Adjusting Z Axis Jib

[adrian]

I would like some general advice on adjusting a Z axis jib on a Mikron WF1 and what to do if you think the table is hard to raise and lower by the handwheel. Mechanically the Mikron setup is almost identical to the Deckel apart from one turn of the handwheel lifts the table 2mm on the Mikron and 2.5mm on the Deckel.

Having just rebuilt my machine I adjusted the jib with just the main carriage assembly in place, no X axis mount or table to give 0.04mm clearance measured with a feeler gauge.

Now with the full weight of the X axis and table in place I am somewhat surprised how much effort is required to raise and lower the table. I don’t have much experience of operating other machines apart from my FP1 which is a lot lighter in construction and much easier to crank the table up and down.

I decided to readjust the jib thinking it was too tight. I adjusted the jib until it was tight then backed off half a turn and it made no difference to the effort required to lift and drop the table.

I checked the leadscrew with all the weight off and it turns smoothly as you would expect. The leadscrew thrust bearing is fully greased, so it’s not the drive system.
I also checked the alignment of the leadscrew nut, which was fine so it’s either the friction on the slideway or the friction caused by the weight on leadscrew and nut causing the problem.

Not sure how to resolve apart from going to the gym to bulk up a bit.

Cheers Adrian.

 

[AlfaGTA]

First question is are your vertical ways (Z”) square box (FP2) or dovetail (FP1)?
Sort of looks like dovetails in the photo, just confirming.
Cheers Ross

 

[adrian]

Hello Ross

The ways are dovetail which considering the combined weight of the Z axis assembly a bit of a design compromise. I would estimate the weight of the assembly to be at least that of an FP2 and may be a bit more. Mikron construction is very solid and heavy.

A clue may be without the table attached there's not much difference in the effort require which is odd.
I think without the table the Z axis assembly centre of balance is roughly on the leadscrew, so there should be minimal lateral load and friction on the dovetail.
With the table together with heavy vice etc attached, the centre of balance moves away from the machine putting a higher load on the dovetail, thus increasing it's friction.

I would assume box ways offer lower friction for heavier loads as you don't have the tightening effect of the dovetail angle.

 

[AlfaGTA]

What weight and kind of way oil are you using?
Is the effort constant over the total travel? Is the effort the same when first starting as when continually moving.
How is it delivered.
Machine looks gorgeous by the way, nice work.
Cheers Ross

 

[j-holland]

Hello Ross

The ways are dovetail which considering the combined weight of the Z axis assembly a bit of a design compromise. I would estimate the weight of the assembly to be at least that of an FP2 and may be a bit more. Mikron construction is very solid and heavy.

A clue may be without the table attached there's not much difference in the effort require which is odd.
I think without the table the Z axis assembly centre of balance is roughly on the leadscrew, so there should be minimal lateral load and friction on the dovetail.
With the table together with heavy vice etc attached, the centre of balance moves away from the machine putting a higher load on the dovetail, thus increasing it's friction.

I would assume box ways offer lower friction for heavier loads as you don't have the tightening effect of the dovetail angle.

a few thoughts--
loosen all screw fasteners holding lead screw to base and lead screw nut to its pylon--fidget with these and gage elevation resistance
pull gib and insert skinny borescope in cavity otherwise occupied by gib--the
dovetail geometry of your machine greatly increases probability of binding when compared to box configured tools--I had similar experience with Aciera F5 cnc with dovetail ways--extent of galling and servo motor overload on this $103,000 tool was a gutcheck--Aciera series machines typically incorporate dovetail ways--message on the Aciera is gib float with gib acting like splitting wedge--a problem not typically encountered on my box way tools

 

[adrian]

I started using ISO68 for lubricating the ways which I use on my FP1 without any problems.
I then tried slipway oil and think there was a marginal improvement, not sure what grade it is as it’s no longer in it’s original container. The interesting thing is the stiffness is constant, it’s not sticking and then easier, also there’s only a very marginal difference between moving the table up or down which is odd.

I tried setting the jib at the top, bottom and middle of the table travel and it makes no difference. I don’t think there is much wear on the machine because there is still original scraping on the carriage ways as shown below. There is no vertical scoring on the jib or way so friction should be normal, what ever that is for a dovetail way.

As the machine is now fully assembled I think the best solution for accurately setting the jib would be take the weight off the carriage with a hoist and use long shim strip may be 0.03 or 0.04mm to adjust the clearance. Unfortunately there is no information in either the Mikron or Deckel manuals as to jib clearance, so I am only guessing at around 0.03mm

 

[thanvg]

Hi there,

this could be an objective thing, since heavier slides need more force to move up. My FP1 copy was very very light on Z, my FP2 not so much, my FP3 not so much at all.

Yet, if it were a weight thing, moving the table down would have a lot of difference. Could it be your bevel gearing for the Z handwheel? Could there be something incorrectly preloaded in there?

