Micromill Repair

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Benny
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Micromill Repair

Post by Benny » Fri 08 Feb , 2008 16:27 pm

My milling machine (micromill 2000) is broken. There is a brass (or brass plated) threaded piece about 1/4" in diameter that is pressed into the table of the mill. The threaded rod that allows front to rear movement of the table is going through it. This brass insert has pulled out of the table. I have tried to reinstall it, but it keeps coming out.

Benny
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Joined: Fri 20 Oct , 2006 15:27 pm
Location: USA

Micromill Repair

Post by Benny » Fri 08 Feb , 2008 16:28 pm

Attached is a link to an exploded view of the mill. http://www.sherline.com/CNCmillEX.pdf
Look at the “Y” saddle in the low, right center of the page, you’ll notice the “Y” insert nut (50200/51200) goes into the saddle from the back and is held in place with a set screw (40520) coming up from the bottom. You will need to remove the “Y” saddle from the machine base to get at this set screw. The set screw needs to be tighten enough to hold the insert nut in place, but not to much or it will be crush the insert nut and bind up the lead screw. Parts will need to be cleaned and medium strength threadlock used when reassembled.

(EDIT: I've attached the sherline document in case the above link ever changes)
Attachments
CNCmillEX.pdf
(196.16 KiB) Downloaded 1036 times

Benny
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Posts: 201
Joined: Fri 20 Oct , 2006 15:27 pm
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Micromill Repair

Post by Benny » Fri 08 Feb , 2008 16:28 pm

I need a little more help. Can you assist?

Benny
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Micromill Repair

Post by Benny » Fri 08 Feb , 2008 16:33 pm

Here is a list of things you can look at when repairing Micromills with the same problems, it takes time to do this kind of work. We recommend that you contact an authorized Denford technician for a service call, but if you think you can handle on your own …
There is a mix of SAE & Metric bolts being used. Use the proper size Allen wrench. After studying the exploded view, the set screw for the ”Y” axis insert nut is coming in from the top of the saddle. You will need to remove the “X” axis machine table to get at the set screw.

Remove the “X “axis
1.Go to the Sherline website to download and print the exploded view of the mill. http://www.sherline.com/CNCmillEX.pdf Make enlargements if you can.
2.Unplug the machine from the wall.
3.Pull the plastic plug/cap out of the hole in the cone shaped Stepper motor mount/adapter for the “X” axis.
4.Turn the “X” lead screw by hand to line up the set screw in the coupler with the hole in the adapter and use an Allen wrench to loosen the set screw.
5.Unbolt and remove the “Y” stepper motor and home switch mounting bracket.
6.Unbolt the cone shaped adapter from the “Y” saddle.
7.On the back side of the saddle, near the left, is a set screw that locks the “L” shaped Gib adjustment wire in place. Loosen the set screw and pull out the Gib and the “L” wire. Note how this was installed, it has to back in the same way.
8.Remove the X-axis lock (P/N 50190, some machines do not have this).
9.Remove the machine table.

Remove the “Y axis.
1.Pull the plastic plug/cap out of the hole in the cone shaped Stepper motor mount/adapter for the “Y” axis.
2.Turn the “Y” lead screw by hand to line up the set screw in the coupler with the hole in the adapter and use an Allen wrench to loosen the set screw.
3.Unbolt and remove the “Y” stepper motor and home switch mounting bracket.
4.Unbolt the cone shaped adapter from the “Y” saddle.
5.On the left side of the saddle, near the front, is a set screw that locks the “L” shaped Gib adjustment wire in place. Loosen the set screw and pull out the Gib and the “L” wire. Note how this was installed, it has to back in the same way.
6.Next to the Lead screw is a brass toothed Backlash Lock (looks like a thin brass gear), loosen the bolt that holds it (do not remove).
7.Remove the saddle from the machine base.
8.Remove the set screw from the bottom of the saddle.
9.Remove the brass insert nut from the “Y” lead screw.
10.Remove the “Y” lead screw. The backlash nut (brass top hat with a gear shaped brim, looking piece) will stay on the lead screw.
11.Inspect the lead screw, look for any nicks or gouges in threads. Replace if needed.
12.Inspect the Brass insert nut. Make sure it turns smoothly on the lead screw. IF NOT, ORDER A NEW INSERT NUT, BACKLASH NUT, BACKLASH LOCK & LEAD SCREW.
13.Clean up any nicks & gouges on the outside surface of the insert nut with a file, flush with brake cleaner.
14.Flush out the holes in the saddle for the set screw and insert nut with brake cleaner. All of the chips and oil/grease must be removed. Let dry.
15.The set screw for the X-axis insert nut is from the bottom of the saddle, you may want to check that also. Clean, lube and re-install using thread lock.

