Mini mill table binding

[redvan22]

Hi,
My microlux mini mill table binds at both ends and seems loose in the middle.
I followed the instructions for lapping the gib and after the 320 grit paper, its looking real good so I thought it must be the dovetails so I started polishing them following the instructions in another posting about them and here's the issue....
After three hours of applying Mother's polishing compound and back and forth motions, I still have binding. So, am I doing the right thing or is there a better way?
Mike.

 

[tech610]

I had the same problem with my 20 years old Grizzly mini mill. I tried lapping, but that didn't work for me. I tried scraping, but gave up almost immediately. So I used flat and triangular files. On the bottom of my table I could see the contact surfaces wear. With leadscrew removed I kept filing and testing for ease of movement moving the table by hand. It did improve somewhat to the point that I decided that it was good enough.
The table will always bind a little on ends because of its weight hanging up in the air and the center gets used the most.

 

[RJSakowski]

A common cause of the table binding on an older mill is due to wear in the central portion. As you tighten the gib to reduce play, you overly tighten the gib for the ends of travel.

If you have a backlash compensating lead screw nut, that can be another source of binding. As the central portion of the lead screw wears, backlash increases in that region. Adjusting the nut to reduce backlash will reduce clearance at the ends of travel which can cause binding.

Another cause of tight end travel is a slight misadjustment of the end caps. As the lead screw nut gets closer to the end cap, any misalignment becomes more critical.

To check if this is the cause, loosen the gib slightly and look for binding at the ends of travel. If you still have binding at the ends of travel, then the prime suspect is the end caps.

With the table positioned at extreme travel, loosen the end cap and retighten. The end cap will self center and you should have reduced or eliminated the binding. Do the same for the opposite end.

 

[homebrewed]

I have a Micromark mini mill as well.

How much use has your mill had? If you bought it new, did it exhibit this problem right out of the box?

This mill's design only captures the feed screw at one end (near the handwheels) so if it binds up at both extremes it can't just be due to a misalignment of the end caps vs. feed screw nut. That's not to say you don't have TWO problems you're dealing with.

Moving the table so the feed screw nut and end cap are closest together, then loosening/tightening the end cap and feed screw nut mounting screws is the recommended way to "adjust" the table for minimum binding.

Little Machine Shop has replacement feed screws and feed screw nuts, if you determine the problem is due to wear in them.

Out of curiosity, which axis is exhibiting the problem? There are some design differences between the X and Y axes that MIGHT have a bearing on the problem. That's sort of a pun, only appreciated by those who have one of these machines....

 

[redvan22]

Homebrew,
The machine is fairly new but hardly used due to several problems i didn't know how to fix until recently. This is one of them. I never realized the end cap could be a source of pain. I will try that first as it binds more when the table is extremely to the left. The axis is, I believe, the "X" (left to right).

Mike

 

[redvan22]

Well, believe it or not Homebrewed, i cranked the handle until the table was all the way to the left and when it started to bind, I loosened the end cap screws behind the handle and I actually saw the end cap move and the bind was much less, not gone but much less. Wow, what a difference.

Now, there are two set screws under the table that hold a bronze piece that the threaded rod of the table goes through and i believe this has some influence on the bind too. Originally this block was loose and thinking that if there are set screws, they should be set so, should they, and if so, when do they get set and in what position should the table be in ?

Mike.

 

[royesses]

According to the little machine shop the feed screw nuts retaining screws should allow the nuts to move without any slop. The nuts can travel up and down this way to stop binding.

Roy

 

[redvan22]

Thanks Rotesses but, I'm not sure you understood me based on the terminology you used. On the mini mill parts diagram from LMS, the bronze piece I'm talking about is part #23. It sits in a slot with two allen set screws. The slot is sloppy and if the set screws are loose when the handle is turned, the bind increases because the block shifts to the front or back, depending on the direction of travel, not to mention that slack increases in the axis travel. If I tighten them down, when the table is to the far left, a lot of the bind disappears but returns when I move the other way. (I need to move the table left to get to the screws because the end cap interferes.)

Mike

 

[royesses]

Yes, #23 is what I was talking about. It is not supposed to be sloppy. It should be tight but allow a little bit of movement up and down. I adjusted mine different since I have a power feed on my table. When I first got my mini mill I removed the feed screws and nuts and washed them in solvent. Then I adjusted the table gibs without the feed screws to give smooth travel while keeping the gibs as tight as possible. Then I reassembled everything and oiled it up well. As the mini mill is used everything wears in and gets smoother. Also the nut holding the hand wheel on sets the preload on the thrust bearing. If too tight it can cause binding. Being tight on both ends sounds more like gibs and wear in the center of travel.

Roy

 

[royesses]

I think Tech610 has about the same Ideas as I had with my mini mill. I did use a set of files to knock down high spots. And then polished with 400 grit wet or dry paper. Every mini mill and mini lathe I've seen has had similar binding problems. I just worked at it until I had it good enough to live with. The table has gotten much smoother as I have used the mill through the last 4 or 5 years. One thing that has helped is using a high moly grease on the the gibs, dovetails and feed screws. With the power feed the feed screw is supported on both ends and is adjustable on both ends so it is easier to get it close to right on. I also installed a ball thrust bearing kit on the Y feed screw and that helped the Y feed to operate smoothly. I keep the gibs tight on the Z axis so as to limit height change when I lock the Z axis.

Roy