X axis spring back on vice squaring ?

[ti5m]

Hi there,

I have just done a CNC conversion on a new Optimum MH28V mill and am having a strange thing happen when i went to indicate my vice in for the first time on the new machine.

I indicated the vice in with my DTI in the quill but when i move in the X axis to the other side of the vice jaw and stop the reading on the DTI will keep moving for another 0.02mm ? Then settle back to 0. I move the table in the other direction along the X axis and same sort of thing where the DTI will overshoot a bit and then come back to 0 ?

I thought it might be the way oil from my one shot oilier backing up and the pressure was pushing on the table and then when the table is not moving the oil pressure dissipates and lets the table fall back into place but thas probably a long shot ???

I just cant figure out what might be causing it. Has anyone else had this happen ? Its hard to indicate the vice in as when the table is moving its out of square. But when the table is stopped it settles back into square ?

Things i have done to problem solve:

Tried a different DTI = same result
Tried DTI on a mag base instead of in the quill = same result
Checked and adjusted gib tighter/looser = same result
Loosened fixed and floating bearing blocks and realigned = same result

Here is a video of what is happening



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[handlewanker]

Hi, as it's only the X axis that is moving I would "guestimate" that you have a way oil cushion build up that is pushing one side of the X axis dovetail away.....as soon as the motion stops the oil build up drains away.......you could try a thinner way oil........perhaps the seals at the end of the X axis dovetails are allowing this to happen......remove the seals at one end and see what happens.

A moving body with a fluid between it will "aquaplane" when the body is in motion.....it's called dynamic something or other.......can't remember the exact term.

If the forward motion is slow the pressure dissipates but with fast motion you get a denser layer between the 2 surfaces that will create a pressure.....having slack gibs will exacerbate the problem......thjs will create a void for the pressure to move the slides back and forth.

Do a test........with a dial indicator against one end of the table.....grip the table on the ends and attempt to rock it sideways against the dovetails......the dial indicator could move a few thou but if it moves a lot the gibs are too slack.

Slack dovetail jibs are one solution people use on a manual mill retrofit to overcome dovetail friction and stepper motor stalling......one reason why linear rails are so good in that concept as they work practically metal to metal without jamming up.

If this pans out to be the cause, you might need to have a more powerful stepper motor or servos to move your axes.....slack gibs are NOT the way to go......maybe thinner way oil.
Ian.

[ti5m]

Hi Ian,

Sounds like what it might be possibly. I am using Moble vactra #2 way oil so not sure if they do a thinner one ?

As a test i did try to really tighten up the X gib over tight and the motor still drove it ok but it didnt change the behavior of things. Its a 640 Oz-in NEMA 34 from Homann Designs.

I dont have any seals on the ends of my dovetails.

I guess i could try wiping some of the oil off the x axis and see what that might do as a test ? Or disconnect the oil lines to the X axis to relieve the back pressure ?

[handlewanker]

Hi, be careful on wiping the oil off as the X axis does do a bit of speed and that means you do need to be riding on a film of oil at all times.....cast iron does not like running on a dry surface.

It's also possible, but not very likely, that the dovetails are not all that well mated.....hardly likely on a new mill but it could happen.........my last course of action would be to strip the table off and blue up the slides.....that takes some skill and is time consuming.

The truth is, the dovetails must guide the table in 2 planes accurately.....any variation from the truth is a strip down to look and see situation.
Ian.

[atomarc]

Interesting! I wonder if you might shed more light on the problem if you put something on each end of the table and trammed them to see if the problem was still there when the table was at the extremes. If you have a second DTI or even a indicator, maybe setting it up to read the top of your vise jaw as you did your test may narrow your search.

What I find interesting is the slo-mo speed at which the dial comes back to zero. It sure looks like parts floating on a oil film that slowly ebbs away...but a typical oil film wouldn't be .002 thick would it?

Make sure the saddle is tight and not wiggling. A ballnut that's not 100% aligned with the ends could possibly be putting the table in tension.

