G0704 missing thrust washed on left hand x axis feed

[MAlcocer]

G0704 missing thrust bearing on left hand x axis feed

About half way through my clean up of my G0704. Had the x and y completely disassembled and noticed that there is no thrust bearing on the inside of the left side x axis feed. Looking at the parts list from grizzly there does not appear to be one but I can't see why it would not hurt to have one. The part number is P51200. The reason I am asking is to try and remove the backlash I have in the x axis (+.006"). The y is solid and has bearings on both sides but also only has the one feed handle. Any help would be appreciated.

 

[MAlcocer]

Re: G0704 missing thrust bearing on left hand x axis feed

Answered my own question this morning. Took a thrust bearing from the y axis and placed it on the inside of the left side x axis and with proper tightening of the acorn nuts I now have no noticeable backlash in the x and it still operates smoothly. I still need to measure the actual backlash but it feels minimal. $9 part from amazon with prime shipping if anyone is wondering.

 

[brav65]

Nice work isn't it nice when you are actually as smart as you think you are! I just wish I had more of those moments:thumbzup3::thumbzup3::thumbzup3::thumbzup3:

 

[kd4gij]

Good you gotit.

 

[bladehunter]

Just one thing to consider, one side is usually left "floating" to allow for expansion and contraction of the various machine components. From my understanding one side (ie r\h) is fixed to contain the leadscrew laterally and the opposing bearing (l\h) is there to stop the leadscrew "whipping". Hence the reason ballscrew supports (bearing) come in pairs with one being "fixed", usually a pair of opposed angular contact bearings and the floating side is just a standard roller type bearing.

Theorectically with both ends being "fixed" there is a chance of compressing or stretching the leadscrew due to variences in temperature.

Is it the backlash you fixed or was the leadscrew itself moving laterally ?

Backlash with the standard leadscrews is taken up by adjusting the X aixs nut, which in reality works for a while then goes out again.

The best way I found to combat backlash on a manual mill was installing a DRO, even the cheaper iGaging type are quite good. A lot easier than counting turns and such. I say this with the outlook of a hobbyist in the learning stages.

 

[MAlcocer]

Still very new to this so I may have a few things backwards. What I was trying to fix is the x axis would take a good part of a rotation when I reversed direction to engage the table again and move it in the opposite direction. I tried adjusting the nut attached to the table but that only made the screw stiffer. Adding the bearing on the inside and adjusting the tightness of the acorn nuts at each end removed this play.

 

[tmarks11]

The drawing in the Grizzly manual shows a single bearing on the left hand side, so I think you found the problem.

But I agree with blade hunter...

That being said, usually a pair of angular contact bearings is used provide thrust support for the lead screw from one side, and the bearing at the other end floated to act as a journal bearing (this would be the missing bearing on your mill). I am not sure why the pair of angular contact bearings (acting as thrust and journal bearings) on the right hand side are allowing axial movement of the lead screw. They should be preloaded to get rid of any movement.

The G0704 drawing in the grizzly website doesn't show any detail of the end caps on the table, so it is difficult to see how the bearings are captured in place. I would expect to see a nut and washer to hold the bearing in place, and than the hand wheel loosely attached with another nut. Looks like grizzly skipped the nut that would be used exclusively to preload the bearing pair. So any time you take off the hand wheel, you are messing with bearing preload. hmmm.

 

[bladehunter]

You've got it right tmarks.

Whilst I don't have a G0704 I do have a TopTech BF20L, more or les the same machine.

The nut holding the handwheel does provide the preload.It looks like 2 thrust bearings on the right side and one on the left. So one would expect the right side nut to provide the preload and the left side nut just there to hold the handwheel on the leadscrew.

To adjust the backlash did you adjust the two bolts on the leadscrew nut itself ?

The purpose of those adjusting screws is to vary the distance of the gap and thereby adjusting the crests of the nut so they engage tighter on the leadscrew. Which is the cause of backlash.

The folowing picture gives an explanation of backlask better than my words.



Even tho the picture shows two seperate nuts, a slitted nut as on your mill is basically the same thing. Adjusting screws 67 has the affect of adjusting the tension or compression dpending on the consrtuction of the nut.

Hope this helps a little.

 

[MAlcocer]

It does help. Thank you for all of the help. That is the but I adjusted. I could not resolve the backlash to less than .006 with that but which is why I started looking elsewhere for a solution. When I adjusted screws 67 it only made it more difficult to turn the lead screw. I will go back over it today and see if I missed something.

All that aside wouldn't it take a good amount of heat or temp variance to cause the lead screw to stretch or compact? I live in California and our typical temp swing in this area is very minimal. As an example, today we will be going from 49° to 64°

 

[Baithog]

Its not the 49-64 that matters, unless you plan to adjust your bearings on a weekly basis. I lived in Graton for a time. It gets fairly cool in winter and hot in summer in your area. The weather service average is high 30's to low 80's, but the potential range based on records runs from 20 to 105 or so. That wouldn't matter if you have tight temperature control, like an IC fab, but you're probably working in the garage like most of us. There is a valid engineering reason not to fix both ends of the lead screw.

Just what amount of backlash are you trying to achieve? The spec for your mill is 3 to 6 mills, so you are in spec.

Pursuing near zero backlash is a common activity for the less experienced machinists. I certainly did my share when I got my first lathe 40 years ago. I ended up having to replace a set of lead screw nuts due to my amateur engineering. Fortunately someone taught me how to live with reasonable backlash. I really think that you should get rid of your 'improvements', adjust the machine the way it was designed, and learn to be a machinist. Even bridgeports and high dollar CNC machines have backlash.