[CNC-Dude]

I have been playing with checking the backlash on my axis and as expected, both machines show slightly different distances. Clearly, the one with the largest backlash will be in need of some tuning. But before I go there, I am curious as to how much BL do you guys see on your side?

Also, have you had to ever change the bearing preload, or for the most part you get desired improvements by simply adjusting the gibs?

To give you my information:

Machine #1 has about 0.0005 BL on X and Y, and 0.001 on Z.
Machine #2 has about 0.0015 on X, 0.002 on Y and 0.0015 on Z

I will play with the gibs on machine #2 but according to Tormach's manual, they are almost on spec.

[EvolveES]

on our PCNC 1100 we keep it adjusted so that all three axes are less that 0.0005" if it gets above that we will re-adjust it. It takes patience, but it is possible to improve the adjustment. To get all that you can out of the machine can involve looking at all aspects, from the gib adjustment, to the bearing pre-load, to the level of the base of the machine (which i learned the hard way). The bearings you can measure the preload by indicating the end of the ball screw while changing directions back and fourth, if it moves then the bearings are not tight enough (it's kind of a pain to do the Y because of removing the bellows). if you adjust the bearings too tight the machine will make a kind of a bad grumble sound when slowly moving. I think with attention to detail you can achieve much better performance than the tormach baseline specs. We have had little difficulty hitting +/-0.001 and we rae new to machining also. good luck

[adamvs]

I'd be exstatic to get .0005.

My backlash / lost motion is:
X: .0015-.002 ( it is more in the middle of the travel, not sure what that's about )
Y: .0012
Z: .0004

My Y axis needs some gib adjustment, but it is a pain as Evolve mentioned. I'm going to take another look at the preload on the X axis, It seems a little more noisey than the other two at low speed.

[pickled]

My 1100 series 2 clocks out with the following numbers

X: 0.0014
Y: 0.001
Z: 0.0008

[adamvs]

So I did a little maintenance of my 1100, The preload was a little tight on the X axis - I backed it out until there was just a scosh of drag on the movement. But I have a persistant problem: There is some dead angular motion on the X axis, which explains the .002 of backlash I was seeing. I setup a 'gauge' using some cardboard with some marks on it, and the I'm gettin about 3.1 degrees of slack before the table moves. I put an indicator on the table and the end of the ball screw and they both move at exactly the moment the slack is taken up. Here's what I get:

.2 pitch on the ball screw = .000555 movement on the table per degree.
.000555 * 3.1 degrees = ~.0017 of lost motion ?!?

Any ideas? Judging from the damage on the jaws of the vises that came with the machine, it looks like it had been crashed pretty badly more than once. Is it possible the ball nut loosened up?

[SCzEngrgGroup]

I would check that all the bearing blocks, bearing retainer plates, and ballscrews are still securely bolted in place. Those bolts have a tendency to come loose, from vibration.

Regards,
Ray L.

[adamvs]

I would check that all the bearing blocks, bearing retainer plates, and ballscrews are still securely bolted in place. Those bolts have a tendency to come loose, from vibration.

Regards,
Ray L.

I suspect as much. Is there a way to get to them without taking the table off?

[SCzEngrgGroup]

I suspect as much. Is there a way to get to them without taking the table off?

I don't have a Tormach, so I don't know. But, generally, yes, there is. The ballnut mounting bolts are usually accessible under the table and saddle, by removing the bellows/way covers, and moving the table/saddle to one side. The X ballscrew bearing mounts are usually just bolted under the ends of the table, and the Y ballscrew bearing mounts are usually bolted to the base casting, under the saddle. The ballscrew bolts will usually be the only ones that are hard to get to, but some long 3/8" drive hex drivers, and a couple of extensions, will usually do the trick. There are typically four bolts holding the ballnut to its mount, four bolts holding each bearing mount to the table/base, and four more bolts holding each bearing retainer plate to its mount.

Regards,
Ray L.

[mountaindew]

My series 3 clocks out the following numbers.
x = 0,0007
y = 0.0006
z = 0.0009 - 0.001

Center t slot clocks at 0.0000 over total x travel

y axis gib could be a little tighter.
Overall table flatness is in specification but not near as tuned as evolveES' had done with his machine in another thread.
I have been messing with it but have not zeroed in on method to improve it. I need to try the 3 point method he used and see if this presents any results or if I live with it.

Great info here!
Helps me see how my machine is performing.
md

Just checked it and recorded the results in a log.
Another user had mentioned they wished they kept results from past and I took note of this for myself.

[adamvs]

Ray, thank you for the info. I'll look into it over the next few days. I rebuild engines for my Miata pals so I happen to have all that stuff, and then some.
For all those adding to this thread, check the backlash in a few places: the center of travel and the ends. I'll bet you'll find some differences.
So far I've lived with this by altering machining strategy to approach dimensions from the same direction on the ball screw, which has been very accurate.

[MichaelHenry]

I suspect as much. Is there a way to get to them without taking the table off?

I found the X ball nut on my Series I mill was loose. I don't remember all the details now, but the process of getting to it wasn't too bad. I disconnected the X-stepper coupling, removed the X gib, and slid the table to the right far enough that support was needed under the right-hand side of the table. I blocked it up with wood.

