[dude_chevy]

When I have the Z up high, and tighten down the z lock screws, with a dial indicator on the spindle it only moves about .002". Then when I rlease the lock and move the Z down close to the table, and tighten down the lock screws again the spindle moves .012" to .015". What could be causing this? How can I fix it?

David

[Topdecking]

The gib is probably loose or not flat?

[dude_chevy]

I forgot to inclulde that my machine is a G0704. It was purchased new in august this year.

I have tightened the gib to where you cant hardly move the Z and still get the same result. I wonder if the Z colum is larger at the top than it is at the bottom.

David

[dick cnc]

I forgot to inclulde that my machine is a G0704. It was purchased new in august this year.

I have tightened the gib to where you cant hardly move the Z and still get the same result. I wonder if the Z colum is larger at the top than it is at the bottom.

David

I hate to say it but you could be right. The column may be way out I personally have had terrible luck the Chinese iron. It wouldn't surprise me the column dovetails were out .010 they have no quality control

[hoss2006]

I forgot to inclulde that my machine is a G0704. It was purchased new in august this year.

I have tightened the gib to where you cant hardly move the Z and still get the same result. I wonder if the Z colum is larger at the top than it is at the bottom.

David

I had a problem with one of the brass nibs that the lock lever pushes against the gib strip, it jammed in the hole and didn't let the gib strip fully seat, it was tight at the bottom and sloppy at the top.
Try checking yours with a feeler gauge top and bottom.
Another cause could be a warped/bent gib strip.
Hoss

[COMachineist]

When I have the Z up high, and tighten down the z lock screws, with a dial indicator on the spindle it only moves about .002". Then when I rlease the lock and move the Z down close to the table, and tighten down the lock screws again the spindle moves .012" to .015". What could be causing this? How can I fix it?

David

Hi
I have the same problem with my G0704. I am scraping in my machine so every thing is parallel, square and flat. I have also hand scraped the gib's which are terrible. My Z column was .003 larger across the ways at the top than at the bottom and the column is no where near flat. mine was like .002 higher at the ends which in it's self makes it hard to tram the head to the column. I had to shim the column at the base to get my face mill to cut flat at the bottom or near the bottom of the z travel. When I'm done I hope to have every thing down to .001 at the extremes of all three axis or as close as possible given the stiffness of this light machine.
Just my 2 cents worth.
CH

[dude_chevy]

I am starting to feel like I made a mistake in buying this machine. Because of how bad out it is I have to drill holes .015 over size ussually to get my parts to work. I figuring out why now.

Guess I should have spent the extra money and got a bridgeport.

David

[dude_chevy]

I am starting to feel like I made a mistake in buying this machine. Because of how bad out it is I have to drill holes .015 over size ussually to get my parts to work. I figuring out why now.

Guess I should have spent the extra money and got a bridgeport.

David

[dude_chevy]

Sorry guess I just had to vent.

So what is hand scrapping and what tools are needed? This is my only machine and I don't have surface tables or anything fancy like that?

David

[dude_chevy]

ok, so I measured my z movement with feeler gauges. First I am going to explain how I done it.

I moved my z as high as it would go. On the scale the pointer lined up with the 7.5 mark. I locked down the the z and checked the gap between the gib and the vertical slide at the top and bottom. I repeated this at 5.5, 3.5, 1.5, and 0.


7.5 0 top .015 bot
5.5 .002 top .017 bot
3.5 .009 top .015 bot
1.5 .012 top .012 bot
0 .014 top .005 bot

I welcome any and all suggestions. Thanks,
David

[SCzEngrgGroup]

I would suggest you start by determining if the ways are parallel. You can do this by removing the head from the column, and laying some short, straight rods, probably 1/2" diameter or so, along the dovetails on both sides, then measure the distance across the outsides of the rods, perpendicular to the ways. Check at several places along the full length. If the ways are parallel, you should get the same dimension no matter where you measure. I'm guessing you'll find either the column or carriage is tapered, and will require either re-machining or scraping to make them parallel. Once the ways are parallel, then you may need to re-work, or replace, the gib strip, to get a good fit.

Regards,
Ray L.

[dude_chevy]

I would suggest you start by determining if the ways are parallel. You can do this by removing the head from the column, and laying some short, straight rods, probably 1/2" diameter or so, along the dovetails on both sides, then measure the distance across the outsides of the rods, perpendicular to the ways. Check at several places along the full length. If the ways are parallel, you should get the same dimension no matter where you measure. I'm guessing you'll find either the column or carriage is tapered, and will require either re-machining or scraping to make them parallel. Once the ways are parallel, then you may need to re-work, or replace, the gib strip, to get a good fit.

