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Pm940pdf is out of z axis gib adjustment
- Thread starter FE427TP
- Start date
Thanks for all the replies. We have a pretty decent local hardware chain that had sheets of brass and shim stock. Got a piece of .010 and a small roll of .005. The .010 was too thick for the gib to go deep enough but the .005 thick stuff I was able to seat the gib just under flush with the top of the head. So about 3/4” higher. I might try to make a little brass plug to seat under the gib lock screw as it had chewed up the back of the gib. The end of the screw almost looked like it was made to have a ball bearing in front of it. Kind of pointed but with a cup about half the size of a BB gun BB
- Joined
- Jan 20, 2015
- Messages
- 361
I use either rulon or moglic to rehab gibs.
Moglice is used if I can use clay to create a dam to inject into in place. If I cant I grind the back flat(they almost always are warped) and glue on some rulon(similar to turcite) to the taper. Then blue/scrape the back (surface that I ground) and then install/blue/scrape the rulon to the way.
Moglice is used if I can use clay to create a dam to inject into in place. If I cant I grind the back flat(they almost always are warped) and glue on some rulon(similar to turcite) to the taper. Then blue/scrape the back (surface that I ground) and then install/blue/scrape the rulon to the way.
Hi @FE427TP
I quickly went back and looked at my measurements and my calculations. At that time I found my ideal 940M gib thickness would follow the following equation:
T=0.447-0.00877*z. (inch per inch of length)
Here, T= thickness in inches. z is the distance from the start of the saddle-way opening at the wide end. So at z=0 the opening would be 0.447" across the thickness of the gib and it would taper towards the bottom at 0.00877" per inch of length down the saddle way. Hence, adding a shim of 0.00877 (say 0.009") would cause the end of the gib to move upward by 1 inch if your machine has the same taper as mine. Since you know the TPI of the your machine's clamping bolt you can also figure out how many turns it takes to effectively change the filling of the gib hole by a few thousands.
Of course the 0.447" would in concept be the thickness of the wide end of the gib if it had been cut off perfect for my machine. YOUR machine will probably be different as all of these machines are made a little different. However, this number is not important for your task.
By the way, since the gib is a trapezoidal shape, and the ways are cut with a 55 degree cutter you can calculate all of the dimensions of the gib along the length. So the diagonal vs the thickness, as well as the flat face width, vs position z are related via trigonometric equations. I also measured the diagonal of the gib hole on my machine. (Not the gib, but the hole, as my gib is not very good. It was tedious to do so as I had to measure it the full ~12 inches of z length of the saddle, depth of the gib hole.) I measured it about every 3/4 inch or so in order to get enough data points to be confident in the measurements) and then compared this to the theoretically predicted value. Do to this I had to take into account that the inside corner of the way and the saddle way are not completely cleared by the cutter as the corner of the cutter has a radius. Nevertheless, after doing this I found an equation for the gib diagonal to just fit the hole to be:
Dia=1.387-0.0084*z (inch per inch of length)
These two equations would then completely describe the gib hole between the way of the column and the way of the saddle. A gib made to both of these dimensions would just fill the hole, but of course would not be adjustable!!!. So the gib has to be made with a smaller over all diagonal width just in case there are errors in making with Thickness.
You can measure your gib and see what the numbers are for the one that you got from the factory. Take a bunch of measurements along the length so that you can plot the results as there will be variation at different points. They are not that well made that they are not truly linear or accurate. My thickness rolled off at the ends. As I mentioned before mine was even bowed in both the length and the width directions and the diagonal was not that great either. The width and the diagonal are significantly smaller than desired and so the gib moves about in the hold a lot. This is the reason that for my system the bolt heads do not catch much of the ends of the gib. At the small end the bolt head did not catch the gib at all.
Dave L.
I quickly went back and looked at my measurements and my calculations. At that time I found my ideal 940M gib thickness would follow the following equation:
T=0.447-0.00877*z. (inch per inch of length)
Here, T= thickness in inches. z is the distance from the start of the saddle-way opening at the wide end. So at z=0 the opening would be 0.447" across the thickness of the gib and it would taper towards the bottom at 0.00877" per inch of length down the saddle way. Hence, adding a shim of 0.00877 (say 0.009") would cause the end of the gib to move upward by 1 inch if your machine has the same taper as mine. Since you know the TPI of the your machine's clamping bolt you can also figure out how many turns it takes to effectively change the filling of the gib hole by a few thousands.
Of course the 0.447" would in concept be the thickness of the wide end of the gib if it had been cut off perfect for my machine. YOUR machine will probably be different as all of these machines are made a little different. However, this number is not important for your task.
By the way, since the gib is a trapezoidal shape, and the ways are cut with a 55 degree cutter you can calculate all of the dimensions of the gib along the length. So the diagonal vs the thickness, as well as the flat face width, vs position z are related via trigonometric equations. I also measured the diagonal of the gib hole on my machine. (Not the gib, but the hole, as my gib is not very good. It was tedious to do so as I had to measure it the full ~12 inches of z length of the saddle, depth of the gib hole.) I measured it about every 3/4 inch or so in order to get enough data points to be confident in the measurements) and then compared this to the theoretically predicted value. Do to this I had to take into account that the inside corner of the way and the saddle way are not completely cleared by the cutter as the corner of the cutter has a radius. Nevertheless, after doing this I found an equation for the gib diagonal to just fit the hole to be:
Dia=1.387-0.0084*z (inch per inch of length)
These two equations would then completely describe the gib hole between the way of the column and the way of the saddle. A gib made to both of these dimensions would just fill the hole, but of course would not be adjustable!!!. So the gib has to be made with a smaller over all diagonal width just in case there are errors in making with Thickness.
You can measure your gib and see what the numbers are for the one that you got from the factory. Take a bunch of measurements along the length so that you can plot the results as there will be variation at different points. They are not that well made that they are not truly linear or accurate. My thickness rolled off at the ends. As I mentioned before mine was even bowed in both the length and the width directions and the diagonal was not that great either. The width and the diagonal are significantly smaller than desired and so the gib moves about in the hold a lot. This is the reason that for my system the bolt heads do not catch much of the ends of the gib. At the small end the bolt head did not catch the gib at all.
Dave L.