# New Grizzly G0729 Mill...Finally!



## Rick H (Oct 22, 2014)

Well after a couple of years of lurking around on various machine web sites I finally took the plunge and ordered a milling machine of sorts.  Yeah I know, most say buy old B-Ports and be happy, but not in the cards for me.  I don't have the room for a big milling machine and my budget isn't all that great to jump into a full size machine.

The reason I opted for the G0729 was that it is a true knee mill and I liked that feature.  It weighs about 700+ pounds and is small enough to fit into my modest workshop area.  I am waiting for a Kurt vise to arrive and some other items so I haven't tried any real milling yet.  I have played with some precision hole drilling and so far so good save for one area which I will describe in detail shortly.

Table movement was on the loose side in both X and Y axis so I adjusted the gibbs.  Backlash for X-axis is about .005 and y axis is about .006.  I haven't trammed a mill in over 40 years but if I'm doing it correctly I have about .001 on the X axis and less on Y.  Y is what concerned me most because of the somewhat difficult process to adjust it on this mill, but until someone else checks it for me I think it is pretty good.  There is one thing I noticed about the Y-axis table movement in that it gets very difficult to turn the hand wheel when the table is in the extreme far left position.  The hand wheel starts getting difficult to turn about 2 to 2.5 inches before table movement is used up.  there are no problems in the far right position.  This problem existed before I adjusted the X-axis table gibb.

The other more concerning problem that I discovered deals with the quill movement.  I ran several drill test holes in various materials and noticed I wasn't getting near the depth accuracy I thought I would.  In fact my test numbers were in my estimation, all over the board.  At first I blamed it on the fine down feed wheel as it is graduated one turn is .100 but in truth it is only supposed to give .080 in depth.  So at first I believed it was me trying to get used to the .100/.080 ratio.  To help myself out a little I installed a digital readout on the quill and I thought that would yield more accuracy.  It was then that I discovered there was backlash in the quill that was creating the problem.  I would reach my desired hole depth on the DRO and would stop the quill feed but I noticed the quill continued to drop after I stopped the feed.


Once I actually saw the quill drop I looked closely at it and noticed if I put upward pressure of about 8 pounds or so, the quill moved upward.  When I released pressure on it the quill dropped down to a rest position.  I placed an indicator on the quill and measured this up and down movement between .012 and .020 depending on how hard I applied upward pressure.  This movement doesn't take place when the quill is all the way up or if it is locked.   So at least I figured out WHY my drilled hole depth was always deeper than I wanted.


Now I know backlash in the quill and down feed control is ever present but I didn't think it should be quite this much.  I have an old Craftsman DP that I had had for many years and it has backlash in the quill but only about .006.  On a lark, I sent Grizzly Tech Service an email describing my situation and they called me and advised the amount of backlash in my quill is within their specs and that they don't consider this a problem until it exceeds 1 MM.  I have about half that much in mine. 

So my question to the educated members of this forum is this, is .012 to .020 too much quill backlash in this machine?  I certainly can work around this issue and yes, I can use the knee if I had to, but I would like some opinions in this area.  If in fact this isn't "normal" per se what can I do to eliminate or reduce this amount?  Or am I being overly picky about this matter.  Sorry for the long post just trying to understand what is going on......thanks in advance.

Rick H.


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## chuckorlando (Oct 23, 2014)

I dont have an answer for you as I just dont know whats ok. But if you are feeding in one direction there should be no effect from backlash I dont believe. It would run to depth and maybe kick up but not down. You sure that after it kicks out that it does not some how continue to rotate a little like a lathe chuck would? If it drills holes .02 deeper then it should then that aint cool. If it was a consistent .02 then you could adjust to compensate but with .01 varying the best you could do is shoot for the middle and deal with up to .005. Is there no way to adjust things?

Look at the threads at the end of the travel and see if they got a chip in there.


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## JimDawson (Oct 23, 2014)

The only thing I can suggest on the tight Y axis is to play with the gib a bit.

