@Christianstark
To answer your question. NO! Not suppose to be this loose. NO you should not see much nod of this sort. There are different sources of nod. In my machine I got this sort of nod down to about 0.001" at the tool after a lot of work and study about gibs!!! In fact before I started this study the vertical gib was not really working at all. But I was not educated enough until I studied it to even know!
I have the PM940M-VS-CNC machine. Yes, all of the Chinese machines seem to have one problem or another or more! The geared head on the 940M is quite heavy and it would fall when the power was turned off. i.e. the stepper motor magnet clogging was insufficient to hold it up. In fact if things were not adjusted just right, gib, it would miss steps on the way up. So I worked on my column gib a lot and still have things to do to make it right. But currently it is working.
So there is considerable drag on the gib as the head is moved up and down. Indeed when going up, with no gib clamping screws, the gib would fall out the bottom by about 1.5". This is means that the gib moved down until it was very tight! You are not suppose to do this as it may get too tight to move! Could it crack the saddle???? In my case, with out the gib clamp screws in place the gib would also walk out the top a little when the head moved down! But this is not as dramatic, but is a good way to get an over tight gib looser.
Anyway, Your gib is too thin. Mine was too think by about .005 to .007" If you clamp your head to the column via external means, Big C-clamp or wood clamp, you can then take the screws out and pull out the gib. If stuck just tap it out with a flat pointed punch or something similar. It will come loose and you can just pull it out. Take some measurements. Measure the length and the thickness at both ends. This will give you the taper or slope. Unless you want to do some complicated, time consuming measurements on the saddle, like I did, you will just have to assume that it has the correct taper to fit your Saddle cut. Anyway, via the taper you can compute how far off the thickness of your gib is by measuring how far down you need to move our gib to make it just tight. You do not want it sticking out the big end by more than your screw will reach so you do not want to increases its thickness too much. The little end screw is just there to trap the gib from moving during motion of the head (i.e. the two screws hitting both ends prevent it from moving).
You can ask Matt to get you a replacement (he said he would for me), but you are going to have to provide him with exactly what dimensions you want. This is not so easy to figure out! especially when you find out that the gib tappers in both thickness and in width and not necessarily at the same rate. You want to get the the width right too so that the corners at the screw heads will catch the screw heads for pushing/clamping during/after adjustments. I did figure it out and if you really want to know how I did it let me know. It would take a bit to explain and involved a lot of customized measurements of the machine.. I have yet to ask Matt to have another gib made for me as I still have other problems with the machine.
I decided to have the big end of gib just stick out the end a bit. I then computed how much thicker it needed to be to achieve this. I then put attached a shim to the back side of the gib to make it thicker. It really does not have to be anything special as it does not rub as the head moves. It is against the saddle side. In my case, I went searching for materials of the proper thickness that were sticky tape on one side. If you just put a non-sticky shim you have to make sure that it does not escape by some other means. I found various duct tape (Not the paper and clothe kind, but the stuff that is Aluminum with sticky on one side to wrap your heading ducts with. I happened to have 3 different old roles of this and they were of different thicknesses so I picked the one that was 0.005-0.007". I stuck it to the back side of the gib and trimmed it to fit. It works! But the story is not complete. There is now another problem. The gib is too short!
Just for the record, the gib tappers both in thickness and in width. It is a trapezoid in cross-section so as to fit the hole both at the top and the bottom and have a corner sticking out to catch the screw heads. The width of the gib are the corners that are caught by the screw heads. They taper to fit into the way corners. In my case the 55 degree shape. I think that at the factory they have made up these gibs with extra length. For each machine, because the saddle ways are cut independent of the column ways being cut, they are custom fit. They probably slip the gib into the hole until it is tight and then cut the gibs off to length specifically for your machine. So they cut your gib off incorrectly or the starting material was too thin to begin with. Hence, it falls into the hole between the ways when not clamped at the ends. Since it was clamped before perhaps it means that it was not clamped correctly. (Speculation: If they had the bottom screw in place when they did their cutting measurement, they may have just pushed the little end behind the screw head a the gib was pinch into being tight. It was not actually tight against the ways.)
The small end of my gib did not stick out very far for the screw to it the end of the gib. Hence the gib would slide over and be parallel to he screw head cap. It clamped it but not down the length. It simply wedged the gib against the screw head and the column way in much the manner that the side clamps lock the head in place. Because my small end was now well up into the hole, the thick end was properly located. I had to make a washer to fit on the small gib end screw. This washer fit the screw head hold but had a finger on it to reach into the way to hit the small end of the gib.
Prior to all of this I actually could never adjust my gib correctly before. Now I can do an ok job of this. But once I got it working just sort of got busy with other stuff.
If all of this is not written clearly just let me know and I will try again. I was in a hurry to answer your question.
Dave L.
