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Thread: Homann Designs TM20LV (BF20,G0704) conversion

  1. #37
    Registered phomann's Avatar
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    A little more progress, that is if dismantling is called progress.

    I've removed the column although I had to buy a 12mm Allen Key first. You can see where I plan to extend the cut-out.

    As can be seen on the photo of the base, I could also extend the Y-axis but as the Y-nut is at the far end of the saddle, it already extends over the end of the dovetail when fill extended, do for the moment I'll leave it as it is.

    The last image shows the underside of the base. I thought about looking at driving the Y-axis from the rear, but I'd need to drill a hole throgh the back and the webbing. That looks a bit beyond by skills.

    Would it be possible to drill the hole on a drillpress?

    It would be nice to have the Y-Axis stepper out of the way though. Also, the Y-Screw would need to be a little longer. Currently a 300mm long screw is needed for a front mounting.

    Cheers,

    Peter.

    Attached Thumbnails Attached Thumbnails Homann Designs TM20LV (BF20,G0704) conversion-z_column-jpg   Homann Designs TM20LV (BF20,G0704) conversion-basetop-jpg   Homann Designs TM20LV (BF20,G0704) conversion-basebottom-jpg  
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    Homann Designs - http://www.homanndesigns.com


  2. #38
    Gold Member Bubba's Avatar
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    Peter,
    When I drilled the webbing on my RF32, I did it by using a hole saw on the end of an extension rod and powered that with a normal power drill. Worked very well and as you know, cast iron cuts fairly easily.

    Art
    Country Bubba (Older Than Dirt)


  3. #39
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    Hi Art,

    Thanks for the reply. I rechecked the base, and it is too low at the back. The hole would almost break the top surface of the base where the column attaches.

    Cheers,

    Peter

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    Homann Designs - http://www.homanndesigns.com


  4. #40
    Gold Member Bubba's Avatar
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    Oh well, the best laid plans and all that rot:{(

    But it was a thought.

    Art
    Country Bubba (Older Than Dirt)


  5. #41
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    Yes....

    I drew up the dxfs for the table X endplates last night and ran them through Sheetcam. Over the weekend I'll make them out of 12mm Corian.

    I plan to assemble it first the Corian to check that all the dimensions are correct first before cutting it out of 12mm aluminium. Corian cuts very easily and it will be relatively quick to re-cut them on my little Taig mill if necessary.

    I should be able to used these endplates to assemble the X-axis set up the X-axis nut holder, which will be my biggest concern at the moment.

    I'm using these ballscrew bearing blocks.
    FK12 16mm BALLSCREW END SUPPORT BEARING BALL SCREW CNC | eBay

    I haven't see anyone else use these on a conversion yet, and wonder why as they make the assembly a lot easier and quicker. My guess is that they are a little expensive, but in the scheme of things it is not too bad.

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    Homann Designs - http://www.homanndesigns.com


  6. #42
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    I wouldn't trust them unless they can provide some real bearing specifications. They claim a matched "C7" pair but C7 has no meaning for ball bearings.



  7. #43
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    Hi,

    The ones I have are sourced from Taiwan SYK-?????????? SONYUNG Industry Co.,Ltd-Ballscrew Support Unit,Nut Bracket,Motor Bracket

    Many of the ebay units are Chinese copies, and have a different cover over the bearings.

    Anyhow they seem nice in the hand, but time will tell once they are installed.

    BTW the manual states that the C7 refers to the applicable ballscrew accuracy grade.

    Cheers,

    Peter

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    Homann Designs - http://www.homanndesigns.com


  8. #44
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    Default Prototype X-Axis End Plate

    Last night, I made a prototype end plate for the X-Axis.

    I drew it up in DraftSight, then loaded the dxf file into Sheetcam and created the G-Code.

    The end-plate is cut out of 12mm Corian. I used Corian, as it is easy to cut, yet stable enough to be used to check the alignment etc. I'm even considering that I may be able to use the Corian endplates on the mill to allow me to cut the final plates out off 12mm aluminium, rather than cutting them on my Taig mill.

