[aaepl]

Hi all,

Okay I'm a newbie, both to this forum and to CNC in general, so please bear with me.

I am working on a recently refurbed fadal 8030 and it appears that I have a z axis repeatability problem when jogging. If I use a dial indicator and jog the head up and down at various rates and return to the same depth based on the monitor numbers, the dial indicator can be out anywhere up to 0.005".

Now if I run the same test but use a program to run the head up and down my repeatability is within machine spec +-0.0004 inches. In both tests I locked the spindle and ran the dial indicator down onto the bed.

Is it possible that when you jog, the backlash compensation is not accounted for? If this is the case, that means setting tool offsets would become a nightmare if you are manually jogging down to a height block. Any ideas?

Thanks.

[Delw]

I was told long ago DONT use the handwheel on any machine for setting backlash.
write a small simple program.

also when setting your offset via a handwheel you wont get perfect offset dims.
there is a few factors one being the handwheel and 2 being the amount of friction you use.
if you need off set exact, set them off a block then back them off a few and run your part bringing them in.

[aaepl]

I was told long ago DONT use the handwheel on any machine for setting backlash.
write a small simple program.

also when setting your offset via a handwheel you wont get perfect offset dims.
there is a few factors one being the handwheel and 2 being the amount of friction you use.
if you need off set exact, set them off a block then back them off a few and run your part bringing them in.

Hi Delw,

Thanks for the fast reply! Regarding the backlash settings, these were factory set, and I have re-checked them using the program given in the maintenance manuals. As far as I can tell they are fine.

That is a pain that you can't get accurate offsets using the jog wheel. I take your point that I can set it, back it off 0.005" then run the program and gradually reduce it. But if you set tools up off each new job and not a fixed reference on the bed, that is a painfully slow process.

Has anyone else come across this problem - that the jog wheel does not give accurate positioning? Or do most people use an automated tool setting system and therefore not run into this issue?

Thanks again!

[Delw]

as far as setting tool offsets I set all my tools, set a piece in the vise then hit the button.
measure and ajust form there. I do it on every machine I ever had lathes and mills with the exception of my haas. It has a tool setter. I just hit the button and so far its never been a problem and accurate to the .0001. thats all on bar stock stuff reworks and castings I back off .010( except the haas)
the setting of tools is thorugh a macro which runs a feed rate so its better already.

don't forget that you have tool pressure that screws things up also that should be taken into consideration. on hard or tough cutting metals I always run a rough and finish too.

I set pretty much 90% of my jobs off the location face of the Jaws then use work offsets to adjust height.

for example lets say I am running a 4" tall part of a standard everyday set of soft vise jaws. All my tools are set off the vice jaws, then I pop in 4" on the work offset, next parts I run is 2" high I change the work offset to 2"
if its a part that is already finished on one side then I just set the workoffset .010 over what every the part height is and run the part, check and drop the work offset accordingly.
I very rarely every have to set each individual tool up on ever job. I can run for weeks and never change offsets.

when you say accurate offsets what type of aaccuracy are you looking for? remember your using feel to set the tool.so accuracy really aint there.
I use a piece of paper I am betting all mine are with in .001-.002 of each other reason being I do it everyday and have been for 20+ years, AFter a while you can tell by feel of sliding a pcs of paper and the drag it has. change papers and your screwed LOL it feels different. I always use printer paper. nothing piss's me off more when my wife buys CHEAP printer paper cause my feel of setting the tools are always off.
I also never use the .0001 setting to set offsets, always the .001 setting.
While my haas in incrediably fast setting tools I can run them fast on the fadal as well. settings tools usually take about 10 mins on the fadal if that.

After a while you will get to know your machine and get the feel of setting offsets. it wont take long maybe a few weeks tops then you will be accurate.

you can get them all close run a part then adjust alot faster than you can fiddle fart around with blocks and the handwheel trying to get it just right. Why waste time? Ive seen guys take hours to set 10 tools up then back everything off and run them one at a time.

oh yeah dont forget a piece of paper is about .0025 thick, that means that when you set your tool on that paper you have .0025 of cushion before the tool touches the jaws.