To reassemble the Y-axis
1.Press the insert nut in to saddle from the back. Use a wood dowel or piece of plastic rod. DO NOT USE A METAL SCREWDRIVER, you will put a nick in the threads and it will bind up on the lead screw.
2.Put a drop or 2 of medium strength thread lock (Blue Loctite) in the set screw hole. You want a little of the thread lock to ooze around the insert nut to help lock it in place.
3.Run the set screw in and just snug it up against the insert nut.
4.Put some light grease on the lead screw and reinstall the lead screw. (As you turn the lead screw into the insert nut it should feel free and smooth). Gently tighten the set screw for the insert nut until you feel the lead screw tighten a little as you turn it in. Back off the set screw just a bit .The lead screw should turn smoothly and easily in and out of the insert nut. Keep turning the lead screw in until it is a half way in.
5.Turn the Backlash nut on the lead screw down till it touches the saddle and tighten the bolt in the backlash lock (the teeth on the backlash nut and backlash lock will engage, we will adjust this later).
6.VERY Lightly coat the dovetail ways on the machine base with light grease.
7.Re-install the saddle on the machine base.
8.Re-install the Gib and the “L” wire gib rod. Gently press the Gib back into place while lining up the “L” rod and tighten the set screw on the “L” rod.
9.To adjust the Gib, push and pull the saddle along the machine base. The saddle must move smoothly and easily along the length of the base and not have any play that will let the saddle twist on the base. Check the twist on the base by gently trying twist the “X” on the base, if the Gib is to loose, the saddle will twist on the base when you twist the “X”. Loosen the set screw before you make an adjustment and re-tighten before moving the saddle. You can tap the Gib in with a small hammer to take up play if there is too much. If the Gib is set too tight the stepper motor will stall trying the move the saddle on the base in the “Y” axis. This takes time and very minute adjustments to get the right feel.
10.Reinstall the cone shaped adapter.
11.Reinstall the stepper motor and home switch mounting bracket.
12.Tighten the set screw in the adapter on to the stepper motor shaft.

Reassemble the X-axis
1.VERY Lightly coat the dovetail ways on the machine table with light grease.
2.Re-install the table on the saddle.
3.Re-install X-axis lock, if needed.
4.Re-install the Gib and the “L” wire gib rod. Gently press the Gib back into place while lining up the “L” rod and tighten the set screw on the “L” rod.
5.To adjust the Gib, push and pull the machine table along the saddle. The table must move smoothly and easily along the length of the saddle and not have any play that will let the table twist. Adjust the same as the Y-axis.
6.Reinstall the cone shaped adapter.
7.Reinstall the stepper motor and home switch mounting bracket.
8.Tighten the set screw in the adapter on to the stepper motor shaft.

Adjustments
1.Turn on the computer and machine and connect, Home the machine as usual.
2.Jog the “Y” axis. How does it sound? Is the stepper motor straining? If Yes, loosen the Gib a touch.
3.With the “Y” moving normal, take a look at the backlash. When you jog the “Y” in & out there should be no lag in the lead screw/saddle movement. If there is lag/play loosen the bolt on the backlash lock and with a small screw driver turn the backlash nut on the lead screw, to tighten it up a bit, and re-tighten the backlash lock bolt. If you make it to tight, the stepper motor will strain.
4.Jog the “Y” axis again. How does it sound? Is the stepper motor straining? If Yes, loosen the backlash nut a touch. Use the small screwdriver blade to hold the backlash nut from turning when you tighten the backlash lock bolt.
5.Do the same for the X-axis, steps 2, 3, 4.

Testing
1.With a CAD program, draw out a test piece with circles, lines at angles, polygons, zig-zags and text, using a new cutter and material you normally use with the machine.
2.Run the test program and watch the ”Y” axis while the machine is running. Look for any hesitation in the lead screw/saddle movement.
3.Look at the designs cuts in the material. The cuts should be crisp and clear. If there is jaggedness (when the X & Y are working together), you will to need to adjust the Gib and backlash.
4.Watch the “X” axis also, make adjustments as needed.

You need to develop a sense of feel/touch as to how the parts need to move, with the right amount of tightness, but not too tight.

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Re: Micromill Repair

Post by Denford Admin » Tue 07 Dec , 2010 10:19 am

If you check the Micromill User Manual here:
viewtopic.php?f=36&t=3130

There is detailed information and photographs on setting up the GIB strips in section 13

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