Another obligatory New PM-833TV and PM-1340GT Ordered!

davidpbest said:
However, I basically followed the same process Keith Rucker describes in the video link
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Thanks David. Excellent videos. I watched several of them. I don't have a surface grinder either....a lot of work without one if much material had to be removed.

So I am still working on my CNC Mill. It seems to have lots backlash of problems on all axes! I never realized this until I actually started measuring the backlash as a function of position along the ways and found it varied a lot. I still seem to have considerable analysis to do before trying to fix anything and it may cost me more to fix it than I payed for it!!! Anyway, I have almost given up on the z-axis and so have just started looking at the y-axis. If the gib is completely loose then the backlash is only about 0.0015" which is probably acceptable for now. However, if the gib is tightened down then backlash is ok at one end of travel and terrible at the other end (many thousandths!!!). This leads me to believe that the problems are not just the gibs but also the ways themselves. However, I do not currently have a micrometer that will reach this distance so I have to find or build one before I can measure it. Of course the way side separations for each axis are different (z~4.5, x~6.5, y~9.5), so will probably build some sort of measuring device to determine parallelism. I am uncertain as to how I will determine if the ways spacing or the flatness of each are the problem. So I am actually going back and watching Keith Rucker's prior videos, i.e #13 etc. Just watching them is taking a while!!!
 
B2 said:
Thanks David. Excellent videos. I watched several of them. I don't have a surface grinder either....a lot of work without one if much material had to be removed.

So I am still working on my CNC Mill. It seems to have lots backlash of problems on all axes! I never realized this until I actually started measuring the backlash as a function of position along the ways and found it varied a lot. I still seem to have considerable analysis to do before trying to fix anything and it may cost me more to fix it than I payed for it!!! Anyway, I have almost given up on the z-axis and so have just started looking at the y-axis. If the gib is completely loose then the backlash is only about 0.0015" which is probably acceptable for now. However, if the gib is tightened down then backlash is ok at one end of travel and terrible at the other end (many thousandths!!!). This leads me to believe that the problems are not just the gibs but also the ways themselves. However, I do not currently have a micrometer that will reach this distance so I have to find or build one before I can measure it. Of course the way side separations for each axis are different (z~4.5, x~6.5, y~9.5), so will probably build some sort of measuring device to determine parallelism. I am uncertain as to how I will determine if the ways spacing or the flatness of each are the problem. So I am actually going back and watching Keith Rucker's prior videos, i.e #13 etc. Just watching them is taking a while!!!
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If you like Keith’s videos on gib topics, you might find Stefan’s videos even more helpful. And here is a video that might help checking parallelism.

Curious if you’re running the original lead screws in your mill of if you’ve replaced them with ball screws. Perhaps these videos could be helpful? I did quite a bit of gib-fit alterations/tuning to the gibs on my PM-935 and it helped a lot.
 
davidpbest said:
Curious if you’re running the original lead screws in your mill of if you’ve replaced them with ball screws.
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Thanks David,

After watching Keith Rucker's videos I am actually pretty discouraged. I do not have anywhere near the facilities, equipment, or metrology equipment to do the work he was discussing. I am much better equipped in electronics and optics. I am afraid my mill ways maybe worst than his lathe's before he started the restoration and yet my Mill is essentially new, but 3+ years since the purchase... and the way it came from the factory. I have not used it all that much. It does work and I have made several things.... it is just not any where nearly as accurate as it was suppose to be...... and I while I realized the z-axis had lots of problems I did not realize until recently how bad Y axis is (X axis is still TBD). I probably paid more for my PM940M-CNC-VS than you did for your PM935 (which every one praises, Taiwan vs China). Anyway, from the factory, it was a CNC. PM stopped selling them and has not found a different CNC to put in to its sales portfolio yet. It is probably not the same as the PM940M machines sold today and may not have been the same as the ones they were selling then. They look similar and probably came from the same place in China, but have to be somewhat different by definition. The basic concepts are the same and you might think the castings are the same, but who knows .... Anyway, it came with 5 TPI ball screws and ball screw nuts and fantastic accuracy "specs." Not the 10TPI Acme screws as come with the non-CNC machine. Also the ways are cut at 55 degrees not 60 as most US machines seem to be.

Anyway, do not pay too much attention to my comments right now as I am just a little discouraged. I am not complaining about PM as a company. Matt has been very cooperative in the past and I have not push him on these 940 issues ... at least not yet. After I get farther along I hopefully will have measurements of the way's parallelism that I can trust. Then I will let you know. I am just hopeful that I am doing something wrong and that there is an easier fix than re-cutting the ways (somewhere?) and extensive scrapping.
 
B2 said:
Thanks David,

After watching Keith Rucker's videos I am actually pretty discouraged. I do not have anywhere near the facilities, equipment, or metrology equipment to do the work he was discussing. I am much better equipped in electronics and optics. I am afraid my mill ways maybe worst than his lathe's before he started the restoration and yet my Mill is essentially new, but 3+ years since the purchase... and the way it came from the factory. I have not used it all that much. It does work and I have made several things.... it is just not any where nearly as accurate as it was suppose to be...... and I while I realized the z-axis had lots of problems I did not realize until recently how bad Y axis is (X axis is still TBD). I probably paid more for my PM940M-CNC-VS than you did for your PM935 (which every one praises, Taiwan vs China). Anyway, from the factory, it was a CNC. PM stopped selling them and has not found a different CNC to put in to its sales portfolio yet. It is probably not the same as the PM940M machines sold today and may not have been the same as the ones they were selling then. They look similar and probably came from the same place in China, but have to be somewhat different by definition. The basic concepts are the same and you might think the castings are the same, but who knows .... Anyway, it came with 5 TPI ball screws and ball screw nuts and fantastic accuracy "specs." Not the 10TPI Acme screws as come with the non-CNC machine. Also the ways are cut at 55 degrees not 60 as most US machines seem to be.

Anyway, do not pay too much attention to my comments right now as I am just a little discouraged. I am not complaining about PM as a company. Matt has been very cooperative in the past and I have not push him on these 940 issues ... at least not yet. After I get farther along I hopefully will have measurements of the way's parallelism that I can trust. Then I will let you know. I am just hopeful that I am doing something wrong and that there is an easier fix than re-cutting the ways (somewhere?) and extensive scrapping.
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Let's take this off-line - I'll DM you.
 
davidpbest said:
Let's take this off-line - I'll DM you
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Good idea. But first is there a hard cover edition of your book on carbide inserts? Thought I would ask as I only saw paperback versions on Amazon.
 
B2 said:
Good idea. But first is there a hard cover edition of your book on carbide inserts? Thought I would ask as I only saw paperback versions on Amazon.
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My publisher does not offer hardback editions. Sorry. The paper and color printing used in the paperback is excellent quality, as is the binding. I'll DM you some sample pages.
 
Its ok. I am on my way to Amazon. I have only heard good things about your book.
 
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