[NC Cams]

Note to MXTRAS: you may need to do some gib adjustment loops.

Here's why: if the gibs are too tight, you will turn the handle but the table won't move and the mount will flex - something has to give (mounts bend, screw stretches, bearings compress, etc). W learned by doing that you over tighten the gibs and then start to loosen them 1/4 turn at a time until the table movement versus hand wheel "movement on the dial" coincide.

When you play with gib adjustment (with dial indicator and time, forget feel) you can get the table to move with no to minimal B/L and the mounts won't deflect.

Like I said in earlier post, we have direction change "flats" of 0.0001 or so as measured with super precise cam measuring machine.

We take our time, have the high buck ball screw bearings, preloaded ball screws (sadly rolled but quite adequate), stock Bidgeport yoke and well tuned servos (thanks to Brian at BPT Machine in Carol Stream IL).

Regarding the yoke issue, it shouldn't be that difficult to make one out of steel billet (IE: 4140PHT). We are a community of "machinists" aren't we??? 8-)

[Bryscnc]

MXTRAS, keep us posted on the progress. I have been pondering the ballscrew conversion and have contacted Elrod. Then after hearing Elrod's pricing decided to go with Rockford. I haven't purchased them yet, but I'm thinking that Hiwin might be the way to go. Ground screws sound so much better then rolled. Thanks for all your research you've helped me greatly. Keep up the good work.

[mxtras]

Thanks for the kind words! I will post up a write-up with plenty of pics of the Hiwin ball screw installation when the event occurs - count on that.

Cams - the deflection test was just that - a test. I had the gib locked down tight in order to measure the lost motion and where it was coming from - the screw, the bracket or the bearing. The torque required to break the gib away from the lock was measured several times and I was using a slightly lower torque for the deflection tests to assure the table did not move - I also had an indicator between the saddle and the table just in case it did, I would be able to see it. The saddle and the table gibs were adjusted using an indicator when the machine was re-furbished about a year ago and will be done again prior to tuning the drive system with the new screws. I appreciate your input - thank you! And oh - I can't afford the time to make the yoke right now - I am sure I will be OK with the "universal" yoke provided by Hiwin - I am not killing the machine - just using it!

And I am sorry - but I had a late night at the shop, so the deflection results will once again be delayed.

:wave:

Scott

[vmax549]

Scott what are you going to do with the old screws you take out. I have an old 57 model BP that needs a better set of screws in a bad way. She is an old girl but a faithfull companion over the years. Terry Parker

[mxtras]

Terry (vmax549) -

The screws are on their way to you along with the dog bone and the nuts. I hope they work out for you. If not - let me know and we will work out their return. I understand your machine is smaller than the one these came out of.

I bought the HiWin rolled screw kit and installed it last week. It would have been a very simple thing, but I ran into a few issues. Without any issues the installation might take 2 hours, but with the issues OI encountered, it took me more like 9 hours. The end result is really nice. I have not done a final adjustment on the gibs, shimmed the support bearings or taken B/L readings yet. THese things will be done a bit later when the controller is assembled and installed on the machine. The motion is really smooth with no noticable slop in the crank handle.

One issue with installation was interference. The table nut contacted the bottom of the table. I hate to bust out a grinder and take it a brand new precision component but that's exactly what I did. A 3/8" chamfer on one corner and the interference was gone.

The other issue was alignment. The yoke is a pretty critical thing and it just was not made identically to the stock bracket. This is a very long story and I spent a lot of time debating on what to do to resolve the issue - I did not want to immediately blame the new bracket but it sure did look to be the problem. The bottom line is I ended up elongating the mounting holes so that my stock X and Y bearing supports would line up and work without modification with the screws in alignment to the ways. The pain was that my mill was torn down so I had to go to a local machine shop to elongate the holes. They were gracious enough to allow me to use one of their mills. If they had not, I would have spent a few hours putting mine back together for a 10 minute job, then tear it back down. I was glad the guys on the floor remembered who I was (I give that shop a lot of work through Mitsubishi).

I used the original location pins to locate the nose of the Y axis screw and aligned from there, using a small amount (.0015") of shim under one side of the bracket to maintain the Y screw perpendicularity to the support bearing mounting surface.

I will post pics and a write up of the ball screw installation in a seperate thread - hopefully later in the week. My time is very limited these days....

:wave:

Scott