PDA

View Full Version : Tight Saddle on Bridgeport



gordob
09-09-2011, 05:11 AM
Hi All,

As some of you have undoubtedly seen on Practical machinist (applogies if this is blasphemy) i have been having issues with the knee of my bridgeport after it "fell off" the Knee crank screw (you could turn the knee crank and no height change)

i fixed the problem which involved me stripping down the knee of everything (saddle and table[bed]). I am now at the re-assembly stage of the Mill and have loosened off all of the backlash adjustment screws and gib screws, yet the friction of the table is still abnormally high. (To answer the inevitable question your thinking, the ways are not screwed, the saddle and bed would slide smoothly like glass before this task)

Has anyone got any ideas how i can reduce the friction? If you need more info to answer, let me know and i will supply it to you

Thanks in advance,
Gordo

Deus Machina
09-09-2011, 05:16 AM
How far did you loosen the gibs? Try shoving the thing into place and readjusting from there.

IME--at least on vertical surfaces, horizontal may be a little different--having things too loose can let them tilt and bind.

rmw
09-09-2011, 05:25 AM
This may or may not help, but I had a similar problem on a lathe cross slide - simply couldn't figure out what had made it harder to turn. I finally found where I had made a VERY small ding on the brass half nut while reassembling. I took it to the mill and faced it a few thou, and things are back to normal.
HTH,
Greg

EVguru
09-09-2011, 08:40 AM
If you've run the knee off the end of its leadscrew, then I think there's every chance that you've distorted the end of the nut.

aboard_epsilon
09-09-2011, 08:45 AM
I farted around for hours on mine ..

that is the lead screw ..NOT THE GIBS

You can have it loose on the nuts ..but when you tighten the bolts holding the dial on ..it keeps on going tight ..

i cant remember what i did in the end..it was years ago ..but involved a lot of guess work ...taking the four bolts out, AND dial off and starting over several times.

all the best.markj

aboard_epsilon
09-09-2011, 08:49 AM
BTW ..How do you pronounce gibs

is it jibs .
.or as in Bee Gee's gibs

all the best.markj

Alan Smith
09-09-2011, 09:00 AM
Mark I was always told it was pronounced the same way as gill as in fluid measure and not gill as in fishes respiratory apparatus. If that makes sense!

Alan

Carld
09-09-2011, 09:17 AM
A jib is a sail.

Carld
09-09-2011, 09:24 AM
Gordo, have you tried the saddle without the feed screw in place and adjusted the gib as you slide the saddle back and forth by hand with the ways oiled. I assume your doing the saddle first and then the table.

JoeLee
09-09-2011, 09:26 AM
A jib is a sail.

A jib is the top extension boom of a crane.

JL.......................

lynnl
09-09-2011, 10:56 AM
Well, I'm looking at my Webster's now. Looks like I've been in error all my life.

According to my dictionary, the "g" in the words 'Giant' and 'Gibberish' is pronounced as "ji...", but the "g" in 'Gib' (the machine tool part) is pronounced like the g in 'Ghost'.

I'll probably remember that for about 3 or 5 days, then revert back to my old habit.

Rustybolt
09-09-2011, 11:47 AM
BTW ..How do you pronounce gibs

is it jibs .
.or as in Bee Gee's gibs

all the best.markj


loke andy gibb

hard G

At least in this part of the rustbelt.

gordob
09-10-2011, 07:13 AM
Ok, so after three hours of fiddling, i have the gib adjusted to a point where the saddle glides as smooth as it did previously.

the Screw seems to have MORE than enough play in it (Considering i can feel the amount of play within the backlash adjustment) - im worried about backing off the adjustment screw further in case i cause myself other issues.

The knee screw is fine now, and works perfectly (thankfully)

PS: i do believe "gib" is pronounced as it sounds (similar to 'gibson') not Jib as in the sailing term

aboard_epsilon
09-10-2011, 08:11 AM
Mark I was always told it was pronounced the same way as gill as in fluid measure and not gill as in fishes respiratory apparatus. If that makes sense!

Alan

yeah, but i don't know how to pronounce gill either ...so not making sense lol

Funny, it's not in the Oxford online dictionary or the Cambridge online dictionary or the Longman online dictionary ...not as gib or gibb ..word not recognized ..Oxford only list it as short for Gibraltar

all the best.markj

gordob
09-10-2011, 06:22 PM
Getting back to the Point. I now only have a tight leadscrew

:P

Black_Moons
09-10-2011, 06:50 PM
If you've run the knee off the end of its leadscrew, then I think there's every chance that you've distorted the end of the nut.

Im gonna go with EVguru here, Seems likey that a 200lb knee falling off the last thread could easily disort the thread in the nut when it came down (And maybe even the top thread of the screw)

aboard_epsilon
09-10-2011, 07:10 PM
Getting back to the Point. I now only have a tight leadscrew

:P

is that the knee screw or the saddle screw

if it's the saddle screw ..this is very hard to adjust ..and may take you multiple attempts to get it right ..i seem to remember, may have something to do with the way the four bolts pull the dials back in .

all the best.markj

gordob
09-10-2011, 10:12 PM
its only the Saddle screw. The Knee Screw is perfect.

I think i have tried getting it to work about 6 times now (6 processes of removing the dial and the four bolts) still with no avail. Its the only issue remaining for me.

Just a thought, could the backlash adjustment screw be tightening down on the leadscrew when i loosen the adjustment. For example, by me loosening the adjustment screw, it could be pushing on the screw (if you could picture the two half nuts pulling the screw apart from the centre??) i think thats the only thing i havnt tried

duckman
09-10-2011, 10:17 PM
Let me get this straight,you removed the table, and the saddle, so you had to remove the dog bone (also known as the nut holder), and then you put every thing back together, was the dog bone pinned if not it probably is not in alignment. I've worked on a lot of BRPTs that the pins had been removed, usually there removed when a machine has been scraped, the dog bone can be twisted, or moved to much to the side it takes a lot of fiddling to get every thing in alignment.

gordob
09-10-2011, 10:34 PM
Yes, i Removed Both Table and Saddle (including the Dogbone which WAS pinned) I ensured i re-pinned the dogbone when i was re-assembling it to ensure it was aligned properly.

Are you suggesting i should remove the pins from the Dogbone and then install them once the leadscrew is installed and correctly adjusted?

What could you suggest considering this machine has not been scraped and is in original condition?

Thanks for your help

gordob
09-11-2011, 03:58 AM
And the Winner is: DUCKMAN

thanks to your input, you have provoked a thought in my head that prompted me to slacken off the 4 bolts on the Dogleg (halfnut assembly) which immediately brought my friction levels to perfection.

After some steady adjustment and a fair degree of fine tuning, my leadscrew on the Saddle is Perfect

Problem Solved
Thankyou to all those with input

jugs
09-11-2011, 04:03 AM
Tight Saddle on Bridgeport !!!!


Didn't think anything on a Bridgeport was tight :rolleyes: :D


from the 1984 edition Oxford shorter Dictionary (approx 187,000 entries on 2,700 pages :eek: )

Gib a piece of wood or metal to keep some part of machine in place- can be pronounced gib as in gibbon, or jib as in the sail/crane. So there :p

Gib is also -
-a castrated cat,
-the gristle hook on a salmons lower jaw,
-a term of reproach.

As it's Sunday - here endeth the lesson, now let us pray for more scrapbinium

gordob
09-11-2011, 04:17 AM
Wouldnt have guessed Gib to be pronounced either way...

I think i like the alternate meaning of a Gib as being a "Castrated Cat" could used in a time of cursing something or someone...