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  1. #25
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    Re: Bridgeport ballscrew retrofit, design the yoke

    Quote Originally Posted by WilliamT4450 View Post
    Jeff,

    There are internal clearances in the BP Knee Mill that must be observed. For example, the yoke at times runs close to the Z-Axis jack screw. Therefore, material from the Y-Axis ballnut must be removed to provide adequate clearance for it to pass the jack screw.

    Similar clearance issues will be found with the X-Axis ballnut. So when you look for screws and flanges, be sure to look for Bridgeport Retrofit nuts and screws. You can confirm the nuts you've selected by comparing with other nuts on the market that are known to fit and provide adequate clearance.

    The best documentation on the internet will be found from Hiwin. Hiwin drawings show the cuts necessary for the flanges to pass smoothly inside the knee without interference. Use the Hiwin Yoke drawing with the X and Y drawings to see how the flanges are indexed for the necessary clearance.

    These drawings are for 32mm screws, but the clearances are still the same for 25 or 32 mm screws.

    I used the BP yoke and 25mm screws on my machine for a while. They worked OK, but I was unhappy with the precision. I installed a Hiwin retrofit kit last year. Very happy with it.

    For the Hiwin Manuals
    https://www.hiwin.com/downloads.html#manuals

    For the Hiwin Yoke
    https://www.hiwin.com/pdf/7l0002a3.pdf

    For Hiwin Y-Axis Ballscrew
    https://www.hiwin.com/pdf/a10jsia1.pdf

    For Hiwin X-Axis Ballscrew
    https://www.hiwin.com/pdf/a10jsga1.pdf
    Thanks for your comments. It does help me.

  2. #26
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    Re: Bridgeport ballscrew retrofit, design the yoke

    William, can you explain to me why and how the 25mm screws didn't work as good as the Hiwin retrofit. I understand that the 25 mm screws are smaller compare to the Hiwin retrofit but if both systems have the same backlash on the same BP, the precision should be the same. At least this is what I understood. I really want to convert my BP into CNC at the lower possible cost (I'm cheap). I'm new to this milling machine world, I started last year when I got my manual BP. I like this tool, it makes me happy. If I have to spend more money to get a Hiwin retrofit, maybe I will, but before I order any parts, I need to better understand what I don't understand. Thanks for your help.

  3. #27
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    Feb 2018
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    Hi Bill,

    Really good post but +1 on wanting more information on this. Do you recall any figures on the lack of precision that concerned you? Others on this forum (myself!!) may not have as critical a need for accuracy as yourself it would be useful to put it into context. I can live with 0.5 to 1 thou whereas other chaps need tenths

    Was it the linear precision that bothered you as I understood this was solvable via software, was it the lack of repeatability perhaps due to the yoke or ballscrew flexing, was it the backlash or something else?

    Your posts are much appreciated

    Cheers!
    David

  4. #28
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    Re: Bridgeport ballscrew retrofit, design the yoke

    Hello guys ,
    My bridgeport is now running 3 axis cnc with mach 3 free demo software, and i am pretty happy with it, since it is a hobby for me.
    x and y axis ballscrew are cheap aliexpress custom made double nut ballscrew 25 mm diam 5 mm lead just like this one https://www.aliexpress.com/item/1pcs...ddresstype=600

    The chinese supplier did a very nice job on the shaft tolerances , he reached the dimension to 0.0003in from my drawing dimension. I got both ballscrew completely machined to fit the bridgeport for about 350 $CAD shipping included !!

    I made a yoke to fit the chinese nut bolt pattern using the hiwin yoke 2d drawing ( see down the post) I machined a complete solid yoke made of aluminum 6061 t6( enough stiff for what i do with the machine ) The crucial dimension of the yoke is the distance from the two axis to the yoke fixation surface, and the perpendicularity of those axis / surface. I measured my old yoke and added about 0.003 in to the distance in order to compensate for wear( since it is a 1975 BP, and the ways have a little wear on the dovetail).

    The third axis is the 6 inches quill, which is not so accurate because of the rack and pinion configuration. It does the job when i have tons of holes to drill. I set Mach3 with backlash compensation , and it is handling it pretty well. I now plan to take the quill motor out and install it using a planetary gear ( ali express chinese nema 34 size!!! ) unit on the knee power screw for better accuracy.

    I will try to put down some picture soon.

    So for V8kid and jfroux_1 , if you guys have little money to spend on that project i suggest you start with chinese ballscrews. And btw, if you use those dfu2505 ballscrews , the nut flange dont need to be machined since it clears inside the knee.

