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Posted by Robert Swinney on April 25, 2006, 12:56 pm
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> davefr@gmail.com wrote:
>> I want to make some small brass sleeve bearings with my Smithy 3 in 1
>> machine. I'm having a difficult time getting a consistent wall
>> thickness. The material I'm working with is 1/4" brass rod and I'm
>> trying to get bearings about 1" long and with an ID of about 1/8".
>> Here's what I'm doing:
>>
>> 1. Insert brass rod into head chuck.
>> 2. Insert a 1/8" drill bit into a chuck that fits the tailstock taper.
>> 3. Start the machine and drive the drill bit into the rotating rod.
>>
>> I'm not getting perfectly drilled holes in the exact center of the rod.
>> My machine is aligned correctly but it seems like the drill bit
>> sometimes wanders a little off course due to flex.
>>
>> I'd like to improve my technique. Any suggestions on a better setup??
>>
>
> Use a screw machine bit which is shorter and stiffer than a jobber's
> length drill bit. Run the machine at its fastest speed and clear the chips
> often, using a hunt/peck motion. The idea of drilling starting with a
> center drill and going from both ends also has merit. If your hole were
> larger I'd recommend drilling undersize and then boring but I can't
> imagine a boring bar that can bore a 1/8" hole 1" deep.
>
> This is tricky country, you are boring 800% of the diameter of the drill.
> Is there any chance you could get away with using two identical pieces
> each 1/2" long?
>
> GWE
As Grant says, you are way beyond the definition of "deep hole drilling".
Deep holes are usu. always difficult to maintain center. Use a center drill
to start, and then a stub length drill (screw machine drill) for the hole.
Good idea to center up and drill from both ends, also. Best results can be
obtained by drilling under size and reaming to finish. Another thought is
to use larger stock, say 5/16; drill, ream and then insert a mandrel of some
sort into the bore and turn the OD down to 1/4.
Bob Swinney
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> machine. I'm having a difficult time getting a consistent wall
> thickness. The material I'm working with is 1/4" brass rod and I'm
> trying to get bearings about 1" long and with an ID of about 1/8".
> Here's what I'm doing:
>
> 1. Insert brass rod into head chuck.
> 2. Insert a 1/8" drill bit into a chuck that fits the tailstock taper.
> 3. Start the machine and drive the drill bit into the rotating rod.
>
> I'm not getting perfectly drilled holes in the exact center of the rod.
> My machine is aligned correctly but it seems like the drill bit
> sometimes wanders a little off course due to flex.
>
> I'd like to improve my technique. Any suggestions on a better setup??
>