Good luck and keep us posted, I would love to know the outcome of this bizarre problem.

Stuart

[ninefinger]

...
What I find interesting is the slo-mo speed at which the dial comes back to zero. It sure looks like parts floating on a oil film that slowly ebbs away...but a typical oil film wouldn't be .002 thick would it?...

Stuart

Note that he is using a metric DTI so that 0.02mm is equal to 0.0007" or less than a thou. Could the oil film be half a thou? Absolutely. The question is why it builds up and bleeds away in one direction. Ideally it should be equal font and back and wouldn't introduce this error.
I'd try taking the gib out and checking it on a flat surface for any bend.
Or try this - its a long shot but easy enough - disconnect the line from the one shot oiler. Bending a hose can reduce its volume, pumping oil into the ways, which then bleeds out slowly when you stop.

One detail question: Do you have double ball nuts with preload by chance? Torque from the ballscrew on a ballnut with high preload could be a reason for the movement being positive one way and negative the other way.

Interested to know the answer to this mystery.
Mike

[ti5m]

Thank for the helpful tips.

I tried a few things and i think am making some progress ( at the expense of introducing other problems).

So i put my other DTI on the top of the vice jaw as well as the one on the face of the same fixed jaw. I see no spring back on the top of the jaw. Only the DTI touching the face.

I also tried a DTI out on the far end of the X table and see a twisting motion where the DTI on the vice sees a movement in the +direction and the DTI at the far right end of the table sees a movement in the -direction. So that got me thinking maybe there is indeed a loose gib situation. I pushed and pulled on the table and saw about 0.05mm deflection. So i went and tightened up the Y gib a half turn and the X gib a half turn then pushed and pulled on the table and saw 0.04mm deflection. Keept adjusting the X and Y gibs till i got the deflection down to 0.02mm. Gibs are really really tight at this stage ( super tight actually). Went about 2 full turns from where they where on both x and y.

Ran the DTI along the face of the vice jaw again and see only the tiniest little bit of spring back. Something like 0.0005mm. I call that good.

Only now with the gibs that tight it gave double the backlash. Backlash setting in Mach3 was 0.018mm for X and 0.02mm for Y . Now they are 0.5mm for X and 0.04mm for Y. I think the ballscrews are now twisting under the extra strain (2005 screws).

Next thing i will try is disconnecting the oil lines going to the X axis and see if there is back pressure there.

[ti5m]

Just an update.

Doing some more investigation work and it seems to be coming from the Y axis. I loosed off the gib on the X axis as it was really very tight at this stage and i didnt like to run it quite THAT tight so i backed it off a 1/4 turn and ran another test and it didnt make anything worse. So i backed it out another 1/2 turn and surprise it didn't change the reading at all. So i backed it out to where it was before i tightened it and the DTI reading is still good.

So that was an interesting find and made me wonder about the Y axis gib and what would happen if i backed it off too. So i loosened it 1/4 turn and the problem started to come back. Loosened it some more and it got worse.

So it was in the Y axis after all which is a bit strange as the Y is not moving when i am tramming the vice in. Only the X axis should be moving so that's why i thought it must be something in the X axis that's not right.

I did try disconnecting the oil pipes to the X and Y axis but didn't see anything come back under pressure while moving the X and Y around.

[handlewanker]

Hi, the too tight gibs are a no no as that will give you more problems,,,,,they should be adjusted to "ideal" run tightness.......... I think the run tightness will give you the miniscule variation at all times as there is a running clearance between the metal faces and oil is elastic......probably most people haven't noticed it on their machines.
Ian.

[handlewanker]

Just an update.

Doing some more investigation work and it seems to be coming from the Y axis. I loosed off the gib on the X axis as it was really very tight at this stage and i didnt like to run it quite THAT tight so i backed it off a 1/4 turn and ran another test and it didnt make anything worse. So i backed it out another 1/2 turn and surprise it didn't change the reading at all. So i backed it out to where it was before i tightened it and the DTI reading is still good.

