Help! Bridgeport Draw-bars getting hot.
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  1. #1
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    Default Help! Bridgeport Draw-bars getting hot.

    Hello all.
    Long time reader of the forums... I finnaly signed up for an account so I can talk and be apart of the conversation.
    Nice to meet you all! ANYWAYS!

    I need some help. I work at a college machine shop and I have 9 J-Head Bridgeports in my shop... this last semester I've noticed the students complaining about the draw-bars heating up. sometimes there's some "weird sounds" or vibration in the bar when it is slowing down. It also seems to always be the same few machines that have this issue.

    When this happens I would pull the draw bar out of the machine and inspect it. other than being hot, nothing looks wrong. I have oiled the bar and put it back... sometimes that fixes the issue. other times I have replaced the draw-bar and that has fixed the issue. but it seems to be coming back every so often.

    In all my years running Bridgeports (9 years) I've never had this happen to me.

    Is it possible that there is something else going on with the machines? could it be operator error? (I make sure they aren't over tightening the draw bar...)
    Has anyone seen this before?

    I've been keeping up on preventive maintenance... but I don't have much repair experience.

    Thanks for any help!

    -Luke

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    Since there is nothing to heat the drawbar itself, the heating must be coming from something else. Its inside a hollow spindle that has bearings attached. When you checked the drawbar did you check the spindle and the bearings?

    Tom

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    Tom,
    Vari-Speed or V-belt Bridgeports?
    Upper bearings, not the spindle bearings are the likely heat source.
    A student likely will report the drawbar is 'hot' when they grasp the hex end.
    Heat is transferred to the hex from a local source such as the upper bearing in the
    variable speed Bridgeport.
    A simple check is to start the mill when it is cold and run it about 500 rpm. Place your hand on the top plate of the
    vari-speed head and check for heating. If this bearing seizes the inner race will damage the journal surface of the upper
    spindle. This bearing can easily be replaced by removing the top plate/retainer.
    The upper bearing is a precision class Fafnir M9107NPP .
    If there is a vibration check the journal diameter for undersize.

    The step pulley mill upper bearings are in a 'cartridge' and access requires motor removal as well as the aluminum housing.
    speed-change-plate-pivot-sleeve.jpglist-1-2-.jpgj-head.jpgj-head-parts-list-1-50.jpg
    Regards, John
    Last edited by jhruska; 11-19-2019 at 07:08 PM.

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    It is a vari speed by the way.
    Thanks Tom!
    I'll pull the plate off the top and check the upper bearing

    I hadnt pulled anything apart or checked the spindle or bearings.

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    This is the bearing from Timkin - Fafnir and I think they have morphed into the SKF family.
    upper-spindle-bearing-vari-speed.jpg
    John

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    Barry says it sounds mostly like an oversized washer on the drawbar. Second choice would be a bad upper spindle bearing.

    Jon
    H&W Machine Repair

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    At the high school, we put a power drawbar on a Jet clone of a Bridgeport. The original drawbar washer was badly made. While evidently case-hardened, the case was so thin and the bulk metal was so soft that both sides of the washer had been badly deformed and galled by crushing and tighten/loosen turning contact between the drawbar and the end of the spindle. (The mating face of the old drawbar itself was not marred, go figure.) When we made up the replacement drawbar to fit the power head, I made a replacement washer from O-1, hardened and tempered, and surface ground the faces parallel, and it has held up very nicely so far.

    If the washer doesn't come out when you lift out the drawbar, a magnet on a stick will retrieve it off the top end of the spindle.

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    I agree with Tom and Jon. The drawbar is just transferring heat from contact. It only comes in contact with the threads of the spindle. Heat generated at that point is only going to come from a few sources of close proximity to the threads. Spindle bearings, or an extremely hot tool are the only things close to that locale.

    When I bought my mill, I noticed the drawbar had previously gotten so hot the threads had a blue tint. I was worried the spindle bearings were cooked, but I measured the spindle runout at only 2 tenths, and they ran quiet. I replaced the drawbar nevertheless because the threads on it weren't super great. I've never had any issue with it heating up myself.

    A big endmill pushed hard with no coolant can transfer a lot of heat to the spindle, especially if it's pushed to abuse. Something to think about.

    The other obvious thing - are the students oiling the head regularly? As you know, oil should be slowly dripping out of the spindle over night, if it's oiled well.

    That's assuming the drawbars are straight and not rubbing against the upper plate, or anything bizarre like that.

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    Quote Originally Posted by Randalthor View Post
    I agree with Tom and Jon. The drawbar is just transferring heat from contact. It only comes in contact with the threads of the spindle. Heat generated at that point is only going to come from a few sources of close proximity to the threads. Spindle bearings, or an extremely hot tool are the only things close to that locale.

