Hello and Bridgeport Mill advice needed

[Andyboy66Participant @andyboy66]

Hello all – new member here located in Milton Keynes and looking for some advice please.

I have recently purchased a Bridgeport Series 1 J Head mill and am currently getting familiar with the machine.

There are You-Tube videos that I have found helpful for things like gib adjustment and backlash adjustment however I cannot find anything on one issue I have spotted related to the the knee travel

The issue is as follows:

The knee runs upwards normally when the handle is turned clockwise. On occasion – not every time – when turned anti-clockwise there is approx 360 degrees of rotation where no resistance can be felt on the handle and the knee does not lower. After about a turn some resistance can be felt on the handle and the knee will then drop a visible distance with a dull thud. From this point on if I keep turning anti-clockwise the knee lowers normally.

I have carried out the following in an attempt to understand what is going on and eradicate the issue;

1 – raised and lowered the knee to full extents top and bottom and cleaned and oiled the slide-ways.

2 – Attempted an adjustment to the vertical gib but was unable to do so. I removed the gib cover and felt wipers and tried turning the gib adjusting screw but it is solid. It moves neither clockwise or anticlockwise despite applying good purchase with the blade of the screw driver.

After carrying out No 1 above the issue seemed to go away temporarily. However 20 minutes into a small job it re-appeared. Like I say – it is not there all the time.

I hope I have given sufficient description for people to chip in.

Any ideas as to the root cause and how I might pin-point and rectify the issue? All advice would be very much appreciated.

[Andyboy66Participant @andyboy66]

Knee dropping with a thud

[clogsParticipant @clogs]

sounds just like the gibs are set to tight or there's a ton of swarf in there even the oily gunge (old lube) dosen't help any……

it's gotta to be real tight to hold up the weight of the table……

the only prob with my J head is how much u need to crank the hndle to get long travel……(athritus)…..

soon to be fixed by a geared elec motor……….

if u want photo's or a copy of the manual just pm message me…..no probs…anytime…..

clogs

[MuzzerParticipant @muzzer]

Yes, you are doing well to have the gib strip so tight the knee won't fall under gravity. You've got the weight of the table, saddle and knee bearing down on it.

Are you sure the knee gib locks aren't tightened? You should find the gib adjuster easier to loosen if you are lowering the knee, especially if it is only held up by the gib itself.

It must be a bugger to raise the knee now, as presumably it appears to be twice as heavy as normal….

Murray

[Andyboy66Participant @andyboy66]

Thanks "Muzzer" and "clogs" (Love the names!)

Over-tight gibs certainly would explain both the issue (knee not descending smoothly) and the observation that even lots of torque on the gib adjustment screw did not persuade it to rotate in either direction.

How might I go about getting the gib to move given that the screw will not budge?

I'm thinking – give a few sharp taps to the gib from the underside with a pin-punch or similar and try to move it in the opposite direction of the taper (i.e. upwards). If this loosens it enough for the screw to then rotate I can loosen the gib off until I get free movement and then re-adjust to obtain the correct setting.

Now if it is indeed full of crud and chips as "clogs" suggested then this may not resolve the problem fully and is another problem to solve.

What do you think – is this a sensible next step?

[Clive FosterParticipant @clivefoster55965]

Crud and stuff in the gib lock system is a likely cause. Its essentially impossible to clean things out on an assembled machine and there is no provision for external forced lubrication to help keep things clear. Stuff can grow under the gib too.

Mine was seized on purchase. (As was the head. But the price was right and vendor agreed to get me the parts as he'd not bothered to test it before putting it on E-bay.).

A right battle to get it all apart. Lots of Plus Gas and patience with things orientated correctly for the Plus Gas to run in. Underneath the gib was nearly as evil as the coolant sump in the base.

Clive.

[KWILParticipant @kwil]

You have not answered Muzzer's question about knee gib locks (two), located on vertical face of knee (gib side, ie left hand)

[Andyboy66Participant @andyboy66]

Thanks Clive, appreciate the input.

Well spotted KWIL.

I don't think the knee gib locks are engaged. However – you say two ! – locks on the vertical. I did not know there were two – there is one to the left of the machine just below the vertical crank handle. This is rotated anti-clockwise as far as it will go so in theory should be allowing the knee to travel freely. (As long as it is not jammed).

Where is the other lock?

I'm going to be really embarresed if this is the cause !

[clogsParticipant @clogs]

just had a quick look……

without getting down and dirty (Sunday roast in 10mins) …….hahaha

I can only see 1 knee operating rod for the lock…..left side from the front….up the hole……

mines an early 70's J head …..

clogs, that's cos I wear em……….hahaha……..

[Ian Skeldon 2Participant @ianskeldon2]

I remember only too well receiving a sharp smack to the back of the head for doing exactly the same thing, the solution is to oil the slide ways. My Myford has oil cups on each side of the verticle slide for doing this but if yours doesn't just use a finger on the slide itself (each side of course). I hope this cures the problem.

Ian

[Andyboy66Participant @andyboy66]

Hi Ian, Thanks for the input.

As I said in my original post I did oil the slide ways; I cranked the knee all the way down and then cleaned the slides above with tissue and then oiled. Then raised the knee all the way up and did the same on the under side. After I did this the issue I described seemed to go away and there was virtually no back lash on the handle. But it returned half an hour later once I'd been using the mill.

The oil system was empty so I added some oil and gave it a few pumps. Maybe this needs a closer look at.

[KWILParticipant @kwil]

Yes the Bpt Manual parts breakdown does show one Knee Lock adjacent to the crank handle, however my Bpt Knee is fitted with two locks acting directly through the gib area casting from the side on the vertical face.

[Clive FosterParticipant @clivefoster55965]

The sprung pump oiling system fitted to Bridgeports isn't a proper force oiling system. It's delivery rate controlled. Actual pressure at the output is pretty low. Pressure is only a little more than enough to ensure that oil is provided to the gibs so that surface tension and capillary effects draw it onto the surfaces to be lubricated when the sliding ways are moved back and forth.

Fine when new and pretty good for years if the machine is properly looked after as per book with the pump pulled most days and things moved around to distribute the oil. If the moving around bit is forgotten and pump pulling relegated to "every fourth time I think about it" or thereabouts the oil in the feeds and restrictors eventually varnishes up so nowt gets through to the gibs. All the flow goes to the open holes supplying the feed screws and knee bevel assembly. The non flowing metering devices gum up too, easily seen on inspection. Once it gets to this stage you will never get satisfactory results short of a strip and clean. Hard work and expensive as there appears to be no way of getting the flow restrictors properly clean again. Even ultrasonic methods don't seem to do lasting job.

It really would have helped if Bridgeport had provided figures for how long the pump handle should take to descend when all is working properly. Something I meant to note post rebuild and forgot. As seems to be common with intermittently used machines mine occasionally takes noticeably too long to descend indicating partial blockage somewhere. So far pulling the pump three or four times in succession and being anal about moving things has restored normal performance with visible oil left on the sliding ways. Clean machine oil is a pretty good, albeit slow, at stripping old oil varnish and gum.

Clive

[Chris Evans 6Participant @chrisevans6]

When I first got my Bridgeport mill it was a bit dry on the ways. For the first couple of fills in the oil pump tank I used ISO32 oil instead of ISO 68. This seemed to get things going again.

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