[dgapilot]

Hi all,
I'm finally getting my machine (2006 vintage Bridgemill) all set up and have the X & Y backlash down to about .006 which I think I can live with for now. My Z is about .060 with the spring masking it. Soooo I want to add a ballscrew to the Z. I really don't want to spend $750 +- from JT for the full set at this point, so can anyone supply some detailed pictures of how the ball nut and drive pulley get mounted to the bracket with a bearing. It just doesn't look like there is enough clearance in the existing hole to have a hollow shaftgo from the pulley thru a bearing in the bracket and then connect to the ball nut. Also, is it a 5/8 screw, or did they drop down to a 1/2" screw for the Z.

Please post pics here, or email to [email protected]

Thanks,
David

[smallblock]

According to their website, you can buy just the Z ball screw seperately.

[GaryV1959]

dgapilot,
the ballscrew attachment is for use with the CNC package only,for manual use you still have to use the handle on the side for Z axis adjustment..
If you are going to CNC convert the mill it is a pretty simple setup.
But the large pulley that they use has the ballscrew mounted inside of the pulley an I have never seen one of those anywhere.
I can send you a picture of the CNC Z axis if you need it but give me a few days to post one.
Thanks
Gary

[dgapilot]

Gary,
My machine is set up as CNC, but no ball screws. From the pictures I've looked at, it looks like the ball nut is threaded into a thimble that fits into the CNC bracket with thrust bearings top and bottom. Then it looks like the pulley is bored to match the thimble and secured with set screws.

The hole in my cnc bracket is 1.010" and I was figuring on pressing an oillite bushing in with an ID of .875" Make the thimble with the od section of a slip fit for the .875 id of the bushing and a clearance hole thru for the .631" ball screw. If I recall, an .875 id thrust bearing has an od of 1.375, so the end with the id thread for the ball nut will have an stepped od of 1.375.

I'm not sure if that is the way Shoptask set it up, but that is what it looks like from what I've seen.

I'd like to know what size pulley they use. I don't know if it is the same pulley I already have, only bored out to meet the thimble, or a completely different pulley. I'd also like to know what the part number of the belt is.

Any help you can give, will be appreciated.

[GaryV1959]

dgapilot,
I will see if I can get some info for you today and post a few pics later on..
Gary

[digitalmdj]

Here is a picture of mine. I am going to change it to a preloaded type. It will require me to enlarge the hole on the top of the gearbox to fit. The nut was machined by a friend. I drew the print and he made it in no time. This arrangement allows you to use the hand feed also.

[dgapilot]

digitalmdj,
Looks like yours is a Tripower or Patriot. The Z axis on the Bridgemill is quite a bit different. the ball screw doesn't go thru a gearbox, it attaches to an arm that goes out at an angle from the spindle, and bypasses the rack and pinion set up that has LOTS of backlash.

Thanks for the pics anyway.

David

[digitalmdj]

Post some pictures so I can see. Maybe I can think of something that will work. I seen some pictures of a conversion but I can't remember where at the moment.

[sharpshooter90]

Here is a picture of the Bridgemill ball screw setup. The ball nut screws into the pulley that comes with the machine, and is loctited in place, then the aluminum clamp collar compresses the threads a bit to keep it secure. You need a couple of torrington bearings on each side of the pulley. This one is the standard select fit screw and nut, but you could use the double pre-loaded nut as well.

[dgapilot]

Sharpshooter,
So they just take some pulley stock and turn it down to 1.000 then bore and thread the .938-16 thread in the end and let it ride in the bracket without a bushing? Not a lot of wall thickness left after threading it! I guess that's how they can compress it with the aluminum ring. Do you recall what size (how many teeth) of the pulley and what size belt? From the looks of it, the belt that goes from the stepper to the pulley on the fine feed will be to long once I change to the ball screw set up.

Thanks for the picture. I saw it on another thread, just couldn't quite figure out how it was all put together. I'm not sure I like the idea of the pulley shaft just running inside the bracket with no bushing or bearing other than the thrust bearings. I guess the Z doesn't really cycle that much, so I guess it's ok.

Was this picture taken while you were installing it? It doesn't look like the screw is thru the nut and attached to the bracket.

David

[sharpshooter90]

David,
The pulley and aluminum collar were factory made parts. The pulley is a 42 tooth like the X and Y. I picked that picture off another site when I was thinking of putting CNC on my Bridgemill. You could bore out the bracket and put in a caged needle bearing from McMaster Carr- its a bit thicker than the bracket, so you would need to machine a small spacer as well. Measuring the center distance, it looks to be the same belt as on the Y axis.

[digitalmdj]

That is the same as my setup. I just made a nut that allows me to use the hand feed. I don't understand your problem.

[GaryV1959]

digitalmdj,
I have the Eldorado bridgemill and my gearbox does not look like that, mine looks like the picture that sharpshooter posted..
I ended up taking my Z axis handle off and then had to put a peice of tape around the shaft to keep the drive from engaging because if the hand feed gets engaged then the cnc ballscrew will not turn..
What model shoptaske do you have , it does look like the newer model and shoptaske has changed models a bunch of times over the years , I started with a used 1720 then sold it for the bridegmill and I think it was the first model because they added more options to the bridgmill a few months after I ordered mine..
Gary

[sharpshooter90]

Dga-
Digital has a newer Tri Power machine with power feed gearbox on mill head, so his has the gear drive plus manual operation. On the older machines like yours the mill quill is strictly manual feed or power feed with CNC. Instead of tape, I used a spring behind the engagement knob to keep it in position, but I could still engage it whenever I wanted.

[digitalmdj]

Alot of the parts are interchangable between machines. My mods will work on your machine. I am changing the ball nut to a preloaded type. They are compact enough to work just fine. I will post a picture of my mill gearbox with the new nut is installed. I have to machine a bigger hole in the gearbox case to fit the longer ball nut. They are 174 dok=llers a piece so I bought one to make sure it was going to work. These are fully adjustable so you can remove all the backlash.

[digitalmdj]

Here is a picture of my mill ball screw. I modified the housing to fit the preloaded ball nut.

[distshooter]

Here is a pick of Z axis as supplied by Shoptask.

As you can see, the nut is welded to the gear. Two welds, 180 apart.

[sharpshooter90]

Actually the nut is threaded into the gear, then 2 tack welds to keep it from unthreading.

[smallblock]

Actually the nut is threaded into the gear, then 2 tack welds to keep it from unthreading.

The new Patriot has a re-design so that the interior assembly is held in place by double jam nuts and the ball screw threads in from the bottom so you don't need to remove the gearbox. The standard screw is a high precision acme with about 0.004" lash. But if the speed of a ball screw is what you need, it only takes about 5 minutes to install it.