    When I bought my mill, I noticed the drawbar had previously gotten so hot the threads had a blue tint. I was worried the spindle bearings were cooked, but I measured the spindle runout at only 2 tenths, and they ran quiet. I replaced the drawbar nevertheless because the threads on it weren't super great. I've never had any issue with it heating up myself.

    A big endmill pushed hard with no coolant can transfer a lot of heat to the spindle, especially if it's pushed to abuse. Something to think about.

    The other obvious thing - are the students oiling the head regularly? As you know, oil should be slowly dripping out of the spindle over night, if it's oiled well.

    That's assuming the drawbars are straight and not rubbing against the upper plate, or anything bizarre like that.
    The upper bearings look fine. I pulled the cover off really quick and it looks fine, also I dont think its the draw bar or the students taking big cuts.
    Is it possible its the spindle bearings then? is that going to be a pain to replace?
    Also... I'm noticing the problem machines sound bad when running at high motor RPMs. keeping the motor speed low seems to help keep the problem from happening.

    When you are talking about oiling, which area are you talking about? the oiler cups? or oiling the top itself?

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    What else is hot?
    Bottom end of the quill or top end where the drawbar enters.
    Bob

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    Quote Originally Posted by CarbideBob View Post
    What else is hot?
    Bottom end of the quill or top end where the drawbar enters.
    Bob
    I can't seem to replicate the heat from these machines right now... I ran the spindle for about 5 mins and its not hot. I don't think the quill or spindle was hot from what I remember, but I cant be sure.
    BUT. when running at high motor RPMs (400 spindle speed in low gear) I hear some rattling and you can feel vibration if you put your finger on top of the drawbar while its running.
    the rattling seems to sound worse in certain spots if I move the quill up and down. quill movement seems smooth though.

    checking another machine that doesn't have this problem, and there is no vibration in the drawbar or nasty sounds.

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    My two cents!!

    Two weeks ago, on a customers 4 HP B-port clone with a drawbar getting hot enough to burn the operators fingers I did this;

    Replaced the spindle bearing. This is the 60102RS bearing that resides in the pulley housing immediately above the top half of the spindle vari-drive sheave, not to be confused with a precision bearing in the spindle itself.

    Replaced both nylon bushings in the motor vari-drive sheave as well as the snap ring that holds the spring retainer on the vari-drive assembly.

    The belt was beat and cooked but of course I didn't have the correct replacement so that was 'fail'

    After putting the mill back in service it was quiet as a church mouse and the drawbar was never hotter than the operating temp of the rest of the head.

    I believe the oscillating motor drive sheave created enough friction in the drive belt to heat the spindle sheave and transfer that heat to the drawbar. The spindle bearing may have contributed to this as well.

    That's my take on it.

    Stuart

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    5 min isn’t long enough to tell anything, otherwise, some good leads above...

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    The rattle is usually the sleeves in the Vari-Disc. They are worn and have separated from the epoxy.
    Unless the drawbar is flopping around because there is no tool in the spindle.
    When the sleeves are shot it usually is time to install a new belt.
    At teardown inspect for worn keys.
    Purchase sleeves and keys for the spindle and motor and a belt. Basic get er done parts.
    John

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    Quote Originally Posted by LabTechLuke View Post

    When you are talking about oiling, which area are you talking about? the oiler cups? or oiling the top itself?
    I was referring to the oil cups. One of the oil cups oils the precision spindle bearings and drips down to the end of the spindle. Oil should sling on the student's clothes/apron when they start it up in the morning.

    There is no purpose in putting oil down the top of the hole where the drawbar is inserted. It is a good idea to oil the threads of the drawbar every now and then to prevent galling. But that won't make the spindle run any cooler.

    Sounds like John and Atomarc probably have the diagnosis. The nylon bushings in the vari-drive need to be renewed.

    H&W sells convenient kits for that kind of thing.

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    Quote Originally Posted by HWElecRepair View Post
    Barry says it sounds mostly like an oversized washer on the drawbar. Second choice would be a bad upper spindle bearing.

    Jon
    H&W Machine Repair
    Imagine my surprise to see a Fort Wayne shop here.

    I was at Applied Metals for about eight months and am now at Boyd's in wolf Lake.

    As for the heating issue, when I carried my FLIR thermal imager into the shop, everyone thought it was just another non-contact thermometer.

    By the time I used it to pinpoint any of a number of bad bearings, there were some who were won over.

    It resides in the bottom drawer of my toolbox and gets quite a bit of use in the machinery repair shop where I work.

    Give it a shot. A GOOD IR imager will tell you the source of your heat pretty quickly.

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