    The holes for the 6mm cap screws that fasten the end-plate to the table were drilled to 6mm, so it is a tight fit. I did this to see how accurately the holes in the table were drilled. The bolts fitted up very well, so they may have been machine/jig aligned and drilled. This is in contrast to the locating pins which were obviously hand drilled as the holes are not even perpendicular.

    Later on it may be necessary to increase the clearance on these holes so that some slight adjustment is available. That is also the reason that the countersink diameter on these holes is quite large.

    If you notice the fit, the top of the side plate is slightly below the table sides. I'm not sure what this means in terms of fit. When I measured up the original plate. The lead screw centre appeared to be 50mm from the top of the plate, and the mounting holes appeared to be 25mm below the top of the plate. The mounting holes were 160mm apart. These were the dimensions I used as I figured that the mill was built of a blueprint somewhere and it was logical to use these dimensions.

    The FK12 bearing block is held in with four M4 bolts.

    I also put in four holes tapped for M6 bolts. These will be used to mount the plate that will hold the stepper or servo motors. The plate will have elongated holes that will allow me to tension the timing belts. There are holes either side of the centre as I haven't decided yet which side of the table I'll be mounting the motors.

    The next step is to make the plate for the FF12 bearing block. It requires a slightly smaller hole.

    Attached Thumbnails Attached Thumbnails Homann Designs TM20LV (BF20,G0704) conversion-fk12_xaxisendplate_m1-jpg   Homann Designs TM20LV (BF20,G0704) conversion-fk12_xaxisendplatemounted_m2-jpg   Homann Designs TM20LV (BF20,G0704) conversion-fk12_xaxisendplatemounted_m3-jpg   Homann Designs TM20LV (BF20,G0704) conversion-fk12_xaxisendplatemounted_m4-jpg  

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    Homann Designs - http://www.homanndesigns.com


  9. #45
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    One thing I'm thinking of changing is to change the mounting of the FK12 bearing block from the other side. That way the inside of the flange will line up with the end of the table and the ballscrew length needed will not be dependant on the thickness of the end-plate.

    That way, it would not matter if the end plate material was 12mm or 1/2" plate.

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    Homann Designs - http://www.homanndesigns.com


  10. #46
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    I tried putting the bearing block on the inside but there is not enough clearance to the underside of the table. It's probably less than 1mm but I think I'll just leave them on the out side.

    I also made up the other end-plate for the floating bearing block.

    It's almost time to order some ballscrews .

    I'm not sure on what diameter to have on the end for the timing pulleys. I am tossing up between 10mm, 3/8" or 8mm.

    At this stage I'm thinking of getting 3/8" as there seems to be a better range of XL pulleys and also the stepper shafts are 3/8"

    Cheers,

    Peter.

    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com


  11. #47
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    I'm still not completely decided about the X axis ball nut mounting method.

    I could cut a slot in the saddle and mount it like the G0704. The only issue that concerns me is that the saddle is only ~10mm thick where the slot will be made.

    That would mean that the bolts that jam the holder in place would have to be M4 or M5 bolts.

    From experience is this going to be sufficient?

    Cheers,

    Peter.

    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com


  12. #48
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    I've been working on ways to mount the Y-axis belt drive set-up and motor. Attached is an image of my planned layout.

    Dos anyone have experience on using a such a long belt (XL) as I'm concerned that it is too long. The length is needed so I can tuch the motor out of the way, rather than it sticking out the front.

    The idler bearing is set quite low so that I can use a smaller pulley on the motor and get a 2:1 ratio.

    Cheers,

    Peter

    Attached Thumbnails Attached Thumbnails Homann Designs TM20LV (BF20,G0704) conversion-y-axis-jpg  
    -------------------------------------------------
    Homann Designs - http://www.homanndesigns.com


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