...05&postcount=4

This applies to X4 also, but for X4 I suspect the head weighs less than the SX3 so even less charge required in strut.

It needs 2 struts, one on each side of the head, so that in-accurate vertical motion does not break tiny 0.20mm drills. Sideways tilt occurs with one strut.

The ideal stroke is as stated in the third link.

[Ariel_HT5_John]

I am thinking of removing my gas strut and using a counter balance weight. I have problems when i am 3d machining. I have done the backlash in all axis but the Z axis is not repeatable. When 3d raster machining when on a reversal the head is not lifting to the correct position and too much metal is being removed. Would be interested if other people have had this problem. If raster with only down moves all is ok.

When using a counter balance weight i assume the head has to be heaver than the counter balance weight ??

[neilw20]

I call it head nod.
There is always drag on the slides, and when the screw pulls the head down, while going down the z position lags slightly as the downward pull is rear of the dovetails slides.

Getting the gib very straight helps.

You measure the head nod with with a DTI.

Jog down to a position, zero the DTI and the DRO for the Z.
Now with very fine jog steps, (ctrl up arrow on Mach3) move upwards and the DTI will continue to indicate going down.

Just when it changes directions to go up, the reading on the DRO is the amount of head nod, at the tip of the DTI

Mine is 0.035mm (0.0014"). Beat that!! Good luck below 0.050mm!!

At every down move in the program I overshoot by that amount and go up to the desired position.

You could write a macro to do it. I just put the correction in a variable, like #999=0.035.
Say I want to move down to -1.000 this is my code.

(Correction established at start of program)
#999=0.035
F123 (some feed so G1 works)0
.. (other positioning stuff)
G0 Z0 (rapid close to position)
G1 Z[-1+[#999[] (overshoot below desired position - head lags)
G1 Z-1 (Moves down although programmed to go up)
(Now we are at correct depth)

You don't need to do it for every Z move.
Just Z down moves DOWN to finished size to finished size.
No correction is needed for moves UP to a position.

It is better for the strut balance to be correcting for less than the weight of the head so the there is always some load on the screw and not just hovering in mid space.

On my SX3 the strut is 20KG. Original one was lots more than the weight of the head! The strut should be skinny part down otherwise gas leaks past seal because no oil on the seal.

The head nod value varies with lubrication on the Z ways.
It gets worse as the oil is displaced. Oil every 15-30 minutes.

I use teflon based oil.

Initially you will get MUCH worse than 35 microns. Expect over 100 or more.

1. Get the gib making even contact top and bottom. Use blue or some marking method every 5 or 10 times around this loop.
2. Keep adjusting (un screw bottom, screw down top adjustment a small amount. Retighten bottom.
3. Make sure not getting stuck - rapid to top and bottom.
4. Measure.

Back to step one until you can't get it any tighter. Spend at least an hour, or it is not worth the trouble.

From when you start, the top gib screw will advance at least one turn or you haven't made it yet! Put a mark on the screw head.

Making a small program to run it up and down when very tight should smooth out the tight spots, until next time.
Expect it to vary with temperature too.

I just measure at start of job, and put it in the #999 variable.
I have run 2000 hours of a job repeating to 0.002mm after a big learning curve.

Unless the column is attached to a brick wall or similar you will be 20 times worse off.

Column bend -- actually flex at the base attachment point and the base -- not the column, for a 5KG cutter load attached to a brick wall is 0.015mm

Free standing 0.3mm (0.012") for a 5KG load change. Makes the head nod look small?
A worn 10mm cutter can easily load vertically to 5-10KG.

[Ariel_HT5_John]

My problem is the raster maching 3d Ie the the table is moving X+ the Z-.The head gets to a set Z position Y will them move say 0.25mm the table will the move X- and Z+ and so on. Its on the reversal that the head is not moving up the correct ammount.

When i do the back lash on the machine i remove the backlash figgures restart the mach 3. I jog the head down with a dti under the spindle nose set the dti to zero jog the machine down a set distance say 1mm then send it back up 1mm in mach then note the short fall thats the back lash setting. This method works well and has done in the past on my Bridgeport and Hurco.

My Syil X6 has linear slides on the Z axis.

My machine also has some odd things happening. If you press the e stop when the spindle is not running after about 20 sec the spindle starts up as slow speed for about 2 revs. ??

[neilw20]

This is NOT BACKLASH.
Backlash is bi directional.
Head nod is only in one direction.
You need head nod compensation, and where do you find that?

You need a macro for headnod, unless you rewrite the trajectory planner.

[mikemill]

Neil
Interesting you say ram should be positioned downwards, as my strut has just failed after four years work!! must admit it was dry
Have ordered one from Syil UK will keep an eye on oil

Cheers
Mike

[neilw20]

Order one locally from a car parts supplier.
Low cost at the right place.

The Syil one is well over 50-60 KG -- much too strong.
Get one charged to 20KG is all I have now.
When compressed it is higher than that.

Look back at post 1 and read why.

Extend your Z travel at the same time. Too easy.

[mikemill]

Neil
Thanks for the advice, but is not the Z hight limited by the ball screw and limit switch, can't see how you extend this?

Mike

[neilw20]

Will it run to the top of the column?
What stops it at the top? The screw or the strut?
What stops it at the bottom?

[Ariel_HT5_John]

Just to say the machine is now sorted i got to the bottom of the non repeatabilty of the backlash in the Z axis the lead screw was moving !! the retaining nut that is on the lead screw was not tight it was allowing movement in the Zaxis. I also looked at the X & Y axis the X was ok on the Y managed to remove a small amount but i did find the cap screws holding the bearing to the machine casting were not tight.

I quite like your system of increasing you macine stiffness / damping But what happens if your workshop has a 10 deg C temperature change. Have you created a bi metal/brick strip!!

It would still be interesting to compare gas strut to a counterbalance system. The gas strut must have some damping built in. On my X6 machine the strut overhangs the table which is a pain when i have a large vice fitted as i have to jog the table to a safe place when i home the machine as the mounting of the strut overhanges the table. The other advantage of getting rid of the strut i can then change the bellows cover for some thing better. A few years ago i had a Hurco Hawk 30 machine the bed way cover between the bed and the z axis box ways had what i called a roller blind fixed to the Y axis saddle and head of the machine there was a roller which kept the rubber sheet at 90 degs as the head went up or down or table +- the blind extended etc.

[neilw20]

Damping. Once it stiff and tight, and the inertia of the whole heavy head, I think damping is what happens to a towel when I wash.

[Megaplow]

Looking forward to the extra 100mm of travel!

I just ordered a 45kg strut today from McmasterCarr for $21. 45 is over the suggested 35-40kg, but it is still less than the 50-60kg that the original strut had.

From the link below I found the part number 4138T62.
McMaster-Carr

Joe