Mini Mill X axis shift

[redvan22]

While working on my mini mill today I was milling a 1/4" slot in a piece of Delrin along the Y axis when suddenly the table shifted about 3/32" along the X axis. Never saw this happen before and immediately stopped thinking that something was about to give way and ruin my piece.

Before I breakdown my setup and start taking the table apart I thought it would be a good idea to ask others with a similar machine and maybe they can point to a specific area or component.

I have the Micromark Mini Mill 84630

Mike.

 

[PNW_Guy]

Were you climb cutting? How much backlash do you have? Did you have the X axis lock engaged?

 

[redvan22]

Were you climb cutting? How much backlash do you have? Did you have the X axis lock engaged?

Yes I was climb cutting.
There's a little backlash. I've done some work to tighten it up but there is still some.
No, I rarely lock the X.

There's not a lot I can do. It's a simple mill. There's a brass block that the shaft goes through that's supposed to assist in reducing the backlash but it doesn't seem to help.

 

[benmychree]

The table lock should have been tightened to prevent the table from moving.

 

[ChazzC]

Yes I was climb cutting.
There's a little backlash. I've done some work to tighten it up but there is still some.
No, I rarely lock the X.

There's not a lot I can do. It's a simple mill. There's a brass block that the shaft goes through that's supposed to assist in reducing the backlash but it doesn't seem to help.

As @PNW_Guy was digging into with his questions is the core of your problem: you should always lock the table travel in the “stationery” direction (X in this case) to avoid the possibility of unwanted movement. Although 0.090” is a lot of movement, it could be additive from backlash and a loose lead screw. Delrin isn’t too grabby, but depending on the depth of your slot and if you were using a 4-flute end mill and using a high feed rate, I can see how a combination of factors could make this happen.

Your mill is of an older generation (I know it is current with MicroMark) and could be improved significantly with some changes (solid column& 2” riser block, replacing the coil spring on the head with an air spring). The instructions discuss gib adjustment, which can also impact sudden movement, but I didn’t see any discussion of backlash: the Y-Axis can be a pain on these mills, but the C-Axis usually is easier - the LMS Generic Mini-Mill User's Guide is better than what MicroMark provides, but doesn't address address the adjustment of the lead screw nuts for backlash reduction. The LMS instructions for replacing the metric lead screws with inch lead screws (yes, I know the instructions say conversion to metric, but their instructions are the same for all lead screw swaps) do include some discussion on adjusting these nuts (pages 4 & 7). Basically, these bras nuts and the adjusting screws act similarly to the cross slide lead screw nut on a Mini-Lathe by tilting the nut to reduce the "slop" between the screw & nut.

 

[redvan22]

As @PNW_Guy was digging into with his questions is the core of your problem: you should always lock the table travel in the “stationery” direction (X in this case) to avoid the possibility of unwanted movement. Although 0.090” is a lot of movement, it could be additive from backlash and a loose lead screw. Delrin isn’t too grabby, but depending on the depth of your slot and if you were using a 4-flute end mill and using a high feed rate, I can see how a combination of factors could make this happen.

Your mill is of an older generation (I know it is current with MicroMark) and could be improved significantly with some changes (solid column& 2” riser block, replacing the coil spring on the head with an air spring). The instructions discuss gib adjustment, which can also impact sudden movement, but I didn’t see any discussion of backlash: the Y-Axis can be a pain on these mills, but the C-Axis usually is easier - the LMS Generic Mini-Mill User's Guide is better than what MicroMark provides, but doesn't address address the adjustment of the lead screw nuts for backlash reduction. The LMS instructions for replacing the metric lead screws with inch lead screws (yes, I know the instructions say conversion to metric, but their instructions are the same for all lead screw swaps) do include some discussion on adjusting these nuts (pages 4 & 7). Basically, these bras nuts and the adjusting screws act similarly to the cross slide lead screw nut on a Mini-Lathe by tilting the nut to reduce the "slop" between the screw & nut.