So that was an interesting find and made me wonder about the Y axis gib and what would happen if i backed it off too. So i loosened it 1/4 turn and the problem started to come back. Loosened it some more and it got worse.

So it was in the Y axis after all which is a bit strange as the Y is not moving when i am tramming the vice in. Only the X axis should be moving so that's why i thought it must be something in the X axis that's not right.

I did try disconnecting the oil pipes to the X and Y axis but didn't see anything come back under pressure while moving the X and Y around.

OK......that is a good result.....I think you might have a gib on the Y xis that is not all that flat.........easy to pull out and test etc.

If the Gib is OK the problem might lie in the actual machining of the dovetails on the Y......it's a big job to strip out the table and Y saddle just to blue up and see.

The last thing is.......if the Y axis saddle is constructed on the light side it will flex if the gibs are over tightened........this will affect the X axis too as the table runs in the saddle top dovetails.

IF......the Y axis dovetails are suspect in their machining and fit.....that is a manufacturing error.....bad workmanship etc.....it's a bit late to claim on the warranty once you've retrofitted it etc......your only recourse is to refit the Y axis dovetails, but that takes quite a bit of skill to achieve.
Ian.

[mactec54]

Thank for the helpful tips.

I tried a few things and i think am making some progress ( at the expense of introducing other problems).

So i put my other DTI on the top of the vice jaw as well as the one on the face of the same fixed jaw. I see no spring back on the top of the jaw. Only the DTI touching the face.

I also tried a DTI out on the far end of the X table and see a twisting motion where the DTI on the vice sees a movement in the +direction and the DTI at the far right end of the table sees a movement in the -direction. So that got me thinking maybe there is indeed a loose gib situation. I pushed and pulled on the table and saw about 0.05mm deflection. So i went and tightened up the Y gib a half turn and the X gib a half turn then pushed and pulled on the table and saw 0.04mm deflection. Keept adjusting the X and Y gibs till i got the deflection down to 0.02mm. Gibs are really really tight at this stage ( super tight actually). Went about 2 full turns from where they where on both x and y.

Ran the DTI along the face of the vice jaw again and see only the tiniest little bit of spring back. Something like 0.0005mm. I call that good.

Only now with the gibs that tight it gave double the backlash. Backlash setting in Mach3 was 0.018mm for X and 0.02mm for Y . Now they are 0.5mm for X and 0.04mm for Y. I think the ballscrews are now twisting under the extra strain (2005 screws).

Next thing i will try is disconnecting the oil lines going to the X axis and see if there is back pressure there.

It's nothing to do with the oiling system, the Gibb is not flat, as others have suggested, and may be the table ways have not been scraped correct, The Ballscrew mounting also if not parallel with the table travel, will cause the same problem, this is not an unusual problem with these Chinese Mills, a lot have had to fix the gibbs and the ways on these machines, you are using the right oil, you can never have too much, although to much will just spill everywhere and be wasted, but it will not cause this problem

[ti5m]

I just took the Y gib strip out and put a machinists square blade across it and it dose appear to have a very slight bend in it. I could only just fit a 0.0015" feeler gauge between the gib and square at the worst spot. I dont suppose they can be straightened can they ?

[handlewanker]

Rubbish.....that is not a typical case of "a problem with these Chinese mills" .....the mill has been retrofitted, probably with balls crews so this is the op's own DIY build problem if that be the case.

However, my opinion on the possible misalignment of the ball screw mounts would be to cause a progressive tightening of the table as it neared one end or the other, IE the screw out of parallel to the X axis.....this is not the phenomena that is apparent, so could be ruled out.

The machining of the slideways possibly is the problem but I suspect that the XY axis saddle casting is the cause as it "could' be flexing under load.

The fact that there is a result from adjusting the Y axis gibbs point more to this

Two things can happen.......you either live with it.....IE pretend it's not there and get on with the job etc ..... or do a complete tear down.....again.......as the rebuild could have introduced a problem that the manufacturers were not guilty of.

