# rohm drill chuck disassembly



## porthos (Jan 25, 2019)

as the title says; i need to get my rohm drill chuck apart ita mod. BB13-3 keyed chuck. can't find anything on the internet (even thoughh it may be there), what the chuck does is; after center drilling a piece of round stock, then going to  drill (lets say 1/4 inch) the drill walks off the center drill hole. i have a new jacobs (usa made) that does not do that. i "cooked" the drill in my ultrasonic cleaner and no change. so my next step is to disassemble it.  i have a new MT-2 arbor with a morse #3 taper to install (just in case). i don't think that this comes apart like a Jacobs. any help. or, is it possible to send it out for a rebuild??


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## mmcmdl (Jan 26, 2019)

More info needed on this one . Got pics ? Is your head trammed ? You say a  piece of round stock . Are you on center of it ? If you use a 1/4 CD and 1/4 drill the same length , does it do it ?

Best to post a pic , sounds more like a set-up problem .

If what you are trying to say is ..........

I'm drilling a hole off center of a shaft and my drill is walking , that explains it . Its not the drill nor the chuck . 

You need to send a flat bottom EM to full circle at least the diameter of the drill . Then center drill and drill . Sounds like this is what you're experiencing . Your drill will flex being it's only cutting on the high side of the shaft . 

If I'm mis-interepting what you're saying , disregard this .


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## Cooter Brown (Jan 26, 2019)

Pics or it didn't happen...


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## darkzero (Jan 26, 2019)

Sounds like the drill bit is not sharpened evenly. Assuming it's not a drill bit issue, have you measured the runout out of the chuck? Is the drill bit still tight in the chuck after drilling. How are the condition of the jaws?

I don't see reason to disassemble the chuck unless the grease is old & hard or you need to replaced worn out jaws.


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## Tozguy (Jan 26, 2019)

porthos said:


> after center drilling a piece of round stock,



A 60 deg center drill is not ideal for preceding a drill.



porthos said:


> i "cooked" the drill in my ultrasonic cleaner


 
What is the objective of cooking the drill bit?

Unless the Rohm chuck has an obvious problem (sticking, wobbling, etc.) there are other more probable explanations for the drill walking.


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## Chiptosser (Jan 26, 2019)

Your Rhom chuck will come apart the same way as a Jacobs.
You definitely need to re-lubricate the inside of the chuck.


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## porthos (Jan 26, 2019)

if a 60 degree center drill is not ideal for preceeding a drill, what should I be using??  and, what would the center drill be used for?? next question :  I indicated a .500 pin gage in the drill chuck placed in the headstock. get .004 runout. same pingage in a collet gives .0005 runout.  is .004 acceptable runout for a drill chuck??


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## Cooter Brown (Jan 26, 2019)

How is the drill chuck being attached?


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## Tozguy (Jan 26, 2019)

porthos said:


> if a 60 degree center drill is not ideal for preceeding a drill, what should I be using??



For spotting a hole, a drill with a larger tip angle than the drill that follows it should be used.  This allows the second drill to locate in the bottom center of the hole. 
Use a spotting bit or stub bit for best results. A centre drill is designed to prepare a seat for a center, these are usually 60 deg. Most drill bit tips have a much larger angle, like 118 deg for example. A centre drill is not much good for anything else but cutting center divots unless you are really stuck.



porthos said:


> same pingage in a collet gives .0005 runout.


 
Standard drill chucks are not as precise as standard collets. Some drill chucks are built for more precision than others. Some collet systems offer more precision than other collet systems. I'm not surprised by your results.
There is a trade off between versatility and precision. By design a collet offers less range in size but more precision than a drill chuck. 



porthos said:


> is .004 acceptable runout for a drill chuck??


 If a drill chuck is clean and is functioning as it was designed then what you see is what you get. If you require a minimum of precision then buy a drill chuck that has the level of precision you need guaranteed by the manufacturer. 
Otherwise jobber length drill bits are so flexible that a bit of run out of the chuck is immaterial. Locating and preparing the starter hole or divot is more important than run out of the chuck. 
There is much to the geometry of a drill bit tip for the job at hand but that is beyond the scope of my post.


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