Delw

[Jake E.]

I have noticed an issue with backlash as well when setting my workshifts based in X and Y. We run several different parts (usually changing setups 4-5 times a week) and each part uses either different jaws (we use 4" chick vises with aluminum jaws) or requires reskimming the jaws due to wear. For the Tool offsets, we use an Elbo Controlli Presetter for the tools and then set the Z using a 1" block off of different areas of the vise. The Z is not as much an issue as the X and Y is. Usually when setting offsets, I repeat picking up the offsets 3-4 times to ensure I am getting the same number (within .001"), but that requires me to pick up the offset, then move .020 away and then using .001" increments, coming back into the stop.

[aaepl]

Okay thanks for the input guys. I appreciate it.

I guess what I am trying to establish here is whether I have a problem with my machine. If what I am experiencing is 'normal' then I'll find ways of compensating. If its abnormal then I'll go digging.

Jake E I am interested in the problem you mentioned with X and Y offsets. Have you done a test using a dial test inditicator to see if your Jog positioning is repeatable? Are you working on a Fadal? I have only done this in the Z and for me it is not repeatable. Some runs up and down I get back to the exact point (i.e. screen number and depth gauge number match) but other times it can be out as much as 0.005".

If you do a finish cut across the entire work piece then sure, there won't be a visible problem. But there are many situations where a 5 thou difference between tools can be significant. Sure I can follow procedures like what Delw suggested, and that will mask the problem, but I want to know if what I am experiencing is 'normal'.

Cheers.

[alex gitzel]

Make sure your gibs are not too loose/or too tight.also jog down so you can get to the screw ,put it in e-stop and go and turn the screw back and forth to make sure the coupling and screw are not loose the direction change should be smooth(no loose spots).

[Delw]

Are you using a indicator to check your zdepth moves? if you are then just for the hell of it make a program( you can use fast feeds) if it doesnt repeat you have a problem.
if your not using indicator then thats your problem
Get a .0001 indicator, a quality one, brown and sharp, interrapid etc etc. dont use junk.

one other thing. Run 2-4 parts with some dimensions X Y Z , get all your tools set then run the 2-4 parts if the parts comes out right don't worry about anything else, sometimes to we get too picky and over do things, I been there done it.

Delw

Okay thanks for the input guys. I appreciate it.

I guess what I am trying to establish here is whether I have a problem with my machine. If what I am experiencing is 'normal' then I'll find ways of compensating. If its abnormal then I'll go digging.

Jake E I am interested in the problem you mentioned with X and Y offsets. Have you done a test using a dial test inditicator to see if your Jog positioning is repeatable? Are you working on a Fadal? I have only done this in the Z and for me it is not repeatable. Some runs up and down I get back to the exact point (i.e. screen number and depth gauge number match) but other times it can be out as much as 0.005".

If you do a finish cut across the entire work piece then sure, there won't be a visible problem. But there are many situations where a 5 thou difference between tools can be significant. Sure I can follow procedures like what Delw suggested, and that will mask the problem, but I want to know if what I am experiencing is 'normal'.

Cheers.

[Jake E.]

Jake E I am interested in the problem you mentioned with X and Y offsets. Have you done a test using a dial test inditicator to see if your Jog positioning is repeatable? Are you working on a Fadal? I have only done this in the Z and for me it is not repeatable. Some runs up and down I get back to the exact point (i.e. screen number and depth gauge number match) but other times it can be out as much as 0.005".

Yeah, it is a Fadal. Not using a dial indicator, just an edge finder.

[Delw]

Yeah, it is a Fadal. Not using a dial indicator, just an edge finder.

Thats the problem your using an edge finder to do precision work you might as well use paper and the feel method.
when setting backlash use ONLY a good Dial Indicator, otherwise its like using a glass of water to lever your machine.

Delw

[Neal]

Here, Here!!! DELW is again the utmost guru! Listen to him for he gives GOOOOOD advice!

Neal

[Delw]

Here, Here!!! DELW is again the utmost guru! Listen to him for he gives GOOOOOD advice!

