G0484 all tuned up - now I have gear backlash issues

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AlphaGeek
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G0484 all tuned up - now I have gear backlash issues

Post by AlphaGeek » Mon Aug 09, 2010 2:55 pm

Sorry for the long absence -- it's been a busy couple of months.

The good news: I've finally got my G0484 in reasonably good tune!
* Column and table ways have been worked back and forth enough to break in nicely
* Gibs on same can now be run nice and snug across full range without binding/stiction
* Column z-axis ways are (finally) properly aligned and perpendicular to table
* Head rotation zero-degree point is dialed in, and more importantly, I've figured out the head-bolt-tightening methodology to achieve a specific alignment on my machine
* DRO scales (caliper-style for Shumatech DRO) all installed and aligned
* Spindle pulled and rough groove for setscrew ground to mirror finish; setscrew ground to slightly rounded profile
* Spindle reinstalled with splined shaft oriented for best fit with drive splines
* Mounting bracket for fine-feed worm drive modified to enable optimal engagement of worm drive with gear on shaft

The bad news: over the last couple of months, the geartrain has started making increasingly alarming "gravel crusher" grinding noises in the low range. Worse, now that the spindle splines engage with less slop it's obvious that there's serious excess backlash in the geartrain -- 1.5 to 2 degrees of rotational free play in low range, and 5-plus degrees in high range.

Since my warranty is good for another month and a half, I sent email to Grizzly tech support today detailing the issues and asking for help. While I'm waiting on a response, I'd like feedback on just how excessive the backlash I'm seeing really is. I know the rock crusher noises are probably failed bearings, so that issue isn't in question.

I requested that if I have to exchange it, that I swap just the head and not the whole mill. Hopefully they'll be willing to do that, because I'd hate to have to re-do all the work on the column, ways, DRO mounting, etc.

Thoughts?

-AG
Rule number one: Everything takes longer and costs more.

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mechanicalmagic
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Re: G0484 all tuned up - now I have gear backlash issues

Post by mechanicalmagic » Mon Aug 09, 2010 9:45 pm

AlphaGeek wrote:The bad news: over the last couple of months, the geartrain has started making increasingly alarming "gravel crusher" grinding noises in the low range. Worse, now that the spindle splines engage with less slop it's obvious that there's serious excess backlash in the geartrain -- 1.5 to 2 degrees of rotational free play in low range, and 5-plus degrees in high range. I'd like feedback on just how excessive the backlash I'm seeing really is.
AG,
IMHO excess clearance in a gear train causes increased noise. Insufficient clearance causes extreme wear and early failure. In lightly loaded situations (like your mill) I expect the gears will outlive you, if you use it every day. My gear head lathe has at least 10 degrees of play in the headstock, and the threading lead screw probably has 30 degrees. I have no problem with my machine.
AlphaGeek wrote:I know the rock crusher noises are probably failed bearings, so that issue isn't in question. -AG
Well, my experience with bad bearings brings the following thought. Bad bearings sound worse with higher load and higher speed.
Gear trains sound worse when they hit a resonance and more load.

Perhaps the average temp in your shop has increased over the months, and the oil is no longer providing the same cushion for the gears. What weight oil do you have in the head?
Dave J.
Every day I ask myself, "What's the most fun thing to do today."
9x48 BP clone, 12x36 lathe, TIG, MIG, Gas, 3 in 1 sheetmetal.

AlphaGeek
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Re: G0484 all tuned up - now I have gear backlash issues

Post by AlphaGeek » Tue Aug 10, 2010 3:04 am

mechanicalmagic wrote:
AlphaGeek wrote:The bad news: over the last couple of months, the geartrain has started making increasingly alarming "gravel crusher" grinding noises in the low range. Worse, now that the spindle splines engage with less slop it's obvious that there's serious excess backlash in the geartrain -- 1.5 to 2 degrees of rotational free play in low range, and 5-plus degrees in high range. I'd like feedback on just how excessive the backlash I'm seeing really is.
AG,
IMHO excess clearance in a gear train causes increased noise. Insufficient clearance causes extreme wear and early failure. In lightly loaded situations (like your mill) I expect the gears will outlive you, if you use it every day. My gear head lathe has at least 10 degrees of play in the headstock, and the threading lead screw probably has 30 degrees. I have no problem with my machine.
I do understand that some play is necessary -- but the amount of play in my mill's gearbox seems well outside the acceptable range, if only because I got to experience some really exciting (aka awful) driveline grinding, pounding and hammering recently as the shockwaves oscillated back and forth through the geartrain. It's actually much more of a problem in the low-range gears, probably because the slow spindle rotation means there's little momentum to keep things moving.
mechanicalmagic wrote:
AlphaGeek wrote:I know the rock crusher noises are probably failed bearings, so that issue isn't in question. -AG
Well, my experience with bad bearings brings the following thought. Bad bearings sound worse with higher load and higher speed.
Gear trains sound worse when they hit a resonance and more load.