0.010 to 0.020 quill backlash is a bit much IMO.  I think the only way to compensate for the backlash is to bias the quill upward with a counter balance.  A gas spring or an air spring is about the only practical way to do this.  Here is what I did http://www.hobby-machinist.com/show...CNC-Conversion?p=199564&viewfull=1#post199564


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## Rick H (Oct 23, 2014)

Thanks for replies guys.  Just to clarify what I think is happening is that when drilling hard material the backlash in the quill is taken up in reverse.  When I get to the point where I want to stop drilling the quill continues downward through sheer weight until the backlash is used up so to speak at which time it finally stops drilling.  This doesn't seem to be as much of an issue with soft material as the quill isn't forced upward reversing the backlash.  Make sense??

I know I can work around this issue the same as working with backlash in table feeds, but it is really aggravating when trying to drill a specific hole depth.  And I know I could use the knee for this but I would hope I could find a way to drill a reasonably accurate hole by using the quill and save the knee for milling work.  

I was somewhat disappointed in the reply from Grizzly as I had hoped they would have shown a little more concern in this issue, but that wasn't what happened.  They also gave me no real answer regarding the X-axis table adjustment being tight to one side only.  So from what I have read I only have a couple of options and that is to have a new down feed gear made to tighter specs or to possibly have my current parts plasma coated to remove some of the backlash.  Or someone suggested making a collar that would fit around the quill and be suspended by two springs that would counter weight the quill and keep it from dropping.

In any event, I am just looking for some suggestions before I take any action one way or another.  If this backlash problem were only .004 or .005 I suppose it wouldn't concern me as much, but .015 to .020 seems somewhat extreme to me.  Thanks again for the help.

Rick


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## JimDawson (Oct 23, 2014)

One trick I use sometimes, is to put some tension on the quill lock, enough that the quill cannot fall by gravity, but not so much that the quill requires too much force to move.


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## Rick H (Oct 23, 2014)

I didn't think of that one Jim, but I will try it.  I'm not sure if it will work very well though as the fit between quill lock and quill is pretty iffy.  Thanks for the idea though.......

Rick


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## Rbeckett (Oct 23, 2014)

Rick that is great that you also found where the excess play is too.  You should be able to tighten the large nut on top of the spindle and eliminate most or nearly all of that falling and going deeper than you planned.  Take a pic of the top of the quill and we will tell you the procedure for loosening and tightening the bearing preload.

Bob


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## Rick H (Oct 24, 2014)

Hi All:  Jim:  I tried your little trick last night on 10 holes that I had to drill of different depths.  None of the holes I drilled varied more than .002 which is really good for my needs.  Thank you very much for the help!

Bob:  I have attached a picture of the spindle head for you.  It appears that the nut you are referring is somewhat of a special one.  Is this the nut that you are talking about?  I assume there must be some type of set procedure for tightening or loosening this nut in order to keep the correct preload on the bearings?  Any adjustment advise will be greatly appreciated! 

Thanks to ALL!!

Rick




P.S.  I ran into another problem today while I was trying to fly cut a 4" x 2" piece of Delrin.  After about 5 to 10 minutes the X-axis power feed quit working.  This was the first time I have really used it and I was shocked to have it quit on me.  The motor runs fine when you engage the unit, but there is no turning of the X-axis shaft.  It's as if some sort of clutch or something gave out.  I called Grizzly Tech Service again and the gent I spoke with said I'll have to call back Monday and speak to someone in PA about this.  Apparently thy had already gone home for the day in PA.  Are there any adjustments on this power feed or is the unit Kaput!!

Thanks again!!!


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## JimDawson (Oct 24, 2014)

Rick H said:


> Hi All:  Jim:  I tried your little trick last night on 10 holes that I had to drill of different depths.  None of the holes I drilled varied more than .002 which is really good for my needs.  Thank you very much for the help!



You are quite welcome.  I'm always happy to help out.


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## iron man (Oct 24, 2014)

I have a GO727 it had a bunch of little problems but I expected and knew that going into it I have made a ton of modifications to it just to make it more accurate and to americanize it and now I have a very nice little mill. 