Neal

Now neal I never said that,
I suck with fadals I still cant get my machine to not give me a error #12 error when doing helix work ie g3 or g2 x y and z moves.

Seriously though can you really use an edgefinder to set backlash on a machine?
using an edgefinder on hits the outer most part of the part, if you have even the slightest burr you will get a bad reading if you move your y axis even the slightest, if your part is angled off the z plane you will get an bad reading if you move the z axis at all during the process.

Dont get me wrong I use a edge finder quite often, but unless your part is perfectly square to the locator(jaws) or you dont move the y or z axis when setting up the x axis your going to not be exact.

Delw

[Neal]

An edge finder is fine for fixture offsets if you are very careful and double check for a repeating reading. For the backlash the indicator is indicated [snicker].

Neal

[aaepl]

Hi guys,

Thought i'd give an update. Okay it turns out the problem I am experiencing is not isolated to jogging manually although that is where I first became aware of it.

I just ran a simple high speed surface finish scallop program where the tool runs along the x for about 200mm gradually reducing in height (about 1/4 inch), then returning along the same path to the start point. After the first run I measured the tool depth (accurately). After the second run the tool was 0.005" closer to the job than when it started! After the third run it was 0.005" lower. I repeated this at least 5 times with the tool dropping 0.005" each time! It is not a coding issue - it is a basic program with a repeat function and I make it stop at the start point so I can measure depth.

Make sure your gibs are not too loose/or too tight.also jog down so you can get to the screw ,put it in e-stop and go and turn the screw back and forth to make sure the coupling and screw are not loose the direction change should be smooth(no loose spots).

I checked the ball screw - I could turn it by using two hands and it was certainly not loose in either direction.

Could gibs cause this problem or should I be looking elsewhere like at the axis cards?

Any suggestions would be appreciated

[aaepl]

Forgot to ask - should there be survey data for the z axis? I have survey data for x and y but nothing for z. Is that normal?

Thanks

[Neal]

Normally speaking the Z axis does not get a survey from the factory. If you are doing 3D surfacing then I recommend that you have the Z lasered and survey installed.

Neal

[DareBee]

If it drops exactly .005 EVERY SINGLE pass repeating perfectly to infinity than it is NOT mechanical.
There has to be something wrong with CPU or a board or something.

[aaepl]

If it drops exactly .005 EVERY SINGLE pass repeating perfectly to infinity than it is NOT mechanical.
There has to be something wrong with CPU or a board or something.

Yes you are right, I pulled the trigger on that conclusion a little early. It did drop exacly 0.005" five times but it didn't do it indefinitely.

I now know what the problem is. I marked the z axis motor housing and the motor coupler, and found that the alignment between the two marks was always perfect even when I observed repeatability problems at the spindle. Therefore the problem is downstream of the z axis servo. The only thing left in the system is the gibs and straps.

I tinkered with these in accordance with the manual and instantly my offset problems changed. I haven't yet fixed it but I know that the gibs are the issue. I believe the problem I am experiencing is "stick-slip". When I rapid down to a certain depth the gibs hold the head up a fraction. When I work the machine around at about that height for a while the head falls down to the actual height it should be. That fall I measured is up to 0.04".

I am using the right waylube, so it has to be gibs. I'll let you know how I go with the adjustments.

Thanks to everyone for their input.

[aaepl]

Okay, I have got it fixed. I found the top gibs to be three full turns too loose. On the bottom one was too tight and the other a bit loose. The z now repeats within 0.0005".

I figured that given the gibs weren't adjusted properly I would double check the backlash values. I found that the z axis had 0.0015" of backlash. That seems a bit high doesnt it? It seems to repeat fine though so i don't know if it is worth hunting down that play. It is a new ballscrew so that is ruled out.

I am yet to complete the x and y axis backlash checks, but what are normal backlash values? I use a fadal 8030 so it is quite a large bed.

Please forgive these newbie questions, I'm on a steep learning curve.....

[jwasilk]

I am not very good at the Fadal, but making our way through. On x and y when we move .05 dro the indicator shows .060, we have been changing the numbers with the SV command, then shutting it down, there is no change. Can somone help us for the next move. Thanks.