As this is a manual mill retrofit I expect that (can only be) the original spindle was quill activated......that means the new rebuild would be with the quill locked up and the head casting doing the Z axis travel instead of the quill......shock horror if the quill is still being used.

This means you will have the "head nod" syndrome that all quill origin mills have when the head is used for Z travel.

I have to wonder why, when this problem(s) has been highlighted in so many manual mill retrofits, the dovetails are not removed by machining and linear rails fitted throughout .....or else you live with it and pretend I does not exist.

BTW Mac, according to the EBAY listing the BF20 is made in Germany........it "might" be a Chinese import stocked by a German dealer.....get your facts right instead of rubbishing anything that hints of Chinese.
Ian.

[handlewanker]

I just took the Y gib strip out and put a machinists square blade across it and it dose appear to have a very slight bend in it. I could only just fit a 0.0015" feeler gauge between the gib and square at the worst spot. I dont suppose they can be straightened can they ?

Hi....forget it, that small amount is not even a problem to worry about as the gib will flex slightly as it's adjusted in the dovetail........not knowing the method of adjustment I would guess that there are a number of grub screws pressing on the side of the gib to adjust it in the dovetail.........tapered gibs are a luxury you would only find on a more expensive machine.
Ian..

[ti5m]

Hi Ian,

It dose have tapered gibs. Its one of these Mills https://www.machineryhouse.com.au/M652

It is made in China but is designed in Germany.

I have some C7 TBI 2005 ballscrews with double nuts on it. C5 A/C bearing blocks to support them. Gecko G201x drivers. Ethernet smoothstepper to a Homann Designs MB-02-V6 Bidirectional Breakout Board.

Here is a picture of my Y saddle with table removed for a better look at how it is.

This is my first ever CNC anything. Coming from a manual Sieg SX2 mini mill so its a bit more mill than i am used too.

[mactec54]

Rubbish.....that is not a typical case of "a problem with these Chinese mills" .....the mill has been retrofitted, probably with balls crews so this is the op's own DIY build problem if that be the case.

However, my opinion on the possible misalignment of the ball screw mounts would be to cause a progressive tightening of the table as it neared one end or the other, IE the screw out of parallel to the X axis.....this is not the phenomena that is apparent, so could be ruled out.

The machining of the slideways possibly is the problem but I suspect that the XY axis saddle casting is the cause as it "could' be flexing under load.

The fact that there is a result from adjusting the Y axis gibbs point more to this

Two things can happen.......you either live with it.....IE pretend it's not there and get on with the job etc ..... or do a complete tear down.....again.......as the rebuild could have introduced a problem that the manufacturers were not guilty of.

As this is a manual mill retrofit I expect that (can only be) the original spindle was quill activated......that means the new rebuild would be with the quill locked up and the head casting doing the Z axis travel instead of the quill......shock horror if the quill is still being used.

This means you will have the "head nod" syndrome that all quill origin mills have when the head is used for Z travel.

I have to wonder why, when this problem(s) has been highlighted in so many manual mill retrofits, the dovetails are not removed by machining and linear rails fitted throughout .....or else you live with it and pretend I does not exist.

BTW Mac, according to the EBAY listing the BF20 is made in Germany........it "might" be a Chinese import stocked by a German dealer.....get your facts right instead of rubbishing anything that hints of Chinese.
Ian.

Did you just crawl out from under a rock, MADE IN GERMANY , I could not stop laughing, your clueless rants are getting better, I did not rubbish the Chinese built machines, just stating the fact that most who convert these machines to CNC, redo and check, the ways, before reassembly

With the "head nod" syndrome, I think you should look at your self, It appears to be that you have the "head nod" syndrome

[mactec54]

Hi....forget it, that small amount is not even a problem to worry about as the gib will flex slightly as it's adjusted in the dovetail........not knowing the method of adjustment I would guess that there are a number of grub screws pressing on the side of the gib to adjust it in the dovetail.........tapered gibs are a luxury you would only find on a more expensive machine.
Ian..

