Excessive Backlash Y axis of Standard MIll- Not the screws or nuts, playing with shims but stays at .035"- Ideas?

jwet

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I have a new to me Grizzly G9959 "Wood Mill"- circa 2001. I bought it from a meticulous Luthier (guitar repairer) who kept it like new and has put about 20 hours on it total- just never used it- kept it oiled and clean. Most of his use was in wood and some aluminum fixtures- really a cream puff. I brought an indicator with me when I looked at it and didn't take any notes (of course) but didn't find any problems with backlash presale. In order to get this beauty into my walkout basement shop, I took it apart, too much probably, to minimize weight and lower the center of gravity for moving. My logic was that I could give everything a good cleaning and lube when I put it back together. After I got it back together I noted this .035+ backlash on the Y axis. I adjusted the nuts but there is no play at the lead screw/nut level. I have been playing with shims in front of and behind the Y axis thrust bearing- its possible one got lost or installed in the wrong place?. The setup is very similar to a Bridgeport. Handle held on by acorn nuts onto keyed Y axis shaft, zeroing dial, thrust ball bearing mounted in flange that mounts to table with big socket head screws. Have tried shims on either side of thrust bearing- always the same. I can push on the table and move something like .030". I must have dicked it up on reassembly- I would have noticed a quarter turn of backlash. Any help appreciated- everything I see about backlash is about adjusting nuts.
 
Go to Grizzly and down load the PDF. But in the meantime here is this. Check and see if you put it back with all components in the correct order.
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Cutting oil is my blood.
 
Thank you very much twhite! I have all the docs (orginal owner saved everything!). Ironically, the documentation though very similar doesn't match my mill. Even the manual that came with it 20 years ago isn't exact in fine details. Like the knee crank for example comes out at a angle and is shown as straight, the knee mechanism on mine uses a bevel gear vs the drawings showing a worm and pinion. You can see this easily- the manual cover photo shows the knee coming out at angle and in the same manual, the knee flange is straight! I've talked to Grizzly, its really strange to them too. These manual problems is part of how I got into this mess. I may call them again. I appreciate the help.
 
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Thank you very much twhite! I have all the docs (orginal owner saved everything!). Ironically, the documentation though very similar doesn't match my mill. Even the manual that came with it 20 years ago isn't exact in fine details. Like the knee crank for example comes out at a angle and is shown as straight, the knee mechanism on mine uses a bevel gear vs the drawings showing a worm and pinion. You can see this easily- the manual cover photo shows the knee coming out at angle and in the same manual, the knee flange is straight! I've talked to Grizzly, its really strange to them too. These manual problems is part of how I got into this mess. I may call them again. I appreciate the help.

It sounds like a simple problem. Just have to figure out what changed.

Pro tip. Take lots of pictures when taking apart. Although I can still mess that up.


Cutting oil is my blood.
 
Twhite- I agree- I've learned my lessons on taking pics- I did take some but no excuse in this digital age for taking tons.

Tom- No problem, I thought I was pretty experienced- this should be easy. I'll double check gibs- good call.

I'm have a good nights rest, a good breakfast, a sharp pencil and a notebook and am going to go after it systematically on this rainy afternoon. It seems to be that it must be engagement between the thrust bearing and the in and out load points and shaft spacers/shims but have played with them and can't seem to change it.

Thanks for the help guys- it might just be commiserating but is appreciated. I'll try to post what I learn if anything.
 
Keep us posted as to what it was.


Cutting oil is my blood.
 
Okay, fellow travellers...when we last heard from our hero, he was just confused...

I removed the front flange which includes two thrust bearings with a fixed spacer between, the dial, handle and lead screw if unscrewed clear of the nut. The screw looks great and no visible/measurable wear if I measure arcross the flats of the acme, the nut look fine but I don't have any quantitave way to measure. I removed my experimental shims. I have figured out that these don't affect backlash since When I bolt the handle up, I take up all the slack in all that. Shims in the position would only change the position of dial or end of the shaft if I had an interference on the dial or not enough thread to buttom out the handle nut to pull it all tight- both are fine- close but fine. I put it all back together paying attention to things and may have the culprit- I think the nut mount has some in an out slop. Unlike a BP, the nuts mount in a little cube mounted to XY table yoke. This need to rotate a bit so it won't bind but should have no fore and aft play. I need to remove the table and unfortunately, its a foul day and my engine hoist is in a friends storage locker 100 miles away- he's "borrowing" it. Stay tuned. Is it possible to post pictures here? I have a few plus a sketch that might help some poor soul in the future.

Stay tuned and make sure to drink Ovaltine...
Thanks a lot
 
Welcome back to the saga of our hero- at the end of the last episode, he needed tools and time but had inspiration thanks to this board...

Ok, I plucked the X axis table off. Pretty straight forward and I could have done it without the hoist (and the half day of driving to fetch it)- just remove X axis lead screw, loosen the gib, roll up a cart, crank the knee to get it level with the cart top and slide it off the saddle and onto cart. It is a heavy bugger. Next time...

This gave me access to the Y axis and nut. Removed the Y Leadscrew, flange, dial bearing all together (like the explodded drawing above) and then the anti backlash nut, one big socket head cap screw held it up under yoke- it had a somewhat precise round boss on top that fit a reamed hole on the saddle to keep lash down with the yoke. The nut isn't shown in exploded drawing above but is pretty simple. The big mounting screw through the top boss was a bit loose, my logic was that this would let it rotate a bit to make up for run out along the screw without trying to bend the leadscrew- wrong. The nut is an assembly. The body is cast steel with the boss machined in the top, Female acme in the back and an adjustable round steel nut pushed in with a large headed machine screw and a similar lock screw similar to a Bridgeport adjuster. This nut was put together in a collapsed state so the adjustment screws couldn't exert any push on the rim. The screws can only push. To get this right, you thread in the X lead halfway and then give it a good jerk in the out direction, this takes up the slack, pulls the moving nut out and then you can adjust inwards. More lessons- didn't appreciate this subtlety before. Bridgeport have a more positive system, this nut floats in one direction. Got the Y axis mess back together. Can take out all the backlash now to anything I want! But I now have a new problem.

The new problem is that the lead screw is kind of stiff at one point in its rotation on each rotation, its worst in the middle 4" or so of is 12" travel and easy at the ends. This is opposite of a clapped out lead screw- usually giving you stiffness at the ends of travel because if you take out lash for the middle of travel, the ends are less worn and get stiff. I think the lead screw has a bend in it. I had a big crowd of friends over to help me move the mill around the house in its disassembled state. I imagine someone dropping the lead screw on the garage floor or stone path that leads to the walkout basement. I have a small surface plate and some v-blocks. I'm going to see if I can verify this. What do think about find the high spot and giving it a whack with a dead blow until I can't see a bow on the V blocks. My alternative is to got to a shop and have them verify it and flame straighten it.

Stay tuned and drink Ovaltine every morning. Next episoide- "Too Squirrelly Screw?" or "Well Placed Whack with Mallet Cures All"

Thanks in advance guys.
 
I figured out that I can use my removed table as a surface plate with the V-Blocks. What do think of the dead blow whack? I'll see what the magntiure of the wowwee is I guess and go from there...
 
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