The response from grizzly is normal they are not machine operators so they just go by guide lines. You have a good base for a very nice mill it seems they stop short of making an excellent mill for I dont know what reason. I know this is not what you want to hear but I think if you take it apart and look at how it was assembled take some close measurments you will be able to tighten things up quite a bit. I tore mine down completely and found all kinds of assembly mistakes let along some poor engineering. Most of all just take your time you will get it all squared away.. Ray


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## Rick H (Oct 24, 2014)

Thanks Ray.  I have found all sorts of little things wrong with it but the one that concerns me most right now is the loose spindle followed by the tightness in the table moving it to the right.  I knew I wasn't buying a BP or anything even close, but I have literally had to go thru this thing and tighten up every nut and bolt on it.  I discovered the power feed not working today was due to a loose nut on the outside of the right table hand wheel.  Tightened it up and works like a charm again.  So now if I can fix the other two issues I'll be all set until I decide to go into it deeper.   I am also somewhat disappointed in the lack of concern with my two contacts with Tech Service.  The only thing the guy did today was pull out an owners manual and read it to me regarding the power feed.  I told him I had already read the manual and it didn't say squat about my specific issue.  All he did was basically tell me to call back.  Oh well.........


Rick


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## iron man (Oct 24, 2014)

I got the same response they offered to send me a different mill but the problems will remain the same. If I had to do it over I would have just tore it down and re-assembled it like it should be just take one thing at a time look it over real well try and figure out where they went wrong or how it could be made better. Sometimes all it takes is spending a little more time keeping the tolerances tighter otherwise the mill just beats itself to death. You have the mill I wanted but could not afford at the time so I hope you can turn it into a nice machine I am sure you are well on your way good luck. Ray


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## Rick H (Oct 25, 2014)

Thanks Ray.....I feel a little bit better now.  I really agonized for two plus years over which make and style mill to get.  A ton of people I know that are in the trade all said Bridgeport but if that couldn't happen AT LEAST get a real knee mill.  So that's what I did so now I have to see it thru or my wife will kill me!!  I see a DRO in my future though.

Rick


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## chuckorlando (Oct 25, 2014)

Yea it sucks for sure man. But even with a used BP you might be tearing it all apart as well. Only thing aint been off my BP is the knee it's self and the head. And the head needs gone through I just aint doing it till I can do it all inside. Hope it all dont need it, but plane for the worst.

Unfortunatly you might need to pull the table. Try adjusting the gibs but I dont see it doing much. Not if it it's perfect every place but the end. If you make the end right then 90% will be sloppy possibly. But you could have a bur or chip stuck in the screw or a mushroom on the opposite side of the table on a flat or in the way.


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## Rick H (Oct 25, 2014)

Obviously there is a special socket or wrench that they use for adjusting the spindle nut.  Are these sockets available somewhere?  I tried to get some dimensions off the spindle nut itself, but it's buried in the spindle pulley making it difficult to get any accurate readings with the tools I have.  I have to wonder in situations like this why they don't use a standard socket and locking tab instead of making it more difficult with notched round nuts.  From what I can see this nut looks like it might be a left hand thread but I'm not completely sure on that because I can't see but a small amount of threads.

Rick


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## chuckorlando (Oct 25, 2014)

Seems you have two spanner nuts. One after the lower bearings and one after the uppers. No spec on the upper but the lower is listed as 30mm.


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## chuckorlando (Oct 25, 2014)

They say on your pdf that the spanner has been replaced with the one for the 728. I look at the 728 pdf and it simply say's discontinued.


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## visenfile (Oct 25, 2014)

Rick, You can make a spanner.  I have done this for years with tube and pipe.  As a newbie, however , it is interesting I have not seen a foolproof technique for reaching the proper preload on the ?tapered? bearings.  I know how to do this on automotive applications, but on lathes the guys seem to wing it and feel for heat.  The pure approach is a dial indicator reading but hard to achieve.  As a lurker I'm beginning to think used asian is probably not more of a "kit" than new, if I could be guaranteed parts required for repair.


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## Rick H (Oct 25, 2014)

Visenfile:  Well from my days as a line mechanic we used to set differential backlash usually at .005 to .00"..  Never having worked on a milling spindle I would be shooting in the dark on proper pre-load.  I am just guessing but waiting for heat to tell if you have proper pre-load sounds a bit "iffy", but what do I know.  How do you adapt a "tube and pipe" to this type of situation?  Thanks.....

Rick


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## chuckorlando (Oct 25, 2014)

you just mill the 4 tangs to fit the flats. I have ground sockets to fit spanner nuts among other things. They are just 45* apart so pretty easy. You can also buy a spanner socket in various sizes.


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