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PostPosted: Thu Oct 02, 2003 10:43 am 
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Joined: Sat Dec 21, 2002 12:14 am
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Location: Near Cleveland, Ohio
Not being one to refuse a free tool I can fit in the back of my truck I recently dragged a Hamilton Sensitive drilling machine home. Speed range is right around 1,000 to 10,000 rpm.
It needs a little TLC with the biggest problem being that the variable speed is "troubled". The variable speed is achieved via a two cone getup where one cone is steel and the mating cone is rubber- By sliding the contact point between cones one gets a variable speed. PROBLEM is that this machine has been sitting idle for so long that there is a flat spot in the rubber cone. I am considering fixing it by either replaceing the rubber altogether (possibly remake out of urethane) or possibly I can just "re-turn" the existing one to true it back up again.

So.....anyone have any experience with repairing this type of setup????

Any pointers???

Is this machine worth fixing?????


Thanks


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PostPosted: Thu Oct 02, 2003 11:44 am 
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Location: Concord, NC
If it was sitting idle and engaged, it may have just taken a set. Before doing anything, back it off to minimum full engagement and let it run a few hours, It may be that the rubber may heal itself. I'd at least try this before doing anything more serious.

You may want to do this one several days with resting time between and possibly varying the contact pressure. If it doesn't work, you have cost much effort; if it works, you've saved a remanufacturing detail.

BTW, turning the existing pulley down may just give you a pulley with a hard spot.

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PostPosted: Thu Oct 02, 2003 12:03 pm 
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Thanks Will those are some good ideas - certainly worth a try. SO far I have only really run it where the pulley is centered because any other spot causes a pretty good vibration and I was afraid I might hurt something.

I sorta thought the "turning down" option was a last ditch thing - with only moderate hopes of a useable part.
Urethane might be the best bet as it is so forgiving in terms of taking a set. However now that I know this downfall I will leave a reminder on the machine to always shut it off in the LOWEST speed setting.

Thanks for your thpughts!


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PostPosted: Thu Oct 02, 2003 12:54 pm 
Not knowing much about this arrangement, would it be practical to remove the cone and heat to 150 deg or so in the oven? I'm not sure if this would help or not. Just a guess.

Sandy.


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PostPosted: Tue Oct 07, 2003 10:34 am 
Haven't done it but I believe you can turn rubber by either a. freezing it with liquid nitrogen or b. grinding it with a belt grinder or similar. Either one can be messy, though. The other ideas about trying to run it in sound like a better idea to start with. Some heat might help also; maybe a heat lamp aimed at the cone while it runs.


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PostPosted: Sat Oct 11, 2003 1:33 pm 
This may be a stupid question but just what is a sensitive drill press? I've heard the term for years but no one can explain what it is.

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PostPosted: Sat Oct 11, 2003 2:51 pm 
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Others out there, correct me if I am wrong.... A sensitive drill press is one that has a manual quill down feed. That is, its downward pressure is driven by you pulling down on a quill feed handle. It is "sensitive" because you as an operator can "feel" the pressure you are putting on the drill bit, etc. Most drill presses like sold at Sears are sensitive drill presses.


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PostPosted: Sat Oct 11, 2003 3:15 pm 
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Dan, I am NO EXPERT but I was always under the impression that a sensitive drill presswas one designed for "sensitive" drilling operations - this would typically be small precision holes. Small holes of course means HIGH RPM's as well as a VERY PRECISE drill chuck capable of very low runout and very good balance (ie NO VIBRATIONS) As such typical drives seem to be a THIN FLAT belt. The flat belt (as I understand) is used to minimize motor vibrations from being induced into the chuck. These belts are very precise and wear quite evenly (unlike a "V" belt would) and as such asking them to spin quite fast is no problem!!! As a result these drill presses CANNOT transmit high torques to the chuck - it is VERY EASY to just "toss the belt" aka "have the belt come off" if one gets agressive - hole size - etc - so maybe "sensitive" also implies a suggestion for the mode in which the operator uses it!!!!!
Mine's quite OLD but still has the capability to go to 10,000rpm - I think more modern ones (similar sized) will go up to 15 or 20 thousand rpm's.


Well that's what I understood - but again I am no expert.


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PostPosted: Sat Oct 11, 2003 11:14 pm 
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Okay I did a "google" search and found a web site that that explains all the types of drill presses. According to this web site, the simple definition of being hand fed and driven by a belt seems to define a "sensitive drill press", not necessarily its size or speed. I have included the WEB URL below... check it out as it has pictures, etc. The text from this web site giving the definition of a "sensitive drill press" is as follows:

The upright sensitive drill press (Figure 1) is a light-duty type of drilling machine that normally incorporates a belt drive spindle head. This machine is generally used for moderate-to-light duty work. The upright sensitive drill press gets its name due to the fact that the machine can only be hand fed. Hand feeding the tool into the workpiece allows the operator to "feel" the cutting action of the tool. The sensitive drill press is manufactured in a floor style or a bench style.

http://its.foxvalleytech.com/MachShop1/drillpress/drilltypes.htm


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PostPosted: Sun Oct 12, 2003 8:03 am 
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Hi Dan, Well I certainly can't argue your definition as it is well supported, but I will suggest the POPULAR USE of the terms are slightly different at least around the "old timers" I know. My particular machine is LABELED as a SENSITIVE DRILL PRESS but under your description fits far better under the MICRO drill press category - what I will suggest is that possibly the ERA of the persons involved might lean one direction versus another. SIMPLY put I think the names may have evolved over time. My particular machine looks to be of 40's manufacture. That's all just a guess because almost all the machinists I personally know are OLD TIMERS - I wish they were reading this <grin> I have yet to see/hear anyone describe a 20" Powermatic drill press as a sensitive drill press.

Not trying to argue - just giving a different perspective. <smile>


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