Weiss WMD30LV conversion project - Page 2


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Thread: Weiss WMD30LV conversion project

  1. #13
    Member LongRat's Avatar
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    Well, my machine is solidly bolted to the stand. There's absolutely no motion between the two. The stand itself rocks and rolls on my uneven garage floor, but once it is moved into the final position I am going to bolt it to the floor too. It will be rock solid then.



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    Here are the values quoted from the test report. They are written by hand on the paperwork I received. Where there is a number reported like 0.01/300, I am assuming that means 0.01mm total indicated over a measurement distance of 300mm.

    1. Flatness of worktable surface - 0.03/300
    2. Parallelism of T slot to table longitudinal movement - 0.03
    3a. Parallelism of table to table movement (longitudinal) - 0.01/300
    3b. Parallelism of table to table movement (cross) - 0.01/100
    4a. Runout of spindle hole (at spindle nose) - 0.005
    4b. Runout of spindle hole (at 100mm distance) - 0.010/100
    5. Squareness of table longitudinal and cross movement - 0.01/150
    6a. Squareness of spindle axis to table (right & left) - 0.04/300
    6b. Squareness of spindle axis to table (forward & backward) - 0.04/200
    7a. Squareness of spindle sleeve movement to table (right & left) - 0.02/50
    7b. Squareness of spindle sleeve movement to table (forward & backward) - 0.02/50

    There's a small diagram explaining the meaning of each on the report.
    The report and manual generally have good English which leads me to believe they may be the work of the importer rather than the manufacturer. The plaques on the actual mill have the usual Chinese-English translation. I'm pretty happy with the documentation which is in a different league to the photocopied rubbish that came with my Chester X2.



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    Thanks Longrat. Those values look very good and suggest that the machine is good foundation for CNC'ing, unlike (in hindsight) the X2. Just need to convince Weiss to put on a 10k spindle for the same price!



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    I've had a chance to strip some of the bits off the machine and get some pics. Still good news all round, in fact I think the Z axis will be even easier to convert than I had thought. I'm pretty sure I can do it without even taking off the head. The rest of it looks very straightforward too, there's a ton of room everywhere.

    First I took off the motor cover and removed the motor and head top plate. This revealed the primary geartrain. Lucky I did this as some kind soul had left a stray locking washer in the gearbox, if I had done any cutting it could have easily vibrated into the gears and caused mayhem.



    All the gears are steel in this gearbox. It looks to me like the easiest way to increase the speed would be to get a larger pinion on the motor and switch the seconday gear to a smaller one. The gears are helical and the noise in operation is very reasonable, maybe not as quiet as a belt but much quieter than a stock X2 at full RPM. Switching to a 1-stage belt drive would probably mean losing the spindle tacho readout which would be a shame. You can see the tacho disc in the picture, it is a welded steel part ridiculously over-engineered for its purpose, but I'm not complaining!



    Here you can see the spindle itself and some of the steel gears. There are 2 thin steel cover plates to remove to get to see this. There was some grit and loose cast iron dust around here and near the gears, it is worth getting this far in just to clean out that crap. There is a decent amount of grease on the gears though.



    Looking down on the head towards the column, you can see how clearly the Z leadscrew is visible. Very simple design which I think will be simple to convert to a ballscrew drive. The stock screw is dia 22.0mm with a 4mm pitch.



    The top of the column removed, showing the z drive. The small bronze bush takes the axial loading in the 'up' direction. It would have been nice if they had used a thrust race here. The X and Y have thrust races paired up and preloaded. There was a ton of end float in the z thrust assembly causing 0.7mm of backlash. The problem is if you preload it up correctly, the plain bush inevitably imparts a lot of friction. I think if someone wanted to keep it manual, putting paired thrust bearings in here would be a very nice upgrade. As it is with a CNC conversion, they will be installed of course - probably angular contacts but I have used axial thrust bearings on the X2 with good results.



    Here is the column covering plate. They do use a thrust bearing for this side of the z drive. To give you an idea of the size, the ID of the bearing is 17mm.



    There's the z screw removed. Very simple. There is no constraint on the bottom end of the screw in the column. From a fully assembled mill to this stage takes literally a couple of minutes.



    Here is a view of the saddle sliding on the Y axis. Don't worry, that isn't rust, just looks that way in the photo. It's not the same as the red packing grease I've seen before, it is closer to an oil than that but very sticky. It has done a very good job of keeping the metal in good condition. Again the tail end of the Y screw is unconstrained, and there seems to be a good amount of space in which a ball nut could be fitted. Still might need a little grinding on the nut flange for the larger nuts. The stock leadscrews are dia 20mm in X and Y.