Perhaps the average temp in your shop has increased over the months, and the oil is no longer providing the same cushion for the gears. What weight oil do you have in the head?
Dave J.
Good points, and I gave this some thought before realizing there's a piece of info I left out -- the rock-crusher noise is present mostly in low range, low and mid gear. Low range, high gear does not have anywhere near the same noise level. Based on my limited knowledge of the gear layout, I think it's entirely possible that the bad bearings are on a shaft shared by the low and mid gears. And yes, the bearing noise gets markedly worse with significant load, to the point that I'm not really keen on using low-low or low-mid without hearing protection right now.

-AG

PS: The right-angle iron turned out to be invaluable when getting the column aligned -- both as a reference surface and as a support for the head when I needed to loosen the column bolts to swap in shims. I tried doing the job with a piece of hardened/ground rod held in a collet and an indicator attached to the table -- and it just about drove me nuts before I took the rod to my surface plate and figured out that it's NOT close to perfectly straight. Let me know if you want it (and your brass shim stock) back anytime soon. I've cleaned up many of the dings and deformities on the iron, but it's not going to be a metrology showpiece anytime soon. ;)
Rule number one: Everything takes longer and costs more.

AlphaGeek
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Re: G0484 all tuned up - now I have gear backlash issues

Post by AlphaGeek » Tue Aug 10, 2010 3:19 am

Forgot to answer the question about oil:

http://www.mcmaster.com/#2158k15/=8c8f4k

I used Mobil ISO-68/SAE-20 based on the recommendations in the manual and confirmation from Grizzly tech support. I suppose I could try swapping it out for something from the "gear oil" section further down the page, but it seems like a bit of a jump to go from SAE-20 to SAE-80W or higher. Thoughts?

-AG
Rule number one: Everything takes longer and costs more.

AlphaGeek
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Re: G0484 all tuned up - now I have gear backlash issues

Post by AlphaGeek » Wed Aug 11, 2010 1:08 am

Heard back from Grizzly tech support today -- they don't have a headstock available to ship out to me (surprise) so my choices are (a) send whole mill or headstock up to Washington for repair, or (b) pull and inspect the gears/bearings myself and have them send me whatever replacement parts I might need. Being an inquisitive type, and far too lazy to remove the headstock and ship it, I'm pretty sure I'll be picking option (b).

If there's interest, I'll document the process and post pictures. At the very least I'll be shooting before and after video clips to document the sounds made in the various gears. I'll probably do the teardown this weekend if anyone in the Bay Area wants to stop by and check it out -- just drop me a PM.

-AG
Rule number one: Everything takes longer and costs more.

tlfamm
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Re: G0484 all tuned up - now I have gear backlash issues

Post by tlfamm » Thu Aug 12, 2010 4:33 pm

AG: here's one vote for full photo documentation of disassembly/reassembly ...

Sorry you need to take a new mill apart ...

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Falcon67
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Re: G0484 all tuned up - now I have gear backlash issues

Post by Falcon67 » Thu Aug 12, 2010 4:56 pm

Since I have a head stock just like it, X2 on the pictorial.
Chris -
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EdK
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Re: G0484 all tuned up - now I have gear backlash issues

Post by EdK » Thu Aug 12, 2010 6:26 pm

I would also like to see your documentation of the tear-down and fix since my Enco version of that mill has a leak in the head. I'm going to tear it apart and replace the seals and probably replace the spindle bearings with some USA bearings while I have it torn apart.

Ed
Vectrax 14x40 lathe, Enco RF-45 clone mill, MillerMatic 180 MIG.