Hi Christian
To answer your question. NO! Not suppose to be this loose. NO you should not see much nod of this sort. There are different sources of nod. In my machine I got this sort of nod down to about 0.001" at the tool after a lot of work and study about gibs!!! In fact before I started this study the vertical gib was not really working at all. But I was not educated enough until I studied it to even know!
I have the PM940M-VS-CNC machine. Yes, all of the Chinese machines seem to have one problem or another or more! The geared head on the 940M is quite heavy and it would fall when the power was turned off. i.e. the stepper motor magnet clogging was insufficient to hold it up. In fact if things were not adjusted just right, gib, it would miss steps on the way up. So I worked on my column gib a lot and still have things to do to make it right. But currently it is working.
So there is considerable drag on the gib as the head is moved up and down. Indeed when going up, with no gib clamping screws, the gib would fall out the bottom by about 1.5". This is means that the gib moved down until it was very tight! You are not suppose to do this as it may get too tight to move! Could it crack the saddle???? In my case, with out the gib clamp screws in place the gib would also walk out the top a little when the head moved down! But this is not as dramatic, but is a good way to get an over tight gib looser.
Anyway, Your gib is too thin. Mine was too think by about .005 to .007" If you clamp your head to the column via external means, Big C-clamp or wood clamp, you can then take the screws out and pull out the gib. If stuck just tap it out with a flat pointed punch or something similar. It will come loose and you can just pull it out. Take some measurements. Measure the length and the thickness at both ends. This will give you the taper or slope. Unless you want to do some complicated, time consuming measurements on the saddle, like I did, you will just have to assume that it has the correct taper to fit your Saddle cut. Anyway, via the taper you can compute how far off the thickness of your gib is by measuring how far down you need to move our gib to make it just tight. You do not want it sticking out the big end by more than your screw will reach so you do not want to increases its thickness too much. The little end screw is just there to trap the gib from moving during motion of the head (i.e. the two screws hitting both ends prevent it from moving).
You can ask Matt to get you a replacement (he said he would for me), but you are going to have to provide him with exactly what dimensions you want. This is not so easy to figure out! especially when you find out that the gib tappers in both thickness and in width and not necessarily at the same rate. You want to get the the width right too so that the corners at the screw heads will catch the screw heads for pushing/clamping during/after adjustments. I did figure it out and if you really want to know how I did it let me know. It would take a bit to explain and involved a lot of customized measurements of the machine.. I have yet to ask Matt to have another gib made for me as I still have other problems with the machine.
I decided to have the big end of gib just stick out the end a bit. I then computed how much thicker it needed to be to achieve this. I then put attached a shim to the back side of the gib to make it thicker. It really does not have to be anything special as it does not rub as the head moves. It is against the saddle side. In my case, I went searching for materials of the proper thickness that were sticky tape on one side. If you just put a non-sticky shim you have to make sure that it does not escape by some other means. I found various duct tape (Not the paper and clothe kind, but the stuff that is Aluminum with sticky on one side to wrap your heading ducts with. I happened to have 3 different old roles of this and they were of different thicknesses so I picked the one that was 0.005-0.007". I stuck it to the back side of the gib and trimmed it to fit. It works! But the story is not complete. There is now another problem. The gib is too short!
Just for the record, the gib tappers both in thickness and in width. It is a trapezoid in cross-section so as to fit the hole both at the top and the bottom and have a corner sticking out to catch the screw heads. The width of the gib are the corners that are caught by the screw heads. They taper to fit into the way corners. In my case the 55 degree shape. I think that at the factory they have made up these gibs with extra length. For each machine, because the saddle ways are cut independent of the column ways being cut, they are custom fit. They probably slip the gib into the hole until it is tight and then cut the gibs off to length specifically for your machine. So they cut your gib off incorrectly or the starting material was too thin to begin with. Hence, it falls into the hole between the ways when not clamped at the ends. Since it was clamped before perhaps it means that it was not clamped correctly. (Speculation: If they had the bottom screw in place when they did their cutting measurement, they may have just pushed the little end behind the screw head a the gib was pinch into being tight. It was not actually tight against the ways.)
The small end of my gib did not stick out very far for the screw to it the end of the gib. Hence the gib would slide over and be parallel to he screw head cap. It clamped it but not down the length. It simply wedged the gib against the screw head and the column way in much the manner that the side clamps lock the head in place. Because my small end was now well up into the hole, the thick end was properly located. I had to make a washer to fit on the small gib end screw. This washer fit the screw head hold but had a finger on it to reach into the way to hit the small end of the gib.
Prior to all of this I actually could never adjust my gib correctly before. Now I can do an ok job of this. But once I got it working just sort of got busy with other stuff.
If all of this is not written clearly just let me know and I will try again. I was in a hurry to answer your question.
Dave L.