    With the X ramped over all the way to the limit you can see the surface of the ways, which appear to be hand scraped. The travel is certainly very smooth with no tight spots, and I can't detect any play whatsoever in the gibs or anywhere else.

    I've measured up everything, should be able to order some screws and nuts/bearings pretty soon. I've got a CNC router to build at the same time so I have to finalise the screws I want for that before I can order. I'm going to go with 'linearmotionbearings2008' on Ebay. I've heard good things about this seller and for the price it has got to be worth a try. Especially for the 20 and 25mm screws which are pretty expensive elsewhere. If anyone has anything to say about dealing with this person and his products, please post your thoughts. I've read a thread about the stuff on the zone with backlash reports ranging from zero to 50 microns. I was planning on double nuts. I'd like to aim for backlash under 25 microns if possible (0.001").



  5. #17
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    Excellent images and description. Do you think you can use the original nuts to mount the ball nuts? i.e. bore them out and thread them for the nut flanges? Or are going to make new steel ones? Looks like you'll have to support the Z axis screw, the Y will probably be ok.



  6. #18
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    Based on the nuts I *think* I will use, the existing nuts are probably not big enough to do that.
    I wasn't planning to support the free end of the Z screw. I don't anticipate I will be able to drive it at very high RPM. Any reason you say that? I hope I haven't missed something that might make it a lot more difficult...



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    Hi Longrat - great pictures of the disassembly, and I'm glad to hear the head appears to be all metal gears.

    How does that Z-axis screw attach to the head? Is that round post on the acme nut tightly held to the head, or does it just rely on gravity to keep it in contact with the head assembly? I guess I'm just a bit worried that that connection could be another possible source of Z-axis backlash...

    As for securing the lower end of the Z-ballscrew - how would you actually go about it anyway? Is the lower end of the colum open enough for you to fit a bearing holder in from the bottom?

    Cheers,
    Joe.



  8. #20
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    The round post on the nut fits nicely into a round hole of the same diameter in a block screwed to the back of the head. This allows the screw a rotational degree of freedom with respect to the head. The post fits the hole pretty well, but this will be a source of backlash I am sure. I'm planning to solidly bolt this together when I make a ballnut carrier, so there won't be any movement then.



  9. #21
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    Quote Originally Posted by LongRat View Post
    The round post on the nut fits nicely into a round hole of the same diameter in a block screwed to the back of the head. This allows the screw a rotational degree of freedom with respect to the head. The post fits the hole pretty well, but this will be a source of backlash I am sure. I'm planning to solidly bolt this together when I make a ballnut carrier, so there won't be any movement then.
    Sounds like a good plan!

    Is the head entirely supported by the Z-axis screw, or is there a gas-spring or something similar to help raise it? Also, how well can you lock the quill - I assume you're going to just CNC the Z-screw?

    I got an exciting phone call today - my WM18 is apparently in stock a month early, so I may have it within a week or so. So, kindly get your finger out and perfect the CNC conversion

    Cheers.



  10. #22
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    Haha, good news Digits. We might both be running under CNC control well before Christmas at this rate!
    There is a gas spring inside the column, I forgot to mention that. It is pretty nicely packaged and out of the way, it shouldn't interfere with the screw or nut.
    There's a proper quill lock on the left side of the head. You can see the lever in my 6th picture down in post #16, just under the E-stop button. I fully intend to leave it locked most of the time, although there have been times when I've just wanted to manually bang a hole in something and currently I have to power up the PC and controller to do it, so it will be useful for manual drilling.



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    Default chinese scales too?

    Dear LongRat:

    Your machine is great! Wish I could get one...

    Now, I see in your pics that, besides the continuously variable speeds, in two ranges plus
    tachometer, it also has a "chinese scale" to display the spindle position!. Did it come with
    the machine or you installed it? What about the X & Y? do they also come with chinese
    scales? Also, how do they control the speed? Does it have a 3-phase motor plus VFD or
    is it a simpler scheme?

    Nelson



  12. #24
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    Nelson,
    The Chinese scale is a factory fit item that comes with it. It only reads the quill extension, not the main Z. There is no DRO system or scale fitted to X or Y. For my CNC conversion, I won't be needing them anyway, and the quill DRO will probably never get used. Nice feature if you were going to use the machine in manual mode though.
    The spindle is controlled by a DC motor with DC speed control. It isn't an AC motor with a VFD, which would be nice. However that is possibly above what you could expect for a machine of this price, and the DC hardware does seem to be pretty nice quality. I wish it had a higher top speed, which wouldn't cost any more to have, but that is my only complaint - and I expect to be rectifying that in the future.



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Weiss WMD30LV conversion project

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