Another clueless rant, the .0015 bend in the gib is more than the amount that showed up at the Vice

Again you don't have a clue about these machines, they have a Gib with a single adjustment screw

His Gib could easily be straightened by simple no stress lapping

[handlewanker]

Mack.........on Ebay the BF20 is specifically stated as being made in Germany........browse if you will......with ground slideways all round........possibly the ones supplied by our local Machinery House dealership do get ones that are outsourced in China.

If you were a machine tool fitter, or knew what you were talking about, you would know that a thou and a half deviation on a tapered gib is nothing to worry about as it fits in a tapered dovetail gap and so will take up the taper of the gap when tightened........ but you ain't.

if you blued up a tapered gib and found a thou and a half bald spot in the middle of the gib it would take 5 minutes with a scraper to render it good......as I have done many times before when machine fitting.


LOL......"it can easily be straightened"........which way Mac/???.....bend it back so it has a gap on t'other side???.....you are not a tradesman or you'd know you can't bend a gib to get it straight on both sides........maybe in the USA it can be done, but in the real world it can't.....you have to fit it.

The head nod syndrome that you are totally ignorant of is one that occurs when the head casting is used to act as the Z axis instead of the quill......something that it's not designed to do.

In normal circumstances a manual mill, such as the BF20, ALWAYS has the head locked to the column and achieves Z axis movement with a quill, but when it's converted to CNC the quill is more often than not locked up due to it's too short travel......but it sometimes is used for the Z axis move by personal preference of the user.

The gib on the head casting is then slackened off to allow the stepper motor to move it easily........this results in the head rocking back and forth on the dovetail......or as it's called Head Nod....AND THIS PHENOMENA HAS BEEN NOTED COUNTLESS TIMES ON THIS FORUM..........this has nothing to do with the problem being discussed so why bring up?
Ian.

[mactec54]

Mac........on Ebay the BF20 is specifically stated as being made in Germany........browse if you will......with ground sideways all round........possibly the ones supplied by our local Machinery House dealership do get ones that are outsourced in China. Ian.

More of your uneducated BS, Some models have had Ground ways for more then 12 years, and they are all made in China, this is the same sales ploy that they do with the Router Spindles with Bearings made in Germany, Just another sales ploy, wake up

LOL......"it can easily be straightened"........which way Mac/???.....bend it back so it has a gap on t'other side???.....you are not a tradesman or you'd know you can't bend a gib to get it straight on both sides........maybe in the USA it can be done, but in the real world it can't.....you have to fit it
Ian.

It would help if you could read, show me where I said anything about bending the Gib to straighten it

[handlewanker]

Mac...... Mac......sigh........you did say straightening .....in post # 17......LOL.....whether or not it's by tapping or pressing, it's the same result in the end......... THE PROCESS FOR GETTING RID OF THE HOLLOW IS CALLED FITTING BY SCRAPING.......at least it was when I was machine tool fitting.

How on Earth can you STRAIGHTEN a tapered gib......if one side has a thou and a half hollow in it .......when you try to straighten a tapered gib the other side that contacts the corresponding taper in the table dovetail will just push the "straightened" gib back again against the saddle dovetail.

Perhaps you aren't aware of tapered gib fitting so I'll not be more sympathetic to your ignorance if you attempt to profess your ignorance further.

Now, if that had been a parallel gib that gets adjusted with grub screws pressing against the back side.......yes, you can straighten it, but it would be like a dog's back leg in the process.

For a thou and a half you wouldn't bother as any parallel gib will show some bending that will come straight by careful adjustment of the grub screws.......you need to have parallel gibs with substantial thickness to ensure they don't bend.

A parallel gib is just a strip of steel that rubs on cast iron which as everyone knows is an ideal metal to metal combination.....with lubrication of course.

BTW.......I take it as a personal insult when you state in your post #19 ......."uneducated BS"......you may be ignorant of machine tool fitting but I served a 5 year apprenticeship to know my stuff, and a further 50 years + in the trade in various fields.
Ian.