ChazzC,
I have made some improvements like the air spring to solve a sudden head dropping issue I was having. I have also done some brief work on the dovetails of the table to eliminate tight spots. I think my greatest issue is with the brass block and the table lead screw. I checked it before and it was loose.
I'm going to lock the table in the X axis as needed to finish my piece and then take a good look at the block and lead screw and see what can be done.

Thank you.

 

[ChazzC]

ChazzC,
I have made some improvements like the air spring to solve a sudden head dropping issue I was having. I have also done some brief work on the dovetails of the table to eliminate tight spots. I think my greatest issue is with the brass block and the table lead screw. I checked it before and it was loose.
I'm going to lock the table in the X axis as needed to finish my piece and then take a good look at the block and lead screw and see what can be done.

Thank you.

The X-Axis nut adjustment set screws are under the right end of the table. You'll need to run the table to the far left to get easy access to them. snug them up and see how the X-Axis travel is, and loosen one side or the other to get the minimal backlash on the nut.

There is only one Y-Axis adjustment screw, and that's hidden under ihefront rubber swarf cover. For the Y-Axis, run the table all the way to the rear and snug up the screw; run the table forward and if the hand wheel feels looser, snug up the screw just a little.

As described in the LMS lead screw replacement instructions, the hand wheel mounting screws/nuts also play a part in the overall adjustment.

If you see that the adjustments lessen up, you may want to try removing the set screw(one at a time), cleaning the screw & threaded hole with alcohol, placing a dab of Vibra-Tite (or clear nail polish) on the set screw & letting it dry before re-assembling - the Vibra-Tite/nail polish act like a nylon locking plug holding the screw in place while allowing adjustment (unlike thread lockers).



Good luck,


Charlie

 

[homebrewed]

I own the same Micro-Mark. That much movement seems excessive for a relatively unworn nut and feed screw. It's possible that the feed screw nut wasn't firmly held in place and that's what caused the movement. Other possibilities include loose gibs. The straight gibs on this machine are a bit fussy -- too loose and you get unwanted motion, too tight and the handwheels become difficult to turn.

The X axis is far better than the Y axis, simply because the X axis has thrust bearings on the feed screw so you can tighten down the nut (on the end of the handwheel) much more aggressively than on the Y axis. I have seen an aftermarket replacement bearing block for the Y axis, but IIRC it has just one thrust bearing so you still have one metal-on-metal "bearing" surface to put up with. It is reported to be better, but it can't be as good as the X axis in that regard.

 

[verbotenwhisky]

While working on my mini mill today I was milling a 1/4" slot in a piece of Delrin along the Y axis when suddenly the table shifted about 3/32" along the X axis. Never saw this happen before and immediately stopped thinking that something was about to give way and ruin my piece.

Before I breakdown my setup and start taking the table apart I thought it would be a good idea to ask others with a similar machine and maybe they can point to a specific area or component.

I have the Micromark Mini Mill 84630

Mike.

Have you checked to see if you have a gib backing out?

 

[ChazzC]

I own the same Micro-Mark. That much movement seems excessive for a relatively unworn nut and feed screw. It's possible that the feed screw nut wasn't firmly held in place and that's what caused the movement. Other possibilities include loose gibs. The straight gibs on this machine are a bit fussy -- too loose and you get unwanted motion, too tight and the handwheels become difficult to turn.

The X axis is far better than the Y axis, simply because the X axis has thrust bearings on the feed screw so you can tighten down the nut (on the end of the handwheel) much more aggressively than on the Y axis. I have seen an aftermarket replacement bearing block for the Y axis, but IIRC it has just one thrust bearing so you still have one metal-on-metal "bearing" surface to put up with. It is reported to be better, but it can't be as good as the X axis in that regard.

The Phenom Engineering kit has a thrust bearing for the inner surface and a Teflon washer for the outer: not a perfect solution, but other than shortening the key no machining required.

I sent an email to Phenom as their website says they are relocating and not shipping until May - not sure if it’s left over from earlier this year or they mean next year. I suspect the latter as I’m pretty sure I looked at their website a few months ago and didn’t see the notification at that time.