BR,
Thanos

 

[EmGo]

I would like some general advice on adjusting a Z axis jib

Shiver me timbers, matey ! Splice the mainbrace and veer the downhaul ! Tighten the windward sheet and cast off the leeward ! two degrees right rudder, and point 'er up three degrees ! Cast aside the centerboard and don't forget to prime the outhaul !

and whatever you do, don't ever ever pee upwind !

 

[Richard King]

The way scraping is light. Set a surface gage with a .0.0005" indicator on the back of the knee with the indicator set close to the gage ans measure the depth of the scraping. It should be a minimum of .0.0005 and a maximum of .002". Also if you can check the flatness of the ways with a straight edge or parallel. I am assuming it it worn on the ends and one or all are high in the middle especially the gib. That being said you will need to rescrape it or leave the gib looser. Just seeing the scraping doesn't mean alot if it is .0.00005 or 0 depth as it doesn't leave any room for oil. You get stick slip and eventually it will gual. If you can't scrape, learn how or hire someone to check and scrape it. Then or leave the gib loose so it moves smoothly.

Then check the gap or looseness with a magnetic base and indicator. Check the lost motion. You can look on YouTube under Keith Rucker on how to how to adjust gibs. I showed him this method. If your not scraping it you may have to leave it loose .003" and then when tightening it, lock it after raising it.

 

[adrian]

Shiver me timbers, matey ! Splice the mainbrace and veer the downhaul ! Tighten the windward sheet and cast off the leeward ! two degrees right rudder, and point 'er up three degrees ! Cast aside the centerboard and don't forget to prime the outhaul !

and whatever you do, don't ever ever pee upwind !

Aye Aye Captain, tiver me shimbers.

 

[adrian]

The way scraping is light. Set a surface gage with a .0.0005" indicator on the back of the knee with the indicator set close to the gage ans measure the depth of the scraping. It should be a minimum of .0.0005 and a maximum of .002". Also if you can check the flatness of the ways with a straight edge or parallel. I am assuming it it worn on the ends and one or all are high in the middle especially the gib. That being said you will need to rescrape it or leave the gib looser. Just seeing the scraping doesn't mean alot if it is .0.00005 or 0 depth as it doesn't leave any room for oil. You get stick slip and eventually it will gual. If you can't scrape, learn how or hire someone to check and scrape it. Then or leave the gib loose so it moves smoothly.

Then check the gap or looseness with a magnetic base and indicator. Check the lost motion. You can look on YouTube under Keith Rucker on how to how to adjust gibs. I showed him this method. If your not scraping it you may have to leave it loose .003" and then when tightening it, lock it after raising it.

 

[adrian]

No doubt the scraping on the ways will be worn on a forty year plus machine and the depth nothing like it left the factory. At least on this machine the depth although shallow seems even and I don’t have the skill or measuring equipment to re-scrape a slide way. Finding someone in the UK would be difficult and very expensive.

 

[Richard King]

Pete and Demon somebody are members here and live n the Uk is a good scrapers. If not your going to have to leave the gib loose or try to make it like new will score the ways

 

[adrian]

Pete and Demon somebody are members here and live n the Uk is a good scrapers. If not your going to have to leave the gib loose or try to make it like new will score the ways

Thank you for that information, useful to know. Major down side of re-scraping would be having to completely dismantle the machine again. I don't have the energy or enthusiasm for that at my age.

 

[Richard King]

Then leave the gib loose and lock it when using it.

 

[Peter from Holland]

Does it also moves heavy when the gib is loosend significantly ???
Hearing that it is also on the downstroke makes me wonder if something before the ways is at fault
Like Thanvg indicated
Damaged the nut perhaps at reassembling ?? Had that once
Peter

 

[Peter from Holland]

I tried to look it up but cannot find it
Is the Z nut a 2pieces one ?? I do not think so (The X and Y are )
But if it is that may be binding

 

[thanvg]

I tried to look it up but cannot find it
Is the Z nut a 2pieces one ?? I do not think so (The X and Y are )
But if it is that may be binding

Doesn't seem like a two-piece nut from the picture Peter (the first OPs pic)

 

[adrian]

I tried to look it up but cannot find it
Is the Z nut a 2pieces one ?? I do not think so (The X and Y are )
But if it is that may be binding

Hello Peter
I checked the nut and leadscrew by taking the weight off the carriage assembly. All turned freely and smoothly from the handwheel. Also checked alignment of the lower splined drive assembly and the leadscrew thrust bearing and that was fine. It all points to friction on the slideway. Problem is I have no reference as to what it should be, for all I know this may be normal, it's just a lot heavier than I would have expected.

 

[thanvg]

Hello Peter
I checked the nut and leadscrew by taking the weight off the carriage assembly. All turned freely and smoothly from the handwheel. Also checked alignment of the lower chain drive assembly and the leadscrew thrust bearing and that was fine. It all points to friction on the slideway. Problem is I have no reference as to what it should be, for all I know this may be normal, it's just a lot heavier than I would have expected.

As I said above, if it were an issue of 'it's too hard to lift because of weight that I am not used at' then it would have considerable difference when you moved downwards.
So it's something else