Regards,
Ray L.

Measured the column as Ray L. suggested. It measured the same all the way down with in about .002". I Measured the vertical slide, it had a .090" taper. So I figured that should match the taper in my gib. The gib is .082" smaller at the bottom than at the top.

Could I bound a stainless steel shim to the bottom part of my gib, then sand it to match the taper?

David

[hoss2006]

ok, so I measured my z movement with feeler gauges. First I am going to explain how I done it.

I moved my z as high as it would go. On the scale the pointer lined up with the 7.5 mark. I locked down the the z and checked the gap between the gib and the vertical slide at the top and bottom. I repeated this at 5.5, 3.5, 1.5, and 0.




7.5 0 top .015 bot
5.5 .002 top .017 bot
3.5 .009 top .015 bot
1.5 .012 top .012 bot
0 .014 top .005 bot

I welcome any and all suggestions. Thanks,
David

Looking like a problem with the gib strip, it's not uncommon in some bf20's and particularly in x3's, it gives a problem called head nod.
Take the gib strip out and check all sides for flatness on a good flat surface, a granite surface plate is best, glass may do too.
Check my site under accessories for some small affordable ones.
They are also useful to help repair the strip by blueing the strip (a sharpie works too) and making light passes over fine emery sheet on the plate to see the high spots.
Hoss

[COMachineist]

Hi David
Ii is scraping the high points until the surface is flat with 50% bearing surface, and about 20 points/square inch. You can Google machine scraping, hand scraping. You tube has several videos on it. Google Biax power scraper to see the power tools. I just have some Anderson hand scrapers a home made straight edge to mark the ways with and a cheap 24"x24" granite b grade surface plate. I'm self taught, I used a book by Connelly "Machine Tool Reconditioning"2 videos and book on scraping. I did some practicing on and old Chinese lathe that was so lose and out of spec you could not hold 100 thou on it. You can take a class from Rich King or get his video. There are other people that teach it but not sure who they are. The worst thing you can do is get in a big hurry you easily destroy your machine if you don't take your time and think things through. Make a plan to find the problem plan what needs to be done. Spend what ever time you need to get the skills and do a plan as to how you will repair it. I wrote down every thing that was wrong and every step of the way. every measurement. Every thing.
If your machine is still under warranty I would burn you the phone to get stuff replaced or the machine replaced first.
Good Luck
CH

[691175002]

I had the same problem with my g0704 gibs, and I suspect most if not all chinese machines are similar (although not all users notice it).

It is fairly easy to fix, a flat surface and some 400 grit sandpaper will dramatically improve the gibs with only a few minutes of work.

Doing better than that will require scraping which is a more involved process. I have a fairly detailed run through of how I improved the accuracy of my g0704 in my build log, and there is some information on the gibs as well.
http://www.cnczone.com/forums/bencht...ans_g0704.html


You hit diminishing returns in accuracy fairly quickly so I would only recommend doing what you feel is necessary.

[COMachineist]

I had the same problem with my g0704 gibs, and I suspect most if not all chinese machines are similar (although not all users notice it).

It is fairly easy to fix, a flat surface and some 400 grit sandpaper will dramatically improve the gibs with only a few minutes of work.

Doing better than that will require scraping which is a more involved process. I have a fairly detailed run through of how I improved the accuracy of my g0704 in my build log, and there is some information on the gibs as well.
http://www.cnczone.com/forums/bencht...ans_g0704.html


You hit diminishing returns in accuracy fairly quickly so I would only recommend doing what you feel is necessary.

Hi
I have to be honest here I did follow your thread and that is one of the reasons I decided to scrape in the machine. The biggest reason was after all this work and when my G0704 is fully CNC converted, I want it to stay this way. I have a one shot oiling system ready to go on as well. The scraping and flaking not only looks good but it keeps oil where it needs to be so you don't get galling and early ware, the low spots hold the lub better than lapped or ground surfaces. The other is it prevents wringing or stiction at start of movement which makes things smoother. So the time is well spent for me.
Sorry to hijack your thread.
CH

[dude_chevy]

I called Grizzly yesterday. They are having a second level tech support look at my issue. They are supposed to call me back today or tomorrow. I figure I will wind up fitting my gib and/ or adding a shim.

David