Johnwa
Ultra Member
Grizzly sells a gib for their G0705 round column mill for $30US but won’t ship to Canada.?
https://www.grizzly.com/parts/Grizzly-LONGITUDINAL-GIB/P0705223
https://www.grizzly.com/parts/Grizzly-LONGITUDINAL-GIB/P0705223
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RF30 Basement Install
- Thread starter YYCHM
- Start date
Craig,
I've questioned whether the table Gibb is correct for the machine as well. It looks distinctly different from the saddle Gibb which is giving me no problems at all. I would assume apart from being different lengths the two would have approximately the same proportions.. They don't, but maybe that's just a bad assumption. Without the proper Gibb to mimic making a better one would be a huge challenge I would imagine.
I was thinking last night that maybe placing a very thin shim between the Gibb and the saddle at the narrow end of the Gibb might have some effect without binding the table. I might try that this morning.
Craig
I've questioned whether the table Gibb is correct for the machine as well. It looks distinctly different from the saddle Gibb which is giving me no problems at all. I would assume apart from being different lengths the two would have approximately the same proportions.. They don't, but maybe that's just a bad assumption. Without the proper Gibb to mimic making a better one would be a huge challenge I would imagine.
I was thinking last night that maybe placing a very thin shim between the Gibb and the saddle at the narrow end of the Gibb might have some effect without binding the table. I might try that this morning.
Craig
@trlvn : your observations are right on the money. The interaction of the saddle dovetail, the gib, and the table dovetail are critical for a smooth and accurate operation of the assembly. On this machine, there for sure are issues - with any luck, it is just the gib.
To solve the problem, the gib needs to be “scraped in” to properly fit, at the very least. If there are issues with dove tail angles, the job just got massively more complex.
While addressing the gib issue on the table, one may as well look at the y-axis as well. Although that seems to work fine at this time.
And the problem with the lubrication (or lack there of) of the slide ways: there are machined channels (swirls) but no way to get oil into them without removing the table/saddle to access them each time. Oil galleries need to be drilled into the parts so that lubrication can take place with ease.
These machines are built to a price point. Can all the problems be resolved - with enough effort, most likely. Will it take a lot of time? For sure.
So this morning I set up like this on both the left hand and right hand sides of the machine. The table is centered.
No amount of Gibb adjusting in both the x and y axis would eliminate 0.002 on the left hand side and 0.003 on the right hand side. I had tightened the Gibbs to the point where you could barely crank the table and saddle. So I loosened the Gibbs back to a useable state.
Next I tried tightening the Gibb lock screws to see what effect they would have. I tightened the saddle first and that had no effect. Locking the left side table lock had no effect. When applying the right hand lock the DI swung 0.004 and now there was less than 0.001 (maybe even nil) movement when I pushed and pulled on the table.
Have to think on this now.
No amount of Gibb adjusting in both the x and y axis would eliminate 0.002 on the left hand side and 0.003 on the right hand side. I had tightened the Gibbs to the point where you could barely crank the table and saddle. So I loosened the Gibbs back to a useable state.
Next I tried tightening the Gibb lock screws to see what effect they would have. I tightened the saddle first and that had no effect. Locking the left side table lock had no effect. When applying the right hand lock the DI swung 0.004 and now there was less than 0.001 (maybe even nil) movement when I pushed and pulled on the table.
Have to think on this now.
Doug (@historicalarms) , David (@David_R8) Does your machine have the set screws? My mini-mill had them but no longitudinal adjustments screw.
This might be a simple solution to this issue.
That is actually progress: you may just have to leave the RH gib lock slightly snug all the time to eliminate the free play. Certainly could be a “ workaround” for the time being....
I think I beat you to that conclusion.
I backed off the x-axis Gibb adjustment screw until the table moved nice a free and the tightened the right hand gib lock until all the free play was essentially eliminated and found that the table still moves freely enough to be useable.
