How do I accurately locate and drill holes offcenter in the SIDE of round stock?

How do I accurately locate and drill holes offcenter in the SIDE of round stock?

Joined: July 24th, 2010, 1:44 am

October 8th, 2013, 2:22 am #1

I've been searching the internet and all I'm getting is how to drill holes in the center of round stock.

I recently had some success single point threading a piece of 10mm O1 tool steel and was pleased with the result.......


Now I would like to try duplicating something similar to this R10 end cap but I don't know how to locate and drill the dowel and safety button holes in the side of the stock.............


I made a CAD drawing of the part I want to make which is a steel R9 end plug similar to this.......

Using close fitting drill shanks it was pretty easy to measure the outside of two drill shanks and then locate them on center in the CAD program but how in the world would I locate and drill these holes in the correct position relative to each other. LOL....it was a hassle for me to even MEASURE the holes in the existing part to make the CAD drawing!
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Joined: June 7th, 2010, 12:14 am

October 8th, 2013, 3:52 am #2

To drill cross holes not on the diameter.

Using the dimensions you measured to produce your CAD drawing.

First mount the work piece securely to the mill table in Vee blocks, or just a standard mill vise with the work up on parallels. Long way on the X axis. Make sure the piece or the vise is TRAMMED!

Use an edge finder to locate the reference edge of the cylinder.
The reference edge is the one your measurements came off from.
Set your Y dial or DRO.
Move over the required Y distance for the first hole and lock the tables Y movement.
Do the same in X, finding the reference END of the part and set the X axis. Don't forget the .100 edge finder radius when setting your dials!

Move over to the required X distance, to your first hole to be drilled. Keep the backlash in mind if using dials!

Lock the table.

Using a center cutting end mill of the same size or swn, spot the drilled hole location based on the table movement numbers. Spot just deep enough to make a full circular cut.

Without moving the table in X or Y, (or write down the dial numbers and direction) replace the end cutting mill with a spot drill, or the shortest, stoutest drill bit you have to make a starting hole.
"Center drills" for a lathe are NOT the correct tool for this, but are often used until spot drills are discovered!

After the hole location is spotted, drill through with a SHARP twist drill the next size under the desired hole size. Follow with a reamer to produce an on sized finished hole.

Move to the next hole location and repeat.

Viola!

If you lose location, and need to pick up a hole, stick a snug fitting drill bit in the hole and then find the location with a test indicator swinging from the quill.
Close enough can come just by poking a drill chuck mounted drill bit into the hole and then carefully tightening the vise while you manipulate the table to achieve no deflection of the drill bit when the work is secure. (+/- .005 or so depending on care)

The key to off diameter drilling is the flat produced with the end mill ON LOCATION. The work goes quickly with a DRO in that tolls need not be changed between holes, i.e. all locations can be milled flat noting the positions, then all positions can be spot drilled, then all positions can be pilot drilled, then all positions can be reamed (if the same size etc.)

looks like fun!

ps in a factory setting, a drill jig would be used with close fitting drill guide bushings to fix the hole locations on the work piece

Last edited by CalG on October 8th, 2013, 4:07 pm, edited 1 time in total.
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Joined: January 31st, 2010, 8:47 am

October 8th, 2013, 3:27 pm #3

Well written tutorial on how to drill offset holes in round stock... like Cal says the small flat created with a center cutting end-mill is the secret.

Spot drills are the secret to improved accuracy for hole locations; however, I admit using and breaking the tip of many center drills in work until learning why spot drills are better.

Airguns are a gas

Boomer
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Joined: June 7th, 2010, 12:14 am

October 8th, 2013, 4:03 pm #4

A feature to exasperate the novice and pro alike!
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Joined: May 8th, 2001, 4:06 pm

October 8th, 2013, 7:01 pm #5

I've been searching the internet and all I'm getting is how to drill holes in the center of round stock.

I recently had some success single point threading a piece of 10mm O1 tool steel and was pleased with the result.......


Now I would like to try duplicating something similar to this R10 end cap but I don't know how to locate and drill the dowel and safety button holes in the side of the stock.............


I made a CAD drawing of the part I want to make which is a steel R9 end plug similar to this.......

Using close fitting drill shanks it was pretty easy to measure the outside of two drill shanks and then locate them on center in the CAD program but how in the world would I locate and drill these holes in the correct position relative to each other. LOL....it was a hassle for me to even MEASURE the holes in the existing part to make the CAD drawing!
i.e., normally just spot mill a flat, center drill, then drill. Or, you could also start with square stock, drill all your holes, then turn to round and face/cutoff to length in the lathe. Lots of math involved to get it correct to your drawing.
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Joined: January 31st, 2010, 8:47 am

October 9th, 2013, 11:45 am #6

A Digital Read Out is your best friend forever when working with a drawing.

Airguns are a gas

Boomer
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Joined: September 21st, 2007, 12:13 pm

October 9th, 2013, 9:15 pm #7

X2 for the DRO's..n/t
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Joined: December 18th, 2008, 4:51 am

October 10th, 2013, 1:28 pm #8

I've been searching the internet and all I'm getting is how to drill holes in the center of round stock.

I recently had some success single point threading a piece of 10mm O1 tool steel and was pleased with the result.......


Now I would like to try duplicating something similar to this R10 end cap but I don't know how to locate and drill the dowel and safety button holes in the side of the stock.............


I made a CAD drawing of the part I want to make which is a steel R9 end plug similar to this.......

Using close fitting drill shanks it was pretty easy to measure the outside of two drill shanks and then locate them on center in the CAD program but how in the world would I locate and drill these holes in the correct position relative to each other. LOL....it was a hassle for me to even MEASURE the holes in the existing part to make the CAD drawing!
Great instructions. I did this exact type of thing. I made a Rear plug and tube for the UK Tommy trigger for my newest gun. Its a 30 mm tube with my piston and internals as well as rear plug and cocking arm. Its daunting and I did ruin a few attempts. It was even worse than a 1 to 1 copy as I had to increase the size of the plugs diameter to 30 mm from 27 and retain the pin depth ratio so the trigger would mount at the needed depth for engagement ! I am looking for my pics

http://www.capairgunresearch.com

"When Power and smoothness matter"
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