Mill – Mods & Upgrades – Tuning
The very first thing you are going to want to do with a new machine is tear it apart and clean it. I think the factory expects that’s what you are going to do because besides cleaning all that shipping gunk off of all the machined surfaces, it really needs to be tuned. That means adjusting everything that is adjustable.
One of the most important tuning tasks is to adjust as much of the backlash from the axis drive screws as you can. Now, there are some people who will want to tell you to get ball screws because they can operate with zero backlash, but even after you install ball screws you STILL have to adjust out the backlash! The Owner’s Manual implies it is possible to adjust the backlash by just sticking an Allen wrench where the arrow points, but in reality you can’t. So as long as you are going tear it apart to clean it you might as well adjust it then.
You know how after you tackle a project you say to yourself, “Dang, I could do it a lot better and faster if I ever have to do THAT again.”? Well, this is what I’ve learned so you can do it right the first time. My unit came fully assembled, and all I had to do was bolt it and the tray to the stand; so I’ll presume your unit is likewise all together.
We’re going to take the table and the X and Y axis mechanism apart and clean it good, and oil/grease it good, and tune it while we put it back together. Then we’ll do the Z axis mechanism next. Get out your Owner’s Manual and open it up to the Parts List and Exploded View of the table assembly – it’s page 44 in my book – because I’m going to refer to parts by name and (number).
What you’ll need
· A gallon of WD40 at the hardware store (about $15) and a little spray bottle.
· Rag or paper shop towels
· A firm bristle cleaning brush
· Primrose Armor Plate with Moly-D Machine and Way Oil (H8257) from Grizzly for the ways.
· Multi-purpose axle grease from an auto parts store for the gears
· An air-compressor would be good.
Disassembly
1. Remove the cross way cover (23) from the rear of the table (54), and the lock levers (15) and stop block (69) on the front of the table.
2. Mark the right and left table endplates (56) & (52) because mine are NOT interchangeable – they are slightly different. Make an inconspicuous hard mark on it (but NOT on a machined surface), because if you just label it with a magic marker or masking tape or something like that the cleaning step will remove it. (Like use a center punch to make a small dot on the right one, and two dots on the left one).
3. Remove both table hand wheels (58) and endplates. You might have to use a mallet and screwdriver (or something) to whack the endplates loose because they are aligned with pins that make them fit quite snugly.
4. Slide the table off to one side. Beware, that thing is pretty heavy. If it is too tight to just slide off, remove the gib screw (16) on the right side (facing to the right) and nudge the table back and forth. Hopefully it will push the gib (72) out with it. Removing the gib will release the grip on the table so you can remove it easily.
5. If you haven’t already, remove the gib and mark it as belonging to the X-axis. It is almost identical to the one you’ll take off the Y-axis pretty soon, but mine aren’t interchangeable, so it’s good to label which one is which. Again, make a hard mark on it, but NOT on a machined surface – so that would be like on the right end next to the notch. Also, don’t worry about marking right-side/left-side; it can only be reassembled one way.
6. Undo the two screws on the right side of the cross slide (68) that hold the half-nut (6) in place and remove the X-axis screw and nut. And go ahead and remove the nut from the screw.
7. Remove the lock levers on the right side of the cross slide.
8. Remove the screws that hold the cross bearing block (74) in place, and turn the hand wheel to remove the Y-axis screw assembly out to the front.
9. Go ahead and disassemble the screw assembly.
10. Slide the cross slide off to the front. If it is too tight to just slide off, remove the gib screw on the right side (facing the front) and nudge the cross slide to the rear. Hopefully it will expose the gib so you can grab it and remove it. Again, removing the gib will release the grip on the cross slide so you can remove it.
11. If you haven’t already, remove the gib and mark it as belonging to the Y-axis.
12. Remove the two screws on the rear of the cross slide and remove the Y-axis screw.
Cleaning and Greasing
· Work over a trash can to contain your mess.
· Scrub all of the disassembled parts with the WD40 and your fingers and/or scrub brush and/or rags to remove all the shipping goop.
· Especially get all that stuff out of the bearings (there’s 5 sets of them). If you’ve got it, use some compressed air to blow the junk and cleaning materials out and off of them.
· Thoroughly pack the ball bearings in grease. Yeah, it’s a mess, but it comes off your hands nicely with WD40.
· Coat the drive screws in grease.
· Coat the mating surfaces of the ways and the gibs with oil.
Notes
· There are 2 different sizes of bearings: 3 larger and 2 smaller. The larger ones are for the X-axis, and the smaller ones are for the Y-axis. Both endplates on the table are machined to accept 2 bearings each, but only one pair is necessary on one side, and the bearing on the other side is just to keep the screw aligned while cranking on the hand wheel. My unit came with the two bearings on the right side, and one on the outside of the left side, though I suppose that arrangement could be swapped without consequence.
· There are two sizes of lock washers that were behind the nuts on the hand wheels: 2 smaller ones and a larger one. The smaller ones are for the X-axis, and the larger one is for the Y-axis.
· The larger axis screw nut goes on the Y-axis and the smaller one goes on the X-axis. Actually, you can’t confuse them, because the X-axis screw is a right-hand thread, and the Y-axis screw is a left-hand thread.