I discovered that in this configuration the right side of the Gibb is being pushed away from the saddle dove tail by about 0.007 using a feeler gauge. I can completely insert a 0.006 gauge but a 0.008 won't enter.
I'm going to tram the vise now with my new TDI to see what that's doing. If it trams ok, then there may be two things I could do. Stuff a feeler gauge behind the Gibb and leave it there or drill and tap the saddle and install a long set screw with a locking nut on it. Installing an adjusting set screw on both the left and right hand sides might not be a bad idea.
What do you think?
We know more about how this Gibb is messed up now. Not tall enough and not thick enough at one end at least. Who knows what the other end is doing.
……. So now we are getting somewhere. The vise trammed to 0.004 over 4.5". Now that that table isn't bouncing around I was able to bump it down to 0.0005 over 4.5".
Craig
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Set screws or T screws?
Brent H
Ultra Member
Hey @YYCHobbyMachinist, reading over your post with the gib measurements I have a few concerns with the fact that your gib is tapered in more than one way.
The Gib should remain constant in height along its length. It should not be high enough to be taking the weight of the table but needs to be consistent to ensure proper fit to the dovetails.
This is depicted in the top sketch of the drawing
:
The second sketch shows what you would see if you planed off the table surface down to the gib. The intention of the gib is to allow you to tighten it in on the wedge to obtain an equal "x" dimension (basically) you can see that the taper in the top is equal and opposite the gib so that the gib establishes a proper parallel running surface between the table and the base. Since the gib is fixed to the table and moves with it, it will always be parallel
The bottom pic shows that the gib should be equal in the other plane so that the height is constant. This is to allow the table to sit properly on the base so that those swirly oil passages can create a nice slippery surface. If the gib was tapered in this direction it would tend to then be the piece that rode on the ways and would have load on it from the weight of the table and what you were machining
Your gib seems to taper in 2 directions such that height is diminishing along the length of the gib. - wear?
On the bottom of your table I would think one dovetail is straight and the other tapers. The base sides should both run parallel to each other. (Maybe opposite but I can't see that far from here LOL)
For a crude reference but may give you an indication on the gib, if you measure the distance across the dovetails on the base and then measure the distance of them on the top, you can do some math and find out what the taper should be. Then measure up the gib and see if the taper angle is correct. If the angle of the gib is too steep the small end will not be in contact with the base properly to establish that parallel sliding fit.
You can see the dotted line in the drawing that is the reference for the base. There will be a space to allow for the fitting of the gib. Don't forget to account for that when you do the math for the angle.
The gib for my compound was off by over 0.020" and I think it might not have been original to the lathe. The new one is excellent. I think the rule of thumb for gib tapers is 1/4" per foot or about 1.2 degrees - but it still needs to fit your machine, so that would only be ball park
The Gib should remain constant in height along its length. It should not be high enough to be taking the weight of the table but needs to be consistent to ensure proper fit to the dovetails.
This is depicted in the top sketch of the drawing
:
The second sketch shows what you would see if you planed off the table surface down to the gib. The intention of the gib is to allow you to tighten it in on the wedge to obtain an equal "x" dimension (basically) you can see that the taper in the top is equal and opposite the gib so that the gib establishes a proper parallel running surface between the table and the base. Since the gib is fixed to the table and moves with it, it will always be parallel
The bottom pic shows that the gib should be equal in the other plane so that the height is constant. This is to allow the table to sit properly on the base so that those swirly oil passages can create a nice slippery surface. If the gib was tapered in this direction it would tend to then be the piece that rode on the ways and would have load on it from the weight of the table and what you were machining
Your gib seems to taper in 2 directions such that height is diminishing along the length of the gib. - wear?
On the bottom of your table I would think one dovetail is straight and the other tapers. The base sides should both run parallel to each other. (Maybe opposite but I can't see that far from here LOL)
For a crude reference but may give you an indication on the gib, if you measure the distance across the dovetails on the base and then measure the distance of them on the top, you can do some math and find out what the taper should be. Then measure up the gib and see if the taper angle is correct. If the angle of the gib is too steep the small end will not be in contact with the base properly to establish that parallel sliding fit.
