# Go755 Help Needed



## negatronix (Jul 1, 2015)

Hey everyone! It's been a while since I've been on the forum here. 

I am having a nasty issue with my GO755. I recently had the machine grab the part, and lock up which snapped a 7/8" roughing EM.

This crash seems to have knocked my machine out of calibration a bit. The head twisted, and the table seems rather jumpy. The biggest problem seems to be that after I re-calibrated things the machine is really unstable during a cut. The quill bounces up and down and the gearbox sounds really noisy. The cut is straight/true however. The quill bounce happens even if I lock it preventing me from lowering or raising it.

I am not by any stretch an expert with much of this yet, but if anyone has any ideas about what may be causing the instability, slop, and bouncy quill please let me know.

Thanks,
-Kory

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## TomS (Jul 1, 2015)

negatronix said:


> Hey everyone! It's been a while since I've been on the forum here.
> 
> I am having a nasty issue with my GO755. I recently had the machine grab the part, and lock up which snapped a 7/8" roughing EM.
> 
> ...



Sounds like a hard crash.  Could be a bent spindle.  Put a dial indicator on the spindle taper and check it for run out.  Run out should be less than .0005".  If the spindle is bent that would explain the problems you are experiencing.

Tom S


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## JimDawson (Jul 1, 2015)

Is the quill bouncing or is the spindle bouncing?  With the quill locked it really can't bounce unless the whole head is bouncing.  It is however possible for the spindle to bounce in the bearings inside the quill.  Hitting it that hard could bend a spindle or damage the bearings.  It's also possible to have damaged the gears in the head.


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## negatronix (Jul 2, 2015)

-Tom- I don't believe the spindle was bent. I checked the spindle and there is no wobble.. at least with my Manager's Special indicator from Grizzly. I also re-indicated both my vise, and rotary table since the crash. I think part of why the crash happened was due to some slop in my table. As my tool was exiting a cut it grabbed and crashed.

-Jim- The quill is moving as is the spindle. If there is any load put on a tool it bounces. As I apply pressure even drilling a hole the downfeed steps with the bouncing. The tooling is sharp, and the cuts/holes don't show any chatter.. ie.. the cuts are clean. It feels like there should be something preventing the tool from resisting the cut by travelling up. When the lock is locked, the issue still happens.

I talked to a tech at Grizzly, and he thinks that a bearing may be the culprit... however there is no wobble or play unless the machine is under load.

The tech felt the next step should be to pull the motor and open up the gearbox to look for a broken gear or the like.... uuuggghhhh

-Question- Has anyone pulled a gearbox apart on a GO755 or similar? Is this a huge can of worms I might be getting myself into, or is it pretty straight forward. Are there special tools required, and will I be forced to replace seals, circlips etc.. finally, is there any form of "timing" for the gears to be assembled, or do they just go in with no specific order/sequence.. I'm just trying to get a visual for the the job.

-Thanks,
Kory

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## JimDawson (Jul 2, 2015)

negatronix said:


> Jim- The quill is moving as is the spindle. If there is any load put on a tool it bounces. As I apply pressure even drilling a hole the downfeed steps with the bouncing. The tooling is sharp, and the cuts/holes don't show any chatter.. ie.. the cuts are clean. It feels like there should be something preventing the tool from resisting the cut by travelling up. When the lock is locked, the issue still happens.




I would be having a hard look at the quill lock also, it might be damaged.  Some careful prying with a prybar might be in order here, you might be able to see where the slack is at.


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## TomS (Jul 2, 2015)

The Precision Mathews forum on this site has a thread on changing seals that gives you the basics on removing the gear box cover so you can inspect the gears and bearings.

Tom S


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## negatronix (Jul 2, 2015)

Well... I pulled it apart, and should have stopped at just removing the motor. 

Everything inside looks perfect, chip free, sharp, no metal flakes in the oil.  

I have noticed that there is backlash/freespin in the spindle. With the motor removed, I could grab the spindle and turn it about 1/8".
I do not recall that being normal.  

Any thoughts?

Thanks for the help folks!

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## wrmiller (Jul 2, 2015)

Could have hammered the spindle splines.


