Bridgeport jammed knee

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Bridgeport jammed knee

This topic has 27 replies, 8 voices, and was last updated 22 February 2011 at 12:04 by Chris Gunn.

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13 February 2011 at 15:39 #64031
Chris Gunn
Participant
@chrisgunn36534
I just moved my Bridgeport, and after some shuffling about I got it where I wanted it. an hour or two later I went to raise the table, and found it jammed tight. The raising handle and lifting screw seem free enough as far as I can tell. Further investigation revealed that the gib strip was sticking out about 1/2″ below the bottom of the knee casting, which I had not noticed before. Can anyone have a quick look to see if theirs is the same? I imagine the gib is not normally this far out. Even further investigation revealed that the top of the gib strip which normally locates on the adjusting screw was broken off, and by the dirt and colour of the break, had been broken for some time. This has then allowed the gib strip to move lower than normal, making the table tight. In fact the knee has always been on the tight side, and has occasionally stayed in an up position when lowering, and then dropped an 1/8th with a bump when lowering. I imagine that when I moved the machine, and jarred it a bit when barring it across the workshop, the knee has dropped a fraction more, and jammed. I tried tapping the gib with a brass drift, but it did not move, and as luck would have it, the knee is well down, so I cannot get a good swing at it. My next move will be to make a steel yoke a pretty close fit around both sides of the dovetail below the table, and a corresponding one to sit on the top of the knee, and put a pair of holes in these so I can pull them together with studs, and push the gib up. I envisage removing the gib completely, and either replacing it or repairing it. The repair I had in mind was to drill a hole for an 8mm stud in the end of the gib, and make a plate to sit over the gib in place of the current wiper with a clearance hole for the stud, which I can use to pull the gib up, and a tapped hole for a second screw to push the gib down. Before I start I would welcome any thoughts/advice/ pifalls to avoid. If anyone has a spare gib I would also be interested. Thanks for looking,

Chris Gunn
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13 February 2011 at 15:39 #21797
Chris Gunn
Participant
@chrisgunn36534
13 February 2011 at 16:14 #64033
David Clark 13
Participant
@davidclark13
Hi There

Can you cut a bit of bar to fit in the gap between the bottom of the gib and the base of the machine?

If so, you should be able to lower the table a bit while the gib strip remains static and so frees itself.

regards David
13 February 2011 at 16:52 #64036
JasonB
Moderator
@jasonb
Or a couple of bits of plate with one side cut at a slight angle and use them as folding wedges, best squeezed together with a clamp rather than knocked in with a hammer.

J
13 February 2011 at 16:59 #64038
NEIL SMITH 1
Participant
@neilsmith1
Mine is about flush with the knee,what about a piece of threaded rod with a nut each end,and a suitable bit at the top,then unscrew them.
13 February 2011 at 17:09 #64039
Keith Long
Participant
@keithlong89920
Can I just ask: –

If you succeed in moving the gib to free off the knee – where is the knee going to go and where are vital bits of you when it does go?

Please make sure the knee can’t fall any further before you try and get it moving freely.

Keith
13 February 2011 at 17:29 #64041
NEIL SMITH 1
Participant
@neilsmith1
A crowbar may move it!
13 February 2011 at 18:32 #64047
KWIL
Participant
@kwil
My gib is around 1/2″ up from the bottom of the knee.

Place the table as directly over the knee screw as you can, have the table slightly to the right to relieve the pressure on the lower left hand side. Put a strop around the table and over the ram, just in case you take a tumble, then try David’s piece of bar.

I will PM you with some other details which may help.

K
13 February 2011 at 19:01 #64050
David Clark 13
Participant
@davidclark13
Hi There

I thought the lead screw was still conected?

Can’t go far if it is.

It would be under total control.

regards david
13 February 2011 at 19:28 #64052
NEIL SMITH 1
Participant
@neilsmith1
The pressure can also be relieved with a jack.
13 February 2011 at 20:01 #64057
KWIL
Participant
@kwil
David, If you take the gib out, it will have a will of its own.
13 February 2011 at 20:01 #64058
Chris Gunn
Participant
@chrisgunn36534
Thanks for the info so far, I will try and answer the points raised, first it is difficult to get a jack of any sort right under the gib, as the base casting is curved, and so are the raised sides of the drip tray, so I cannot easily span the base under the gib. For the same reason it is difficult to get a pry bar under it and get a good purchase on it. The target is only 1/8″ by 1″ and nicely chamfered as well. The leadscrew is still connected. I like the idea of taking the weight one one side relieveing the pressure, my intention is to get the gib moved up, it looks like it could be up to an inch out of position, and once I can get the table moving on the lead screw, and the gib loose, I can block everything up, lower the table, and make it safe before removing the gib. Thanks again for all your time and trouble. I will keep you posted. Chris Gunn
13 February 2011 at 20:09 #64060
NEIL SMITH 1
Participant
@neilsmith1
It may help if you removed the drip tray?
13 February 2011 at 21:19 #64063
Anonymous
Hi Chris,

You may find the following link informative:

http://www.practicalmachinist.com/vb/general/knee-stuck-gib-jammed-141376/

Regards,

Andrew
13 February 2011 at 21:24 #64064
David Clark 13
Participant
@davidclark13
Hi Kwil

I never said take the gib out.

I thought the idea was to free it up so it was not as tight?

Then you would be able to see if the gib was broken at the top.