You can see the dotted line in the drawing that is the reference for the base. There will be a space to allow for the fitting of the gib. Don't forget to account for that when you do the math for the angle.
The gib for my compound was off by over 0.020" and I think it might not have been original to the lathe. The new one is excellent. I think the rule of thumb for gib tapers is 1/4" per foot or about 1.2 degrees - but it still needs to fit your machine, so that would only be ball park
No—the Nuts of Education.
OK, here's my favourite fabrication trick of all time. I discovered it years ago for finding centers, and finally wrote it down in my shop book this March. I've got lots of fancy center scribers, both mechanical and electronic, but always come back to this method because it always works. In the pic below I exaggerated the error in the two scribed lines just to make the point; but in practice they wouldn't be this far apart. What I like most about the method is it self-compensates for imprecision. In fact, you require a margin of error for this trick to work properly.
You need a Sharpie (I prefer silver) and a cheap carpenter's scribe* (adjustable wood gauge) with a steel point (not pencil). I stopped using marking fluid years ago. Sharpie is cheap and dries instantly.
- In the approximate center (as located just by eye) of your stock, scribble a wide Sharpie mark by wiggling the marker perpendicular to the stock's long edge. It doesn't have to be exactly on centre—just wide enough to overlap your margin of error.
- Set the carpenter's scribe to the approximate center of the stock's thickness. In fact, avoid perfection in this step; either slightly OVER the approximate center or slightly UNDER the approximate center is better than getting it perfect (a few mm off center is best).
- Scribe one line; then put the carpenter's scribe on the other side of the stock and scribe a second line.
- Place your centre punch in the middle of the two scribed lines and mark the location.**
** The human eye is great at finding the center of two lines if they are within its focal length (~22 mm). As this distance decreases, the accuracy goes up exponentially. At a few mm (or just slightly larger than the width of a center punch), most people can locate the center to within a few thousands of an inch.
You'll be amazed at how accurate this trick is. I figured it out years ago when I needed to drill indexing holes in tubing for telescopic legs on tables. I'm sure CNC guys on the forum will laugh at it as your world is different than mine. But I remember being in my late 20's when I figured this out and what a stress reliever it was. It was like when I discovered how to cut a birdsmouth in a rafter without doing any calculations or measuring—a huge time saver.
I also attached the log book page where I documented this, but it may be too difficult to read my chicken scrawl. It may not work for your projects, but is another arrow in the quiver for future reference.
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DPittman
Ultra Member
Thats exactly how I do it also and it works very well (suppressing my urge to add an exclamation mark).
Hey Brent, I agree with your description and my Y-axis Gibb looked to me like it would meet that criteria. The X-axis Gibb, well, it just looked plain weird to me. The height h in your first sketch appeared to taper away from the adjustment slot side and in fact has a rather obvious 2" long ground out spot on the every end of it. John though that might have been done to make it fit? As far as I could tell by eye balling it, one side in the other plane was flat and the opposite side was tapered but appeared to be double tapered. By that I mean a taper began and then increased mid span (if that makes any sense). I don't think that Gibb is accomplishing much on the narrow end at all. Setting the Gibb lock on the left side doesn't lock the table every well. Anyways that's my take on it, John's and Rudy's observations may differ.
I wonder how I could make a casting of it and send it to you????
Craig
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1) Then why didn't you tell me years ago instead of leaving me to figure it out with all my mistakes LOL?
2) I appreciate the absence of the exclamation mark. The Kool-Aid is pretty sweet right?
Gee that sounds like a PITA to use. Why would they use lock nuts on table locks? Set screws with lock nuts sounds like Gibb adjusting screws to me.
Craig
Yup they are a PITA. Plan to change that!
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