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## negatronix (Jul 2, 2015)

wrmiller19 said:


> Could have hammered the spindle splines.


That's kinda what I'm thinking. Should there be rotational slop/play on the spindle?

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## wrmiller (Jul 2, 2015)

Not that much. 

Reason I suggested this is because I put a aftermarket pulley kit on my PM-25 and shortly after I was running a 3/8" carbide rougher, full pass width at a DOC of 1" and hammered the outer splines on the part supplied in the kit. Ended up making a replacement bearing carrier using the original splines that came with the mill. And I ordered a bigger mill to handle the larger jobs.


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## tmarks11 (Jul 3, 2015)

wrmiller19 said:


> I was running a 3/8" carbide rougher, full pass width at a DOC of 1"



I would assume you are talking aluminum, but still...



...must have been a slow feed rate (<8 ipm or you were going to stall your motor).


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## coolidge (Jul 3, 2015)

wrmiller19 said:


> I was running a 3/8" carbide rougher, full pass width at a DOC of 1"



I dub you Billzenegger, do you speak with an Austrian accent and say "I'll be back" all the time?


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## wrmiller (Jul 3, 2015)

Er...no...it was 1" thick 1018 steel. 

I believe that the only reason I had that issue with the splines was that the bearing carrier (female splined component) that I received with the pulley kit only had half the engagement surface on the spindle splines compared to the original. If I'd had the original piece, the mill would have been fine. Spindle splines showed no damage.

Granted, I would not suggest a novice, or anyone actually, attempt what I did but it went surprisingly well with no bogging down of the motor (better ratios with the pulley kit over the stock config), and I had everything as rigid as absolutely possible with lots and lots of cutting fluid. Smoking, light blue chips flying everywhere (including on my arms...ouch). And yes, very slow feed rate. Definitely pushed the PM-25 past it's design limits, but he held up. I'll never abuse him like that again. 

OP: sorry for the hi-jack.


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## toolman (Jul 8, 2015)

I'm not familiar with this particular machine, but spline wear shouldn't affect vertical slack. IMO, you have a bearing or adjustment issue. There's a possibility that the bearings were never fully seated when it was assembled and the crash loosened everything up.


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## negatronix (Jul 9, 2015)

So.... here is an update if anyone is interested.

I pulled the top off of the head and found that, as Toolman mentioned, a bearing was not fully seated, which was causing a mis-alignment on the high/low gearshaft. One of the bearing seats molded into the bottom of the main head casting was cracked off, allowing the bearing to easily slip in or out. There were no chips/chunks in the gearbox, so my guess is that it was built with that defect.

I was on the phone a few times with Grizzly, and the machine is still under warranty, and they are looking into sending me a new head, or machine.

I'll post another update soon.

-Kory

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## toolman (Jul 10, 2015)

Glad to hear it's going your way!


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## GarageWrench (Jul 10, 2015)

negatronix said:


> So.... here is an update if anyone is interested.
> 
> I pulled the top off of the head and found that, as Toolman mentioned, a bearing was not fully seated, which was causing a mis-alignment on the high/low gearshaft. One of the bearing seats molded into the bottom of the main head casting was cracked off, allowing the bearing to easily slip in or out. There were no chips/chunks in the gearbox, so my guess is that it was built with that defect.
> 
> ...



Would love too see some pics of the gear box w/defect? 

Buck


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## negatronix (Jul 10, 2015)

GarageWrench said:


> Would love too see some pics of the gear box w/defect?
> 
> Buck


Unfortunately I didn't take any pics. However, if Grizzly will not replace the broken part/head I will have to figure out a way to repair it myself. I will at that time post some pics and also a few pics of my repair process. 

-Kory

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## negatronix (Sep 14, 2015)

Update- Grizzly replaced the entire head and gave me another year warranty. It took them a while, but were incredibly courteous through the entire process.

I had the time to install the new head, and it sounds much quieter than the previous unit. I haven't had time to perform the break in or change the oil but should have time to get to it this week. I'll post again once I have milled something with an update. Hopefully the issue has been resolved.

-Kory



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