· The gibs are wedge shaped, and the ways on the cross slide are a wedge opposite of the gib, so as you adjust the screw pair forcing the gib to the right or left (or front/back as the case may be) it creates parallel surfaces of variable width for the ways of the base (and table) to mate with. So the screws move the gib, and the gib sets the width of the ways, allowing a wobble-free movement; though over-tightening the screws will cause the gib to seize the ways. In other words, you want the placement of the gib to secure the ways (by moving the screw pair together in or out), not the bowing of the gib (by over-tightening the both of the screws inward).
· The screws on the split-nuts allow an adjustment to eliminate backlash by pinching the threads. If you aren’t familiar with the term let me explain: there is a microscopic gap between the threads of a screw and a nut, and if the coupling is used to position the nut by the rotation of the screw (as in this case) that gap will reflect in a discrepancy between the rotation of the screw and the movement of the nut – that “slop” in the rotation of the screw that that doesn’t move the nut is called “backlash”. The higher the precision of the surfaces of the screw and nut the lower the friction between them, but there will ALWAYS be some degree of backlash. So the solution is to grease them up good, and pinch two nuts together so they will cancel out each other’s backlash. Ball screws, by the way, introduce a reduction in inherent friction (by the use of ball bearings instead of sliding metal on metal), but they will also have a backlash, and the method of eliminating it is basically the same. The object is to adjust it ONLY as much as necessary, AND NO MORE. Over-tightening the backlash-adjustment will introduce unnecessary friction between the nut and the screw, and that will lead to premature breakdown.
· Oh, and by the way, this inexpensive machine was not designed or built with a very high level of precision (Grizzly seems to demand a little more from their suppliers than others, but not THAT much). So as you inspect the fine details of the materials and craftsmanship (or lack thereof) don’t freak-out! You can spend a lot of time and money replacing poor quality materials and/or re-surfacing poor quality craftsmanship, or you could have just purchased a higher quality/priced machine in the first place. But we opted for the lower-price version, didn’t we? So we’ll make the best of it we can. As it is used, it will wear more than a higher precision machine would – that’s to be expected; don’t worry about it – that just means keep we need to be on the lookout for the need to re-adjust everything every now and then. Now don’t let me mislead you on this point – this doesn’t mean we got screwed and are stuck a piece of junk – NOT AT ALL!!! This just means we need to understand our limitations and compensate for it in the care of our tools and the development and exercise of our craftsmanship in using them. That challenge is part of the fun anyway.
Assembly and adjustments
1. Put the gib screws on the right-front-facing and on the front-left-facing.
2. Put the adjusting screws into the Y-axis screw nut just barely snug tight. Thread the nut on the screw an inch or so and tighten the adjusting screws until the nut just begins to bind on the screw. Remove the nut.
3. Assemble the Y-axis screw assembly, consisting of:
a. Screw
b. Bearing
c. Bearing block
d. Bearing
e. Hand wheel
f. Lock washer
g. Acorn nut
Don’t over-tighten the nut – it provides pressure to the bearings, and over-tightening will cause the bearings to seize.
4. Insert the Y-axis screw assembly into the base, and just leave it hanging there.
5. Hold the screw nut in place (in the base) with the adjusting screws facing backward and thread the screw into it just an inch or two.
6. Make sure you get the right gib to install with the cross slide. Install the gib screw in the front, but not the back.
7. Make sure the 2 nut retaining screws are in the back of the cross slide, and they are not protruding into the slot.
8. Hold the gib on the cross slide and slide it into place on the base. Hold the screw assembly up (to lower the nut out of the way) so the cross slide slides over it. You might need to extend the gib an inch or two to get the ways to mate properly, then you can push the gib up into place.
9. Lift the nut on the screw assembly into the slot on the cross slide and make sure it all fits in place.
10. Put the two bearing block screws in place and tighten them. This will lift the screw assembly into place and the nut to its proper position in the cross slide.
11. Tighten the nut screws.
12. Test the backlash, buy turning the hand wheel back and forth. With no adjustment it will exhibit a few thousandths – like maybe as much as 10. If there is ANY at all you can adjust it at this time.
13. To adjust out the backlash, unbolt and remove the cross-slide (reversing steps 10 thru 5), lift the nut (still on the screw) out of the cavity so you can reach the adjusting screws, and tighten them both just a little, then follow steps 5 thru 11 again to re-assemble and re-test it.
It might take 3 or 4 iterations, but if you are careful to note how much affect adjusting the screws has on the reduction of backlash (or seizing of the screw as the case may be) you will quickly get the hang of it. The object is to find a happy median between reducing backlash and increasing friction.
14. Put the right-rear-facing gib screw in place and adjust it and the right-front-facing screw so that the cross slide moves smoothly without wobbling or seizing, and tighten them only snugly (don’t over-tighten them).
15. Put the adjusting screws into the X-axis screw nut just barely snug tight. Thread the nut on the screw about a foot with the adjusting screws pointing outward, and tighten the adjusting screws until the nut just begins to bind on the screw.
16. Set the screw on the cross slide with the nut in its slot, with the adjusting screws pointing to the right.
17. Make sure the 2 nut retaining screws on the right side of the cross slide, and they are not protruding into the slot.