[adamvs]

Thanks, Michael. That doesn't look so bad at all. I'll try to get into it this weekend. Just did a quick measurement and I beleive I can leave the coolant shroud in place and easily get to all the ballnut screws. I'm going to remove the screws one at a time and get a little blue loctite on then, if yours is still still apart I would recommend that. BTW, very clean 1100 ( my series II has the 'sand blasted' look - like it took a tour in Afganistan ).

[EvolveES]

The ball screws were the one thing that i have not touched on the machine yet, but it is cool to hear that they are accessible, would anyone be able to take a few pics of the tools you used and where you fed them in and such just to document for people who will attempt this later. I have thought about cutting a small window in the stand i made and i could easily lay on my back and reach through the window, but that would only take care of the Y axis. I am curious how to easily reach the X axis. Thanks for the updates, this is some great info

[MichaelHenry]

BTW, very clean 1100 ( my series II has the 'sand blasted' look - like it took a tour in Afganistan ).

That picture was taken quite a few years ago and it doesn't look so new today. In fact, the coolant spatter along the back wall makes a good case for a full enclosure, but there's not enough room in this location. Good point about the Loctite, especially if Blue is the one that can be removed without heat. I can never keep the colors or numbers straight.

Mike

[adamvs]

I got into it yesterday and did the same thing MichaelHenry did to expose the X axis ball nut, and try to improve on the .002 backlash in the X-axis. It takes about 10-15 minutes to remove the shrouds, uncouple the X-axis motor, unbolt the X-axis coupler housing and motor mount. Getting the gib removed is a little tricky as the you need to remove the oil line ferule nut, which is easy to get to but difficult to unscrew as it is positioned in the sharp angle of the dovetail way. I have a 10mm open wrench which is ground down to something that looks like a fork, this works well enough. From there with the coupler block supported ( so you don't bend the ball screw ), and the gib removed, the table easily slides off the end.
My X-axis was pretty dirty, so I took the opportunity to clean it up. Some observations:

1) The ways coating that Tormach touts was in excellent shape, no detectable wear.
2) The ball nut mounting screws and ball nut yoke screws were actually ok. Some needed a little snugging-up, but I wouldn't say any were loose. BTW, the yoke is held down with four 6mm allen screws, which use a 5mm hex key. The Ball nut itself is mounted with six 5mm screws, which use a 4mm hex key.
3) The "hand scraped" gib, was not hand scraped in the sense you would think of on a Bridgeport mill way. It looked more hand chiseled, if anything. It seems the idea here is a gib that has limited friction by limiting the contact area on one side. Imagine a flat surface gib vs one that had a pebbled surface.
Attachment 272814 Attachment 272816 Attachment 272818

Got it oiled, put back together and went to readjust the gib. Best I could do was .0018. But I noticed I could move the table by pushing on it about .0015, I think this is due a minute gap between the gib and the way. If I tightened the gib, this 'pushing' gap went down to about .0005, but lost motion due to friction on the gib went up to about .0024! I thought maybe the there was some looseness in the Y axis gib that might account for this, but if I pushed the saddle with a 2x4 I couldn;t see anything on the DTI.
So there it is. It seems there is some sort of sweet spot between loosening the gib and creating a gap ( therefore lost motion ), and getting the least amount of backlash/ lost motion. I'm stumped. The problem seems to be in the gib, and the fact I can only get the best result by having this .0015 gap.

[MichaelHenry]

Maybe I missed it, but did you check the angular contact bearing preload?

Also, how old is your mill? It looks to be a Series I or maybe II from the pictures. I have an early Series I mill and have wondered about the fit on the X-axis gib before, but the mill accuracy has met my needs so I haven't pursued it. I'm wondering if the fit or "hand scraping" of the gibs on the early mills might have left a little to be desired.

Mike

[adamvs]

Maybe I missed it, but did you check the angular contact bearing preload?

Yup, I rechecked the other day. It's tight to just a little bit drag on the movement. I'll check them again when, because being able to push the table does not rule slop in the preload. If I could get a thou out of the lost mostion, I'd be ecstatic!
I have a series II #1845 I believe, I think it's 2011 manufacture. There didn't seem to be any noticable wear on the dovetails.

I'm wondering if the fit or "hand scraping" of the gibs on the early mills might have left a little to be desired.

Yeah, that was little funky, IMO. Do you remember what yours looked like? I wonder if anyone has made a gib out of bronze and milled in all the oil grooves.

[luv2ride]

My machine is an '09 1100 and I have scraped the gibs some because of the bow and lack of contact. Here is a shot to show the contact and you can see the scraping through the blue.

Tormach Photos by usarmyfly | Photobucket

Here is a link to the library instead.

[adamvs]

My machine is an '09 1100 and I have scraped the gibs some because of the bow and lack of contact. Here is a shot to show the contact and you can see the scraping through the blue.

I clicked on your link, but it came up: error! Can you post the image directly.

[popspipes]

I clicked on your link, but it came up: error! Can you post the image directly.

The link worked for me.