bridgeport 2j quill stepper question

[Sparky_NY]

I am looking at converting the z axis to cnc on my bridgeport series 1 variable speed. The whole conversion is a hybrid of sorts, a micro mill table converted to cnc that will be put up on the bridgeport table. I only do hobby stuff and small parts. Rather than convering a entire micro mill I figured I would go this route and get the benefits of the bridgeport head, its tooling, kwik switch spindle, ridgidity and so forth.

Now for the problem. I would like to cnc the z axis on the bridgeport but much lighter duty than the normal. I have a xylotec stepper controller and a 425 oz in stepper that I hope I can get away with for the Z. I am thinking of a 3:1 timing belt drive with ballscrew. (can do 4:1 if more torque is really necessary). I realize the belt reduction will lower the axis speed, that is not really a concern for my purposes. Peck drilling may not be a option.

Remember, its only for hobby use, in my garage, for small parts. Although not the greatest it will be great for those tiny aluminum parts with compound curves that drive me nuts with a rotary table and all the math.

SO, do you think I can get away with a 425 oz in stepper and 3:1 drive? That is the biggest motor my drive box can handle due to current limitations. If not its going to have to be manual for the z axis.

After much reading and searching I found a couple of people that claimed to use a small stepper such as this with reasonable success but no details.

[Sparky_NY]

I built the quill drive with a 425oz motor and 3:1 belt drive.

It works great. I have set the rapid at 60 ipm in mach3, it may be capable of more but that was fast enough for me. I have since made a fair number of pieces with no issues.

Considering my original question got no answers, I thought I would post a followup in case the info may be of use to others.

[klxrcr]

could you post some pictures?
Sounds interesting to say the least, a micro mill table on a bridgeport....like some sort of parasite? just kidding though I understand your logic. small parts, small table, small cheap motors, big rigidity.

[Sparky_NY]

Originally Posted by klxrcr could you post some pictures? Sounds interesting to say the least, a micro mill table on a bridgeport....like some sort of parasite? just kidding though I understand your logic. small parts, small table, small cheap motors, big rigidity.

I have had a lot of fun learning cnc with that setup, so much fun I decided to cnc the main bridgeport table. The quill Z axis is already done. I am in the process right now of making up motor mounts for NEMA 34 motors for the x and y, got the gecko 201's in hand, and ordered/received a rockford ballscrew kit for the 42 inch table. The present 425oz Z motor is wired in series to keep the current down and running on 24V. It will be changed to parallel wiring and 40 volts which should improve its performance even further.

The little x/y table works nice but I learned a few things along the way. First, it was a big mistake to use Roton rolled ballscrew stock. I paid extra for the nuts to be packed with oversize balls but still the backlash is between .003 and .006 depending on the axis. It would have been much better to get nook setup from homeshopcnc. Second mistake, I used those flat ball type thrust bearings. Those bearings are another weak link adding to the backlash and positioning errors. Knowing what I know now, there are cheap angular contact bearings on ebay, around 3/8 ID that would be far better used in pairs. Its been hard to hold much more than +- 5 with the current setup and rather than improving it I decided to bite the bullet and cnc the main bridgeport table.

I have some fixtures, such as collet fixtures, spin indexers etc. that are just too big to use on the tiny x/y table. The T slots on the tiny table use about 1/4 bolts which are pretty small to trust if any milling force is generated.

The tiny table is coming in real handy to make the motor mounts for the BP and the bigger motors.

I'll take some pics when I pull the x/y table off. With the homebrew enclosure and such you can't see much of interest right now.

[klxrcr]

I am going to call Rockford this week to get a quote for 9x42 Bridgeport screws, How much were yours? And more importantly how is the quality?

[Sparky_NY]

Originally Posted by klxrcr I am going to call Rockford this week to get a quote for 9x42 Bridgeport screws, How much were yours? And more importantly how is the quality?

Direct from Rockford they are $850. There was a price increase a while back. McMaster Carr has the Rockford kit for the 42 inch table for just under $700, that is where I ordered them. Shipping was only $12 to NY. I am betting McMaster goes to closer to $850 when their existing stock is gone. I'd jump on it, I think they only had 1 set left. Their part number is 29995A74
you can order it right online. Without the part number its impossible to find either online or with their customer service people for some reason. Details, installation manual etc. can be found on Rockford Ballscrew's website.

As a further note. Rockford has a angular contant bearing kit for the bridgeport. It consists of 4 pcs of 7204b angular contact bearings and 4 spacer washers. (2 inside, 2 outside) to set the preload. The kit is just over $100 from Rockford. McMaster does not carry the bearing kit.

As for the quality. They are rolled screws, .003 max cumlative lead error with double ballnuts on each axis preloaded for zero backlash. The kit comes with a new center yoke. You would have to spend a LOT more to get much improvement over this. I will be installing mine in the next week so cannot comment on actual performance but the quality looks very nice. The preload is adjustable if the need arises in the future.

I just finished making my motor mount brackets today. Next is to pull the table and install the Rockford ballscrew kit.

[klxrcr]

Originally Posted by Sparky_NY Direct from Rockford they are $850. There was a price increase a while back. McMaster Carr has the Rockford kit for the 42 inch table for just under $700, that is where I ordered them. Shipping was only $12 to NY. I am betting McMaster goes to closer to $850 when their existing stock is gone. I'd jump on it, I think they only had 1 set left. Their part number is 29995A74

I ordered them online, same price as you said, $696.43. I guess Monday I'll find out if they still have any. I'll probably order the Rockford bearing kit too its not a bad deal.

Let us know how the retro works out and thanks for the info you saved me a couple hundred bucks!