    I hope it helps you

  5. #29
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    Re: Bridgeport ballscrew retrofit, design the yoke

    Here is my Yoke for BP, and some other pic from that project








  6. #30
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    Re: Bridgeport ballscrew retrofit, design the yoke

    Quote Originally Posted by daroc30 View Post
    Hello guys ,
    My bridgeport is now running 3 axis cnc with mach 3 free demo software, and i am pretty happy with it, since it is a hobby for me.
    x and y axis ballscrew are cheap aliexpress custom made double nut ballscrew 25 mm diam 5 mm lead just like this one https://www.aliexpress.com/item/1pcs...ddresstype=600

    The chinese supplier did a very nice job on the shaft tolerances , he reached the dimension to 0.0003in from my drawing dimension. I got both ballscrew completely machined to fit the bridgeport for about 350 $CAD shipping included !!

    I made a yoke to fit the chinese nut bolt pattern using the hiwin yoke 2d drawing ( see down the post) I machined a complete solid yoke made of aluminum 6061 t6( enough stiff for what i do with the machine ) The crucial dimension of the yoke is the distance from the two axis to the yoke fixation surface, and the perpendicularity of those axis / surface. I measured my old yoke and added about 0.003 in to the distance in order to compensate for wear( since it is a 1975 BP, and the ways have a little wear on the dovetail).

    The third axis is the 6 inches quill, which is not so accurate because of the rack and pinion configuration. It does the job when i have tons of holes to drill. I set Mach3 with backlash compensation , and it is handling it pretty well. I now plan to take the quill motor out and install it using a planetary gear ( ali express chinese nema 34 size!!! ) unit on the knee power screw for better accuracy.

    I will try to put down some picture soon.

    So for V8kid and jfroux_1 , if you guys have little money to spend on that project i suggest you start with chinese ballscrews. And btw, if you use those dfu2505 ballscrews , the nut flange dont need to be machined since it clears inside the knee.

    I hope it helps you
    350 $CAD shipping included !! ??
    I’m just a hobbyist, and to tell you the true my Bridgeport is a new tool to me. I really want to convert my BP into a CNC at the lowest cost possible and get a good reliable machine that I’ll use less than 150 hours per year.
    Why did you have to build a new yoke? I thought we can just dump the old ACME screw guts out of it and a ballnut for a 25mm screw fit perfectly. I’d like to get the ballnut flange hole drill by the supplier when I’ll order the ballnut flange. I can’t find the pattern needed on the ballnut flange. Do you know where I can find a draw with the pattern needed? I prepared a draw that I want to send to different ballscrew suppliers and I need to add this pattern.
    When you use your BP CNC with Mach 3 backlash compensation how happy are you with the results?

  7. #31
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    Re: Bridgeport ballscrew retrofit, design the yoke

    Jfroux_1 Exactly, both screws machined in china using my drawings and shipped for 350$ CAD.
    I build a new yoke in order to the save the original parts intact.
    You will find the bolt pattern in the supplier drawing infos from who you will buy the screws. The orignal yoke has no threaded holes for a ball screw nut.
    Mach3 Back lash compensation is working very well for me. Even with the rack and pinion setup on the quill.

  8. #32
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    Re: Bridgeport ballscrew retrofit, design the yoke

    Daroc30, the price is impressive! Other than the price, how can you compare the accuracy for the x and y when you compare to a Bridgeport CNC equipped with a Hiwin setup? I’m sure that those cheap china ballscrew do not last very long compare to Hiwin quality, but for a hobbyist that uses this equipment for less than 300 hours per year, is long life a factor?

  9. #33
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    Quote Originally Posted by jfroux_1 View Post
    Daroc30, the price is impressive! Other than the price, how can you compare the accuracy for the x and y when you compare to a Bridgeport CNC equipped with a Hiwin setup? I’m sure that those cheap china ballscrew do not last very long compare to Hiwin quality, but for a hobbyist that uses this equipment for less than 300 hours per year, is long life a factor?
    for sure its not the same quality as hiwin, chinese screws are probably rolled screws and hiwin are ground screws. For what i do it is plenty enough , i selected a double nut to increase its axial load capacity hence increasing its life. the long life is not a factor for me , i will probably never change them. And as i said, if a backlash appears in few years, i can extend its life by throwing some backlash compensation and/ or screw mapping into mach3

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