AlphaGeek
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Re: G0484 all tuned up - now I have gear backlash issues

Post by AlphaGeek » Fri Aug 13, 2010 2:19 am

Message received loud and clear. I'll take lots of photos of the teardown and inspection and post those first -- then when the parts arrive I'll follow up with a second set of the actual replacement process. It helps that my oldest son (12) is quite into photography and videography these days, as I'll be able to enlist him to get at least some of the pics.

-AG
Rule number one: Everything takes longer and costs more.

AlphaGeek
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Re: G0484 all tuned up - now I have gear backlash issues

Post by AlphaGeek » Wed Aug 18, 2010 9:57 pm

I'll file an initial report now, followup with some pictures later tonight.

I found several issues that must be corrected. Not all of these were on my original list of stuff I anticipated seeing during teardown and inspection.

First issue discovered: I found a surprisingly large quantity of metal particles and chips in the headstock. It appears that the Asian semi-skilled laborers who assembled this mill made a desultory effort at cleaning out the head casting, then used some kind of yellow spray coating to more-or-less glue down anything that was left. This included chips from various boring and tapping operations, grinding dust, etc. Nice.

Next, and probably related to the debris issue above, several of the bearings are damaged. Given the relatively minor expense of buying good Japanese bearings, I ordered replacements for the whole lot from VXB today. (About US$70 including tax & ground shipping.) I'll include a list of bearings required in my next post. Fun fact: this spindle design appears to be used in virtually every mill-drill, and employs preloaded tapered-roller bearings that are also automotive parts. :)

The most interesting discovery wasn't damage to the gear teeth (more on that in a minute) -- it was the poor fitment of the keys and keyseats. Basically, it looks like they took one fast pass with a 2-flute mill to make the keyseats in the gear shafts (leaving lobes on the sides of the resulting undersize slots) and then used a surface grinder to reduce 6mm keys to fit. The problem is that the gear hubs were actually broached correctly for a close or sliding fit, as appropriate, leading to excess rotational play. I spent a bunch of time deciphering the appropriate section in Machinery's Handbook to see how it *should* have been made, and long story short I have >0.21mm clearance in places where it should total <0.02mm.

I've ordered 6mm keystock, which I'll cut to the lengths needed and round the ends on the grinder. However, the keyseats need to be cleaned up so they're straight and of the correct dimension. I don't think I can grind a perfectly straight 6.0mm slot freehand with a Dremel :roll: so this will mean either buying a day-pass at Techshop or begging a favor of someone willing to mill the slots into shape.

Finally... gear tooth damage. I'm going to cut and paste from my email to Grizzly tech support wherein I list the damaged gears needing replacement:

P0484216 severe scoring and impact peening on small and medium gear tooth surfaces
P0484227 scoring on teeth of small gear
P0484231 scoring and impact peening on gear teeth
P0484232 scoring on gear teeth
P0484233 scoring on gear teeth

Basically, all of the gears with hardened teeth were in fine shape -- normal wear marks, but no scoring or peening on the tooth surfaces. The "soft" gears (basically, most of the gears on the intermediate shafts) had both debris damage (scoring & scratches) and impact damage from the teeth slamming together, due in large part to the keyway fitment issues noted above.

Sent off email to Grizzly today requesting replacement parts. Hopefully they won't be balky, since the list above is more than half the gears in the headstock. On the other hand, I can always send them a picture of the magnets covered with metal chips and debris I've cleaned out of the mill.

-AG
Rule number one: Everything takes longer and costs more.

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mechanicalmagic
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Re: G0484 all tuned up - now I have gear backlash issues

Post by mechanicalmagic » Wed Aug 18, 2010 10:29 pm

Geek,
My shop is open for keyseating, IF I have a proper cutter. I have a pile of very odd size end mills (HSS & Carbide), but few keyseat cutters. (But, I can modify width in the lathe with the toolpost grinder.)

Sooner is better.
PM or email.
Dave J.
Every day I ask myself, "What's the most fun thing to do today."
9x48 BP clone, 12x36 lathe, TIG, MIG, Gas, 3 in 1 sheetmetal.

Harold_V
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Re: G0484 all tuned up - now I have gear backlash issues

Post by Harold_V » Thu Aug 19, 2010 1:27 am

I would recommend key seats be sized by using undersized end mills, doing proper offsets. The end result should be superior, considering you'll be able to climb mill both faces of the seat, and have total control over the finished size.

Harold
Wise people talk because they have something to say. Fools talk because they have to say something.

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