Clamping a small part for drilling

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  #1  
Old 10-12-16, 04:41 PM
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Clamping a small part for drilling

I'm making kind of a bushing and I have to enlarge a hole in a nylon spacer. I did one of two well enough but I damaged my clamps because the spacer spun against the rubber of the clamp. How would you clamp a 3/8" diameter spacer to enlarge the hole? I just tried a small file that I could fit about 2" into the hole but it seemed very slow and it will probably quickly clog the file if it makes any progress at all.
 
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Old 10-12-16, 05:07 PM
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There is no great way to hold it unless you have a lathe.
Even then it would be a challenge.
I might have tried to find a bushing with the right size hole.
McMaster Carr is one great source for things like this.
 
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Old 10-12-16, 05:13 PM
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Maybe I'll put the spacer in the chuck of my old drill and clamp the drill down and drill through the chuck with my new drill.
 
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Old 10-12-16, 05:19 PM
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Not a great plan.
A three jaw chuck will not hold it evenly.
A drill will make an oval shaped hole.
Need a reamer for a really round hole.
What the spacer for, how accurite does it need to be?
 
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Old 10-12-16, 06:05 PM
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It doesn't have to be very accurate. I want to put a 1/4" bolt through a 1/2" threaded hole without damaging the threads in the 1/2" hole and without too much wiggle room. This is for an exercise bike. Sometimes I'll be screwing a pedal in the 1/2" threads but when I'm using the crank shortener that I'm building I'll be using that undersized bolt.
 
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Old 10-12-16, 06:13 PM
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Drill a 3/8 hole in a piece of wood. Cut the wood in half through the center of the 3/8 hole. Now you can just clamp the wood. Example:

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Old 10-12-16, 06:17 PM
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Still does not make much since.
Why not just use stacked up steel washers?
I can see a 1/4" bolt just shearing off being used like that.
 
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Old 10-12-16, 06:32 PM
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Originally Posted by Tolyn Ironhand
Drill a 3/8 hole in a piece of wood. Cut the wood in half through the center of the 3/8 hole. Now you can just clamp the wood.
Yeah, sound good. Maybe I can think of a way to give the wooden hole some teeth. I've thought of poking the spacer with nails. Maybe I'll do that.

I can see a 1/4" bolt just shearing off being used like that.
Yeah, but this is for an elderly man who won't exert much pressure on the pedals, and the other end of the crank shortener will be attached with a hose clamp or two for more strength. But maybe I'll use a 1/2" bolt after all. I wanted to avoid too much screwing and unscrewing in the treaded crank. Here's a diagram of the entire setup from when I was planning on using a 1/2" bolt. I keep flip flopping with my plans.:
 
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Old 10-12-16, 07:13 PM
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OK, so, I'm afraid of the 1/4" bolts I was going to use. I'm going to use 1/2" bolts that actually fit the threads. No need for the nylon bushings after all...now I have to shop for good quality 1/2" fine threaded bolts. One standard and one with left hand threads. Ugh...

EDIT: I'll go ahead with the 1/4" bolt for now. No way will it break in the first week, and I'll keep an eye on my father. If it works out, I'll upgrade to a 1/2" bolt.
 

Last edited by Borad; 10-12-16 at 08:48 PM.
  #10  
Old 10-13-16, 05:38 AM
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I would bore a hole through the existing crank for the new bolt location. With your contraption it will be difficult to keep the bolt perpendicular. The hole in your steel plate will soon wallow out unless you find a way to securely hold it in place. You can weld the head of the bolt or install a nut on the other side of the plate to tighten the bolt onto the plate. That would also provide the spacing you're trying to do with a plastic spacer.
 
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