Then you could figure out what to do with it.

regards David
13 February 2011 at 22:50 #64069
NEIL SMITH 1
Participant
@neilsmith1
The practical machinist site certainly is informative and very amusing too,the method described first obviously works,but I wonder how many home workshops would have what would be needed to lay a Bridgeport on it’s back,drill a 1″ dia. hole in the base and heat the knee to 300 deg.?
14 February 2011 at 09:53 #64086
KWIL
Participant
@kwil
David, that is fine, I did not imply that you said remove gib, but my comment was a caution to others, that the mass of the knee + table was not a thing to be light hearted about. Knee 257lb, Saddle 142lb and Table (48″) 365lb , nearly 7cwt!!

I can only say that the problem of the jammed gib must have been long standing and possibly due to lack of maintenance, oiling/adjustment and must have been observable as a stiffness or slack, initially, which would have affected cutting depth as the knee rocked before binding. It is interesting to note that the adjustment is one of tighten screws to move gib until slight stiffness is felt!!

http://WWW.shophardinge.com displays spares and prices, it also has an up to date downloadable Manual with part numbers etc for those who need this.

Edited By KWIL on 14/02/2011 09:54:33
14 February 2011 at 18:57 #64103
Chris Gunn
Participant
@chrisgunn36534
Thanks for the additional information, reading the Practical machinists link has cheered me up no end. Just to confirm, the drip tray has been removed, it is the cast rim around the base that contains the suds that has curves in all the wrong places.I can confirm there was a bit of stiffness since I had it, as mentioned before, i think it was like it when I bought it, again from Practical machinist, it is obviously a problem with these machines, my tip for the day is remove the wiper cover before buying a used machine and check it. I am going to make a start in the morning, watch this space.

CG
15 February 2011 at 22:29 #64160
Chris Gunn
Participant
@chrisgunn36534
After my last post, I read the Practical machinists thread right to the end, and there I found the alternative method to release the gib that does not involve tipping the machine on its back, but involves supporting the end of the gib, then backing off the table raising nut, and giving the table a jolt downwards with a sledge hammer. It is then possible for the table to drop 1/4″ or so and start releasing the gib. Accordingly today I made the few parts needed to do this, backed off the table raising nut 1/8″, and set it so an 1/8″ thick packer would just go in, and I marked up the nut, and then had a go, but it did not move a thou. I then broke the head off my sledge, fortunately with out damage to anything. Then I tried warming the knee up a bit with a propane torch, and tried again, and then warmed it some more, and still no joy. However I ran out of time before I could apply more heat, as it did not get it anywhere near hot enough to burn the paint. I will have another go tomorrow when I will have more time.

CG
16 February 2011 at 09:08 #64177
KWIL
Participant
@kwil
Chris READ your PMs before you break anything more serious than a sledge hammer.

K
16 February 2011 at 10:07 #64183
Terryd
Participant
@terryd72465
Hi Chris,

Instead of using hammer blows is it not possible to apply downward force with a jack of some sort (screw or hydraulic), the pressure could then be left semi permanently. I often found that with the sort of problem you have a steadily applied force is less harmful to the job than intermittent blows and eventually will free stuck components.

It can take hours or days to act with the jack left overnight for days, increasing the pressure a little regularly. Don’t overdo it though!

Best Regards

Terry
17 February 2011 at 12:03 #64231
Chris Gunn
Participant
@chrisgunn36534
I am more than pleased to report that I have released the knee. I used the method from the Practical machinist, as I mentioned earlier. I made a wedge to go under the knee to hold up the end of the Gib. I made a clamp arrangement to hold it upright. I removed the screws holding the table raising nut, and backed it off 1/8″ so the table could drop if it had a mind to. I squirted all the joints with WD40, especially on the gib side. Then I made myself an impact hammer with a 5ft tall bar, that screwed into a tenon in the bed. I put a 8″ diameter disc around the shaft on the bed, so this transmitted the impact to the bed. I drilled a 5/32″ hole about 12″ from the top of the bar, and made pin from a bit of 1/8″ rod to go in it. Above the pin I loaded about 28KG of weights, then pulled the pin, and not a lot happened, after 2 or 3 goes. I then set up a medium sized propane torch to warm up the knee casting, and let it play on the casting while I had a good tidy up, maybe 20 to 30 minutes. Then I had another go, and this time I could see from my witness mark that it could have moved a touch, so had anoher go with the impact hammer, and this time there was no doubt, it moved 1/32″, and the next time 1/6″, I released the table nut some more, and then it went 1/4″, and the bottom of the gib was then level with the bottom of the knee, and I found I could wind the table down. I wound it down about 1″, and noted that the gib stayed where it was, and the top of the gib is now sticking 1/2″ above the table. I stopped at that point, feeling pretty pleased, as I need to secure everything before I remove the gib for inspection.

Once again thanks to all who helped me, especially Andrew Johnston who provided the link to the Practical Machinists site, which was worth reading to the end where I found this method, which worked, without tipping the machine over.

Chris Gunn
17 February 2011 at 14:24 #64235
KWIL
Participant
@kwil
Can we have a posted photograph of the gib when you retrieve it please?
17 February 2011 at 15:49 #64237
KWIL
Participant
@kwil
Seems like Knee Clamp Gib BK0001500C055 is the part. US $22 ++
17 February 2011 at 19:42 #64250
Chris Gunn
Participant
@chrisgunn36534
I will take pics of gib when I get it out, I also have pics of the set up and other bits, I will check how to do an album, and post them all at once.

Chris Gunn
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